Preparation method of microstructure silicon / magnesium silicide heterojunction photoelectric detector

Abstract

The invention aims to provide a preparation method of a microstructure silicon / magnesium silicide heterojunction photoelectric detector, and belongs to the technical field of photoelectric detectors. The method comprises the following steps: preparing a magnesium film on the surface of a silicon substrate, generating a magnesium silicide film through a thermal reaction, etching the silicon substrate with the magnesium silicide film to form a columnar microstructure array, etching to penetrate through a magnesium silicide film layer and reach a certain depth in the silicon substrate, preparing a bottom electrode at the interval of the columnar microstructure array, and forming the magnesium silicide film on the bottom electrode. And finally, covering the top layer of the overall structure with a layer of top electrode. Compared with a traditional silicon / magnesium silicide heterojunction device without a microstructure and with a bottom electrode located on the back face of a silicon substrate, on one hand, the microstructure array can greatly enhance light absorption; and on the other hand, the bottom electrode is arranged on the silicon surface spaced by the columnar microstructures, so that better electrode contact can be realized, the contact resistance can be effectively reduced, the transmission speed of current carriers can be improved, and the response speed and efficiency of the detector are further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of photoelectric detectors, and in particular relates to a method for preparing a microstructured silicon / magnesium silicide heterojunction photoelectric detector. Background Art

[0002] Photodetectors are basic components in the field of optoelectronics. Their working principle is based on the photoelectric effect, that is, when light shines on the sensitive material of the detector, the electrons in the material absorb the energy of the photons and generate electron-hole pairs. The movement of these carriers forms electrical signals, thereby realizing the conversion of light signals to electrical signals. As an important branch of photodetectors, infrared detectors realize the function of converting infrared light signals into electrical signal outputs for subsequent processing. In today's society, infrared detectors play an indispensable role in many fields such as security monitoring, environmental monitoring, disaster warning, power system status monitoring, and artificial intelligence perception.

[0003] At present, materials such as InGaAs, InSb, and HgCdTe dominate the preparation of short-wave infrared detectors. However, these material systems have significant limitations. First, most of these materials contain heavy metal elements, which may cause serious pollution risks to the ecological environment throughout their life cycle, from raw material mining, device preparation, use to waste disposal. Secondly, from the perspective of material process compatibility, these materials are incompatible with the widely used silicon-based complementary metal oxide semiconductor (CMOS) process, which greatly limits the further development of detectors in the direction of high integration and miniaturization, and is not conducive to achieving the goal of high-performance, low-cost mass production. In view of this, the development of a semiconductor material that can work efficiently at room temperature, is compatible with silicon-based CMOS processes, and is environmentally friendly has become a key issue to be solved in the field of short-wave infrared detectors. Magnesium silicide (Mg2Si) is an indirect bandgap semiconductor material with unique physical properties. Its bandgap is between 0.6-0.8eV. Theoretical calculations show that the cutoff response wavelength of magnesium silicide detectors can reach about 1800nm, indicating that it has good detection capabilities for near-infrared light. Moreover, the preparation process of magnesium silicide is highly compatible with silicon-based CMOS process, which provides a solid technical foundation for realizing large-scale integrated manufacturing. In addition, magnesium silicide detectors have excellent performance, high sensitivity, can accurately capture extremely weak infrared light signals, and have a fast response speed, which can respond to rapidly changing infrared scenes in a timely manner. In summary, magnesium silicide detectors have broad application prospects in the field of near-infrared detection and imaging technology, and are expected to become an important force in promoting technological innovation and industrial development in this field.

[0004] The most common device structure of magnesium silicide photodiodes is the PN structure. In the 1960s, Stella A et al. discovered that magnesium silicide materials are compatible with silicon processes and have the potential to be used in the preparation of silicon-based photodetector devices, which has attracted extensive attention from researchers. In 2010, Xiao Qingquan, Xie Quan et al. deposited a layer of Mg film on a flat Si substrate by magnetron sputtering, prepared a single-phase semiconductor Mg2Si thin film through diffusion reaction, and explored devices forming heterojunctions with silicon. In 2019, Japanese scholar EI-Amir A et al. prepared an n-Mg2Si / p-Si photodiode by magnetron sputtering. The prepared photodiode showed obvious rectifying behavior, had obvious spectral response at 800 - 1350 nm, and the spectral response reached a maximum value of 0.47 A / W at 1000 nm. The above-mentioned traditional magnesium silicide PN junction detectors have a high response rate, but the response speed is slow and the absorption is low. This is because, in the magnesium silicide PN junction photodetector, electrodes are prepared on the bottom surface of the upper semiconductor and the lower substrate layer semiconductor, and the upper semiconductor serves as the photosensitive surface. Due to the relatively thick lower substrate layer semiconductor, the electric field distribution is weak here, and the photogenerated carriers are collected slowly. That is, the light absorption of the surface planar structure is limited by the light absorption of the material itself.

[0005] Patent CN202311113920.X discloses a microstructure-enhanced magnesium silicide / silicon heterojunction photodetector and its preparation method. This preparation method prepares a magnesium thin film on the silicon surface with microstructures, enabling magnesium and silicon to fuse with each other before the thermal reaction to increase the contact surface. Compared with the up-and-down penetration of the traditional preparation method, the solid-phase reaction time is shortened, and high-quality magnesium silicide thin films can be grown. However, in this preparation method, the electrodes are still prepared on the top of the magnesium silicide material, resulting in problems such as a large distance between the upper and lower surface electrodes and a weak electric field inside the material. Patent CN202410847232.4 discloses a preparation method of an electrode-embedded silicon-based magnesium silicide thin film photodetector. Compared with the surface electrode MSM device, this preparation method can greatly reduce the surface reflection. The porous interdigitated electrodes can ensure sufficient photon penetration through the magnesium silicide material and improve the light absorption. However, in this preparation method, the surface is not microstructurally treated, resulting in a low light absorption efficiency, which is still limited by the absorption value of the material itself. Summary of the Invention

[0006] Aiming at the problems existing in the background technology, the purpose of the present invention is to provide a preparation method of a microstructured silicon / magnesium silicide heterojunction photodetector. In this method, a magnesium thin film is first prepared on the surface of a silicon substrate, and a magnesium silicide thin film is formed through a thermal reaction. Then, the silicon substrate with the magnesium silicide thin film is etched to form a columnar microstructured array, and the etching penetrates through the magnesium silicide thin film layer and reaches a certain depth into the silicon substrate. Next, a bottom electrode is prepared at the intervals of the columnar microstructured array. Finally, a top electrode is covered on the top layer of the overall structure. In this preparation method, the silicon / magnesium silicide heterojunction forms a columnar microstructured array, and the optoelectronic response signal can be collected through the top electrode and the bottom electrode at the bottom of the microstructures. Compared with the traditional silicon / magnesium silicide heterojunction device without microstructures and with the bottom electrode located on the back of the silicon substrate, on the one hand, the microstructured array increases the surface area, provides more regions for generating photo-generated carriers, and at the same time, the columnar microstructured array can play a role in light scattering and light trapping. The incident light is reflected and scattered multiple times inside the microstructures, greatly enhancing the light absorption. On the other hand, the columnar microstructures can serve as good conduction paths, shortening and optimizing the carrier transport path. There are a large number of bottom electrodes distributed on the silicon surface at the intervals of the columnar microstructures, forming numerous collection sites, greatly improving the carrier collection efficiency. Moreover, the microstructured array can cause local electric field enhancement at its bottom and surrounding regions, further improving the separation efficiency of electrons and holes. The above advantages can not only effectively increase the number of generated carriers but also shorten the carrier transport time, further improving the response speed and efficiency of the detector.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A preparation method of a microstructured silicon / magnesium silicide heterojunction photodetector, the method comprising the following steps:

[0009] Step 1: Prepare a magnesium thin film (20) on a silicon substrate (10);

[0010] Step 2: Generate a magnesium silicide thin film (30) through a thermal reaction;

[0011] Step 3: Etch the silicon substrate (10) with the magnesium silicide thin film to form a periodic columnar microstructured array, and the etching penetrates through the magnesium silicide thin film layer (30) and extends to a certain depth into the silicon substrate;

[0012] Step 4: Prepare a bottom electrode (40) on the exposed silicon substrate surface;

[0013] Step 5: Cover a graphene top electrode (50) on the surface of the columnar microstructured array.

[0014] Further, the silicon substrate in Step 1 is any one of intrinsic silicon, n-type silicon, p-type silicon, and SOI substrate or other substrates with a silicon thin film deposited on the surface; the thickness of the silicon thin film should be greater than 1 μm.

[0015] Further, the magnesium thin film in step 1 is prepared by magnetron sputtering, electron beam evaporation or thermal evaporation methods, and the film thickness is 30 nm to 2 μm.

[0016] Further, the temperature of the thermal reaction in step 2 is 300 to 600 °C, and the time is 10 to 600 minutes.

[0017] Further, the columnar microstructure array in step 3 is a circular column or a square column. The diameter of the circular column or the side length of the square column is 30 nm to 2 μm. The center-to-center spacing between adjacent columns is 30 nm to 2 μm, and the height of the column is 100 nm to 2 μm. It is prepared by a photolithography combined with ion etching process.

[0018] Further, the metal electrode in step 4 is prepared by magnetron sputtering, electron beam evaporation or thermal evaporation methods. The electrode material is made of any one or an alloy of at least two of gold, silver, titanium, aluminum, nickel, and chromium, and the thickness is 20 to 200 nm.

[0019] Further, the graphene electrode in step 5 is prepared by a single-layer or multi-layer exfoliation process.

[0020] The present invention also provides a microstructure silicon / magnesium silicide heterojunction photodetector prepared by the above method.

[0021] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows:

[0022] In the present invention, a magnesium thin film is prepared on a silicon substrate in sequence, silicon-magnesium reaction diffusion is carried out to generate magnesium silicide, columnar microstructure etching, metal electrode preparation and graphene electrode preparation are carried out. In this preparation method, a columnar microstructure array is formed in the silicon / magnesium silicide heterojunction, and the photoelectric response signal can be collected through the graphene top electrode and the bottom electrode at the bottom of the microstructure. Compared with the traditional silicon / magnesium silicide heterojunction device without microstructure and with the bottom electrode located on the back of the silicon substrate, on the one hand, the microstructure array increases the surface area and provides more regions for the generation of photo-generated carriers. At the same time, the columnar microstructure array can play a role in light scattering and light trapping. The incident light is reflected and scattered multiple times inside the microstructure, greatly enhancing the light absorption. On the other hand, the columnar microstructure can serve as a good conductance path, shortening and optimizing the carrier transmission path. There are a large number of bottom electrodes distributed on the silicon surface at the intervals of the columnar microstructures, forming numerous collection sites, greatly improving the carrier collection efficiency, and the microstructure array can cause local electric field enhancement at its bottom and surrounding regions, further improving the separation efficiency of electrons and holes. The above advantages can not only effectively increase the number of generated carriers, but also shorten the carrier transmission time, further improving the response speed and efficiency of the detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1It is a schematic cross-sectional view of the preparation method process of the present invention.

[0024] Figure 2 It is a three-dimensional schematic diagram of the preparation method process of the present invention.

[0025] In the figure: 10 - silicon substrate; 20 - magnesium thin film; 30 - magnesium silicide thin film formed by reaction; 40 - metal bottom electrode prepared after etching; 50 - graphene top electrode. Detailed implementation manners

[0026] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the implementation manners and the accompanying drawings.

[0027] Although magnesium silicide photodetectors have achieved good detection performance, devices based on vertical heterojunctions without microstructures have less effective light absorption, low carrier collection efficiency, and slow device response speed; MSM devices based on surface electrodes have high light reflection, less effective absorption, and low device responsivity. Therefore, the present invention is based on device structure and process design to solve the key problems of less effective light absorption, slower device response speed, and low device responsivity of the device.

[0028] Specifically, the present invention provides a preparation method for a microstructured silicon / magnesium silicide heterojunction photodetector. The schematic cross-sectional view of the method process is as Figure 1 shown, and the three-dimensional schematic diagram is as Figure 2 shown, including:

[0029] Step 1: Prepare a magnesium thin film (20) on a silicon substrate (10) by magnetron sputtering, electron beam evaporation or thermal evaporation method. The film thickness is 30 nm to 2 μm, as Figure 1 -a and Figure 2 -a shown;

[0030] Step 2: Perform a thermal reaction to generate a magnesium silicide thin film (30). The temperature of the thermal reaction is 300 to 600 °C, and the time is 10 to 600 minutes. The thickness of the magnesium silicide will affect the light absorption ability, carrier diffusion and transport efficiency, and quantum efficiency, as Figure 1 -b and Figure 2 -b shown;

[0031] Step 3: Use a photolithography combined with ion etching process to etch the silicon substrate (10) with a magnesium silicide thin film to form a columnar microstructured array. The etching penetrates the magnesium silicide thin film layer (30) and reaches a certain depth into the silicon substrate. Parameters such as the spacing and depth of the microstructures will affect the peaks that generate resonance and thus affect the light absorption, as Figure 1 -c and Figure 2 -c shown;

[0032] Step 4: Prepare a bottom electrode (40) on the silicon surface at the intervals of the columnar micro-structure array by using magnetron sputtering, electron beam evaporation or thermal evaporation methods. The thickness of the electrode is 20 - 200 nm, as shown in Figure 1 -d and Figure 2 -d;

[0033] Step 5: Cover a single-layer or multi-layer graphene top electrode (50) on the surface of the columnar micro-structure array, as shown in Figure 1 -e and Figure 2 -e.

[0034] Example 1

[0035] A preparation method of a micro-structure silicon / magnesium silicide heterojunction photodetector, comprising the following steps:

[0036] Step 1. Select an N-type silicon wafer with a resistivity of 0.1 Ω·cm and a thickness of 500 μm;

[0037] Step 2. Prepare a magnesium thin film on the silicon substrate surface by using a DC magnetron sputtering process. The sputtering power is 30 W, the sputtering time is 60 min, and the sputtering atmosphere is an argon atmosphere of 0.5 Pa;

[0038] Step 3. Conduct in-situ annealing in the magnetron equipment chamber to generate a magnesium silicide thin film through a diffusion reaction. The annealing temperature is 390 °C, the heat preservation time is 6 hours, and the pure argon gas pressure in the chamber is 1000 Pa; after the heat preservation is completed, open the chamber and take out the sample to obtain a silicon-based magnesium silicide thin film;

[0039] Step 4. Use photolithography technology, use a mask plate to expose and develop the silicon substrate with a magnesium silicide thin film, pattern a cylindrical micro-structure array, and combine dry etching to etch columnar micro-structures with a diameter of 200 nm and a column center spacing of 100 nm on the substrate. The height of the column is 1 μm, the etching power is 180 W, and SF6 gas and Ar gas are selected as reaction gases;

[0040] Step 5. Prepare an Ag electrode on the silicon surface between the columnar micro-structure arrays by using thermal evaporation. The thickness is 200 nm, the evaporation rate is 0.1 nm / s, and then remove the photoresist on the magnesium silicide surface and the upper layer of Ag;

[0041] Step 6. Prepare a single-layer graphene by using a mechanical peeling process, and use a transfer platform to transfer the graphene to the surface of the columnar micro-structure array, then the required micro-structure silicon / magnesium silicide heterojunction photodetector can be obtained.

[0042] The above are only specific embodiments of the present invention. Any feature disclosed in this specification, unless specifically described, can be replaced by other equivalent or alternative features with similar purposes; all the disclosed features, or all the steps in any method or process, except for mutually exclusive features and / or steps, can be combined in any manner.

Claims

1. A preparation method of a microstructured silicon / magnesium silicide heterojunction photodetector, characterized in that, It includes the following steps: Step 1: Prepare a magnesium thin film on a silicon substrate; Step 2: Thermally react to generate a magnesium silicide thin film; Step 3: Etch the silicon substrate with the magnesium silicide thin film to form a periodic columnar microstructure array. The etching penetrates through the magnesium silicide thin film layer and extends to a certain depth into the silicon substrate; Step 4: Prepare a bottom electrode on the surface of the exposed silicon substrate; Step 5: Cover the surface of the columnar microstructure array with a graphene top electrode.

2. The preparation method of the microstructured silicon / magnesium silicide heterojunction photodetector according to claim 1, characterized in that, The silicon substrate in Step 1 is any one of intrinsic silicon, n-type silicon, p-type silicon, SOI substrate or other substrates with a silicon thin film deposited on the surface.

3. The preparation method of the microstructured silicon / magnesium silicide heterojunction photodetector according to claim 2, characterized in that, The thickness of the silicon thin film should be greater than 1μm.

4. The preparation method of the microstructured silicon / magnesium silicide heterojunction photodetector according to claim 1, wherein The magnesium thin film in Step 1 is prepared by magnetron sputtering, electron beam evaporation or thermal evaporation methods, and the thickness of the magnesium thin film is 30nm - 2μm.

5. The preparation method of the microstructured silicon / magnesium silicide heterojunction photodetector according to claim 1, characterized in that, The temperature of the thermal reaction in Step 2 is 300 - 600°C, and the time is 10 - 600 minutes.

6. The preparation method of the microstructured silicon / magnesium silicide heterojunction photodetector according to claim 1, wherein The columnar microstructure array in Step 3 is a circular column or a square column. The diameter of the circular column or the side length of the square column is 30nm - 2μm, the center distance between adjacent two columns is 30nm - 2μm, and the height of the column is 100nm - 2μm. It is prepared by a photolithography combined with ion etching process.

7. The preparation method of the microstructured silicon / magnesium silicide heterojunction photodetector according to claim 1, characterized in that, The metal electrode in Step 4 is prepared by magnetron sputtering, electron beam evaporation or thermal evaporation methods. The electrode material is made of any one or an alloy of at least two of gold, silver, titanium, aluminum, nickel, and chromium, and the thickness is 20 - 200nm.

8. The preparation method of the microstructured silicon / magnesium silicide heterojunction photodetector according to claim 1, characterized in that, The graphene electrode in Step 5 is prepared by a single-layer or multi-layer peeling process.

9. A microstructured silicon / magnesium silicide heterojunction photodetector prepared by the preparation method of the microstructured silicon / magnesium silicide heterojunction photodetector according to any one of claims 1 - 8.

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