Preparation method of MSM photoelectric detector integrated with columnar microstructure array

Abstract

The invention provides a preparation method of an MSM photoelectric detector integrated with a columnar microstructure array, and belongs to the technical field of photoelectric detectors. According to the preparation method, the columnar microstructure array is integrated on the surface of the semiconductor film, and the latticed interdigital electrode is prepared in the channel, so that surface reflection of the device can be reduced, scattering can be increased, the intensity of reflected light is reduced, light absorption is enhanced, electric field distribution in the semiconductor film is improved, and the performance of the device is improved. Therefore, the collection efficiency of photon-generated carriers in the semiconductor film is improved, the process is simple, and large-scale integration is facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of photodetectors, and particularly relates to a preparation method of an MSM photodetector integrated with a columnar microstructure array. Background Art

[0002] A photodetector (PD) is a key device for converting optical signals in an optical detection system and fiber optic communication. At present, the continuously increasing rate of fiber optic communication systems has put higher and higher requirements on the response rate of photodetectors, and high-speed photodetectors have become an important research topic. The Metal-Semiconductor-Metal photodetector (MSM-PD) has received extensive attention and applications due to its high responsivity, high sensitivity, simple structure, easy integration, and low cost. The MSM photodetector refers to a back-to-back Schottky diode formed by making metal electrodes on the surface of a semiconductor material, which is composed of a photosensitive layer and interdigital electrodes. The interdigital electrodes are composed of two sets of discrete metal strips on the semiconductor surface, and the interval between the interdigital electrodes is the photosensitive surface. Compared with other types of photodetectors such as PIN diodes, the MSM-PD device mainly has the following advantages: (1) Extremely low distributed capacitance. The MSM-PD device is actually two back-to-back diodes. When working, one is forward-biased and the other is reverse-biased, so the device junction capacitance is small and changes little with voltage. At the same time, the MSM-PD is a metal-semiconductor structure without the minority carrier effect, has a small series resistance, extremely low distributed capacitance, and its response speed mainly depends on the transit time of photo-generated carriers between the two electrodes, and has little relationship with the capacitance characteristics, so the device has a high response speed; (2) Extremely small dark current. For the two metal-semiconductor junctions of the Schottky contact, one is forward-biased and the other is reverse-biased. The depletion region of the reverse-biased Schottky junction is longer, reducing the tunneling probability of electrons and holes. Therefore, the dark current between the two poles of the detector is correspondingly reduced, which is 3 to 5 orders of magnitude smaller than the dark current of photodetectors with other structures of the same material; (3) Simple structure and easy process implementation. After growing the semiconductor material on the substrate, only one photolithography process is required to prepare the interdigital electrodes on the surface of the semiconductor material and form a Schottky contact with the semiconductor material. And the entire process is fully compatible with the MOS field effect transistor process, and it is very easy to realize a fully monolithic optoelectronic integrated (OEIC) device.

[0003] In addition to a fast response speed, a high-performance photodetector also needs to have a high light absorption rate to ensure a high quantum efficiency of the detector. To achieve high light absorption in a relatively thin semiconductor material, integrating periodic microstructures into the photosensitive thin film has been proven to be an effective method. The size of the microstructures is on the same order of magnitude as the detection wavelength. Due to the scale effect, both its radiation characteristics and transmission characteristics will be quite different from those of the radiation characteristics under the traditional macroscopic scale. The microstructures can cause multiple reflection and diffraction effects, resulting in various abnormal radiation phenomena. It can not only increase the light propagation path and absorption probability through multiple reflections, but also introduce additional light through the coupling with electromagnetic waves to increase absorption. Therefore, constructing periodic microstructures in the semiconductor thin film can improve its light absorption characteristics in the visible and infrared wavelength ranges. Wu Fengbing et al. integrated a rectangular grating light-trapping structure and a triangular grating light-trapping structure on the surface of a solar cell. Their research results showed that both of these light-trapping structures effectively improved the light absorption rate of the solar cell surface in the visible and near-infrared bands, thereby improving the overall conversion efficiency of the solar cell (Wu Fengbing, et al. Micro-nano light-trapping grating structures in solar cells. Laser Journal. 2010, (005): 15-17); Leem et al. constructed a parabolic sub-wavelength grating structure on the surface of the aluminum-doped zinc oxide thin film of a silicon-based solar cell. Compared with the simple thin film structure, this structure can significantly suppress surface reflection, thereby improving the light absorption characteristics of the solar cell surface for sunlight (J. Leem, et al. Biomimetic parabola-shaped AZO subwavelength grating structures for efficient antireflection of Si-based solar cells. Solar Energy Materials and Solar Cells. 2011, 95(8): 2221-2227); H. Cansizoglu et al. integrated a periodic hole structure in a silicon and germanium PIN photodiode, enabling light to propagate laterally in the semiconductor thin film, and significantly improving the light absorption rate and the quantum efficiency of the detection device in the 800-1700 nm band (H. Cansizoglu, et al. Surface-illuminated photon-trapping high-speed Ge-on-Si photodiodes with improved efficiency up to 1700 nm. Photonics Research. 2018, 6(7): 734-742).

[0004] In summary, the MSM structure can ensure the high-speed response of the photodetector, and integrating a periodic optical trap structure in the semiconductor thin film can enhance the high absorption and quantum efficiency of the photodetector. However, the interdigital electrodes in the MSM structure need to use a small electrode spacing to ensure the rapid drift and collection of photo-generated carriers between the electrodes to achieve a high response rate and bandwidth, as Figure 1 shown (taking a circular device with a diameter of 30 μm as an example). The microstructure size (period) in the semiconductor material needs to be on the same order of magnitude as the detection wavelength to provide a high light absorption rate. In the infrared band with a longer wavelength, a larger microstructure period is required, which makes it very difficult to fabricate an interdigital electrode layer with a small electrode spacing on the surface of the semiconductor thin film integrated with the microstructure. Patent CN201811381512.1 discloses a preparation method of an MSM photodetector. By integrating a periodic optical trap structure in the semiconductor thin film, this preparation method can effectively improve the light detection efficiency of the detector while ensuring the response rate of the MSM photodetector. This method can solve the device preparation and integration problems when the period hole size in the semiconductor thin film is larger than the surface electrode spacing, and at the same time ensure that the MSM photodetector has a small electrode spacing and a large period hole size, so as to achieve a fast response speed and a high quantum efficiency at the same time. However, this method requires a wet etching process to separate the device, and then a periodic optical trap structure is prepared on the back of the device, and the process is relatively complex and not convenient for large-scale integration. Patent CN110752268B discloses a preparation method of an MSM photodetector integrated with a periodic light-limiting structure. By integrating a periodic light-trapping structure in the semiconductor thin film between each pair of electrodes, the detector has both a large light-trapping structure period and a small electrode spacing, and can effectively improve the light detection efficiency of the detector while ensuring the response rate of the MSM photodetector. However, the MSM photodetector prepared by this method is a surface electrode structure, and the strong electric field generated after applying the bias is only distributed on the surface of the semiconductor thin film, resulting in a low collection efficiency of photo-generated carriers in the semiconductor thin film.

[0005] Therefore, how to fabricate an MSM photodetector with high absorption and quantum efficiency, and at the same time the method is simple and easy to implement, has become the key research direction. 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 an MSM photodetector integrated with a columnar microstructure array. By integrating a columnar microstructure array on the surface of the semiconductor thin film and preparing a grid-shaped interdigital electrode in the channel, it can not only reduce the surface reflection of the device, enhance light absorption, but also improve the carrier collection efficiency. At the same time, the process is simple and convenient for large-scale integration.

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

[0008] A preparation method of an MSM photodetector integrated with a columnar microstructure array, comprising the following steps:

[0009] Step 1: Prepare a semiconductor thin film on a substrate;

[0010] Step 2: Etch a number of criss-cross channels on the semiconductor thin film, the channels not penetrating the semiconductor thin film, so as to form a columnar microstructure array on the semiconductor thin film;

[0011] Step 3: Prepare interdigital electrodes at the bottom of the channels, the interdigital electrodes comprising positive and negative parallel electrode strips, with a plurality of interdigital pairs formed between the two electrode strips, there being one interdigital finger in each channel perpendicular to the electrode strips, and branches being formed on each interdigital finger along a direction perpendicular to the interdigital finger, each branch being located within the channel.

[0012] Further, the substrate in Step 1 is any one of silicon, silicon with a silicon dioxide layer on the surface, and germanium substrates; if the substrate selected is silicon with a silicon dioxide layer on the surface, the semiconductor thin film is prepared on the silicon dioxide surface.

[0013] Further, the semiconductor thin film is prepared by molecular beam epitaxy or metal organic chemical vapor deposition methods.

[0014] Further, the material of the semiconductor thin film in Step 1 is any one of silicon, germanium, lead sulfide, lead selenide, indium gallium arsenide, and mercury cadmium telluride.

[0015] Further, the thickness of the semiconductor thin film is 0.3 - 5 μm.

[0016] Further, the columnar microstructure array in Step 2 is prepared by photolithography and reactive ion etching processes.

[0017] Further, the columnar microstructure is any one of square columns and circular columns, with a size of 0.3 - 5 μm, the spacing between adjacent two columns being 0.5 - 5 μm, and the depth being 0.1 - 4.5 μm.

[0018] Further, the material of the interdigital electrodes in Step 3 is made of any one of gold, nickel, chromium, titanium, aluminum or an alloy of at least two of them.

[0019] Further, the thickness of the interdigital electrodes is 10 - 100 nm, the interdigital finger width is 0.1 - 0.5 μm, and the interdigital finger length and number of pairs are determined according to the device size and the spacing of the columnar microstructure array.

[0020] The present invention also provides a high-speed and high-efficiency MSM photodetector prepared by the above preparation method.

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

[0022] 1. The present invention adopts a columnar micro-structure array. When light irradiates the surface with columnar micro-structures, due to the height and spacing of the structures, multiple reflections and interferences of light waves occur between the micro-structures. These reflected light waves can cancel each other out, reducing the probability of total internal reflection and increasing scattering, thereby reducing the intensity of the reflected light and enhancing light absorption.

[0023] 2. The present invention integrates a columnar micro-structure array on the surface of a semiconductor thin film and fabricates a grid-shaped interdigital electrode in the channel, and the interdigital electrode is located in the channel of the semiconductor thin film. Compared with the surface electrode structure, the electric field penetrates not only in an extremely thin layer on the surface of the semiconductor thin film but also in two directions, upward and downward, improving the electric field distribution in the semiconductor thin film, thereby enhancing the collection efficiency of photo-generated carriers in the semiconductor thin film.

[0024] 3. Compared with traditional technologies, the preparation process of the present invention is simplified, facilitating large-scale integration, and can be widely applied to the fields of visible light and infrared detection and imaging technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural diagram of the interdigital electrode in the MSM structure in the prior art.

[0026] Figure 2 It is a top view of the preparation method process of the present invention.

[0027] Figure 3 It is a schematic cross-sectional view of the preparation method process of the present invention.

[0028] The reference numerals are: 10 - substrate; 20 - semiconductor photosensitive thin film; 21 - several channels; 22 - columnar micro-structure array; 30 - interdigital electrode; 31 - branch. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] 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 embodiments and the drawings.

[0030] A preparation method of an MSM photodetector integrating a periodic light-limiting structure. The top view of the preparation method process is as Figure 2 shown, and the schematic cross-sectional view is as Figure 3 shown, including the following steps:

[0031] Step 1: The substrate 10 is as Figure 2 -a and Figure 3 -a shown. The semiconductor thin film 20 is deposited on the surface of the substrate 10 by molecular beam epitaxy or metal-organic chemical vapor deposition, as Figure 2-b and Figure 3 as shown in -b;

[0032] Step 2: On the semiconductor thin film 20, use photolithography and reactive ion etching processes to prepare a number of criss-cross channels 21 as Figure 2 -c and Figure 3 as shown in -c. The channels do not penetrate the semiconductor thin film, so that a columnar microstructure array 22 is formed on the semiconductor thin film as Figure 2 -c and Figure 3 as shown in -c.

[0033] Step 3: On the bottom of the semiconductor thin film channels 21, use magnetron sputtering to prepare a patterned metal interdigital electrode 30. The interdigital electrode includes positive and negative parallel electrode strips. A number of interdigital pairs are formed between the two electrode strips. There is one interdigital finger in each channel perpendicular to the electrode strip. Branches are formed along the direction perpendicular to the interdigital finger on each interdigital finger, and each branch is located in the channel. Adjacent groups of interdigital electrodes form a grid structure, as Figure 2 -d and Figure 3 as shown in -d.

[0034] Example 1

[0035] A preparation method of an MSM photodetector integrated with a columnar microstructure array includes the following steps:

[0036] Step 1: Select a silicon wafer with a silicon dioxide thin film prepared on its surface as the device substrate wafer. The thickness of the silicon wafer is 500 μm, the thickness of the silicon dioxide layer is 3 μm. Clean the surface of the substrate to remove contaminants, and bake the substrate at 200 °C for 30 minutes to remove the water vapor on the surface. Then use molecular beam epitaxy to prepare a lead selenide thin film on the silicon dioxide thin film. The thickness of the lead selenide thin film is 2.5 μm;

[0037] Step 2: Use photolithography and reactive ion etching processes to prepare a number of channels on the lead selenide thin film and form a square columnar microstructure array. The size of the square column is 1 μm, the distance between adjacent two columns is 2 μm, and the depth is 0.5 μm;

[0038] Step 3: Use magnetron sputtering to prepare a patterned metal aluminum thin film on the lead selenide thin film. The thickness of the thin film is 20 nm, and the patterned aluminum thin film forms an interdigital electrode. The thickness of the electrode line is 100 nm, and the electrode width is 0.3 μm.

[0039] Example 2

[0040] A preparation method of an MSM photodetector integrated with a columnar microstructure array includes the following steps:

[0041] Step 1: Select a silicon wafer as the device substrate. The thickness of the silicon wafer is 500 μm. Clean the silicon wafer to remove the contamination on the substrate surface, and bake the substrate at 200 °C for 30 minutes to remove the water vapor on the surface. Then, use the molecular beam epitaxy method to prepare a germanium thin film on the silicon wafer surface. The thickness of the germanium thin film is 1 μm;

[0042] Step 2: Use photolithography and reactive ion etching processes to prepare several channels on the germanium thin film and form a square columnar microstructure array. The size of the square column is 1.5 μm, the distance between adjacent two columns is 1.5 μm, and the depth is 0.3 μm;

[0043] Step 3: Use magnetron sputtering to prepare a patterned metal titanium thin film on the germanium thin film. The thickness of the thin film is 10 nm. The patterned aluminum thin film forms interdigital electrodes. The interdigital electrodes are composed of multiple pairs of electrodes. The thickness of the electrode lines is 120 nm, and the width of the electrodes is 0.2 μm.

[0044] As described above, it is only the specific implementation manner of the present invention. Any feature disclosed in this specification, unless specifically described, can be replaced by other equivalent or similar-purpose alternative features; all the disclosed features, or all the steps in all the methods or processes, except for the mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A preparation method of an MSM photodetector integrated with a columnar microstructure array, characterized in that, It includes the following steps: Step 1: Prepare a semiconductor thin film on a substrate; Step 2: Etch a number of criss-cross channels on the semiconductor thin film. The channels do not penetrate the semiconductor thin film, so as to form a columnar microstructure array on the semiconductor thin film; Step 3: Prepare interdigital electrodes at the bottom of the channels. The interdigital electrodes include two parallel positive and negative electrode strips, and a plurality of interdigital pairs are formed between the two electrode strips. There is one interdigital finger in each channel perpendicular to the electrode strip. Each interdigital finger forms branches along the direction perpendicular to the interdigital finger, and each branch is located in the channel.

2. The manufacturing method of the MSM photodetector according to claim 1, characterized in that, The substrate in Step 1 is any one of silicon, silicon with a silicon dioxide layer on the surface, and germanium substrate; if the substrate selected is silicon with a silicon dioxide layer on the surface, the semiconductor thin film is prepared on the silicon dioxide surface.

3. The manufacturing method of the MSM photodetector according to claim 1, characterized in that, The semiconductor thin film is prepared by molecular beam epitaxy method or metal organic chemical vapor deposition method.

4. The manufacturing method of the MSM photodetector according to claim 1, characterized in that, The material of the semiconductor thin film in Step 1 is any one of silicon, germanium, lead sulfide, lead selenide, indium gallium arsenide, and mercury cadmium telluride.

5. The preparation method of the MSM photodetector according to claim 1, wherein, The thickness of the semiconductor thin film is 0.3 - 5 μm.

6. The manufacturing method of the MSM photodetector according to claim 1, characterized in that, The columnar microstructure array in Step 2 is prepared by photolithography and reactive ion etching process.

7. The manufacturing method of the MSM photodetector according to claim 1, characterized in that, The columnar microstructure is any one of square columns and circular columns, with a size of 0.3 - 5 μm, a spacing of 0.5 - 5 μm between adjacent two columns, and a depth of 0.1 - 4.5 μm.

8. The preparation method of the MSM photodetector according to claim 1, characterized in that, The material of the interdigital electrodes in Step 3 is made of any one of gold, nickel, chromium, titanium, aluminum or an alloy of at least two of them.

9. The manufacturing method of the MSM photodetector according to claim 1, characterized in that, The thickness of the interdigital electrodes is 10 - 100 nm, the interdigital finger width is 0.1 - 0.5 μm, and the interdigital finger length and the number of pairs are determined according to the device size and the spacing of the columnar microstructure array.

10. An MSM photodetector prepared by the preparation method of the MSM photodetector according to any one of claims 1 - 9.

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