A mercury cadmium telluride APD passivation layer, its preparation method and its application

Abstract

This invention discloses a mercury cadmium telluride (HCd) APD passivation layer, its preparation method, and its application. The method includes: liquid-phase epitaxial HCd material based on a cadmium zinc telluride (CZN) substrate; wet chemical etching of the HCd material using a bromine methanol solution and a lactic acid aqueous solution; deposition and growth of a cadmium telluride passivation layer on the surface; followed by closed-tube saturated mercury pressure thermal annealing to form a high-concentration transition layer on the surface of the HCd epitaxial material; and then deposition and growth of a cadmium telluride thin film on the surface of the annealed HCd chip, followed by vacuum heat treatment to obtain p-type HCd material of the desired concentration. The high-concentration diffusion layer formed on the surface of the HCd material through closed-tube annealing significantly reduces surface leakage current and recombination current in the device. The CdTe deposited after closed-tube annealing not only helps to stabilize and adjust the electrical parameters of the HCd material but also improves the quality of the passivation film and reduces damage caused by uneven etching rates. Ultimately, this method is applied to the fabrication of high-performance HCd infrared detectors using APDs.

Description

Technical Field

[0001] This invention belongs to the field of mercury cadmium telluride infrared focal plane detectors, and more specifically, relates to a mercury cadmium telluride APD passivation layer, its preparation method, and its application. Background Technology

[0002] In recent years, with the continuous development of mercury cadmium telluride infrared detectors, APD and long-wavelength mercury cadmium telluride focal plane infrared detectors have gradually become the mainstream of development, which has also put forward higher requirements for the resolution, reliability and sensitivity of the devices.

[0003] The longer the wavelength of mercury cadmium telluride (HCdT), the smaller the bandgap. For long-wavelength / very-long-wave HCdT materials, the surface is prone to accumulation, depletion, and inversion due to contamination and defects, thus increasing the surface leakage current of infrared detectors. For HCdT APD devices operating under high reverse bias voltage, surface defects will reduce their breakdown voltage and significantly increase the tunneling current. Therefore, surface passivation technology is often used to reduce the surface leakage current of HCdT and improve the photoelectric performance of infrared detectors.

[0004] Currently, there are various fabrication processes for CdTe passivation layers. Molecular beam epitaxy (MBE) and metal-chemical vapor deposition (MOCVD) are commonly used for in-situ growth of HgCdTe / CdTe. These techniques can directly grow high-quality CdTe films on the surface of mercury cadmium telluride in a single step, avoiding leakage current caused by surface contamination due to exposure to air. However, MBE growth technology is relatively complex and requires additional cumbersome processes, resulting in limited application of in-situ grown CdTe passivation layers in photovoltaic detectors. Indirect growth of CdTe passivation layers, such as ion beam sputtering, thermal evaporation, and magnetron sputtering, is widely used in infrared detectors. Due to the indirect growth method, contamination is easily introduced, leading to surface accumulation or inversion, which degrades device performance. Furthermore, limited by device fabrication processes, the film density is poor, failing to meet application requirements. Currently, there is no method to solve these problems. Summary of the Invention

[0005] To address the above-mentioned deficiencies or improvement needs of existing technologies, this invention provides a passivation layer for mercury cadmium telluride (HCd) APDs, its preparation method, and its application. The purpose is to improve the leakage current on the device surface by forming a high-component transition layer through tube sealing and annealing. Furthermore, after tube sealing and annealing, a CdTe passivation layer is deposited to regulate the electrical parameters of the material and improve the compactness of the film, thereby solving the problem of high leakage current in current HCd APD devices.

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

[0007] S1, a mercury cadmium telluride chip is provided, the mercury cadmium telluride chip is composed of a zinc cadmium telluride substrate layer and a mercury cadmium telluride layer, wherein the zinc cadmium telluride layer has a thickness of 700µm-900µm and the mercury cadmium telluride layer has a thickness of 7µm-10µm;

[0008] S2, the mercury cadmium telluride chip from step 1 is subjected to bromoethanol wet chemical etching, and then immersed in lactic acid aqueous solution;

[0009] S3, In step 2, a CdTe passivation film is deposited on the surface of the mercury cadmium telluride chip by magnetron sputtering, and the thickness of the CdTe passivation layer is 50nm-400nm;

[0010] S4, Perform saturated mercury pressure closed-tube thermal annealing on the passivation film obtained in step 3.

[0011] S5, A CdTe thin film is deposited and grown on the surface of the mercury cadmium telluride material that has undergone closed-tube heat treatment in step 4, and the thickness of the CdTe thin film is 70nm-300nm;

[0012] S6. The mercury cadmium telluride chip grown in step 5 is subjected to vacuum thermal annealing. The thermal annealing conditions are 200℃-260℃ and the time is 3h-10h.

[0013] Preferably, the composition and ratio of the bromomethanol corrosion solution are 1 mL-4 mL of Br2 and 50 mL-200 mL of methanol; the ratio of the lactic acid aqueous solution is 1 mL-3 mL of lactic acid and 100 mL-300 mL of water, the purpose of which is mainly to remove oxides on the surface of mercury cadmium telluride and reduce the fixed charge at the interface.

[0014] Preferably, the closed-tube heat treatment conditions are as follows: the first heat treatment is performed at mercury saturated vapor pressure, a temperature of 300℃-380℃, and a time of 0.5h-3h. The main purpose of this step is to promote the diffusion of Cd from the passivation layer cadmium telluride into the mercury cadmium telluride epitaxial material, thereby increasing the composition of the surface of the mercury cadmium telluride epitaxial material. The second heat treatment is performed at mercury saturated vapor pressure, a temperature of 200℃-230℃, and a time of 24h-48h. The main purpose of this step is to eliminate the mercury vacancies generated at the high temperature in the first step through low-temperature heat treatment, thereby repairing the electrical properties of the mercury cadmium telluride epitaxial material.

[0015] Preferably, magnetron sputtering is used to grow CdTe thin films with a sputtering power of 60W-100W and a growth rate of 0.5Å / s-1.0Å / s. The main purpose of this step is to facilitate the movement of Hg atoms in the passivation layer after tube sealing annealing, which can better adjust the electrical parameters of the film and improve the quality of the passivation layer.

[0016] 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 between 60℃ and 120℃, RF power between 80W and 300W, and CdTe and ZnS thickness between 100nm and 500nm.

[0017] Preferably, under the protection of nitrogen inert gas, the annealing temperature is 200℃-260℃, and the heating rate is 15℃ / min-26℃ / min. The purpose of this heat treatment step is to convert the n-type mercury cadmium telluride material into the p-type mercury cadmium telluride material of the required concentration, and the n-type high-component transition layer is simultaneously converted into the p-type high-component transition layer.

[0018] According to another aspect of the present invention, a mercury cadmium telluride APD passivation layer is prepared by the method for preparing the mercury cadmium telluride APD passivation layer of the present invention.

[0019] According to another aspect of the present invention, the application of the mercury cadmium telluride APD passivation layer in the fabrication of mid-wave APD and long-wave n-on-p mercury cadmium telluride infrared detectors.

[0020] In general, compared with the prior art, the above-described technical solutions conceived by this invention can achieve at least the following beneficial effects:

[0021] (1) The present invention uses a tube sealing annealing process to form a high composition diffusion layer at the HgCdTe / CdTe interface to suppress surface leakage current and improve device stability;

[0022] (2) Depositing a passivation layer after sealing the tube can precisely control the electrical parameters of the material and promote the diffusion of atoms, improve the quality of the passivation layer, and enhance the consistency of the device. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a mercury cadmium telluride (HCd) APD device. In the diagram: 1-cadmium zinc telluride substrate, 2-HCd epitaxial material, 3-sputtered CdTe layer, 4-sputtered ZnS layer, 5-metal electrode;

[0024] Figure 2 This is a schematic diagram of the formation of the high-component layer before and after the sealing annealing. In the diagram: 1-cadmium zinc telluride substrate, 2-mercury cadmium telluride epitaxial material, 3-sputtered CdTe layer, 6-high-component layer formed after annealing;

[0025] Figure 3 (a) and (b) are secondary ion mass spectra of the passivation layer under different processes;

[0026] Figure 4 (a)-(c) are dark field images of the passivation film of APD devices under different processes;

[0027] Figure 5In the middle (a)-(c), the IV and RV curves of mercury cadmium telluride APD devices under high reverse bias are respectively, under different processes. Detailed Implementation

[0028] 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.

[0029] Example 1

[0030] This embodiment provides a method for preparing a mercury cadmium telluride passivation layer by tube sealing annealing, specifically including the following steps:

[0031] (1) Provide a mercury cadmium telluride epitaxial material 2 based on a cadmium zinc telluride substrate 1, such as Figure 1 As shown.

[0032] (2) The mercury cadmium telluride chip was subjected to wet chemical etching with bromomethanol and lactic acid for 20 seconds.

[0033] (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 CdTe3 begins, with the CdTe rate maintained at 2 Å / s and a thickness of 300 nm.

[0034] (4) Finally, the mercury cadmium telluride material with the passivation layer grown is subjected to closed-tube heat treatment. The closed-tube heat treatment conditions are as follows: the first step heat treatment conditions are mercury saturated vapor pressure, temperature 350℃, and time 1h. The main purpose of this step is to enhance the diffusion of Cd at the interface between the sputtered CdTe layer 3 and the mercury cadmium telluride epitaxial material 2, that is, to allow the Cd in the sputtered CdTe layer 3 to diffuse into the mercury cadmium telluride epitaxial material 2, thereby increasing the composition of the surface of the mercury cadmium telluride epitaxial material 2 and forming a high-composition layer 6 formed after annealing with an n-type high composition transition (e.g., Figure 2 As shown). Figure 2 (b) shows the mercury cadmium telluride material after closed-tube heat treatment. The conditions for the second heat treatment are mercury saturated vapor pressure, temperature 220°C, and time 24h. The main purpose of this step is that the low-temperature heat treatment can fill the mercury atom vacancies generated in the first high-temperature heat treatment and adjust and repair the electrical properties of the mercury cadmium telluride epitaxial material 2.

[0035] Comparative Example 1

[0036] This comparative example provides a conventional method for preparing a passivation layer, which specifically includes the following steps:

[0037] This comparative example uses the same preparation method as Example 1. The difference is that in step (4), the sample is placed in a rapid annealing furnace filled with nitrogen atmosphere for hot annealing treatment. The hot annealing treatment conditions are 260°C and 3h. The main purpose of this step is to adjust the electrical parameters of mercury cadmium telluride epitaxial material by generating mercury atom vacancies.

[0038] See Figure 3 (a) and (b) Figure 3 (a) and (b) are secondary ion mass spectra (SIMS) of the CdTe passivated mercury cadmium telluride (MCH) samples prepared in Comparative Example 1 and Example 1, respectively, after thermal annealing. The figures show that the thickness of the high-component layer without encapsulation annealing is 0.12 µm–0.15 µm. In Example 1, after encapsulation annealing, the thickness of the high-component layer significantly increased to 0.2 µm–0.25 µm. This indicates that encapsulation annealing can increase the thickness of the high-component layer at the MCH interface, which is beneficial for reducing leakage current caused by surface fixed charges and enhancing the breakdown resistance of MCH APD devices.

[0039] Example 2

[0040] The fabrication method of the mercury cadmium telluride APD detector based on the improved tube sealing annealing passivation layer is as follows:

[0041] (1) Fabrication of the mercury cadmium telluride APD infrared detector: Based on Example 1, after the CdTe passivation layer was sealed and annealed, a 100 nm layer of CdTe was deposited on its surface, and interdiffusion annealing was performed at 280 °C for 3 h. The purpose was mainly to facilitate atomic migration during the annealing process, to more accurately control the electrical parameters of the material, and to improve the quality of the passivation film. Subsequently, a photolithographic mask was applied to the surface of the mercury cadmium telluride material, followed by boron ion implantation at a dose of 260 keV and a dose of 3*e15 / cm. 2 The injected 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 region is designed to keep the pn junction away from the injection damage area, reducing device tunneling, generation recombination, and surface leakage current, thereby improving device performance and stability. Finally, the ohmic contact electrode is fabricated by photolithography, ICP etching, metal deposition, and metal lift-off processes on the mercury cadmium telluride material that has undergone drive annealing.

[0042] Comparative Example 2

[0043] The fabrication method of the mercury cadmium telluride APD infrared detector based on the conventional annealed passivation layer is as follows:

[0044] The preparation method of the mercury cadmium telluride APD infrared detector is the same as that in Example 2, except that the passivation layer preparation process adopts the method described in Comparative Example 1.

[0045] Comparative Example 3

[0046] The fabrication method of a long-wave infrared detector based on a conventional tube sealing annealing passivation layer is as follows:

[0047] The fabrication method of the mercury cadmium telluride APD infrared detector is the same as that in Example 2. The difference is that after the CdTe passivation layer is sealed and annealed, no CdTe thin film is deposited. Instead, photolithography masking and implantation are performed directly.

[0048] Dark field images of the passivation layers prepared in Comparative Examples 2, 3 and 2 are shown below. Figure 4 As shown in (a)-(c), dark field images of the conventional annealed passivation layer ( Figure 4 (a) The overall contrast is too bright, indicating poor film density; conventional tube sealing annealing ( Figure 4 (b) The overall contrast of the passivation layer is darker, which is a significant improvement in density compared to conventional annealing. The dense white spots in the center of the image are mercury precipitates. Figure 4 (c) The overall contrast is low and there are no precipitates, indicating that the passivation layer prepared under this condition is of better quality than the other two processes.

[0049] The IV curve corresponding to the mid-wave mercury cadmium telluride APD infrared detector is as follows: Figure 5 As shown in (a)-(c), it can be seen from the figure that the reverse breakdown voltage of the conventionally annealed and passivated mercury cadmium telluride APD curve is small (around -6V), and the device leakage current is large. The reverse breakdown voltage of the device after sealing and annealing is improved to a certain extent, increasing from -6V to -8V, but the pixel uniformity is poor. After depositing a CdTe passivation layer under sealing and annealing conditions, the reverse breakdown voltage of the IV curve is significantly improved, increasing to -10V, and the yield and stability of the device are also greatly improved.

[0050] This invention can significantly reduce surface leakage current and generation-recombination current in devices, improve the breakdown resistance and baking resistance of mercury cadmium telluride APD devices, and enhance device stability, thus having broad application prospects in the field of mercury cadmium telluride APD infrared detectors.

[0051] 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 a mercury cadmium telluride APD passivation layer, characterized in that, Includes the following steps: S1, a mercury cadmium telluride chip is provided, the mercury cadmium telluride chip is composed of a zinc cadmium telluride substrate layer and a mercury cadmium telluride layer, wherein the zinc cadmium telluride layer has a thickness of 700-900µm and the mercury cadmium telluride layer has a thickness of 7-10µm; S2, the mercury cadmium telluride chip in S1 is subjected to bromoethanol wet chemical etching, and then immersed in lactic acid aqueous solution; S3, A CdTe passivation film is deposited on the surface of the mercury cadmium telluride chip in S2 by magnetron sputtering, wherein the thickness of the CdTe passivation film is 50-400 nm; S4, the passivation film obtained in S3 is subjected to saturated mercury impregnation tube-closed thermal annealing treatment, and the conditions for the saturated mercury impregnation tube-closed thermal annealing treatment are as follows: The first step involves heat treatment under the following conditions: mercury saturated vapor pressure, temperature 300-380℃, and time 0.5-3h. The second step involves heat treatment under mercury saturated vapor pressure, at a temperature of 200-230℃, for 24-48 hours. The first step is used to promote the diffusion of Cd from the passivation layer cadmium telluride into the mercury cadmium telluride epitaxial material, thereby increasing the composition of the surface of the mercury cadmium telluride epitaxial material; the second step is used to eliminate the mercury vacancies generated at the high temperature in the first step through low-temperature heat treatment, thereby repairing the electrical properties of the mercury cadmium telluride epitaxial material. S5, a CdTe thin film is deposited and grown on the surface of the mercury cadmium telluride material that has undergone closed-tube heat treatment in S4, and the thickness of the CdTe thin film is 70-300 nm. S6. The mercury cadmium telluride chip that has completed CdTe growth in S5 is subjected to vacuum thermal annealing treatment at 250-300℃ for 1-5 hours.

2. The preparation method according to claim 1, characterized in that, The bromoethanol is composed of 1-4 mL of Br2 and 50-200 mL of methanol.

3. The preparation method according to claim 1, characterized in that, The lactic acid aqueous solution consists of 1-3 mL of lactic acid and 100-300 mL of water. The lactic acid aqueous solution is used to remove oxides from the surface of mercury cadmium telluride and reduce the fixed charge at the interface.

4. The preparation method according to claim 1, characterized in that, The sputtering power of CdTe thin films grown by magnetron sputtering is 100-200W, and the growth rate is 1-3.0Å / s.

5. The preparation method according to claim 1, characterized in that, The deposition of CdTe passivation films is used to promote the movement of Hg atoms in the passivation layer after tube sealing annealing, adjust the electrical parameters of the film, and improve the quality of the passivation layer.

6. The preparation method according to claim 1, characterized in that, In S6, the vacuum thermal annealing process is carried out under the protection of nitrogen inert gas, with an annealing temperature of 200-260℃ and a heating rate of 15℃ / min-26℃ / min. The purpose of this vacuum thermal annealing process is to convert the n-type mercury cadmium telluride material into the p-type mercury cadmium telluride material of the required concentration, and the n-type high-component transition layer is simultaneously converted into the p-type high-component transition layer.

7. A mercury cadmium telluride APD passivation layer prepared by a method according to any one of claims 1-6.

8. The application of the mercury cadmium telluride APD passivation layer as described in claim 7 in the fabrication of mid-wave APD and long-wave n-on-p mercury cadmium telluride infrared detectors.

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