HgCdTe material, surface passivation heat treatment method thereof and infrared detector

Abstract

The invention provides a mercury-cadmium-telluride material, a surface passivation heat treatment method thereof and an infrared detector, the surface passivation heat treatment method of the mercury-cadmium-telluride material comprises the following steps: S1, pretreating the surface of a mercury-cadmium-telluride substrate; s2, depositing and growing a high-component HgCdTe film layer on the surface of the tellurium-cadmium-mercury substrate; s3, depositing and growing a CdTe passive film layer on the surface of the high-component HgCdTe film layer; s4, depositing and growing a ZnS passive film layer on the surface of the CdTe passive film layer; and S5, carrying out passive heat treatment on the tellurium-cadmium-mercury substrate treated in the step S4 under the protection of an inert atmosphere. The three composite passivation film layers are adopted, and the high-component HgCdTe film layer and the HgCdTe substrate material are basically consistent in component, crystal structure and lattice constant, so that the problems that the CdTe film layer preparation process is high in requirement, CdTe / HgCdTe generates stress and dislocation and the like when the traditional CdTe passivation film layer is adopted as the first passivation material layer are solved; the process requirement of preparation of the CdTe passive film layer is reduced, the complexity of a heat treatment process is reduced, and the process window of HgCdTe device processing is widened.

Description

Technical Field

[0001] This invention belongs to the field of mercury cadmium telluride material processing technology, specifically relating to a mercury cadmium telluride material, its surface passivation heat treatment method, and an infrared detector. Background Technology

[0002] Mercury cadmium telluride (HgCdTe) infrared detectors remain among the highest-performing infrared detectors. Surface passivation of HgCdTe is a crucial method for reducing surface leakage current in HgCdTe chips. Before surface passivation, HgCdTe materials are typically treated with a bromoethanol solution to remove the oxide layer and adsorbed impurities. However, treating HgCdTe with a bromoethanol solution disrupts the periodicity of the HgCdTe surface lattice, generating numerous dangling bonds. These dangling bonds result in a high surface charge density on the HgCdTe surface, which needs to be eliminated through subsequent passivation processes.

[0003] Common passivation methods for mercury cadmium telluride (HCd) photovoltaic focal plane array devices include single-layer ZnS passivation and CdTe / ZnS double-layer passivation. When using a single-layer ZnS film as the passivation layer, the ZnS film generates a high fixed charge during photolithography due to exposure to blue light or ultraviolet light, which can form a surface breakdown current on the HCd surface, causing the HCd device to fail. Moreover, the thermal stability of the ZnS film is relatively poor. During heat treatment, Zn atoms diffuse to the surface layer of the HCd, which can easily lead to a decrease in the stability of the HCd pixels. The CdTe / ZnS double-layer passivation process has three problems: (1) Due to the differences in lattice constant and composition between CdTe and HgCdTe, stress and dislocation defects are easily generated at the CdTe / HgCdTe interface. In addition, there are significant compositional differences between CdTe and HgCdTe, resulting in concentration gradients or unevenly distributed regions at the CdTe / HgCdTe interface; (2) The Cd-Te bond is relatively strong and cannot effectively neutralize the dangling bonds on the surface of HgCdTe. The presence of the cadmium cadmium telluride interface state will lead to the surface loading of HgCdTe material. The increased recombination rate of carriers leads to increased leakage current of the device; (3) After the surface of HgCdTe material is passivated with CdTe, a high heat treatment temperature (usually ≥300℃) is usually required to allow Cd atoms to diffuse from the CdTe passivation film to the HgCdTe material, so as to improve the surface composition of HgCdTe material and reduce the dark current of the device. However, the CdTe film will grow grains during the high temperature heat treatment process, which will generate pores at the CdTe / HgCdTe interface, leading to increased leakage current of HCdeTe device and thus causing unstable performance of mercury cadmium telluride device. Summary of the Invention

[0004] The purpose of this invention is to provide a surface passivation heat treatment method for mercury cadmium telluride materials, which can at least solve some of the defects existing in the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for passivating the surface of mercury cadmium telluride material by heat treatment includes the following steps:

[0007] S1. Pre-treat the surface of the mercury cadmium telluride substrate;

[0008] S2. A high-component HgCdTe film is deposited and grown on the surface of the pretreated mercury cadmium telluride substrate.

[0009] S3. A CdTe passivation film is deposited and grown on the surface of the high-component HgCdTe film.

[0010] S4. A ZnS passivation film is deposited and grown on the surface of the CdTe passivation film;

[0011] S5. The mercury cadmium telluride substrate treated in S4 is subjected to passive heat treatment under an inert atmosphere.

[0012] Furthermore, in S1, the surface pretreatment process of the mercury cadmium telluride substrate is as follows: the mercury cadmium telluride substrate is chemically etched using a bromoethanol or bromomethanol solution, and then the chemically etched mercury cadmium telluride substrate is placed in the transition chamber of a magnetron sputtering equipment for 15-30 minutes, wherein the vacuum degree in the transition chamber is maintained at less than 3×10⁻⁶. -6 Pa, the temperature of the mercury cadmium telluride substrate is 60-100℃.

[0013] Furthermore, in step S2, a high-component HgCdTe film is deposited and grown using magnetron sputtering, with the following process conditions: mercury cadmium telluride substrate temperature 60-100℃, high-component HgCdTe film growth chamber pressure 0.02-1mBar, sputtering power 30-150W; and high-component HgCdTe film thickness 50-200nm.

[0014] Furthermore, in S2, the HgCdTe target used for magnetron sputtering deposition of a high-component HgCdTe film is prepared by slicing HgCdTe bulk crystal material and polishing it, and the Cd / (Cd+Hg) atomic ratio of the HgCdTe target is 0.5-0.8.

[0015] Furthermore, in S3, a CdTe passivation film is deposited and grown using magnetron sputtering with a sputtering power of 50-150W and a thickness of 50-300nm.

[0016] Furthermore, in S4, a ZnS passivation film is deposited and grown by magnetron sputtering with a sputtering power of 100-250W and a thickness of 50-300nm.

[0017] Furthermore, in S5, the passive heat treatment temperature is 200-300℃, and the passive heat treatment time is 3-30h.

[0018] In addition, the present invention also provides a mercury cadmium telluride material, which is obtained by the above-mentioned surface passivation heat treatment method for mercury cadmium telluride material.

[0019] Furthermore, the thickness of the high-component HgCdTe film is 50-200 nm, the thickness of the CdTe passivation film is 50-300 nm, and the thickness of the ZnS passivation film is 50-300 nm.

[0020] The present invention also provides an infrared detector comprising the aforementioned mercury cadmium telluride material.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] The passivation heat treatment method for mercury cadmium telluride (HgCdTe) materials provided by this invention deposits and grows a three-layer composite passivation film of HgCdTe / CdTe / ZnS on a HgCdTe substrate. By utilizing the fact that the high-component HgCdTe film has essentially the same material composition, crystal structure, and lattice constant as the HgCdTe substrate, this method solves the problems of high requirements for CdTe film preparation process and stress and dislocation generated by CdTe / HgCdTe, which are inherent in traditional methods of using CdTe passivation film as the first passivation material. This method reduces the process requirements for CdTe passivation film preparation, reduces the complexity of heat treatment process, and broadens the process window for HgCdTe device fabrication.

[0023] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0024] Figure 1 This is a flowchart of the passivation heat treatment method for mercury cadmium telluride material surface according to the present invention;

[0025] Figure 2 This is a schematic diagram of the structure of the mercury cadmium telluride material of the present invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] In the description of this invention, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0028] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation", "connection", and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, an abutting connection, or an integral connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0029] like Figure 1 and Figure 2 As shown, this embodiment provides a passivation heat treatment method for the surface of mercury cadmium telluride material, including the following steps:

[0030] S1. Pre-treat the surface of the mercury cadmium telluride substrate;

[0031] S2. A high-component HgCdTe film is deposited and grown on the surface of the pretreated mercury cadmium telluride substrate.

[0032] S3. A CdTe passivation film is deposited and grown on the surface of the high-component HgCdTe film.

[0033] S4. A ZnS passivation film is deposited and grown on the surface of the CdTe passivation film;

[0034] S5. The mercury cadmium telluride substrate treated in S4 is subjected to passive heat treatment under an inert atmosphere.

[0035] In this embodiment, passive heat treatment refers to a heat treatment method in which only inert gas protection is provided during the heat treatment process, without the provision of tellurium, cadmium, or mercury atmosphere protection.

[0036] In this embodiment, the high component in the HgCdTe film indicates that the Cd / (Cd+Hg) atomic ratio is higher than that in the mercury cadmium telluride substrate. The Cd / (Cd+Hg) atomic ratio in the high component HgCdTe film of this embodiment is 0.5-0.8.

[0037] In this embodiment, a three-layer composite passivation film (i.e., a high-concentration HgCdTe film, a CdTe passivation film, and a ZnS passivation film) is used to passivate the mercury cadmium telluride substrate. The high-concentration HgCdTe film, which has a crystal structure, lattice constant, and material composition essentially identical to that of the mercury cadmium telluride substrate, is used as the first passivation layer. Because the high-concentration HgCdTe film has a similar crystal structure and lattice constant to the mercury cadmium telluride substrate, it avoids the problems of stress and dislocations at the CdTe / HgCdTe interface that occur when using CdTe as the first passivation layer. Simultaneously, the material composition at the interface of the high-concentration HgCdTe film and the HgCdTe substrate is similar, and the surface dangling bond characteristics are similar, making it easier for covalent bonds to form between atoms to eliminate dangling bonds on the HgCdTe substrate surface. The bonding can reduce the charge density at the interface; moreover, the crystal structure, lattice constant, and material composition at the interface of the high-concentration HgCdTe film / HgCdTe substrate are basically the same, making it easier to achieve interdiffusion with the HgCdTe substrate at the same temperature than CdTe. Therefore, the heat treatment temperature of the HgCdTe substrate after the three-layer composite passivation film of high-concentration HgCdTe film / CdTe passivation film / ZnS passivation film can be reduced. At the same time, as the second passivation film, the pores generated during the heat treatment process have a reduced impact on the leakage current of the HgCdTe device surface, reducing the process requirements for the preparation of the CdTe passivation film, thereby reducing the complexity of the heat treatment process and broadening the process window for HgCdTe device processing.

[0038] In some embodiments, the surface pretreatment of the mercury cadmium telluride (MDT) substrate in S1 may include chemical etching and degassing of the MDT substrate surface. Specifically, the MDT substrate may be chemically etched with a 0.2-0.5% (v / v) bromoethanol or bromomethanol solution for 5-20 seconds, dried, and then immediately transferred to a nitrogen environment for storage. Before depositing and growing a high-component HgCdTe film, the stored chemically etched MDT substrate is transferred to the transition chamber of a three-chamber magnetron sputtering apparatus, maintaining a vacuum level of less than 3 × 10⁻⁶ ppm in the transition chamber. -6 Pa, the temperature of the mercury cadmium telluride substrate is 60-100℃, and the mercury cadmium telluride substrate is placed in a transition chamber for 15-30 minutes. During this process, water vapor, air and other substances adsorbed on the surface of the mercury cadmium telluride substrate can be removed.

[0039] Methods for preparing passivation layers on the surface of mercury cadmium telluride (HgCdTe) substrates include magnetron sputtering, molecular beam epitaxy, and thermal evaporation. Specifically, in this embodiment, magnetron sputtering is used to deposit and grow a high-component HgCdTe film. The specific process is as follows: The pretreated HgCdTe substrate sample in S1 is transferred to the HgCdTe growth chamber. The temperature of the HgCdTe substrate sample is maintained in the range of 60-100℃. Argon gas is introduced into the growth chamber to keep the pressure in the growth chamber in the range of 0.02-1mBar. A high-component HgCdTe film with a thickness of 50-200nm is deposited using a sputtering power of 30-150W.

[0040] In some embodiments, during the magnetron sputtering deposition of high-concentration HgCdTe films, HgCdTe targets can be used to directly sputter and deposit the high-concentration HgCdTe films. The HgCdTe targets are prepared by slicing HgCdTe bulk crystal material and polishing it, and the Cd / (Cd+Hg) atomic ratio of the HgCdTe targets is 0.5-0.8. Through the selection and design of the HgCdTe targets, the material composition, crystal structure, and crystal constant of the deposited high-concentration HgCdTe films are made closer to those of the mercury cadmium telluride substrate material. This allows for better neutralization of dangling bonds on the surface of the mercury cadmium telluride substrate, reducing the charge density at the interface, and also making it easier to achieve interdiffusion with the mercury cadmium telluride substrate. Of course, a high-component HgCdTe film can also be formed by dual-target sputtering deposition. Cadmium telluride (CdTe) and mercury telluride (HgTe) dual targets are placed in a magnetron sputtering device. By adjusting the sputtering power ratio of the two targets, the atomic ratio of Cd / (Cd+Hg) in the deposited high-component HgCdTe film can be indirectly controlled to the designed target range (i.e., 0.5-0.8).

[0041] In some embodiments, the CdTe passivation film is also deposited and grown using magnetron sputtering. The specific process is as follows: a mercury cadmium telluride substrate sample with a high-concentration HgCdTe film is transferred to a CdTe growth chamber, and a 50-300 nm thick CdTe passivation film is deposited using a sputtering power of 50-150 W. In this embodiment, the CdTe passivation film covers the HgCdTe surface, reducing dangling bonds and surface state density, effectively reducing the surface recombination rate, and reducing surface leakage current of the device; at the same time, the lattice constant of CdTe is between that of HgCdTe and ZnS, which can serve as a transition layer to alleviate the lattice mismatch between the high-concentration HgCdTe film and the ZnS passivation film, reduce stress accumulation during ZnS deposition, and prevent film cracking or peeling.

[0042] In some embodiments, the ZnS passivation film is also deposited and grown using magnetron sputtering. The specific process is as follows: the sample with the deposited CdTe passivation film is transferred to the ZnS growth chamber, and a 50-300 nm thick ZnS passivation film is deposited using a sputtering power of 100-250 W. In this embodiment, ZnS, as a wide-bandgap semiconductor, possesses high resistivity and excellent insulation properties. The ZnS passivation film effectively isolates the CdTe / HgCdTe surface from the external environment, reducing surface leakage current, thereby reducing device dark current and improving detector sensitivity.

[0043] After the growth of the three-layer composite passivation film, the HgCdTe substrate covered with the high-component HgCdTe film / CdTe passivation film / ZnS passivation film is subjected to passive heat treatment at 200-300℃ for 3-30 hours under an inert atmosphere to complete the heat treatment process of the HgCdTe substrate. In this embodiment, since the high-component HgCdTe film is used as the first passivation material, the crystal structure, lattice constant, and material composition at the interface of the high-component HgCdTe film / HgCdTe substrate are basically the same. At the same temperature, it is easier for HgCdTe to achieve interdiffusion with the HgCdTe substrate than CdTe. Therefore, the heat treatment temperature after passivation of the mercury cadmium telluride substrate can be reduced. In this embodiment, the heat treatment temperature only needs to be 200-300℃.

[0044] In addition, this embodiment also provides a mercury cadmium telluride material, which is obtained by the above-mentioned surface passivation heat treatment method for mercury cadmium telluride material, including a mercury cadmium telluride substrate and a high-component HgCdTe film layer, a CdTe passivation film layer and a ZnS passivation film layer grown sequentially from bottom to top on the surface of the mercury cadmium telluride substrate.

[0045] Preferably, the thickness of the high-component HgCdTe film is 50-200 nm, the thickness of the CdTe passivation film is 50-300 nm, and the thickness of the ZnS passivation film is 50-300 nm.

[0046] The mercury cadmium telluride material obtained in this embodiment can be applied to mercury cadmium telluride devices, such as mercury cadmium telluride infrared detectors. Infrared detectors made from the above-mentioned mercury cadmium telluride material have advantages such as low dark current, high sensitivity, and stable performance.

[0047] The above examples are merely illustrative of the present invention and do not constitute a limitation on the scope of protection of the present invention. All designs that are the same as or similar to the present invention are within the scope of protection of the present invention.

Claims

1. A method for passivating and heat-treating the surface of mercury cadmium telluride materials, characterized in that, Includes the following steps: S1. Pre-treat the surface of the mercury cadmium telluride substrate; S2. A high-component HgCdTe film is deposited and grown on the surface of the pretreated mercury cadmium telluride substrate. S3. A CdTe passivation film is deposited and grown on the surface of the high-component HgCdTe film. S4. A ZnS passivation film is deposited and grown on the surface of the CdTe passivation film; S5. The mercury cadmium telluride substrate treated in S4 is subjected to passive heat treatment under an inert atmosphere.

2. The surface passivation heat treatment method for mercury cadmium telluride material as described in claim 1, characterized in that, In step S1, the surface pretreatment process of the mercury cadmium telluride substrate is as follows: the mercury cadmium telluride substrate is chemically etched using a bromoethanol or bromomethanol solution, and then the chemically etched mercury cadmium telluride substrate is placed in the transition chamber of a magnetron sputtering equipment for 15-30 minutes, wherein the vacuum degree in the transition chamber is maintained at less than 3 × 10⁻⁶. -6 Pa, the temperature of the mercury cadmium telluride substrate is 60-100℃.

3. The surface passivation heat treatment method for mercury cadmium telluride material as described in claim 1, characterized in that, In step S2, a high-component HgCdTe film is deposited and grown using magnetron sputtering. The process conditions are as follows: the temperature of the mercury cadmium telluride substrate is 60-100℃, the pressure in the high-component HgCdTe film growth chamber is 0.02-1mBar, and the sputtering power is 30-150W; the thickness of the high-component HgCdTe film is 50-200nm.

4. The surface passivation heat treatment method for mercury cadmium telluride material as described in claim 3, characterized in that, In S2, the HgCdTe target used for magnetron sputtering deposition of a high-component HgCdTe film is prepared by slicing HgCdTe bulk crystal material and polishing it, and the Cd / (Cd+Hg) atomic ratio of the HgCdTe target is 0.5-0.

8.

5. The surface passivation heat treatment method for mercury cadmium telluride material as described in claim 1, characterized in that, In step S3, a CdTe passivation film is deposited and grown using magnetron sputtering with a sputtering power of 50-150W and a thickness of 50-300nm.

6. The surface passivation heat treatment method for mercury cadmium telluride material as described in claim 1, characterized in that, In step S4, a ZnS passivation film is deposited and grown using magnetron sputtering with a sputtering power of 100-250W and a thickness of 50-300nm.

7. The surface passivation heat treatment method for mercury cadmium telluride material as described in claim 1, characterized in that, In S5, the passive heat treatment temperature is 200-300℃ and the passive heat treatment time is 3-30h.

8. A mercury cadmium telluride material, characterized in that, It is obtained by surface passivation heat treatment of mercury cadmium telluride material as described in any one of claims 1-7.

9. The mercury cadmium telluride material as described in claim 8, characterized in that, The thickness of the high-component HgCdTe film is 50-200 nm, the thickness of the CdTe passivation film is 50-300 nm, and the thickness of the ZnS passivation film is 50-300 nm.

10. An infrared detector, characterized in that, Includes the mercury cadmium telluride material as described in claim 8 or 9.

Images