An improved passivation layer for mercury cadmium telluride apds, method of manufacture and use thereof

Abstract

The application discloses an improved passivation layer of a mercury cadmium telluride APD, a preparation method and application thereof, and the preparation method comprises the following steps: based on liquid phase epitaxy of a mercury cadmium telluride material on a cadmium zinc telluride substrate, a bromine methanol wet etching treatment is performed on the surface of the mercury cadmium telluride material, the surface oxide is removed by immersing the mercury cadmium telluride material in a lactic acid aqueous solution, a cadmium telluride and zinc sulfide passivation layer is deposited and grown on the surface of the etched mercury cadmium telluride material, and finally, the mercury cadmium telluride sample on which the passivation layer is deposited is subjected to high-low temperature annealing in a nitrogen atmosphere. The surface oxide layer is removed by lactic acid treatment, and the quality of the passivation film layer is improved by high-low temperature annealing, and the material surface fixed charge is reduced by low temperature annealing, so that the surface carrier recombination rate is reduced, the leakage current of the device is reduced, and the preparation of a high-performance APD and a long-wave mercury cadmium telluride infrared detector is realized.

Description

Technical Field

[0001] This invention belongs to the field of mercury cadmium telluride infrared focal plane detectors, and relates to a mercury cadmium telluride APD passivation layer. More specifically, it relates to an improved method for preparing a mercury cadmium telluride APD passivation layer, the improved mercury cadmium telluride APD passivation layer prepared by the method, and its application. Background Technology

[0002] In recent years, with the continuous development of third-generation mercury cadmium telluride (HCd) infrared detectors, the performance and reliability of these devices have attracted much attention. Due to the small bandgap of HCd infrared detectors, the tunneling effect becomes more pronounced, especially in APD devices operating at high reverse bias voltages and long-wavelength HCd devices with even smaller bandgap. Therefore, reducing the fixed charge on the surface of HCd and improving the performance of APDs and long-wavelength infrared detectors through surface passivation technology is of paramount importance.

[0003] Currently, passivation film preparation methods are mainly divided into two categories: wet processes and dry processes. Wet processes primarily involve chemical or electrochemical methods, such as anodic oxidation and anodic fluorination. However, anodic oxidation forms oxides on the device surface, leading to the accumulation of fixed charges, which can cause inversion or depletion on the photovoltaic detector surface, reducing leakage current and increasing overall leakage current. Therefore, wet processes are less commonly used in photovoltaic detectors. Dry processes are mainly achieved through vapor deposition, such as chemical vapor deposition, ion beam sputtering, magnetron sputtering, and thermal evaporation. Among these, thermal evaporation deposition has lower atomic energy and poorer passivation film adhesion, chemical vapor deposition is more complex, and magnetron sputtering is simpler and has better passivation film adhesion, making it the mainstream passivation method.

[0004] For magnetron sputtering of CdTe, high-temperature interdiffusion is required to convert the HMCC from n-type to p-type. During this high-temperature transformation, the grains within the CdTe film fuse, and defects aggregate to form pores. However, the formation of pores can easily lead to uneven etching rates and damage the HMCC surface. Furthermore, the formation of pores introduces corresponding interface states and fixed charges, reducing the barrier width of the pn junction and weakening the breakdown voltage characteristics of APD devices. For long-wavelength HMCC devices with even narrower band gaps, the band bending caused by surface fixed charges and defects is usually one or several orders of magnitude of the band gap. This can easily cause inversion, depletion, and accumulation on the material surface, leading to surface leakage and severely reducing device performance. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides an improved mercury cadmium telluride (HCdTe) APD passivation layer, its preparation method and its application. The purpose is to solve the problem of poor film density of the current magnetron sputtered CdTe passivation layer by improving the pre-surface treatment, magnetron sputtering process and optimizing the annealing conditions.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for preparing an improved mercury cadmium telluride passivation layer is provided, comprising the following steps:

[0007] S1. Prepare a mercury cadmium telluride chip, which is composed of a zinc cadmium telluride substrate and a mercury cadmium telluride layer.

[0008] S2, perform wet chemical etching of the mercury cadmium telluride chip from step 1 with bromomethanol for 10-60s, and then immerse it in lactic acid aqueous solution for 10-100s;

[0009] S3, CdTe and ZnS passivation films are deposited on the surface of the mercury cadmium telluride chip in step 2 by magnetron sputtering;

[0010] S4. The passivation film obtained in step 3 is subjected to high and low temperature annealing to improve the quality of the CdTe film.

[0011] Preferably, the thickness of the zinc cadmium telluride substrate is 700-900 μm, and the thickness of the mercury cadmium telluride is 7-10 μm.

[0012] Preferably, the composition and ratio of the bromomethanol corrosion solution are 1-4 mL of Br2 and 50-200 mL of methanol. The corrosion solution should not be left to stand for a long time and should be prepared within 0.5-1 hour before corrosion.

[0013] Preferably, the lactic acid aqueous solution is prepared in the ratio of 1-3 mL of lactic acid to 100-300 mL of water.

[0014] Preferably, CdTe and ZnS thin films are grown by magnetron sputtering, with the cavity vacuum level maintained at 10°C before growth. - 7 mbar, deposition temperature of 60-120℃, RF power of 80-300W, and CdTe and ZnS thickness of 100-500nm.

[0015] Preferably, the high and low temperature annealing is carried out under the protection of nitrogen inert gas, with the low temperature being 70-110℃ and the high temperature being 250-300℃. The low temperature annealing mainly promotes the diffusion between CdTe atoms and improves its crystal quality, while the high temperature annealing mainly controls the electrical parameters of the film.

[0016] According to another aspect of the present invention, an improved mercury cadmium telluride passivation layer is prepared by the improved method of the present invention.

[0017] According to another aspect of the invention, the improved mercury cadmium telluride passivation layer is used in mid-wave APDs and long-wave mercury cadmium telluride infrared detectors.

[0018] In general, compared with the prior art, the above-described technical solutions conceived by this invention can achieve at least the following beneficial effects:

[0019] (1) In this invention, the surface of mercury cadmium telluride is treated with lactic acid to reduce the formation of tellurium oxides on the surface after corrosion by bromomethanol, thereby reducing the fixed charge and defects on the surface. Then, a high-low temperature annealing process is used, where the low temperature is mainly used to promote the migration between CdTe atoms, reduce the number of pores, and thus improve the compactness of the film. Furthermore, long-term low-temperature annealing can reduce surface defects and lower the fixed charge on the surface of mercury cadmium telluride.

[0020] (2) In this invention, a ZnS layer is sputtered onto the CdTe film to improve the physical and chemical stability of the device. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the passivation layer technology for cadmium cadmium telluride (CdTe) layer. In the diagram: 1-cadmium zinc telluride substrate, 2-CdTe telluride epitaxial material, 3-sputtered CdTe layer, 4-sputtered ZnS layer;

[0022] Figure 2 (a) and (b) are SEM cross-sectional images of the passivation layer grown by the original process before and after annealing;

[0023] Figure 3 (a) and (b) are SEM cross-sectional images of the passivation layer grown after the improved process before and after annealing.

[0024] Figure 4 In the middle (a) and (b), the passivation layer grown by the improved process is applied to the mid-wave APD and long-wave mercury cadmium telluride infrared detectors, respectively, showing the IV and RV curves.

[0025] Figure 5 In the middle (a) and (b), the passivation layer grown after the original process is applied to the mid-wave APD and long-wave mercury cadmium telluride infrared detectors, respectively, showing the IV and RV curves. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0027] Example 1

[0028] This embodiment provides a method for preparing an improved mercury cadmium telluride passivation layer, specifically including the following steps:

[0029] (1) Provide a mercury cadmium telluride epitaxial material based on a cadmium zinc telluride substrate, such as Figure 1 As shown.

[0030] (2) The mercury cadmium telluride chip was subjected to bromomethanol wet chemical etching for 20 seconds, and then immersed in lactic acid aqueous solution for 20 seconds. The purpose of this step is mainly to remove the oxide layer generated on the surface after bromomethanol etching.

[0031] (3) Then transfer the chip into the vacuum sputtering chamber, close the chamber door, and wait for the vacuum level to drop to 5*10. -7 After mbar, sputtering of CdTe and ZnS begins, with the CdTe rate maintained at [value missing]. Thickness at 200 nm; ZnS velocity maintained at Thickness of 100nm Figure 1 As shown.

[0032] (4) Finally, the sample is placed in a rapid annealing furnace filled with nitrogen atmosphere for hot annealing treatment. The hot annealing treatment conditions are as follows: the first step of the heat treatment is low temperature annealing at 100°C for 7 hours. The main purpose of this step is to promote the migration between CdTe atoms and improve the quality of the passivation film. The second step of the heat treatment is high temperature annealing at 235°C for 2 hours. The main purpose of this step is to generate mercury atom vacancies to adjust the electrical parameters of the mercury cadmium telluride epitaxial material.

[0033] Comparative Example 1

[0034] This comparative example provides a conventional method for preparing a mercury cadmium telluride passivation layer, specifically including the following steps:

[0035] This comparative example uses the same preparation method as Example 1. The difference is that in step (2), the mercury cadmium telluride chip was subjected to bromomethanol wet chemical etching for 20s and then not immersed in lactic acid aqueous solution for 20s; in step (4), the sample was placed in a rapid annealing furnace filled with nitrogen atmosphere for hot annealing treatment. The hot annealing treatment conditions were 235℃ and 2h. The main purpose of this step was to generate mercury atom vacancies to adjust the electrical parameters of the mercury cadmium telluride epitaxial material.

[0036] Figure 2 Images (a) and (b) are SEM cross-sectional images of the CdTe / ZnS passivated mercury cadmium telluride sample prepared in Comparative Example 1 before and after thermal annealing. Figure 2(a) is a SEM cross-sectional image of the passivation layer before annealing. It can be seen that the columnar crystals inside CdTe are quite obvious, indicating that the CdTe film grown by magnetron sputtering in this process has poor density. Figure 2 (b) is a SEM cross-sectional image of the passivation layer after annealing. Compared with before annealing, the columnar crystals disappeared, but many pores appeared inside the film, which will introduce a large number of fixed charges and defects, as well as cause uneven etching rate and damage to mercury cadmium telluride. Finally, the breakdown resistance of the prepared mercury cadmium telluride APD decreased and the leakage current of the LW mercury cadmium telluride infrared detector increased.

[0037] SEM cross-sectional view of Example 1 before annealing ( Figure 3 (a) Columnar crystals were significantly less than those in the comparative example. Figure 2 (a) The increased number of columnar crystals indicates a denser CdTe passivation layer produced under improved processing conditions. Furthermore, Figure 3 (b) shows a cross-sectional view of CdTe after annealing. There are almost no pores in the film, indicating that the quality of the mercury cadmium telluride passivation layer is significantly improved by combining lactic acid treatment and high and low temperature annealing conditions.

[0038] Example 2

[0039] The fabrication method of the infrared detector based on the improved passivation layer is as follows:

[0040] (1) Fabrication of the mid-wave APD infrared detector: Based on Example 1, a photolithographic mask was applied to the surface of the mercury cadmium telluride material, followed by boron ion implantation at a dose of 250 keV and a dose of 4*e15 / cm. 2 The injected medium-wave mercury cadmium telluride material was subjected to driven annealing heat treatment at 200℃ for 1.5 hours. The purpose of this driven annealing was to form n... - The pn junction principle is injected into the damaged area, reducing device tunneling, generation, recombination, and surface leakage current, thereby improving device performance and stability. Finally, ohmic contact electrodes are fabricated on the mercury cadmium telluride material that has undergone driving annealing through photolithography, ICP etching, metal deposition, and metal lift-off processes.

[0041] (2) Preparation of long-wave infrared detector: The preparation process is the same as in step 1, except that the wavelength of mercury cadmium telluride at room temperature is changed from 4.1 μm to 6.3 μm.

[0042] The IV curves corresponding to the mid-wave and long-wave mercury cadmium telluride infrared detectors prepared in Example 2 are as follows: Figure 4 As shown in (a) and (b), the curves show good reversal, indicating that the improved passivation process has a significant effect on improving the surface leakage current of the device.

[0043] Comparative Example 2

[0044] The fabrication method of infrared detectors based on conventional passivation layers is as follows:

[0045] The fabrication method for the mid / long-wave infrared detector is the same as in Example 2, except that the passivation layer fabrication process adopts the method described in Comparative Example 1. The IV curves corresponding to the mid-wave and long-wave mercury cadmium telluride infrared detectors fabricated in Comparative Example 2 are shown below. Figure 5 As shown in (a) and (b), it can be seen from the figures that, compared with Example 2, the reverse current of the mid-wave and long-wave infrared detector devices is significantly worse, indicating that the passivation layer plays a crucial role in the leakage current of the device.

[0046] This invention can significantly reduce surface leakage current and generation-recombination current of devices, greatly improve the photoelectric performance and baking resistance of devices, and enhance device stability, thus having broad application prospects in the field of infrared detectors.

[0047] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an improved mercury cadmium telluride (HCM) APD passivation layer, characterized in that, Includes the following steps: S1. Prepare a mercury cadmium telluride chip, which is composed of a zinc cadmium telluride substrate and a mercury cadmium telluride layer. S2, the mercury cadmium telluride chip in S1 is subjected to bromoethanol wet chemical etching, and then immersed in lactic acid aqueous solution; S3, CdTe and ZnS passivation films are deposited on the surface of the mercury cadmium telluride chip in S2 by magnetron sputtering; S4, the passivation film obtained in S3 is subjected to high and low temperature annealing to improve the quality of the CdTe film layer; the high and low temperature annealing includes: under nitrogen protection, the first step is low temperature annealing at 100℃ for 7 hours; the second step is high temperature annealing at 235℃ for 2 hours. Low-temperature annealing is used to promote diffusion between CdTe atoms and improve its crystal quality, while high-temperature annealing is used to generate mercury atom vacancies to regulate the electrical parameters of mercury cadmium telluride.

2. The preparation method according to claim 1, characterized in that, The thickness of the zinc cadmium telluride substrate is 700-900µm, and the thickness of the mercury cadmium telluride substrate is 7-10µm.

3. The preparation method according to claim 1, characterized in that, The composition and ratio of the bromomethanol corrosion solution are 1-4 mL of Br2 and 50-200 mL of methanol. The corrosion solution is prepared within 0.5-1 hour before corrosion.

4. The preparation method according to claim 1, characterized in that, The lactic acid aqueous solution is prepared by mixing 1-3 mL of lactic acid with 100-300 mL of water.

5. The preparation method according to claim 1, characterized in that, CdTe and ZnS thin films were grown by magnetron sputtering, with the chamber vacuum level maintained at 10°C before growth. -7 mbar, deposition temperature of 60-120℃, RF power of 80-300W, and CdTe and ZnS thickness of 100-500nm.

6. An improved mercury cadmium telluride passivation layer prepared by a method according to any one of claims 1-5.

7. The application of the improved mercury cadmium telluride passivation layer as described in claim 6 in mid-wave APD and long-wave mercury cadmium telluride infrared detectors.

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