CN105390909A - Terahertz source based on intrinsic semiconductor layer with micro-nano structure and preparation method - Google Patents

Abstract

The invention discloses a terahertz source based on an intrinsic semiconductor layer with a micro-nano structure and a preparation method. The terahertz radiation source is a device based on a Schottky diode structure, and the device includes sequentially arranged from top to bottom: A first metal electrode with a millimeter-sized window; a transparent or semi-transparent Schottky contact layer; an intrinsic semiconductor layer with a micro-nano structure; a buffer layer; a substrate, an ohmic contact layer, and a second metal An electrode; the intrinsic semiconductor layer is a III-V compound semiconductor layer with high electron mobility; the substrate is an N-type or P-type heavily doped semiconductor layer with high electron mobility. The device of the invention has simple structure and mature technology, and can make the terahertz radiation range from 0.5 to 3.0? THz? The radiation intensity in the range is increased by nearly 10? dB; can provide cheap, efficient and room-temperature-operable terahertz radiation sources for terahertz time-domain spectroscopy in explosives, drugs, bacterial virus detection, biological living imaging and analysis and other applications.

Description

Terahertz source and preparation method based on intrinsic semiconductor layer with micro-nano structure

technical field

The invention relates to the technical field of semiconductor micro-nano structure preparation and terahertz source design and preparation, in particular to the preparation of GaAs micro-nano structure and the preparation method of Schottky diode terahertz source.

Background technique

In recent years, research on terahertz waves and their applications has become a research hotspot in the fields of optics and electronics at home and abroad. The frequency of terahertz electromagnetic waves is roughly from 100GHz to 10THz, between microwave and far-infrared bands. Terahertz waves have great scientific value in many fields, such as biological safety detection, biological cell type identification, terahertz imaging, new terahertz electromagnetic wave radar, etc., and will play an important role in the development of the national economy and national security. For a long time, the lack of effective terahertz sources and detectors has become the biggest bottleneck hindering the development of this technology. The development of a new, efficient, low-cost, and portable terahertz source is one of the key scientific and technological issues that need to be solved urgently.

Terahertz sources, represented by photoconductive antennas based on low-temperature growth of GaAs materials, have brought unprecedented bright prospects to the research and development of terahertz sources due to their advantages of cheap price and simple process. THz (pulse half-high width FWHM can reach 1.4THz) or so. However, the number of material defects produced by the low-temperature growth of this device is limited, so the intensity of the terahertz wave generated by the recombination of holes and electrons is low; ) type substrate, due to the existence of defects, cannot withstand high electric field (high electric field will generate a large current and burn the chip); therefore, the acceleration of carriers in the electric field is small, so the frequency band of terahertz radiation is also relatively small narrow. The above two points lead to the low energy conversion efficiency and narrow spectrum of the current traditional terahertz photoconductive antenna.

At present, the invention patents related to terahertz broadband source devices are mainly focused on the structure design of terahertz antennas, and the improvement of the above problems is very limited, such as a composite photoconductive antenna and a terahertz wave radiation source (application number 201210229910.8), a terahertz radiation Greatly enhanced photoconductive antenna (application number 201310104544.8) and a terahertz photoconductive antenna structure (application number 201220718762.1), etc.

Contents of the invention

The purpose of the present invention is to provide a novel terahertz source device based on Schottky diode structure, the core part of the device is the middle intrinsic gallium arsenide layer, and a micro-nano structure is designed on the intrinsic layer. This layer of structure can not only improve the absorption of pump light, but also increase the recombination of photogenerated electron-hole pairs as defect centers, thereby increasing the intensity of terahertz radiation.

In order to achieve the above purpose, the present invention provides a terahertz radiation source, which is a device based on a Schottky diode structure, and the device includes sequentially arranged from top to bottom:

a first metal electrode with a millimeter-sized window;

A Schottky contact layer that is transparent or translucent and capable of forming a Schottky barrier;

Intrinsic semiconductor layer with micro-nano structure;

The buffer layer;

substrate,

an ohmic contact layer capable of forming an ohmic contact, and,

a second metal electrode;

The intrinsic semiconductor layer is a III-V compound semiconductor layer with high electron mobility; the substrate is an N-type or P-type heavily doped semiconductor layer with high electron mobility.

The above-mentioned terahertz radiation source, wherein, the first metal electrode is an Au film or other metal or alloy electrode with a thickness of tens of nanometers to hundreds of nanometers (that is, on the order of 10 ¹ to 10 ² nanometers); The second metal electrode is an Au film or other metal or alloy electrode, with a thickness ranging from tens of nanometers to hundreds of nanometers (that is, on the order of 10 ¹ to 10 ² nanometers).

The above-mentioned terahertz radiation source, wherein, the Schottky contact layer is a NiCr film with a thickness of several nanometers to tens of nanometers (that is, on the order of 10 ⁰ to 10 ¹ nanometers), which is to take into account the transparent conductivity and the Continuity on the microstructure.

The above-mentioned terahertz radiation source, wherein the intrinsic semiconductor layer is an intrinsic GaAs or InP semiconductor layer.

The above-mentioned terahertz radiation source, wherein, the thickness of the intrinsic semiconductor layer is several hundred nanometers to several micrometers (that is, on the order of 10 ² to 10 ³ nanometers); the thickness of the micro-nano structure is several hundred nanometers to several micrometers ( That is, on the order of 10 ² ~10 ³ nanometers).

The above-mentioned terahertz radiation source, wherein, the buffer layer is an N-type silicon-doped GaAs buffer layer.

The above-mentioned terahertz radiation source, wherein the substrate is an N-type GaAs substrate.

In the above-mentioned terahertz radiation source, the ohmic contact layer is selected from an AuGeNi alloy film or an In film, and the thickness is selected from tens to hundreds of nanometers (that is, on the order of 10 ¹ to 10 ² nanometers).

The above-mentioned terahertz radiation source, wherein, the Schottky diode structure may be a metal-intrinsic semiconductor-n-type semiconductor (m-i-n) type Schottky diode, or a metal-intrinsic semiconductor-p-type semiconductor ( m-i-p) type, n-type semiconductor-intrinsic semiconductor-p-type semiconductor (n-i-p) type or p-type semiconductor-intrinsic semiconductor-n-type semiconductor (p-i-n) type can form a Schottky diode structure, where i represents intrinsic semiconductor, and prepare a layer of micro-nano structure on the intrinsic semiconductor layer. This layer structure can not only have a higher absorption rate for the pump laser, but also promote the recombination of photogenerated electron-hole pairs, thereby enhancing the terahertz radiation.

The present invention also provides a method for preparing the above-mentioned terahertz radiation source structure, the method comprising:

Step 1, pretreating the substrate;

Step 2, growing buffer layer;

Step 3, growing an intrinsic semiconductor layer;

Step 4, preparing a micro-nano structure on the intrinsic semiconductor layer;

Step 5, form an ohmic contact on the back of the substrate: prepare an ohmic contact layer and a second metal electrode in sequence; then, make a Schottky contact on the surface of the micro-nano structure: plate a Schottky contact layer, and then form a The first metal electrode of the window.

Further, in step 4, the method of preparing the micro-nano structure can be ultrafast laser processing, chemical etching (wet or dry method), or photolithography; wherein ultrafast laser processing includes different wavelengths , different pulse width, different energy and other effective combination of various strong laser means.

The present invention uses molecular beam epitaxy (MBE) or metal oxide chemical vapor deposition (MOCVD), etc., to n-type (or p-type) heavily doped (doped with Si) gallium arsenide (or other high electron mobility semiconductor system), an undoped intrinsic GaAs layer is grown along the (001) direction. Before the formal growth, it is baked at a high temperature in a vacuum chamber to remove the oxide layer; then a layer of silicon-doped buffer layer of tens to hundreds of nanometers is grown to block the diffusion of impurities in the substrate; Layered material with a thickness ranging from several hundred nanometers to several microns. Then, a micro-nano structure layer is prepared on the intrinsic gallium arsenide layer. The preparation method can choose laser processing, photolithography or etching (including dry method and wet method). Taking laser processing as an example, first determine the incident power parameters, such as the laser power and the number of pulses, to form a structure with a high absorption rate for the incident laser that generates terahertz; secondly, build a laser optical path for preparing micro-nano structures; then , put the gallium arsenide substrate into the vacuum chamber, and place the vacuum chamber on a horizontal-vertical two-dimensional translation stage, the translation stage is perpendicular to the incident direction of the laser; finally, turn on the laser and control it with the LabView program Stepper motor, ablation of a layer of micro-nano structure on intrinsic gallium arsenide. The absorption efficiency of the device developed by the invention to the pumping femtosecond laser can reach 90%. Finally, the micro-nanostructure gallium arsenide samples were processed into devices using modern microelectromechanical systems (MEMS) technology. First, on the back of the gallium arsenide substrate, a layer of gold-germanium-nickel (AuGeNi) alloy or indium (In) and other metals or alloys that can form ohmic contacts are evaporated by thermal evaporation, electron gun, etc., and then in a rapid annealing furnace Annealing treatment is carried out in it to form an ohmic contact, and then a layer of Au or other metals are plated as a protective layer by means of thermal evaporation, magnetron sputtering or electron gun. Secondly, on the surface of the intrinsic layer with micro-nano structure, a layer of transparent conductive film, such as nickel-chromium (NiCr) alloy, is evaporated by means of thermal evaporation or electron gun, so that a Schottky potential is formed between it and the intrinsic layer. base. After that, a millimeter-scale window is formed on the surface of the micro-nano structure by means of photolithography. Finally, a metal electrode (Au film or other conductive electrodes) is evaporated on the Schottky contact layer and the ohmic contact layer as electrodes. In this way, an electric field can be applied across the ultrapure intrinsic GaAs layer.

The invention utilizes the micro-nano structure layer to achieve up to 90% absorption of the incident pumping femtosecond laser; moreover, it can promote the recombination of photogenerated electron-hole pairs and improve the terahertz radiation efficiency and radiation intensity. The device of the invention has simple structure and mature technology, and can increase the radiation intensity of terahertz radiation by nearly 10dB in the range of 0.5-3.0THz. It can provide a low-cost, high-efficiency, and room-temperature-operating terahertz radiation source for the application of terahertz time-domain spectroscopy in the detection of explosives, drugs, bacteria and viruses, and imaging and analysis of living organisms.

Description of drawings

Fig. 1 is a schematic structural diagram of a novel terahertz source of the present invention.

Fig. 2 is a scanning electron microscope image (SEM) of the micro-nano structure prepared on intrinsic gallium arsenide according to the present invention.

Figures 3a and 3b show the influence of the micro-nano structure of the present invention on the radiation characteristics of the intrinsic gallium arsenide terahertz source under the same photocurrent and electric field strength conditions: Figure 3a represents the time domain diagram, and Figure 3b represents the frequency domain diagram.

detailed description

The technical solution of the present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, it is a typical terahertz radiation source of the present invention, which is a device based on a Schottky diode structure, and the device includes sequentially arranged from top to bottom:

a first metal electrode 1 with a window of millimeter size;

A Schottky contact layer 2 that is transparent or translucent and capable of forming a Schottky barrier;

Intrinsic semiconductor layer 3 with micro-nano structure;

buffer layer 4;

Substrate 5,

an ohmic contact layer 6 capable of forming an ohmic contact, and,

the second metal electrode 7;

The intrinsic semiconductor layer 3 is a group III-V compound semiconductor layer with high electron mobility.

The preparation method of the intrinsic semiconductor terahertz device based on the micro-nano structure of the present invention is divided into three parts, which are the growth of the intrinsic material, the preparation of the micro-nano structure, and the source device process. Take a metal-intrinsic gallium arsenide-n-type doped gallium arsenide (m-i-n) Schottky diode with a micro-nano structure on the intrinsic layer as an example, other m-i-p, n-i-p or p-i-n Schottky diodes The base diode is similar to the m-i-n type diode structure. As shown in Figure 1, the micro-nano structure prepared by strong laser processing is used to illustrate the specific implementation of the patent of the present invention. The structure size and area size formed on the device by other micro-nano structure preparation methods Consistent with the implementation of this example.

1. Growth of intrinsic gallium arsenide layer material. In the experiment, methods such as molecular beam epitaxy (MBE) or metal oxide chemical vapor deposition (MOCVD) were used for growth, as follows:

A. Pre-clean gallium arsenide with n-type heavily doped (100) direction first, clean it with an organic solution, clean it with a solution of hydrogen peroxide, sulfuric acid and deionized water, clean it with deionized water, and dry it with high-purity nitrogen .

B. Place the gallium arsenide substrate in the pretreatment chamber for vacuum-pumping and high-temperature baking to remove the oxide layer.

C. Move the substrate into the growth chamber, and start to grow a buffer layer with a thickness of several hundred nanometers and highly doped Si. This buffer layer mainly prevents impurity atoms that are difficult to remove from the surface from entering the intrinsic layer.

D. Turn off the Si source switch and start to grow the intrinsic layer of gallium arsenide. The thickness of the intrinsic layer is critical, generally hundreds of nanometers to several microns, because on the one hand, a sufficient thickness is guaranteed to prepare a layer of micro-nano structure, on the other hand It is ensured that the gallium arsenide prepared with the micro-nano structure can still bear high electric field intensity.

2. Preparation of the micro-nano structure on the intrinsic gallium arsenide layer. The prepared micro-nano structure is shown in FIG. 2 . The femtosecond laser (or ultrafast laser in other bands) from the 800nm laser amplification stage passes through lenses, filters, and beam splitters in turn to become a pulsed light source for preparing microstructures. The gallium arsenide wafer is placed at the end of a vacuum chamber, and the front end is a window to ensure that the laser beam is irradiated vertically to the gallium arsenide at the end of the vacuum chamber through the window. Specific steps are as follows:

A. First cut the gallium arsenide wafer, wash it, blow it dry, heat it, and fix it on the base at the end of the vacuum chamber.

B. Adjust the laser parameters of the laser, mainly the laser power, and the distance between the end of the vacuum cavity and the lens, that is, adjust the spot size (about 75 μm in diameter).

C. Fix the vacuum cavity on a stepper motor that can move on the X-axis and Z-axis, and adjust the position of the vacuum cavity so that the laser beam is located at the upper left of the GaAs wafer.

D. Vacuumize the vacuum chamber with a mechanical pump and a molecular pump until the vacuum degree reaches the requirement, and then prepare to irradiate the gallium arsenide wafer with laser light.

E. Use the Labview program to control the stepper motor to move back and forth along the X axis for 2 mm at a fixed speed, and then move up to 75 μm along the Z axis. Repeat this cycle 20 times to obtain a microstructure area of the order of millimeters. Block the laser immediately after the stepper motor runs to avoid excessive damage.

F. Evacuate the vacuum chamber, take out the gallium arsenide wafer, and complete the preparation of the micro-nano structure.

3. MEMS technology in the later stage of the device. The later stage of the present invention adopts the modern MEMS technology, and illustrates the preparation technology with a metal-intrinsic semiconductor-n-type doped semiconductor (m-i-n) structure. The specific process is as follows:

A. Form ohmic contacts on the back of the gallium arsenide wafer with micro-nano structure, and make electrodes. A layer of AuGeNi alloy or In thin film can be coated by thermal evaporation, and then a layer of Au film or other metal or alloy can be coated with a magnetron sputtering coating machine.

B. After plating two layers of metal film, place it in a rapid annealing furnace for annealing.

C. Make a Schottky contact on the surface of the micro-nano structure, such as coating a layer of NiCr alloy or other translucent alloy film by thermal evaporation.

D. Spread a layer of photoresist (negative resist) evenly on the NiCr film, develop after photolithography, so that there is a millimeter-sized area on the microstructure area with photoresist.

E. Use a magnetron sputtering coating machine to coat a layer of Au film electrodes, and then remove the glue, leaving a millimeter-scale window in the micro-nano structure area.

F. Use conductive silver paste to stick the ohmic contact surface of the device on the copper sheet of the heat-conducting substrate, and connect the copper sheet to the circuit board with a wire; use a wire welding machine or soldering gold wire on the front of the device to come out to the circuit board.

So far, the preparation of intrinsic semiconductor terahertz devices based on micro-nano structure has been completed.

Then place the source device in the time-domain spectroscopy system to test the radiation characteristics, irradiate the pump laser on the small window, and apply a reverse bias voltage between the upper and lower electrodes to radiate wide-spectrum terahertz waves. By changing The size of the bias voltage can adjust the radiation intensity. The radiation characteristics of devices with micro-nano structures are shown in Figure 3. It can be seen that the radiation intensity of terahertz radiation increases by nearly 10dB in the range of 0.5-3.0THz.

Although the content of the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description should not be considered as limiting the present invention. Various modifications and alterations to the present invention will become apparent to those skilled in the art upon reading the above disclosure. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims (10)

1. A terahertz radiation source is a device based on a Schottky diode structure, characterized in that the device comprises sequentially arranged from top to bottom: a first metal electrode (1) with a window with a size on the order of millimeters; A Schottky contact layer (2) that is transparent or translucent and capable of forming a Schottky barrier; Intrinsic semiconductor layer (3) with micro-nano structure; buffer layer(4); Substrate (5), an ohmic contact layer (6) capable of forming an ohmic contact, and, second metal electrode (7); The intrinsic semiconductor layer (3) is a group III-V compound semiconductor layer with high electron mobility; The substrate (5) is an N-type or P-type heavily doped semiconductor layer with high electron mobility. 2. The terahertz radiation source according to claim 1, characterized in that, the first metal electrode (1) is an Au film or other metal or alloy electrode with a thickness on the order of 10 ¹ to 10 ² nanometers; The above-mentioned second metal electrode (7) is an Au film or other metal or alloy electrode, and its thickness is on the order of 10 ¹ to 10 ² nanometers. 3. The terahertz radiation source according to claim 1, characterized in that, the Schottky contact layer (2) is a NiCr film with a thickness on the order of 10 ⁰ -10 ¹ nanometers. 4. The terahertz radiation source according to claim 1, characterized in that, the intrinsic semiconductor layer (3) is an intrinsic GaAs or InP semiconductor layer. 5. The terahertz radiation source according to claim 1, characterized in that, the thickness of the intrinsic semiconductor layer (3) is on the order of 10 ² ~10 ³ nanometers; the thickness of the micro-nano structure is 10 ² ~10 ³ nanometers. 6. The terahertz radiation source according to claim 1, characterized in that, the buffer layer (4) is an N-type silicon-doped GaAs buffer layer. 7. The terahertz radiation source according to claim 1, characterized in that, the substrate (5) is an N-type GaAs substrate. 8 . The terahertz radiation source according to claim 1 , characterized in that, the ohmic contact layer ( 6 ) is selected from an AuGeNi alloy film or an In film, and its thickness is on the order of 10 ¹ -10 ² nanometers. 9. The terahertz radiation source according to claim 1, wherein the Schottky diode structure is selected from metal-intrinsic semiconductor-n-type semiconductor Schottky diode, metal-intrinsic semiconductor-p-type Any structure among semiconductor type, n-type semiconductor-intrinsic semiconductor-p-type semiconductor type or p-type semiconductor-local oscillator semiconductor-n-type semiconductor type. 10. A method for preparing the terahertz radiation source structure according to claim 1, characterized in that the method comprises: Step 1, pretreating the substrate (5); Step 2, growing buffer layer (4); Step 3, growing an intrinsic semiconductor layer (3); Step 4, preparing a micro-nano structure on the intrinsic semiconductor layer (3); Step 5, sequentially plate an ohmic contact layer (6) and a second metal electrode (7) on the back of the substrate (5); then, make a Schottky contact on the surface of the micro-nano structure: Plating a Schottky contact layer ( 2), and then form a first metal electrode (1) with a millimeter-sized window.