JP2004047601A - Iron silicide semiconductor thin film and method of manufacturing the same - Google Patents

Abstract

[PROBLEMS] The optical and electrical characteristics of β-FeSi ₂ have recently been investigated and clarified in detail, and the optical and electrical characteristics of an amorphous iron silicide semiconductor have been gradually clarified. Control of these characteristics is a major issue.
An iron silicide semiconductor thin film characterized in that an optical band gap is changed by hydrogenation. An iron silicide semiconductor thin film wherein the carrier concentration is controlled by hydrogenation. In beta-FeSi ₂ or amorphous FeSi thin film growth methods _X, iron hydrogenated beta-FeSi ₂ or amorphous FeSi _X by incorporating hydrogen into thin film to grow by introducing the hydrogen gas into the atmosphere during film formation A method for manufacturing a silicide semiconductor thin film.
[Selection diagram] FIG.

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an iron silicide semiconductor thin film and a method for manufacturing the same.
[0002]
[Prior art]
Ideally, next-generation industrial materials are made of only low environmental load elements without concern about resource life. As the candidate elements, atmospheric constituent elements (N, O) that do not need to consider resource life, elements with extremely long resource life (Si, Ca, Ga), and elements with high recycling rates (Fe, Cu) are considered. .
[0003]
According to the above idea, various environmental materials such as GaN, Cu ₂ O, β-FeSi _{2 and the} like can be considered as semiconductors. Among them, β-FeSi ₂ is a direct transition type semiconductor that can be epitaxially grown on a Si substrate, has a large absorption coefficient (（10 ⁻⁵ cm ⁻¹ at visible wavelength), and has a band gap of 0.85 eV. For this reason, it is attracting much attention as a next-generation semiconductor material.
[0004]
Specific applications include high-efficiency solar cell materials and optical device materials such as photodiodes and light-emitting diodes, such as those relating to a method for forming a β-FeSi ₂ thin film (Japanese Patent Laid-Open No. 2001-64099) and solar cells ( JP-A-11-103080) and those relating to light-emitting elements (JP-A-2000-133836, JP-A-2001-127338, JP-A-2002-57368, JP-A-2002-76431, JP-T-2001) No. 504277) has been applied for a patent.
[0005]
[Problems to be solved by the invention]
The present inventors have previously developed a method of depositing a β-phase FeSi ₂ thin film while being deposited on a substrate by a laser ablation method (Japanese Patent Laid-Open No. 2000-178713). Further, a patent application was filed for a method of depositing a β-phase FeSi ₂ thin film by a facing target type DC sputtering method (Japanese Patent Application No. 2001-386820). Also, very recently, it has been reported that a film exhibiting semiconductor characteristics can be obtained even when the amorphous state is maintained while the composition ratio remains almost unchanged ("The 62nd Annual Meeting of the Japan Society of Applied Physics", p. 1022, September 2001). On March 11, 2001 ("The 2001 Annual Meeting of the Japan Society of Applied Physics, Kyushu Section Lectures", page 86, December 1, 2001), this is also drawing attention, and related inventions have been patented (Japanese Patent Application 2001). -386824, and Japanese Patent Application No. 2001-388341).
The continuous film formed by such a method was an amorphous film and exhibited an optical band gap of 0.64 to 0.70 eV, and the β-FeSi ₂ film exhibited an optical band gap of 0.85 to 0.92 eV. .
[0006]
The optical and electrical properties of β-FeSi ₂ have recently been investigated and clarified in detail, and the optical and electrical properties of amorphous iron silicide semiconductors have been gradually clarified. Control is a major challenge. When β-FeSi ₂ and an amorphous iron silicide semiconductor are used in various devices in the future, it is necessary to control optical and electrical characteristics. In particular, reduction and control of the carrier concentration and control of the band gap are indispensable.
[0007]
[Means for Solving the Problems]
The present inventor has found that the above problem can be solved by hydrogenating β-FeSi ₂ or amorphous FeSi _X (x is 1 to ∞) of an iron silicide semiconductor.
That is, the present invention is an iron silicide semiconductor thin film characterized in that the optical band gap is changed by hydrogenation.
Further, the present invention is the above-mentioned iron silicide semiconductor thin film, which is made of β-FeSi ₂ having an optical band gap in a range of 0.6 to 1.1 eV.
Further, the present invention is the above-mentioned iron silicide semiconductor thin film, wherein the thin film is made of amorphous FeSi _x (x is 1 to ∞) having an optical band gap of 0 to 1.85 eV.
Further, the present invention is an iron silicide semiconductor thin film wherein the carrier concentration is controlled by hydrogenation.
Further, the present invention is an optical / electronic device using the above-mentioned iron silicide semiconductor thin film.
[0008]
Furthermore, the present invention, beta-FeSi ₂ or amorphous FeSi in the thin film growth methods _X, by incorporating hydrogen in the thin film during the growing by flowing hydrogen gas atmosphere during deposition beta-FeSi ₂ or amorphous FeSi _X (x is 1 to ∞) is hydrogenated, wherein the iron silicide semiconductor thin film is manufactured as described above.
[0009]
In the present invention, the term “hydrogenation” means that hydrogen is bonded to Si atoms and / or Fe atoms of β-FeSi ₂ or amorphous FeSi _X mixed in the thin film during the growth of the thin film. Due to hydrogenation, amorphous FeSi _X has a band gap in the range of 0 to 1.85 eV from about zero in the case of Fe-rich to 1.85 eV in the case of 100% Si, and β-FeSi ₂ has a band gap in the range of 0.6 to 1.1 eV. Can be changed. Therefore, by adjusting the band gap, it is possible to optimize the hybrid of the light emitting and receiving elements and the wavelength of the light to be transmitted and received.
[0010]
Further, the electrical resistance, that is, the carrier concentration can be controlled by hydrogenating β-FeSi ₂ or amorphous FeSi _X. Carrier concentration control is indispensable for device design of light emitting and receiving elements and circuits. Controlling the carrier concentration allows the application of this material to electronic devices. As the degree of hydrogenation increases, the specific resistance indicating the carrier concentration increases once and then decreases. A small amount of hydrogen contained in β-FeSi ₂ or amorphous FeSi _X is composed of Fe, Si and H, and terminates non-bonded electrons contained in the crystal structure of the orthorhombic crystal structure to reduce the carrier concentration, It is considered that the inclusion of a certain amount or more contributes to the generation of carriers.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The iron silicide semiconductor thin film of the present invention can be manufactured by a normal thin film growth method, for example, a physical vapor growth method such as a laser ablation method, a sputtering method, a vapor deposition method, or an ion plating method, or a chemical vapor deposition method. A hydrogenated β-FeSi ₂ film or a hydrogenated amorphous FeSi _X can be grown depending on the difference in substrate temperature around 400 ° C.
[0012]
In the laser ablation method, an atmosphere during film growth using laser irradiation on an FeSi _X target, laser irradiation on a Fe and Si target simultaneously or alternately, or laser irradiation on an Fe target in the case of a heated Si substrate. To adjust the pressure of the hydrogen gas to produce β-FeSi ₂ or amorphous FeSi _X having a controlled hydrogen content.
[0013]
Further, in the sputtering method, sputtering of a FeSi _X target, or simultaneous or alternate sputtering of an Fe and Si target, or a rare gas for sputtering during film growth using sputtering of an Fe target in the case of a heated Si substrate. By flowing hydrogen gas and adjusting the ratio of the flow rates of the sputtering gas and the hydrogen gas, β-FeSi ₂ or amorphous FeSi _X having a controlled hydrogen content is produced. The rare gas for sputtering contains any component of neon, argon, krypton, and xenon.
[0014]
The optical band gap of the iron silicide semiconductor thin film is changed by controlling the amount of hydrogen contained in the thin film of β-FeSi ₂ or amorphous FeSi _X by adjusting the pressure of hydrogen gas in the atmosphere during the growth of the thin film. be able to. Further, by forming a film by changing the amount of inflow of hydrogen, a film having an optical band gap different in the depth direction of the film can be easily formed. As the degree of hydrogenation increases, the optical band gap increases.
[0015]
Similarly, by controlling the amount of hydrogen contained in the β-FeSi ₂ or amorphous FeSi _X thin film, the electrical characteristics of the iron silicide semiconductor thin film are controlled by the effect of reducing the carrier concentration or increasing the carrier concentration. be able to.
The hydrogen content at the boundary where the carrier concentration is reduced or the carrier concentration is increased is about 10 at%, but this boundary depends on the crystallinity of the formed film. Shift toward
[0016]
By using the iron hydride silicide semiconductor thin film of the present invention, an optoelectronic device such as a pn junction light receiving device similar to an optoelectronic device manufactured using an existing Si or GaAs-based semiconductor can be manufactured. Although a film showing a pn junction has not yet been obtained with β-FeSi ₂ or amorphous FeSi _X that has not been hydrogenated, a pn junction film was first realized using the hydrogenated iron silicide film of the present invention. When it is desired to form a pn junction film with silicon, for example, a p-type β-FeSi film may be formed on an n-type Si substrate.
[0017]
Experiment 1
Hereinafter, a method for producing an iron hydride silicide thin film by a laser ablation method and characteristics of the obtained thin film will be specifically described.
After the inside of the vacuum chamber is evacuated to 2 × 10 ⁻⁷ Torr or less by a turbo molecular pump, an ArF excimer laser (wavelength: 193 nm, FWHM = 20 ns) is supplied to the vacuum chamber into which hydrogen flows in a pressure range of 0.1 to 10 Pa. The light was focused on an FeSi ₂ amorphous alloy (99.99%) target having a composition ratio of 1: 2 and irradiated at an incident angle of 45 °, and a film was deposited on a facing Si substrate at a distance of 50 mm. A blade-type rotary filter capable of high-speed rotation was provided between the target and the substrate to capture droplets. The fluence F of the laser pulse was 4 J / cm ² , the repetition frequency was 10 Hz, and the substrate temperature was room temperature (20 ° C.) and 700 ° C.
[0018]
The resulting film was evaluated by SEM observation, X-ray diffraction, light absorption spectrum measurement, and electrical resistance measurement. An amorphous FeSi _X film is formed at 400 ° C. or less, and a β-FeSi ₂ film is formed at 400 ° C. or more. Amorphous FeSi _X and β-FeSi ₂ were hydrogenated by changing the pressure of hydrogen in the atmosphere gas.
[0019]
FIG. 1 shows changes in the X-ray diffraction pattern of the β-FeSi ₂ film when the hydrogen pressure is set to 0 Pa, 0.3 Pa, and 3 Pa (a is 2θ-θ scan, b is 2θ scan). The peak from β-FeSi ₂ is observed even when the pressure of hydrogen is increased, and it can be seen that the β-FeSi ₂ film is growing even when hydrogen is mixed into the thin film. When amorphous FeSi _X is generated, the XRD peak is not observed regardless of the hydrogen pressure due to the amorphous state.
[0020]
Figure 2 shows a typical absorption spectrum of the hydrogenated amorphous FeSi _X. FIG. 3 shows a typical absorption spectrum of hydrogenated β-FeSi ₂ . In both cases, the band gap is increased as compared with the case of hydrogen-free, and fitting can be performed to the square of the absorption coefficient.
[0021]
FIG. 4 shows the dependence of the optical band gap (vertical axis: Eg [eV]) on the hydrogen pressure (horizontal axis: [Pa]). As the hydrogen pressure increases, that is, as the amount of hydrogen mixed in the film increases, the optical band gap increases.
[0022]
FIG. 5 shows the dependency of the specific resistance (vertical axis: ρs [Ω]) on the hydrogen pressure (horizontal axis: [Pa]). The specific resistance of β-FeSi ₂ is one order of magnitude greater than that of amorphous FeSi _X , but both increase once as the hydrogen pressure increases and then decrease. It can be seen that the incorporation of hydrogen into the film terminates non-bonded electrons and reduces the carrier concentration, and that if hydrogen is excessively mixed, non-bonded electrons of hydrogen cause carriers to reduce the electric resistance.
[0023]
Experiment 2
Hereinafter, the method for producing the iron hydride silicide thin film by the opposed target sputtering method and the characteristics of the obtained thin film will be specifically described.
The chamber was evacuated to 10 ⁻⁴ Pa or less using a turbo molecular pump, and Ar gas and hydrogen gas were introduced into the chamber to a total pressure of 1.33 × 10 ⁻¹ Pa. An FeSi ₂ alloy (99.99%) having a composition ratio of 1: 2 was used as a target. The applied voltage and current were 950 mV and 6.0 mA, respectively, and amorphous FeSi _X and β-FeSi ₂ were deposited on the Si substrate at room temperature (20 ° C.) and 700 ° C., respectively, to a thickness of about 240 nm.
[0024]
The resulting film was evaluated by SEM observation, X-ray diffraction, light absorption spectrum measurement, and electrical resistance measurement. At 400 ° C. or lower, amorphous-like FeSi _X is formed, and at 400 ° C. or higher, a β-FeSi ₂ film is formed. By adjusting the ratio of argon gas to hydrogen gas, hydrogenation of amorphous-like FeSi _X and β-FeSi ₂ is performed. went.
[0025]
FIG. 6 shows an X-ray diffraction pattern of the obtained hydrogenated β-FeSi ₂ film. FIG. 7 shows an X-ray diffraction pattern of the obtained hydrogenated amorphous FeSi _X film. As shown in FIG. 6, a diffraction peak of β-FeSi ₂ is observed regardless of the hydrogen partial pressure, and hydrogenated β-FeSi ₂ grows. As shown in FIG. 7, at room temperature, a broad peak is observed regardless of the hydrogen partial pressure, and amorphous FeSi _X grows.
[0026]
FIG. 8 shows a typical absorption spectrum of non-hydrogenated amorphous FeSi _X. FIG. 9 shows a typical absorption spectrum of hydrogenated FeSi _X. The absorption spectrum is almost a straight line when the vertical axis is the square of the absorption coefficient, which indicates that the semiconductor is a direct transition type semiconductor. It can be seen that the hydrogenated thin film has a larger band gap.
[0027]
FIG. 10 shows a typical absorption spectrum of hydrogen-free β-FeSi ₂ . FIG. 11 shows a typical absorption spectrum of hydrogenated β-FeSi ₂ . Like amorphous FeSi _X , it is a direct transition semiconductor, and hydrogenated β-FeSi ₂ has a larger band gap.
[0028]
FIG. 12 shows a change in the optical band gap (vertical axis: Eg [eV]) with respect to the hydrogen partial pressure (P _H2 / P _Ar ). As the hydrogen partial pressure increases, the optical band gap increases, indicating that the optical band gap increases as the hydrogen content in the thin film increases.
[0029]
FIG. 13 shows a change in the specific resistance (vertical axis: ρs [Ω]) with respect to the hydrogen partial pressure (P _H2 / P _Ar ). The resistivity once increases with an increase in hydrogen pressure and then decreases. It can be understood that non-bonded electrons are terminated by mixing hydrogen into the thin film and the carrier concentration is reduced, and that if hydrogen is mixed excessively, non-bonded electrons of hydrogen cause carriers to reduce electric resistance.
[0030]
【Example】
Example 1
An element similar to an optoelectronic element manufactured using existing Si or GaAs-based semiconductors was manufactured using hydrogenated β-FeSi ₂ formed by a facing target type DC sputtering method. The target was composed of a FeSi ₂ alloy (99.99%) having a composition ratio of 1: 2 doped with P (phosphorus) at 10 ¹⁹ cm ⁻¹ and a composition ratio of ^1:15 doped with B (boron) at 10 ¹⁵ cm ^−1. 2 FeSi ₂ alloy (99.99%) was used. After the inside of the chamber was evacuated to 10 ⁻⁴ Pa or less using a turbo molecular pump, a hydrogen gas of 15 sccm was added to the Ar gas and flowed in, and the film was formed at a total pressure of 1.33 × 10 ⁻¹ Pa in the chamber. Was done.
[0031]
Insulating quartz glass was used for the substrate, and the substrate temperature was 600 ° C. First, p-type hydrogenated β-FeSi ₂ was deposited to a thickness of 5 μm on a substrate using a P-doped target, and then n-type hydrogenated β-FeSi ₂ was deposited to a thickness of 30 nm using a B-doped target.
[0032]
14, insulating quartz on a glass substrate 1 by forming a p-type hydrogenated beta-FeSi ₂ thin film 2, further n-type hydrogenated beta-FeSi ₂ thin film thereon by using a hydrogenation beta-FeSi ₂ 3 schematically shows a structure of a pn junction type light receiving element in which an electrode 4 is formed on each of a p-type hydrogenated β-FeSi ₂ thin film 2 and an n-type hydrogenated β-FeSi ₂ thin film 3.
[0033]
FIG. 15 shows the IV characteristics of the device. Similar to a pn junction element using Si, IV characteristics typical of a pn junction were observed when light was not irradiated and when light was irradiated. The intercepts of the V axis and the I axis at the time of light irradiation are called open-circuit voltage and short-circuit current, respectively, and their product corresponds to the maximum power that can be taken out when considered as a photoelectric conversion element. It was found that a clear open-circuit voltage and a short-circuit current were present, and that the device functioned as a photoelectric device. It was confirmed that a pn-bonded film was realized with β-FeSi ₂ .
[0034]
【The invention's effect】
When the iron silicide semiconductor thin film of the present invention is used for various devices, it is possible to control light and electric characteristics by giving a desired band gap, and a photoelectric conversion element having different photosensitivity on the same element. Can also be realized.
[Brief description of the drawings]
FIG. 1 is an X-ray diffraction pattern of a hydrogenated β-FeSi ₂ film produced in Experiment 1.
FIG. 2 is a typical absorption spectrum of a hydrogenated amorphous film (hydrogen pressure: 0.3 Pa) produced in Experiment 1.
FIG. 3 is a typical absorption spectrum of a hydrogenated β-FeSi ₂ film (hydrogen pressure: 0.3 Pa) produced in Experiment 1.
FIG. 4 is a graph showing a change in an optical band gap with respect to a hydrogen pressure of a hydrogenated amorphous film and β-FeSi ₂ produced in Experiment 1.
FIG. 5 is a graph showing a change in specific resistance to hydrogen pressure of a hydrogenated amorphous film and β-FeSi ₂ produced in Experiment 1.
FIG. 6 is an X-ray diffraction pattern of a hydrogenated β-FeSi ₂ film produced in Experiment 2.
FIG. 7 is an X-ray diffraction pattern of a hydrogenated amorphous FeSi _X film produced in Experiment 2.
FIG. 8 is a typical absorption spectrum of a non-hydrogenated amorphous FeSi _X film produced in Experiment 2.
FIG. 9 is a typical absorption spectrum of a hydrogenated amorphous FeSi _X film produced in Experiment 2.
FIG. 10 is an absorption spectrum of a non-hydrogenated β-FeSi ₂ film produced in Experiment 2.
FIG. 11 is a typical absorption spectrum of a hydrogenated β-FeSi ₂ film produced in Experiment 2.
FIG. 12 is a graph showing a change in an optical band gap accompanying hydrogenation of hydrogenated amorphous FeSi ₂ (700 ° C.) and β-FeSi ₂ (30 ° C.) produced in Experiment 2.
FIG. 13 is a graph showing a change in specific resistance accompanying hydrogenation of hydrogenated β-FeSi ₂ (700 ° C.) and amorphous FeSi ₂ (30 ° C.) produced in Experiment 2.
FIG. 14 is a schematic diagram of a structure of a pn junction type light receiving element using hydrogenated β-FeSi ₂ manufactured in Example 1.
FIG. 15 is a graph showing IV characteristics of a pn junction type light receiving element using hydrogenated β-FeSi ₂ manufactured in Example 1.

Claims (6)

An iron silicide semiconductor thin film wherein the optical band gap is changed by hydrogenation. _2. The iron silicide semiconductor thin film according to claim 1, wherein the optical band gap is made of β-FeSi2 having a range of 0.6 to 1.1 eV. Iron silicide semiconductor thin film according to claim 1, wherein the optical band gap (the x that 1～∞) amorphous FeSi _X ranging 0~1.85eV characterized by comprising the. An iron silicide semiconductor thin film wherein the carrier concentration is controlled by hydrogenation. An optoelectronic device comprising the iron silicide semiconductor thin film according to claim 1. In the method of growing a thin film of β-FeSi ₂ or amorphous FeSi _X , hydrogen gas is introduced into an atmosphere at the time of film formation and hydrogen is mixed into the grown thin film to form β-FeSi ₂ or amorphous FeSi _X (x is 1 to 3). 5. The method for producing an iron silicide semiconductor thin film according to claim 1, wherein ∞) is hydrogenated.

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