RU2796548C2 - Nuclear micro-battery - Google Patents

Abstract

FIELD: power engineering.

SUBSTANCE: invention relates to a nuclear micro-battery, which can be used to generate small amount of energy for a long period of time. The battery contains radioactive material that emits photons or particles; and at least one diode that contains semiconductor material placed with the possibility of receiving and absorbing photons or other particles emitted by radioactive material and generating electric charge carriers in response to these reception and absorption. Moreover, the mentioned semiconductor material has a structure of a crystal lattice including aluminum, indium and phosphorus. At least one diode contains a PIN junction or a p-n junction created by the mentioned crystal lattice structure. Semiconductor material is made with the possibility of receiving and absorbing the mentioned other types of photons or other particles and generating electric charge carriers in response to these reception and absorption.

EFFECT: possibility of growing a crystal compound with high crystal quality on traditional substrate (for example, GaAs) to a large thickness, thereby increasing the absorption of particles emitted by radioactive material by the crystal.

25 cl, 21 dwg

Description

FIELD OF TECHNOLOGY

The present invention generally relates to a nuclear microbattery which contains a radioisotope and one or more diodes and in which the radioisotope decays to form photons or particles which are received by said one or more diodes to generate current.

BACKGROUND OF THE INVENTION

The ability to provide small amounts of power over an extended period of time is becoming increasingly important in many applications such as MEMS device technology, biomedicine, and aerospace. For this, nuclear microbatteries can be used, which convert nuclear energy into electrical energy. In a nuclear microbattery, the radioactive source is combined with a conversion material that absorbs the high-energy particles emitted by the radioactive source and generates an electrical current. Unlike traditional power sources such as chemical batteries, micronuclear batteries have important characteristics such as high energy density, stability, resistance to damage, and long service life. For example, micronuclear batteries can provide small amounts of energy for many decades (ex. from ~pW to ~µW).

SUMMARY OF THE INVENTION

The present invention is a nuclear microbattery which contains:

radioactive material that emits photons or particles; And

at least one diode, which contains a semiconductor material placed with the possibility of receiving and absorbing photons or particles and generating electric charge carriers in response to these reception and absorption, moreover, said semiconductor material is a crystal lattice structure containing aluminum, indium and phosphorus.

It has been found that the use of this type of semiconductor material in a microbattery provides the microbattery with exceptionally good electrical performance. This is especially true for microbattery embodiments in which the radioactive source emits x-rays, gamma rays, or beta particles, and the semiconductor material converts these x-rays, gamma rays, or beta particles into electrical charge carriers.

The possibility of using semiconductor material to create an improved microbattery has not been identified, although the use of semiconductor material in photodiodes for other purposes, such as spectroscopy, is known. The radioactive material contains a radioisotope in a concentration sufficient to deliver the aforementioned photons or particles to the diode so that the microbattery generates electrical energy.

The absorption of photons or particles by a semiconductor material leads to the formation of electron-hole pairs.

The crystal lattice structure may be AlInP. This substance can have a lattice matched with a conventional GaAs semiconductor substrate, and therefore can be grown on it with a high crystal quality. The quality of the lattice matched AlInP can be very high compared to the quality of group III-V nitrides and group II-VI compounds with a similar band gap. AlInP doping is also easier to control than for some semiconductors in other II-VI groups.

The lattice structure can have a composition of Al _0.52 In _0.48 P or Al _0.53 In _0.47 P. Such AlInP compositions provide a significant degree of consistency in material parameters with the lattice and make it possible to grow the material on traditional, such as GaAs, substrates. . Also, these ratios make it possible to grow AlInP with a high quality of crystallinity and/or to a relatively large thickness. This is especially valuable because a relatively thick layer of AlInP may be required to increase the probability of absorbing any photon or particle from the radioactive material. However, it is contemplated that the AlInP material may be a crystal structure with a lattice composition of Al _x In _1-x P, where x has a value other than 0.5.

AlInP can be created on a substrate, preferably a semiconductor such as GaAs.

The microbattery may contain electrodes for removing the electric current generated by at least one said diode by generating electric charge carriers.

The at least one diode may comprise a plurality of diodes connected in parallel or in series. The microbattery may contain ≥2, ≥3, ≥4, ≥5, ≥10, ≥15, ≥20, ≥30, ≥40, ≥50, ≥100, ≥150, or ≥200 diodes.

At least one diode may contain a plurality of diodes, with one or more diodes located on one side of the radioactive material, and one or more diodes on the second, opposite side of the radioactive material.

A gap may be created between said at least one diode and the radioactive material, which may be filled with a gas maintained at a pressure slightly below atmospheric. The vacuum in the gap is maintained at a pressure level slightly below atmospheric (relative to air pressure at sea level).

A gap may be created between said at least one diode and the radioactive material, which may be filled with an inert gas. The inert gas can be, for example, helium.

A gap may be created between said at least one diode and the radioactive material, which may be filled with radioactive gas. Such a gas can be, for example, tritium. In such an embodiment, said radioactive material can be a source of beta particles, since the beta particles in tritium have a relatively large mean free path. In embodiments where the diodes are located on opposite sides of the radioactive material, gaps may be provided on either side of the radioactive material, and one or both of these gaps may be subatmospheric and/or filled with an inert gas and/or radioactive gas.

The radioactive material and at least one diode may be housed in a common housing that is positioned and configured to substantially prevent photons or particles of radioactive material from escaping from the housing; or the microbattery may include a shielding element that is positioned and configured to substantially prevent photons or particles of radioactive material from passing through it.

The housing or security element may be made of metal, such as sheet metal or metal foil. Metals such as, for example, aluminum, steel (eg stainless steel) or tungsten can be used. However, other metals or other materials may be used, provided that they prevent the passage of photons or particles of radioactive material through them. For example, it is possible to use a ceramic body or screen.

At least one diode may comprise a PIN junction or a p-n junction formed by said lattice structure.

A PIN junction (eg p ⁺ -in ⁺ ) can be formed by an undoped AlInP layer located directly between a p-doped AlInP layer and an n-doped AlInP layer.

The inclusion of an intrinsic i-layer (with intrinsic electrical conductivity) in a PIN junction can be used to create a relatively wide depletion region and hence a relatively large volume for absorbing photons or radioactive material particles and subsequently generating charge carriers. However, it is also possible to create an AlInP layer in the form of a p-n junction. The p-n junction can be formed by a p-doped AlInP layer in contact with an n-doped AlInP layer. Alternatively, the material of the AlInP layer can be made with a transition in the form of a Schottky contact.

The i-layer thicknesses of the PIN junction may have the following values: ≥5 µm, ≥10 µm, ≥15 µm, ≥20 µm, ≥25 µm, ≥30 µm, ≥35 µm, ≥40 µm, ≥45 µm, or ≥50 µm; and/or i-layer thicknesses of the PIN junction may have the following values: ≤5 Ωkm; ≤45 µm; ≤40 µm; ≤35 µm; ≤30 µm; ≤25 µm; ≤20 µm; ≤15 µm; ≤10 µm; or ≤5 µm. Each of the listed lower thickness limits may be combined with any of the listed upper thickness limits, provided that the limits are not mutually exclusive. Such embodiments are considered in which the i-layer thicknesses are ≥6 µm, ≥8 µm or ≥23 µm.

The provision of such a relatively thick i-layer allows a relatively high proportion of incident photons or particles to be absorbed, resulting in a relatively large amount of charge carriers being generated and the diode becoming relatively efficient at generating current from photons or particles. The relatively high thickness provides a high quantum efficiency of the device for various types of radioactive sources (eg sources of x-rays or beta radiation).

The semiconductor material provides a relatively high attenuation factor for photons or particles emitted by a radioactive source, and especially for x-rays.

The thicknesses of the p-layer and/or n-layer of the PIN junction may be: ≤0.5 μm, ≤0.4 μm, ≤0.3 μm, ≤0.2 μm, or ≤0.1 μm.

The creation of such relatively thin layers limits the absorption of photons or particles by these layers. For example, in the case of using a p-layer (or n-layer) located on the side of the junction facing the radioactive source, a relatively thin p-layer (or n-layer) will absorb a relatively small fraction of photons or particles in such a way that most incident photons or particles can enter the i-layer of the PIN junction, be absorbed in it and generate charge carriers (although it is assumed here that part of the p-layer can also actively contribute to the production of useful charge carriers).

The microbattery may include an electrode on each side of the PIN or p-n junction to energize the junction and/or to remove electrical current generated by the generation of charge carriers in the junction. Moreover, at least one of the electrodes does not partially cover the side of the transition on which it is located, so that the said photons or particles can pass into the transition from the indicated side without passing to the said at least one electrode.

At least one electrode may be annular, perforated, recessed, or interdigitated so as not to completely cover said side and to allow said photons or particles to pass into the junction without passing through the material forming the electrode. For example, at least one electrode may be located only around the perimeter of the side of the transition on which the electrode is located.

At least one electrode can cover ≤ x % of the area of the side of the transition on which the electrode is located, and the value of x is selected from: 40; 35; thirty; 25; 20; 15 and 10.

The microbattery forward bias voltage can be applied to the PIN or p-n junction, and this voltage can have the following values: ≥0.1 V; ≥0.2V; ≥0.3V; ≥0.4V; ≥0.5V; ≥0.6V; ≥0.7V; ≥0.8V; ≥0.9V; ≥1V; ≥1.1V; ≥1.2V; ≥1.3V; ≥1.4V; ≥1.5V; ≥1.6V; ≥1.7V; ≥1.8V; ≥1.9V; and ≥2 V; and/or ≤0.1 V; ≤0.2V; ≤0.3V; ≤0.4V; ≤0.5V; ≤0.6V; ≤0.7V; ≤0.8V; ≤0.9V; ≤1V; ≤1.1V; ≤1.2V; ≤1.3V; ≤1.4V; ≤1.5V; ≤1.6V; ≤1.7V; ≤1.8V; ≤1.9V; and ≤2 V. Any of the upper limit ranges can be combined with the lower limit range, provided they are not mutually exclusive.

Each diode and at least one may have a mesa diode structure. Alternatively, at least one diode may be formed by an ion doping process or may be a planar device with Schottky contacts.

The diode may contain one or more layers to create an electrical contact on each side of the semiconductor material. For example, one of the multiple layers may comprise at least one metal layer and/or at least one semiconductor layer. Examples of metal layers include metals such as gold and titanium. Examples of the semiconductor layer include GaAs or InGe.

Between one or more layers, a bonding layer can be provided to create an electrical contact and a semiconductor material (eg AlInP), for a good connection of electrical contacts with a semiconductor material (eg AlInP). The bonding layer may be a metal or a semiconductor such as GaAs. One of the bonding layers can be the substrate on which the semiconductor material was created (eg AlInP).

The surface of each of the at least one diodes facing the radioactive material may actually be polygonal in shape.

A polygon-shaped surface may have rounded corners. This helps prevent electrical breakdown at corners.

The polygonal surface may have at least 5 sides or at least 6 sides. Due to this, the battery can contain several closely spaced diodes, which allows to optimize the ratio of battery size and power.

The radioactive material may be located within a distance X mm from the semiconductor material of the diode, and the value of X is selected from the values: ≤5; ≤4; ≤3; ≤2; ≤1; ≤0.8; ≤0.7; ≤0.6; ≤0.5; ≤0.4; ≤0.3; ≤0.2; and ≤0.1.

The radioactive material may be a source of x-rays and/or gamma radiation or a source of beta particles and/or neutrons.

These designs have advantages over microbatteries that convert alpha particles and beta particles into charge carriers, since alpha particles can cause significant damage to the device, and beta particles can create an ionization trail along the path of the beta particle, which reduces resistance and lower the battery voltage.

However, it is assumed that the radioactive source may be the source of alpha particles.

The nuclear microbattery diode can convert the photons or particles emitted by the radioactive material directly into electricity using the semiconductor material, or it can first convert the photons or particles emitted by the radioactive material into other types of photons or particles. These other photons or particles can act on the semiconductor material to generate charge carriers.

The radioactive material may actually be a planar mass, the mass thickness of which is selected from: ≤10 mg/cm ² , ≤9 mg/cm ² , ≤8 mg/cm ² , ≤7 mg/cm ² , ≤6 mg/cm ² , ≤5 mg/cm ² , ≤4 mg/cm ² , ≤3 mg/cm ² , ≤2 mg/cm ² and ≤1 mg/cm ² . The radioactive material may actually be a planar mass, the amount of apparent activity of which per unit area is selected from: ≥1 MBq/mm ² ; ≥2 MBq/mm ² ; ≥3 MBq/mm ² ; ≥4 MBq/mm ² ; ≥5 MBq/mm ² ; ≥6 MBq/mm ² ; ≥7 MBq/mm ² ; ≥8 MBq/mm ² ; ≥9 MBq/mm ² ; ≥10 MBq/mm ² ; ≥12 MBq/mm ² ; ≥14 MBq/mm ² ; ≥16 MBq/mm ² ; ≥18 MBq/mm ² ; ≥20 MBq/mm ² ; ≥25 MBq/mm ² ; ≥30 MBq/mm ² ; ≥35 MBq/mm ² ; and ≥40 MBq/mm ² . It should be noted that any of the above mass thickness limits may be combined with any of the above visible activity limits.

It has been found that a high level of visible activity of the radioactive material is preferable, rather than the actual activity of the radioactive material per se (due to the phenomenon of self-absorption in the radioactive material), and that a constant increase in the amount of radioactive material will not permanently increase the visible activity. Accordingly, it is argued that the radioactive material mass thickness value can be optimized such that a good microbattery performance (i.e., relatively high apparent activity) is obtained at a relatively low radioactive material mass thickness.

The microbattery may contain a transducer for absorbing or interacting with photons or particles emitted by the radioactive material and generating other types of photons or particles in response to these absorptions and interactions; wherein the semiconductor material is configured to capture and absorb those photons or other types of particles and generate electrical energy in response to those captures and absorptions. For example, a phosphorus or other scintillator may be used as a transducer to absorb or interact with photons or particles emitted by the radioactive material and generate other types of photons or particles in response to these absorptions and interactions, which then pass to the diode.

For example, the converter may receive neutrons from radioactive material (eg, from an AmBe source) and produce electrons and/or gamma rays in response, which are then incident on a diode to generate charge carriers.

The transducer may be a metal foil such as, for example, Gadolinium foil.

The converter can be designed so as not to directly expose the diode to radioactive material, thereby reducing damage to the diode.

At least one diode may be a non-avalanche diode. The microbattery may not contain a current amplifier and does not amplify the current from the microbattery.

The microbattery may comprise an outer casing defining the volume of the battery, selected from the following values: ≤50 ^cm3 , ≤40 ^cm3 , ≤30 ^cm3 , ≤20 ^cm3 , ≤10 ^cm3 , ≤5 ^cm3 , ≤4 ^cm3 ≤3 cm ³ , ≤2 cm ³ , or ≤1 cm ³ .

The present invention also provides a device that includes a microbattery, as described below, and an electronic device connected to, or capable of being connected to, the microbattery in order to receive power from the microbattery to perform one or more activities.

The device can be configured such that the microbattery supplies electric current to the electronic device without amplifying the current.

Embodiments of the present invention provide a robust, miniature and high performance radioisotope microbattery for low power consumption microelectronic devices. The device can be used in a variety of applications where chemical battery technology is not applicable, such as due to usage, environmental conditions, or volume or weight limitations of the power supply. Embodiments of the invention are used in electronic devices requiring increased reliability in supplying a relatively small amount of energy (e.g. power supply in the power range from 1 pW to 1000 nW) for long periods of time (e.g. ≥ 10 years), for example, in electronic medical implants, tamper-resistant devices, embedded electronics, battery-backed military encryption devices, real-time clocks, asset tracking devices and locators, and sensors designed to monitor structural integrity or environmental contamination. Embodiments of the invention are applicable in devices that are exposed to extreme temperatures, pressures, vibrations or other adverse environmental conditions during use, such as precision guided munitions or smart weapons, precision guided weapons systems and multi-purpose munitions, encryption keys in microelectronic devices , monitoring devices for nuclear waste storage or other extreme environmental conditions such as volcanic activity and geological faults.

Embodiments of the invention are useful where long backup periods are required, such as to boost the main power supply of chemical batteries.

The claimed microbatteries can be used in such areas as technologies for creating devices based on microelectromechanical systems, military and aerospace industries, and biomedicine.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, with reference to the accompanying drawings, various embodiments of the present invention will be described, given by way of example only, in the drawings:

Fig. 1 shows typical dark current characteristics versus forward bias voltage at various temperatures for a photodiode according to an embodiment;

Fig. 2 shows the relationship between log saturation current and temperature for a photodiode;

Fig. 3 shows typical dark current and photocurrent characteristics as a function of applied bias voltage for a photodiode;

Fig. 4 shows typical current characteristics versus forward bias voltage at various temperatures for a photodiode;

Fig. 5A shows open circuit voltage versus temperature for photodiodes, and FIG. 5B shows the found relationship between open circuit voltage and saturation current;

Fig. 6 shows short circuit current versus temperature for photodiodes;

Fig. 7 shows photodiode output power as a function of applied forward bias voltage at various temperatures;

Fig. 8A shows the maximum measured output power as a function of temperature, and FIG. 8B shows the internal conversion efficiency as a function of temperature; And

Fig. 9 schematically shows the geometric arrangement of the radioactive source and photodiodes;

Fig. 10 shows dark current characteristics versus forward bias voltage at various temperatures for a beta voltaic cell;

Fig. 11 shows measured saturation current and ideality factor as a function of temperature;

Fig. 12 shows the dependence of photocurrent characteristics on forward bias voltage at various temperatures;

Fig. 13 shows the dependence of open circuit voltage on temperature;

Fig. 14 shows the dependence of the short circuit current on temperature;

Fig. 15 shows the output power of a beta-voltaic cell as a function of applied forward bias voltage over a range of temperatures;

Fig. 16 shows the maximum measured power output as a function of temperature and the internal conversion efficiency of the beta-voltaic cell as a function of temperature;

Fig. 17 shows actual surface activity per unit area and measured surface activity per unit area of ^{6 3} Ni radioactive material as a function of the mass thickness of the radioactive material;

Fig. 18 shows the dependence of the source emission probability on the energy of the beta particle;

Fig. 19 shows a schematic representation of a microbattery, with arrays of diode cells located on either side of the radioactive material;

Fig. 20 shows a schematic representation of a diode cell according to an embodiment; And

Fig. 21 shows a schematic view of the cell from top to bottom, showing the top ohmic contact.

DETAILED DESCRIPTION

In embodiments of the present invention, the nuclear microbattery contains a radioactive source for emitting photons or particles and at least one diode for receiving these photons or particles and converting their energy into electrical energy.

Next, by way of example only, an exemplary embodiment of a nuclear microbattery will be described for a better understanding of the invention. In this embodiment, the microbattery contains a radioisotope for emitting x-rays and a photodiode for converting x-ray energy into electricity. It should be understood that the invention is not limited to a particular radioactive source or diode containing all of the described layers, or to the specific composition of the various layers in this example.

In accordance with Table 1, a typical photodiode contains the indicated layers. The Al _0.52 In _{0 .48} P wafer layer (layers 3-5 in Table 1) was grown by metal-organic vapor phase epitaxy (HPE-MOS) on an n+ -doped GaAs:Si substrate (layer 6 in Table 1) with misorientation 10 degrees with respect to <1 1 1> A, to suppress the ordered phase as in CuPt, to create a p + -i-n + structure. Al _0.52 In _0.48 P wafer layers were successfully grown on a GaAs substrate to create a Si-doped n+ Al _0.52 In _0.48 P layer with a doping concentration of 2 x 10 ¹⁸ cm ^-3 and a thickness of 0.1 μm ( layer 6 in Table 1) followed by an inner Al _0.52 In _0.48 P layer undoped and 2 µm thick (layer 4 in Table 1) followed by a zinc p+ doped Al _{0 layer, 52} In _0.48 P, with a doping concentration of 5×10 ¹⁷ cm ^-3 and a thickness of 0.2 μm (layer 3 in Table 1). A heavily doped zinc p+ - doped GaAs layer, with a doping concentration of 1×10 ¹⁸ cm ^-3 and a thickness of 0.01 μm (layer 2 in Table 1), was grown over the p + - doped Al _0.52 In _0.48 layer P (layer 3 in Table 1) to improve ohmic contact. Then, for the manufacture of two round mesa-photodiodes with a diameter of 400 μm, methods of liquid chemical etching of the layers were used. To etch round mesa photodiodes, a solution of H ₃ PO ₄ :H ₂ O ₂ :H ₂ O was used, in a ratio of 1:1:1, and then for 10 s a solution of H ₂ SO ₄ :H ₂ O ₂ :H ₂ O in the ratio 1:8:80.

An ohmic top contact was created on a heavily doped GaAs layer (layer 2 in Table 1) by sputtering both a 0.2 µm gold layer and a 0.02 µm titanium layer to form an Au/Ti alloy contact (element 1 in Table 1 ). The top ohmic contact covered 33% of the surface of each 400 µm photodiode. An ohmic back contact was created on the back surface of the GaAs substrate (layer 6 in Table 1) by sputtering a 0.02 µm thick InGe layer (layer 8 in Table 1) and a 0.2 µm gold layer (layer 8 in Table 1).

Each of the two depassivated mesa photodiodes with a diameter of 400 µm was created on a single chip and exposed to 238 MBq from a ^{5 6} Fe X-ray source (Mn Kα=5.9 keV, Mn Kβ=6.49 keV). The X-ray source was located 5 mm from the surface of the photodiodes.

The quantum efficiency of X-ray radiation of a semiconductor photodetector is determined by the percentage of X-ray photons absorbed by the photodetector. According to the Lambert-Beer law and, assuming the accumulation of total charge in the active p-layer and i-layer, the quantum efficiencies of X-rays of 20% and 30% were calculated for each photodiode for photons of 5.9 keV and 6.49 keV, respectively, assuming take into account the dead zone of GaAs. The quantum efficiency (QE) values were calculated according to equation (1) below, assuming that 33% of the surface of each photodiode was covered by the top metal contact. Quantum efficiency is:

Where μ _Ti and d _Ti are, respectively, the linear attenuation coefficient and the thickness of Ti, μ _Au and d _Au are, respectively, the linear attenuation coefficient and the thickness of Au, μ _GaAs and d _GaAs are, respectively, the linear attenuation coefficient and the thickness GaAs, μ _AlInP and d _AlInP are, respectively, the linear attenuation coefficient and the thickness of the Al _0.52 In _0.48 P core. To calculate the quantum efficiency at 5.9 keV and 6.49 keV, the attenuation coefficients Al _{0 ,52} In _0.48 P, equal to 0.1301 µm ^-1 and 0.1004 µm ^-1 (at a compound density of 3.66 g/cm ³ ). To calculate the quantum efficiency at 5.9 keV for GaAs, Ti and Au, the attenuation coefficients were taken to be 0.0837 µm ^-1 , 0.2081 µm ^-1 and 0.8832 µm ^-1 , respectively. To calculate the quantum efficiency at 6.49 keV for GaAs, Ti and Au, the attenuation coefficients were taken to be 0.0645 µm ^-1 , 0.1684 µm ^-1 and 0.718 µm ^-1 , respectively.

The microbattery was examined in the temperature range from -20°C to 160°C using a TAS Micro MT climatic chamber with a dry nitrogen atmosphere (relative humidity <5%). At various temperatures, the characteristics of the dark current and photocurrent of each p ⁺ -in ⁺ photodiode were measured as a function of the applied bias voltage. Forward bias voltage measurements from 0 V to 1.6 V were made at 0.01 V intervals using a Keithley 6487 series picoammeter/voltage source. The error associated with the current values was 0.3% of their value plus 400 fA, at that the error associated with the applied bias voltage was 0.1% of their values plus 1 mV.

Fig. 1 shows typical dark current characteristics versus forward bias voltage at various temperatures for one of the photodiodes. It can be seen that the dark currents increase with the applied forward bias voltage due to the greater magnitude of the electric field in the interior of each photodiode. The amount of dark current in the photodiode also increases with temperature due to the presence of higher thermal energy. For each temperature value, the least squares method of dark current data versus applied bias voltage was applied to extrapolate the saturation current (I ₀ ) in each photodiode.

Fig. 2 shows the measured dependence of the logarithm of the saturation current (I ₀ ) on temperature for one of the photodiodes. Also Fig. 2 shows saturation current (I ₀ ) versus temperature for one of the photodiodes. The value of the considered natural logarithm of the saturation current decreased at higher temperatures. In the temperature range from -20°C to 160°C, the value decreased by 22.19±0.13 for one photodiode and by 22.18±0.10 for the other photodiode. These values are in excellent agreement with the expected reduction of 22.27 calculated on the assumption that the temperature dependence of the saturation current is proportional to exp(-E _g /2kT),

Fig. 3 shows typical characteristics of dark current (filled circles) and photocurrent (open circles) versus applied bias voltage for one of the photodiodes at 20°C. It can be seen that as the forward bias voltage increases, the dark current remains relatively stable and then begins to increase exponentially as a function of the applied bias voltage. The dark current increases exponentially and is proportional to the function exp{qV/nkT}, where n is the ideality factor, k is the Boltzmann constant and T is the temperature. Applying the least squares data to each diode shows a linear dependence of the natural logarithm of the dark current on the applied forward bias voltage. The least squares gradient values are (22.23±0.10) AB ^-1 and (22.36±0.07) AB ^-1 for the two photodiodes, respectively. For these diodes, respectively, the following ideality coefficients were obtained: 1.775±0.008 and 1.769±0.006. These values (close to 2) of the ideality coefficients show that the generation-recombination currents in the device dominated the diffusion currents. Under the influence of the X-ray source radiation of the ^{5 5} Fe radioisotope, the measured value of the current (empty circles in Fig. 3) through each photodiode increased, since photocurrent was added to the dark current. After emission, the X-ray photons were absorbed by the photodiode with the creation of electron-hole pairs as a result of the photoelectric effect. Thus, electrons and holes in the depletion region moved to the p+ - type and n+ - type regions, respectively, generating the observed photocurrent.

Fig. 4 shows typical current characteristics versus forward bias voltage at various temperatures ranging from -20°C to 160°C for one of the photodiodes exposed to X-ray source. Data obtained at 160°C, marked with filled circles, obtained at 140°C, marked with empty circles, at 120°C, marked with filled squares, at 100°C, marked with empty squares, at 80°C, marked with diamonds filled, at 60°C, marked with empty diamonds, at 40°C, marked with crosses, at 20°C, marked with triangles filled, at 0°C, marked with empty triangles and at -20°C, marked with asterisks. It can be seen that at elevated temperatures, the smoothness of the curve of dependence of the measured current in the photodiode on the applied forward bias voltage decreases. The experimental open circuit voltage values were obtained as the points of intersection of the curves with the horizontal axis in FIG. 4.

Fig. 5A shows open circuit voltage versus temperature for a single photodiode. As the temperature rises, the open circuit voltage decreases as it depends on the saturation current. The open circuit voltage (V _oc ) increases logarithmically with decreasing saturation current (I ₀ ), according to the following formula:

where k is the Boltzmann constant, T is the temperature, I _ph is the photocurrent through the device, and I ₀ is the saturation current.

There is a linear decrease in open circuit voltage with temperature. In the range from -20°С to 160°С, open circuit voltage V _os =- AT+V; where A=(0.00460±0.00003) V°C ^-1 and B=(0.871±0.002) V for one photodiode, and where A=(0.00460±0.00002) V°C ^-1 and V =(0.866±0.002) V for another photodiode. Open circuit voltages up to 0.97V have been observed for photodiodes at -20°C. These values are much higher than previously obtained (eg 0.3 V when using a microbattery based on the GaAs ^{5 5} Fe radioisotope at the same temperature). This is due to the higher band gap of Al _0.52 In _0.48 P compared to GaAs.

Fig. 5B shows the found experimental relationship between open circuit voltage and saturation current.

Fig. 6 shows the dependence of the short circuit current on the temperature of the photodiodes. These experimental values of the short circuit current were obtained as the points of intersection of the curves in FIG. 4 with a vertical axis. There was not a well-defined relationship between short circuit current and temperature due to the relatively high error of the picoammeter in measuring low currents of photodiodes located in the climate chamber system.

Fig. 7 shows the output power of a single photodiode as a function of the applied forward bias voltage at various temperatures. Data obtained at 160°C, marked with filled diamonds, at 140°C, marked with empty diamonds, at 120°C, marked with filled triangles, at 100°C, marked with empty triangles, at 80°C, marked with dashes, at 60°C, marked with crosses, at 40°C, marked with filled squares, at 20°C, marked with empty squares, at 0°C, marked with filled circles and at -20°C, marked with empty circles. The output power of each photodiode was calculated by multiplying the applied bias voltage and the corresponding device-measured current. As shown in FIG. 7, as the bias voltage increases, the output power first increases to a maximum and then decreases.

Fig. 8A shows the maximum measured output power as a function of temperature. With increasing temperature, the value of the maximum output power decreases due to the dependence on photo-emf. The maximum value of the output power of 0.62 pW, corresponding to 0.3 μW/Ci, was observed on the photodiode at -20°C. As a result of adding the output powers of two photodiodes with a diameter of 400 μm, the total output power of the microbattery will be 1.2 pW (at -20°C). It is possible to improve the value of the maximum output power of photodiodes by increasing the thickness of the inner layer of Al _0.52 In _0.48 P so that a large proportion of X-ray photons are absorbed and converted into electrical energy.

Fig. 8B shows the internal conversion efficiency as a function of temperature. The internal conversion efficiency was calculated by dividing the maximum output power measured at each temperature by the maximum power (P _th ) obtained from X-ray photons normally absorbed by the photodiode, at 100% photodiode conversion efficiency. The P _th value was determined based on the known values of the source activity, the probability of emission of Mn Kα and Mn Kβ X-rays from ⁵⁵ Fe (0.245 and 0.0338 respectively), the thickness of the beryllium (Be) window (0.25 mm) of the radioisotope X-ray source, the area of the ⁵⁵ Fe radioactive source and the Al _0.52 In _0.48 P layer of the mesa diode, the quantum efficiency of the diode, and the allowable value of the energy for creating electron-hole pairs of 5.8 eV (2.5 times the depletion zone width). The P _th value was determined to be 2.8 pW. As shown in FIG. 8B, the internal conversion efficiency value can reach 22% at -20°C.

In the embodiments described above, only 0.3% of the emitted X-ray photons hit the surface of the photodiodes and only 0.05% were actually absorbed by the photodiodes. The number of photons emitted by the source in any direction in one second was determined based on the known values of the source activity and the emission probabilities of Mn Kα and Mn Kβ X-rays from ^{5 5} Fe (0.245 and 0.0338 respectively). It was found that the number of photons emitted by a radioactive source in one second is 6.6×10 ⁷ . Approximately half of them are emitted in the direction of the photodiodes and, presumably, half of the photons are lost because they are emitted in the opposite direction from the photodiodes. The number of photons incident on the photodiodes in one second was determined to be 1.7×10 ⁵ per second, based on the number of photons per second emitted by the source in the direction of the photodiodes (3.3×10 ⁷ per second), thickness (0.25 mm) beryllium (Be) window of the radioisotope X-ray source and location of the source and photodiodes. Fig. 9 schematically shows the location of the source and detector. The ratio of the surface areas of the photodiodes (0.25 mm ² ) and the surface of the radioactive source (28.27 mm ² ) is 0.0089. The number of photons at the detector is determined by multiplying the number 0.0089 by the number of photons passing through the beryllium (Be) window of the X-ray source in 1 second (1.9×10 ⁷ per second). The number of photons absorbed by photodiodes per second was calculated according to the Lambert-Beer law under the condition of accumulation of a full (100%) charge in the active p- and i-layers. The number of photons per second at the photodiodes was multiplied by the quantum efficiency of the device calculated from formula (1) above, assuming that 3.4×10 ⁴ photons per second are absorbed by the photodiodes.

While the description of the present invention has been made with reference to preferred embodiments, those skilled in the art will appreciate that various changes in form and detail are possible within the scope of the invention as indicated in the accompanying claims.

Various radioactive sources may be used in addition to those mentioned above. A radioactive source can emit photons other than X-rays. Alternatively, the radioactive source may emit alpha particles, beta particles, or neutrons, which are absorbed by the diode and converted into electrical energy.

For example, the radioactive source may be a beta particle emitter such as ⁶³ Ni. An embodiment will now be described in which the microbattery contains a ⁶³ Ni radioactive source (activity 185 MBq; electron energy up to 66 keV) located at a distance of 3 mm from the diode, as described above in accordance with Table 1.

The CASINO computer simulation program (version 3.3) Monte Carlo was used to simulate the interaction of beta electrons in the diode. In particular, the amount of beta-particle energy absorbed in the i-layer of AlInP was studied. The processes of emission of 4000 beta-particles with an energy value between 1 keV and 66 keV and particles falling on the p+ side of the AlInP epitaxial layer were simulated. The simulation showed that beta particles with energies below 22 keV did not reach the i-layer, mainly due to the attenuation of the particle energy in the protective inactive Ni surface layer of the beta particle source used. The attenuation in the top metal contact (covering 33% of the diode surface) and in the dead GaAs layer was a secondary effect, as was the attenuation in the AlInP p+ layer. Beta electrons with energy ≥22 keV left part of their energy in the i-layer. The model assumed that electrons with an energy of 39 keV left the largest part of their energy in the i-layer (17%): beta particles with energies <39 keV lost some of their energy above the i-layer, while beta particles with energies >39 keV easily overcame the i-layer 2 μm thick, leaving only a small part of their energy there (eg, only 8% of the energy from 66 keV was absorbed in the i-layer). Thus, the diode structure in Table 1 is optimized to absorb beta electrons from a 39 keV radioactive source.

However, in a ⁶³ Ni radioactive source, the most probable is the emission of electrons with an energy of 17 keV; the relative probability of emitting electrons with an energy of 39 keV relative to 17 keV is 0.5. For this reason, a ⁶³ Ni radioisotope source of beta particles without a protective inactive Ni surface layer and/or a thicker AlInP i-layer and/or a thinner p+ layer can be used for possible electron absorption over a wider energy range. This will allow a larger percentage of the energy emitted by the radioactive material to remain in the i-layer.

The study of the radioisotope beta-voltaic element in the temperature range from 140°C to -20°C was carried out using a TAS Micro climate chamber to achieve and maintain the study temperature. To control the humidity of the atmosphere in which the element was tested (relative humidity <5%), a stream of dry nitrogen was continuously directed into the climatic chamber. The cell efficiency study was carried out using a Keithley 6487 series picoammeter/voltage source. Forward bias voltage measurements under dark conditions and under the influence of beta radiation from a ⁶³ Ni radioisotope source were carried out in the range from 0 V to 1 V with an interval of 0.01 V. The error associated with the current values was 0.3% of their value plus 400 fA, while the error associated with the applied bias voltage was 0.1% of their value plus 1 mV.

Fig. 10 shows dark current characteristics versus forward bias voltage for a beta voltaic cell at various temperatures. The temperatures studied were 140°С (filled circles), 120°С (empty circles), 100°С (filled squares), 80°С (empty squares), 60°С (crosses), 40°С (filled triangles). ), 20°C (empty triangles), 0°C (filled diamonds), and -20°C (empty diamonds). Obviously, at high temperatures, the dark current through the device increases due to the presence of more thermal energy. As the forward bias voltage increases, a larger electric field is applied to the depletion region of the diode, which leads to an increase in the dark current at each temperature.

The dark current I and the applied bias voltage for a simple p-n diode are related by:

where I ₀ is the saturation current, q is the elementary charge of the electron, n is the ideality factor, k is the Boltzmann constant, and T is the temperature. At each temperature value, the values of I ₀ and n of the diode were determined experimentally using the linear least squares method of the natural logarithm of the measured dark current as a function of the applied forward bias voltage. The equation above was presented in a linear form: Ln/=A+BV, with A=LnI ₀ and B=q(nkT) ^-1 , and a linear least squares method was applied.

Fig. 11 shows the respective dependences of the logarithm of the measured saturation current (left axis, filled circles) and the ideality factor (right axis, crosses) on temperature. The natural logarithm of the saturation current increases with decreasing temperature. An increase in the natural logarithm values by 23.13±0.19 (corresponding to an increase in the saturation current I ₀ by 0.013 pA) was observed in the temperature range between 140°C and -20°C. This is in excellent agreement with the expected increase in the natural logarithm by 20.50 (corresponding to an increase in the saturation current, I ₀ by 0.008 pA). The calculation of the expected growth was made based on the assumption that the temperature dependence of the natural logarithm of the saturation current is proportional to Eg/2kT. In this temperature range, a change in the ideality coefficient was also observed. Since the value of the ideality coefficient was >1.5 at each temperature value, it can be concluded that the generation-recombination mechanism was dominant in relation to the diffusion mechanism. The lower value of the ideality coefficient, which was observed at a higher temperature (1.561 ± 0.003 at 140°C versus 1.682 ± 0.011 at -20°C), can be explained by an increase in the contribution of the diffusion current at elevated temperature.

Fig. 12 shows the dependence of photocurrent characteristics on forward bias voltage at 5 different temperatures. The temperatures studied were 140°С (filled circles), 120°С (empty circles), 100°С (filled squares), 80°С (empty squares), 60°С (crosses), 40°С (filled triangles). ), 20°C (empty triangles), 0°C (filled diamonds), and -20°C (empty diamonds). The open circuit voltage and short circuit current were extrapolated, respectively, as the points of intersection of the curves with the horizontal and vertical axes. At temperatures above 40°C, the current passing through the device increased with decreasing temperature. The opposite trend was observed at temperatures below 40°C. In the temperature range between 40°C and -20°C, the measured current characteristics were scattered, superimposed on one another, thus indicating that the saturation effects from the conduction induced by beta particles prevailed over the thermal mechanism (scattering), the value of which increased at higher temperatures. Beta electrons, losing energy in the AlInP structure, produced electron-hole pairs along their trajectories, which reduced the resistivity in this zone

Fig. 13 shows the open circuit voltage as a function of temperature. The open circuit voltage decreases with increasing temperature.

Fig. 14 shows the dependence of the short circuit current on temperature. Fig. 15 shows the output power of a beta-voltaic cell as a function of applied forward bias voltage over a range of temperatures. The temperatures studied were 140°С (filled circles), 120°С (empty circles), 100°С (filled squares), 80°С (empty squares), 60°С (crosses), 40°С (filled triangles). ), 20°C (empty triangles), 0°C (filled diamonds), and -20°C (empty diamonds). The output power of the beta-voltaic element was calculated by the formula: P=IV. With an increase in the applied forward bias voltage, the output power of the element increased to a maximum (Pm) and then decreased. At temperatures below 40°C, the power characteristics were scattered and overlapped as a consequence of the current results shown in FIG. 12.

Fig. 16 shows the maximum measured output power as a function of temperature (left axis, filled circles) and the beta-voltaic cell internal conversion efficiency as a function of temperature (right axis, open circles). The internal conversion efficiency of the beta-voltaic cell was calculated by dividing the maximum experimental power output value by the maximum power (P _th ). The P _th value was calculated using the following formula:

where A is the activity of the radioactive ⁶³ Ni source (185 MBq), Eт _{i is} the probability of emission of an electron with energy i, A _Ni is the area of the radioactive source (49 mm ² ), A _AlInP is the area of the AlInP detector (0.13 mm ² ), QEi is the fraction of the energy of each electron absorbed in the mesa device (calculated using the CASINO program), and ω _AlInP is the energy of creating an AlInP electron-hole pair (5.34 eV). In the above formula, the activity of the radioactive source has been halved based on the assumption that half of the electrons are lost due to being emitted by the diode. The value of P _th was determined to be 4.3 pW.

On FIG. 16, the maximum output power increases with decreasing temperature, reaching a saturation value of 0.28 pW, corresponding to 0.11 µW/Ci at temperatures <40°C. The observed behavior can be explained by considering the dependence of the maximum output power on the open circuit voltage. The efficiency of a nuclear microbattery depends in part on the apparent activity of the radioactive material used to illuminate at least one diode and in part on the thickness of the semiconductor material to absorb photons or particles emitted by the radioactive material.

For a particular radioactive material, it is possible to determine the actual activity and the apparent activity. At any point in time, activity A, after a period of time t years, is associated with the initial activity A ₀ (at time t=0), by the following expression:

where T _1/2 is the half-life of the radioactive material.

Due to the phenomenon of self-absorption in the radioactive material itself, the apparent activity per unit surface, A app, is determined by the formula:

where C [MBq/mg] is the specific activity of the radioactive material source, t _m [mg/cm ² ] is the mass thickness of the radioactive material and μ _m [cm ² /mg] is the mass attenuation coefficient.

For example, for a radioactive material emitting a beta particle, the mass attenuation coefficient is given by:

where E _max [MeV] is the maximum energy of the beta particle. This beta-radioisotope radioactive material has a specific mass attenuation coefficient (eg for ⁶³ Ni, μ _m =0.828 cm ² /mg).

The specific activity depends on the purity of the radioactive material. For example, the value of the specific activity of high purity radioactive material ⁶³ Ni may be equal to 2072 MBq/mg, and will be less for less pure radioactive material ⁶³ Ni. The specific activity of a typical commercially available ⁶³ Ni radioactive material is 481 MBq/mg.

Fig. 17 shows the actual activity per unit surface (solid lines) and apparent activity per unit surface (broken lines) of ⁶³ Ni radioactive material versus the mass thickness (in mg/cm ² ) of the radioactive material, for a material with a specific activity of 2072 MBq/mg and a material with a specific activity of 481 MBq/mg. It can be seen that the actual activity per unit surface increases linearly with increasing mass thickness, while the apparent activity per unit surface first increases linearly and then, with increasing mass thickness, passes into a plateau to a certain value. In this regard, it is possible to choose the mass thickness of the radioactive material in such a way as to maximize the apparent activity per unit area at the lowest value of the mass thickness, since a larger value of the mass thickness will lead to a greater difference between the actual and apparent activities per unit surface.

It is also important to consider the dimensions of the layers of at least one diode. For example, in the case of a pin or p-n diode, the p-layer thickness can be chosen to be as thin as possible in order to reduce the attenuation of photons or particles of radioactive material. The thickness of the i-layer in a pin junction diode can be chosen large enough so that a substantial part or even all of the photons or particles emitted by the radioisotope material (e.g. even particles/photons of higher energies) are absorbed (e.g. to approximate 100% quantum efficiency ). However, a large thickness of the i-layer does not always increase the efficiency of the microbattery, and perhaps add various problems. For example, the charge collection efficiency may be reduced if the thickness of the i-layer is much larger than that of the depletion layer. In a diode, the depletion region without external bias voltage is fixed by the diode diffusion voltage (which depends on dopant concentrations). Thus, the presence of a depleted layer that is much thinner than the i-layer can affect the efficiency of charge collection due to recombination effects: the generated charge carriers have a high probability of recombination, since they have to travel long distances through the non-depleted material before reaching electrical contacts. Ideally, the thicknesses of the depletion layer and the i-layer are the same. Epitaxial growth of a thick semiconductor structure is also difficult and can affect the quality of semiconductor crystals. Thus, the use of an optimized i-layer thickness makes it possible to obtain high performance microbattery systems in which the electrical output power generated by the microbattery is maximized. For example, simulation showed that for a ⁶³ Ni AlInP microbattery with the highest electron energy of 66 keV, the optimal i-layer thickness is 23 µm.

Now, by way of example only, an exemplary embodiment of a ⁶³ Ni AlInP microbattery will be described to assist in understanding the invention. A battery with parameters of voltage V _m =1.5 V and current I _m =160 nA was considered. In this embodiment, the microbattery contains an array of diodes located on opposite sides of the radioactive material and connected in series such that each array is required to generate a current of 80 nA. However, the diodes could only be located on one side of the radioactive material.

Based on the above requirements, the open circuit voltage (V _OC ) and short circuit current (I _SC ) values can be calculated for each microbattery array. Required open circuit voltage, calculated as:

where β=q/kT. An open circuit voltage of 1.67 V was found to be required.

The duty factor (i.e. the ratio of the actual possible maximum power output to the maximum theoretical power), FF, was calculated according to the formula:

,

,

where υ _OC \u003d V _OC β. The fill factor value is 0.7.

The required short-circuit current I _SC is related to the duty cycle and the required values of I _m and V _m and is given by:

It was found that for the operation of the microbattery matrix with I _m = 80 nA, a short circuit current of 103 nA is required.

After calculating all V _OC and I _SC , the number of diode cells per microbattery array can be calculated based on the activity of the radioactive material and the quantum efficiency QE of each diode cell. Each diode cell has respectively a short circuit current I _SCpp and an open circuit voltage V _OCpp. Thus, the microbattery matrix consists of V _OC /V _OCpp cells connected in parallel to obtain the required V _OC value and I _SC /I _SCpp cells connected in series, resulting in the required I _SC value.

A source of ⁶³ Ni beta particles with a thickness of 3 μm can be taken as a radioactive material (although other radioactive sources and other thicknesses are allowed). The dependence of the radiation probability of such a source on the energy of beta particles is shown in Fig. 18. The initial actual activity of the radioactive source ⁶³ Ni per unit area equal to 7.91 MBq/mm ² will decrease to 6.43 MBq/mm ² after 30 years (the half-life is 100 years). Higher actual activity for a source with the same geometry will not result in an increase in apparent activity, as seen in FIG. 17 due to self-absorption in the source material. A specific activity of 481 MBq/mg would result in a decrease in activity per unit area from 6.43 MBq/mm ² (actual) to 3.88 MBq/mm ² (apparent). Moreover, the amount of useful visible activity per unit area of the source A' _app : is considered to be equal to half of the visible activity per unit area, if only half of the radiation is directed to one microbattery array. The useful visible activity per unit area, A' _app , is given by:

As a result, 1.94 _MBc /mm ² is radiated towards one microbattery array (the other half is radiated towards the other microbattery array).

Each diode cell of the microbattery is considered to have a rectangular shape with an area of 0.8 mm × 0.8 mm. The activity that falls on each cell is given by the formula:

where S _det is the area of the diode cell in mm ² .

The short circuit current of each diode cell is given by:

where E _i is the energy (eV) of the i-th electron hitting the cell surface, QE _i is the quantum efficiency of the cell at the energy of the i-th incident electron, and ω is the energy of creating an electron-hole pair of the cell material.

The quantum efficiency of the cell depends on the energy of the electron and can be determined using simulations. It depends on the dead layers before the active layer, the thickness of the active layer and any dead layer after the active layer. With a decrease in the thickness of any of the upper dead layers (for example, the upper contact) and the p+ layer of the p+-i-n+ diode cell, and with the optimal thickness of the active i-layer, the quantum efficiency can approach 100%. The design of the top contacts can be solved in such a way that the surface open to the radiation of radioactive material is the largest. To accomplish this, interdigital contacts can be used. The thickness of the p+ layer can be reduced to 0.1 µm, which results in a minimum loss of beta particles, especially in the upper part of the beta particle energy graph.

With quantum efficiency taken as 100% for simplicity, the short circuit current per cell is 0.96 nA.

After calculating the short circuit current of the cell, the open circuit voltage of the cell, V _OCpp , is calculated by the formula:

where I _ph is the photocurrent equal to I _SC with an applied bias voltage of 0, and I _SAT is the saturation current. Saturation current can be obtained by measuring the current as a function of the applied forward bias voltage, or can be calculated theoretically:

,

,

where N _C and N _V are the effective densities of state of electrons in the passband and holes in the valence band, respectively, N _A and N _D are the concentrations of acceptors and donors, respectively, D _n and D _p are the diffusion coefficients of electrons and holes, respectively, t _n and t _p are the lifetimes of electrons and holes, respectively, E _g is the band gap of the semiconductor material, and n is the ideality factor of the diode cell. Here, the value of the saturation current I _SAT was used, equal to 2.9×10 ^-17 A (this value was determined experimentally AlInP pin diode with an i-layer thickness of 2 μm). Thus, the open circuit voltage value of each cell is determined to be 0.53 V. The total number of cells N _tot required in each matrix, based on the above conditions, is given by:

. Поскольку предполагалось, что площадь каждой диодной ячейки равна 0,8 мм × 0,8 мм, то площадь матрицы составляет 14,6 мм × 14,6 мм (расстояние между ячейками составляет всего 15 мкм). Поверхность радиоизотопного источника ⁶³Ni между матрицами может перекрываться. Таким образом, радиоизотопный источник ⁶³Ni может иметь начальную активность 1,7 ГБк и площадь 14,6 мм × 14,6 мм.Each array may contain three series-connected elements, with each element having 108 parallel-connected diode cells. Thus, the size of each microbattery matrix is calculated as

. Since the area of each diode cell was assumed to be 0.8 mm × 0.8 mm, the die area is 14.6 mm × 14.6 mm (the distance between cells is only 15 μm). The surface of the ⁶³ Ni radioisotope source between the matrices can overlap. Thus, a ⁶³ Ni radioisotope source can have an initial activity of 1.7 GBq and an area of 14.6 mm × 14.6 mm.

Fig. 19 shows a schematic representation of a microbattery with two arrays of diode cells located on each side of the radioactive material. To prevent the release of radiation of radioactive material, the microbattery may have an outer casing. For example, the housing may be made of tungsten. The regions between the radioactive material and the diodes may be maintained at subatmospheric pressure and/or a gas other than air (eg helium) may be injected into these regions.

Fig. 20 shows a diagram of a diode cell according to an embodiment. The epitaxial AlInP layer of the cell can be grown by metal-organic vapor phase epitaxy (HPE-MOC) on an industrial n-plated (1 0 0) n-GaAs:Si substrate with a misorientation of 10 degrees with respect to <1 1 1>A, to suppress ordered phase as in CuPt.

Doping concentrations p ⁺ and n ⁺ AlInP layers can be 5×10 ¹⁷ cm ^-3 and 2×10 ¹⁸ cm ^-3 , respectively. The thickness of the layers may be 0.1 μm for the p ⁺ - region, 23 μm for the i-region and 0.1 μm for the n ⁺ - region. After growing, to form a square mesa structure (with rounded corners), the plate can be treated with a solution of H ₃ PO ₄ :H ₂ O ₂ :H ₂ O in a ratio of 1:1:1, followed by treatment with a solution of H ₂ SO ₄ : H ₂ О ₂ :H ₂ O, in the ratio of substances 1:8:80 for 10 s. An ohmic back contact, for example, containing 20 nm InGe and 200 nm Au, can be deposited on the back side of the substrate, and an Ohmic top contact, containing, for example, 20 nm Ti and 200 nm Au, can be deposited on the p-side of the mesa device. . The top ohmic contact may only partially cover the surface of each cell, (eg 25%) so that photons or particles incident on the cell are not weakened by the contact.

Fig. 21 is a schematic top-down view of the cell, showing that the top ohmic contact only extends around the perimeter of the cell. However, other designs with large open surfaces are allowed, such as finger-to-toe contacts. As an example, inter-finger contacts with a width of 0.002 mm and an inter-pixel distance of 0.01 mm can be used, covering only 17% of the surface of each cell.

Although the embodiment described above meets certain requirements for a microbattery (V _m =1.5 V and current I _m =160 nA), it is assumed that the microbattery may have other values for the required parameters. Also, the values of the various parameters described may be changed to meet these requirements. For example, the purity of the radioactive source can be increased to reduce the number of cells and the size of each matrix.

While the surface shape of the diode cells has been described as rectangular (may or may not have rounded corners), other cell shapes can be used. For example, in order to prevent possible edge breakdown problems (which may be present at the corners of square cells if the corners are not rounded enough) and to reduce the total distance covered by any two adjacent cells (which will increase for round cells), cells can be polygonal with five, six or more sides.

While mesa diodes have been described, planar diodes can be used (eg to avoid high surface leakage current). These embodiments use ion doping to create zones of high electrical resistance separating the diode cells of the array.

While embodiments have been described in which the radioactive material is located on the p-side of the diode, it is contemplated that it may be located on the n-side. In such embodiments, the substrate (e.g., GaAs substrate) can be etched from the wafer, perhaps so that the thin layer of substrate left serves to mechanically connect the diodes, or alternatively, using an n-type epitaxial layer to mechanically connect the diodes in each array ( possibly with the epitaxial layers either not completely etched through the n-layer and/or possibly with the thickness of the n-type epitaxial layer increased to provide mechanical support). An n-sided compound can then be deposited on this layer, and a radioisotope source can be located in close proximity to it.

Claims (26)

1. Nuclear microbattery containing: radioactive material that emits photons or other particles; and at least one diode, which contains a semiconductor material placed with the possibility of receiving and absorbing photons or other particles and generating electric charge carriers in response to these reception and absorption, and said semiconductor material has a crystal lattice structure, including aluminum, indium and phosphorus , wherein the crystal lattice structure has a lattice composition of Al _0.52 In _0.48 P or Al _0.53 In _0.47 P, and at least one diode contains a PIN junction or a pn junction created by said crystal lattice structure, wherein the nuclear microbattery is either i) capable of directly converting photons or other particles emitted by radioactive material into electrical charge carriers, or ii) comprising a converter for absorbing or interacting with photons or other particles emitted by radioactive material and generating other types of photons or other particles in response to this absorption or interaction; moreover, the semiconductor material is configured to receive and absorb said other types of photons or other particles and generate electric charge carriers in response to these reception and absorption. 2. A microbattery according to claim 1, which contains electrodes for removing the electric current generated by said at least one diode by generating electric charge carriers. 3. A microbattery according to any one of the preceding claims, wherein said at least one diode comprises a plurality of diodes connected in parallel or in series. 4. A microbattery according to any one of the preceding claims, wherein said at least one diode comprises a plurality of diodes, wherein one or more diodes are located on one side of the radioactive material and one or more diodes are located on the second opposite side of the radioactive material. 5. A microbattery according to any one of the preceding claims, wherein a gap is formed between said at least one diode and the radioactive material, which is filled with a gas at subatmospheric pressure. 6. A microbattery according to any one of the preceding claims, wherein a gap is formed between said at least one diode and the radioactive material, which is filled with an inert gas. 7. A microbattery according to any one of the preceding claims, wherein a gap is formed between said at least one diode and the radioactive material, which is filled with radioactive gas. 8. A microbattery according to any one of the preceding claims, in which said radioactive material and at least one diode are placed in a common housing, which is located and configured to substantially prevent photons or other particles of radioactive material from escaping from the housing; or which contains a shielding element located and configured to substantially prevent the passage of photons or other particles of radioactive material through it. 9. A microbattery according to any one of the preceding claims, wherein the thicknesses of the i-layer of the PIN junction are: 40 µm, ≥ 45 µm, or ≥ 50 µm and/or i-layer thicknesses of the PIN junction are: ≤ 50 µm; ≤ 45 µm; ≤ 40 µm; ≤ 35 µm; ≤ 25 30 µm; ≤ 25 µm; ≤ 20 µm; ≤ 15 µm; ≤ 10 µm; or ≤ 5 µm. 10. A microbattery according to any one of the preceding claims, wherein the thickness of the p-layer and/or n-layer of the PIN junction is: ≤ 0.5 µm, ≤ 0.4 µm, ≤ 0.3 µm, ≤ 0.2 µm or ≤ 0.1 µm. 11. A microbattery according to any one of the preceding claims, which comprises an electrode on each side of the PIN junction or p-n junction for energizing the junction and/or removing electric current generated by electric charge carriers generated in the junction, wherein at least one of the electrodes does not cover a part of that side of the junction on which it is located in such a way that said photons or other particles can pass into the junction through said side without passing through said at least one electrode. 12. The microbattery of claim 11, wherein said at least one electrode is annular, perforated, recessed, or interdigitated so as not to completely cover said entire side and to allow said photons or other particles to pass into the junction without passing through the material forming the electrode. 13. Microbattery according to claim 11 or 12, in which at least one electrode covers ≤ x% of the area of the side of the transition on which it is located, and the value of x is selected from: 40; 35; thirty; 25; 20; 15 and 10. 14. A microbattery according to any one of the preceding claims, wherein the surface of each of the at least one diode facing the radioactive material has a substantially polygonal shape. 15. A microbattery according to claim 14, wherein the surface of the polygon has rounded corners. 16. A microbattery according to claim 14 or 15, wherein the surface of the polygon has at least 5 sides or at least 6 sides. 17. Microbattery according to any one of the preceding paragraphs, in which the radioactive material is located within X mm from the semiconductor material of the diode, and the value of X is selected from: ≤ 5; ≤ 4; ≤ 3; ≤ 2; ≤ 1; ≤ 0.8; ≤ 0.7; ≤ 0.6; ≤ 0.5; ≤ 0.4; ≤ 0.3; ≤ 0.2; and ≤ 0.1. 18. A microbattery according to any one of the preceding claims, wherein the radioactive material is a source of x-rays and/or gamma rays or a source of beta particles and/or neutrons. 19. A microbattery according to any one of the preceding claims, wherein the radioactive material is essentially a planar mass with some mass thickness selected from: ≤ 10 mg/cm ² , ≤ 9 mg/cm ² , ≤ 8 mg/cm ² , ≤ 7 mg /cm ² , ≤ 6 mg/cm ² , ≤ 5 mg/cm ² , ≤ 4 mg/cm ² , ≤ 3 mg/cm ² , ≤ 2 mg/cm ² and ≤ 1 mg/cm ² . 20. A microbattery according to any of the preceding claims, wherein the radioactive material is essentially a planar mass with some apparent activity per unit area selected from: ≥ 1 MBq/mm ² ; ≥ 2 MBq/mm ² ; ≥ 3 MBq/mm ² ; ≥ 4 MBq/mm ² ; ≥ 5 MBq/mm ² ; ≥ 6 MBq/mm ² ; ≥ 7 MBq/mm ² ; ≥ 8 MBq/mm ² ; ≥ 9 MBq/mm ² ; ≥ 10 MBq/mm ² ; ≥ 12 MBq/mm ² ; ≥ 14 MBq/mm ² ; ≥ 16 MBq/mm ² ; ≥ 18 MBq/mm ² ; ≥ 20 MBq/mm ² ; ≥ 25 MBq/mm ² ; ≥ 30 MBq/mm ² ; ≥ 35 MBq/mm ² and ≥ 40 MBq/mm ² . 21. A microbattery according to any one of the preceding claims, wherein at least one diode is non-avalanche. 22. A microbattery according to any one of the preceding claims, which does not include a current amplifier and does not amplify the current from the microbattery. 23. A microbattery according to any one of the preceding claims, which comprises an outer casing defining the volume of the battery, selected from the following values: ≤50 ^cm3 , ≤40 ^cm3 , ≤30 ^cm3 , ≤20 ^cm3 , ≤10 ^cm3 , ≤5 cm ³ , ≤ 4 cm ³ , ≤ 3 cm ³ , ≤ 2 cm ³ , ≤ 1 cm ³ . 24. A microbattery according to any one of the preceding claims, which comprises a GaAs substrate, wherein said lattice structure is essentially a lattice matched with said GaAs substrate. 25. An electronic system for receiving power from a microbattery, comprising a microbattery according to any of the preceding claims and an electronic device connected or configured to be connected to the microbattery to receive power for performing one or more operations.

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