A method for fabricating a mid-wave avalanche detector structure operating at high temperature with full depletion of the absorption region.

Abstract

This invention discloses a method for fabricating a mid-wave avalanche detector structure operating at high temperatures with a fully depleted absorption region. This method utilizes a high-component interdiffusion mercury cadmium telluride material on the back side, which is then ion-implanted to form an n-wave avalanche detector. + Avalanche detector formed by push-back annealing in the zone n ‑ The multiplication region is concentrated in the low-component region by controlling the push-junction annealing time and temperature to obtain the maximum gain and mid-wave response. Meanwhile, the built-in electric field formed by the difference in the bandgap width of the absorption region depletes the thickness of the absorption region, thereby realizing the formation of a high-temperature operating mid-wave avalanche detector by weakening the diffusion current.

Description

Technical fields:

[0001] This invention relates to the field of photodetector technology, specifically to a method for fabricating a mid-wave avalanche detector structure operating at high temperatures with the absorption region fully depleted. Technical background:

[0002] Mid-wave infrared (MWIR) detectors are widely used in various fields, including missile early warning and tracking, night vision imaging, target identification, environmental monitoring, astronomical observation, scientific research, and medical and biological applications. However, light absorption caused by carbon dioxide and water vapor in the atmosphere significantly attenuates the system signal. Furthermore, achieving accurate long-range detection and tracking of faint targets in low-light and complex environments requires devices capable of amplifying the signal during detection to improve the signal-to-noise ratio at the receiver output. Avalanche photodiodes (APDs) integrate the detection stage and inherent gain stage into a single device, greatly improving detection accuracy and resolution, thus playing a crucial role in such weak-signal applications. MWIR APD devices typically operate at low temperatures. To reduce cost and power consumption, make them more suitable for harsh environments, and pave the way for expanded versatility in commercial, scientific, and civilian applications, MWIR APD systems need to operate at even higher temperatures. Therefore, the development of next-generation MWIR APDs must simultaneously possess characteristics such as high-temperature operation (HOT), low dark current, and low excess noise.

[0003] Mercury cadmium telluride (Hg) 1-x Cd x The Te MWIR APD, as the most mature avalanche detector currently available, possesses characteristics such as single-carrier collisional ionization, exponentially high gain, and extremely low excess noise. However, current planar homogeneous HgCdTe MWIR APDs typically operate at liquid nitrogen cryogenic temperatures, and are limited by high electron diffusion currents to operate at higher temperatures. Moreover, there are currently no literature reports, either domestically or internationally, on mid-wave avalanche detector structures that achieve high-temperature operation. Summary of the Invention:

[0004] The purpose of this invention is to provide a method for fabricating a mid-wave avalanche detector structure that operates at high temperatures with the absorption region fully depleted, overcoming the shortcomings of existing technologies that cannot operate under conditions of high operating temperature, low dark current, and excessive noise.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A method for fabricating a mid-wave avalanche detector structure operating at high temperature with the absorption region fully depleted includes the following steps:

[0007] Step 1, Interdiffusion of Mercury Cadmium Telluride (MCC) material on the back / surface: The MCC material grown on the CdZnTe substrate is subjected to interdiffusion annealing to obtain a surface passivation layer with varying composition gradient and a back composition gradient region. At the same time, the substrate is calibrated using SIMS.

[0008] The second step is to perform p + p-type annealing doping + P-type annealing doping: P-type Hg vacancy doping of interdiffused materials;

[0009] The third step is to lithographically create ion implantation holes: On the mercury cadmium telluride heteromaterial with the ZnS barrier layer and alignment marks already prepared, positive photoresist is used to lithographically create ion implantation holes.

[0010] The fourth step involves boron ion implantation. After implantation, the sample is immersed in acetone to remove the photoresist, and then immersed in pure hydrochloric acid to remove the surface ZnS blocking layer, yielding n... + district;

[0011] Step 5: Rapid push-bonding annealing, and obtain n based on the SIMS calibration composition distribution. - Doubling zone;

[0012] Step 6: Passivation and corrosion p + / n + Electrode holes: CdTe / ZnS double-layer passivation process is adopted; positive photoresist photolithography is used to form etching electrode holes in each injection hole and p-type region, and etching is carried out in freezing point pure hydrochloric acid and hydrobromic acid;

[0013] Step 7, metal electrode fabrication: Cr / Au electrodes with thicknesses of 50nm / 100nm were prepared using an electron beam evaporation device, then immersed in acetone, followed by metal stripping and removal of photoresist;

[0014] Step 8, In pillar fabrication: In pillar fabrication areas are formed by photolithography with positive photoresist between the electrode holes and the common electrode in each injection area. UBM metal Cr / Au with thicknesses of 100nm / 100nm is first prepared by electron beam evaporation. Then, the In pillar is thermally evaporated on the UBM metal Cr / Au. After fabrication, it is immersed in acetone, and then the metal is stripped and the photoresist is removed.

[0015] Step 9, Device flip-soldering: The structure fabricated in step 8 is interconnected with the external gemstone substrate via In-pillar flip-soldering;

[0016] Step 10, Current-Voltage and Gain Multiplication Test: Use a variable temperature Dewar test system to test the light / dark current-voltage characteristics of devices with different areas.

[0017] The interdiffusion annealing treatment is carried out at a temperature of 300-500℃ for 1-48 hours.

[0018] The p+ type annealing treatment is performed at a temperature of 250-400℃ for 24-72 hours.

[0019] The ion implantation aperture size ranges from 5μm to 50μm.

[0020] The boron ion energy is 120-180 keV, and the dose is 1×10⁻⁶. 13 -1×10 15 cm -2 The beam current is 50-200μA.

[0021] The push-bonding annealing temperature is 150-250℃, and the time is 120-250s.

[0022] After the push-bonding annealing, n - The width of the multiplication region is 1-4 μm.

[0023] The beneficial effects of this invention are as follows: 1. This invention uses a high-component interdiffusion mercury cadmium telluride material on the back side, which is then ion implanted to form n + Avalanche detector formed by push-back annealing in the zone n - 1. By controlling the push-junction annealing time and temperature, the multiplication region is concentrated in the low-component region to obtain maximum gain and mid-wave response. The built-in electric field formed by the difference in the bandgap width of the absorption region depletes the thickness of the absorption region. The device forms a high-temperature operating mid-wave avalanche detector by reducing the diffusion current. 2. By cleverly introducing a component gradient distribution into the conventional mercury cadmium telluride avalanche detector structure, the built-in electric field in the absorption region achieves a fully depleted state of the absorption region, overcoming the limitation of dark current electron diffusion in existing homogeneous structures. The multiplication region uses a narrow bandgap material to achieve greater gain. 3. The structure breaks through the high-temperature dark current limitation of homogeneous mid-wave avalanche detectors. Combining the characteristics of mercury cadmium telluride, such as adjustable composition, lattice matching, high gain, and single carrier multiplication, a mid-wave avalanche detector device with high-temperature operation, low noise, low dark current, and high gain can be realized. 4. The mid-wave avalanche detector prepared by this invention has the characteristics of clear principle, simple process, convenient operation, intuitive judgment results, and great market application potential. Attached image description:

[0024] Figure 1 For process flow diagram;

[0025] Figure 2 This is a structural diagram of a mid-wave avalanche detector formed by the present invention;

[0026] Figure 3 This is a component distribution diagram of a mid-wave avalanche detector formed by the present invention;

[0027] Figure 4 This is a diagram of the electric field distribution of a mid-wave avalanche detector formed by the present invention, in which the absorption region is completely depleted.

[0028] Figure 5 The dark current density plots for devices with a cutoff wavelength of 4.2 μm at 80 K and at a high temperature of 160 K are shown.

[0029] Figure 6 The normalized dark current density (GNDCD) at 80K and 160K at high temperature is achievable for devices with a cutoff wavelength of 4.2μm. Detailed implementation method:

[0030] To simplify the description of this embodiment, some components that are well-known to those skilled in the art but are not related to the main content of this invention may be omitted in the accompanying drawings or description. Additionally, for ease of description, some components in the drawings may be omitted, enlarged, or reduced, but these do not represent the actual product dimensions or the complete structure.

[0031] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0032] The present invention will be further described below with reference to the accompanying drawings. The drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent.

[0033] The present invention will now be further described in conjunction with the embodiments and accompanying drawings:

[0034] This invention relates to a method for fabricating a mid-wave avalanche detector structure operating at high temperatures with the absorption region fully depleted, such as... Figure 1 As shown, it includes the following steps:

[0035] Step 1: Backside / Surface Interdiffusion of Mercury Cadmium Telluride (MCC) Material: MCC materials grown on CdZnTe substrates were subjected to interdiffusion annealing at temperatures of 300-500℃ for 1-48 hours to obtain a surface passivation layer with a compositional gradient and a backside compositional gradient region. Simultaneously, SIMS calibration was performed on the substrate. Figure 2 , Figure 3 As shown.

[0036] The second step is to perform p + p-type annealing doping + P-type annealing doping: P-type Hg vacancy doping of interdiffusion materials at a temperature of 250-400℃ for 24h-72h.

[0037] The third step is to lithographically ...

[0038] The fourth step is boron ion implantation, with an ion energy of 120-180 keV and a dose of 1×10⁻⁶. 13 -1×10 15 cm -2 The beam current was 50-200 μA. After implantation, the photoresist was removed by immersion in acetone, and the surface ZnS blocking layer was removed by immersion in pure hydrochloric acid, resulting in a series of n-type nanoparticles of different sizes. + district;

[0039] Step 5: Rapid push-bonding annealing at 150-250℃ for 120-250s, obtaining n with a width of 1-4μm based on SIMS calibration of the component distribution. - doubling zone, such as Figure 2 As shown;

[0040] Step 6: Passivation and corrosion p + / n + Electrode holes: CdTe / ZnS double-layer passivation process is adopted; positive photoresist photolithography is used to form etching electrode holes in each injection hole and p-type region, and etching is carried out in freezing point pure hydrochloric acid and hydrobromic acid;

[0041] Step 7, metal electrode fabrication: Cr / Au with thicknesses of 50nm and 100nm are prepared using an electron beam evaporation device. That is, a Cr metal layer with a thickness of 50nm is prepared using an electron beam evaporation device, and then an Au metal layer with a thickness of 100nm is prepared on the Cr metal layer using an electron beam evaporation device. After that, the metal is immersed in acetone, and then the metal is stripped and the photoresist is removed.

[0042] Step 8, In pillar fabrication: In pillar fabrication areas are formed by photolithography with positive photoresist between the electrode holes and the common electrode in each injection area. UBM metal Cr / Au with thicknesses of 100nm / 100nm is first prepared by electron beam evaporation. Then, the In pillar is thermally evaporated on the UBM metal Cr / Au. After fabrication, it is immersed in acetone, and then the metal is stripped and the photoresist is removed.

[0043] Step 9, Device flip-soldering: The structure fabricated in step 8 is interconnected with the external gemstone substrate via In-pillar flip-soldering;

[0044] Step 10, Current-Voltage and Gain Multiplication Test: Use a variable temperature Dewar test system to test the light / dark current-voltage characteristics of devices with different areas.

[0045] from Figure 4The electric field distribution diagram shows that the absorption region of the mid-wave avalanche detector formed by this invention is completely depleted, while the high-electric-field multiplication region exhibits collisional ionization of charge carriers. From... Figure 5 , Figure 6 It can be seen that the dark current density of the device with a cutoff wavelength of 4.2 μm at a small bias voltage (gain) of 160 K is less than 8 × 10⁻⁶. -6 A / cm 2 The current is significantly lower than the theoretical minimum limit for electron diffusion current. Even at -13V and a gain of 189, the overall current is still less than 2 × 10⁻⁶ at GNDCD 160K. -6 A / cm 2 The low dark current and high gain level ensure that the avalanche detector can still work well even at 160K.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. All equivalent changes and modifications made within the scope of the claims of this invention should be considered within the technical scope of this invention.

Claims

1. A method for fabricating a mid-wave avalanche detector structure operating at high temperature with the absorption region fully depleted, characterized in that: The steps include: Step 1, Interdiffusion of Mercury Cadmium Telluride (MCC) material on the back / surface: The MCC material grown on the CdZnTe substrate is subjected to interdiffusion annealing to obtain a surface passivation layer with varying composition gradient and a back composition gradient region. At the same time, the substrate is calibrated using SIMS. The second step is to perform p + P-type annealing doping: P-type Hg vacancy doping of interdiffused materials; The third step is to lithographically create ion implantation holes: On the mercury cadmium telluride heteromaterial with the ZnS barrier layer and alignment marks already prepared, positive photoresist is used to lithographically create ion implantation holes. The fourth step involves boron ion implantation. After implantation, the sample is immersed in acetone to remove the photoresist, and then immersed in pure hydrochloric acid to remove the surface ZnS blocking layer, yielding n... + district; Step 5: Rapid push-bonding annealing, and obtain n based on the SIMS calibration composition distribution. - Doubling zone; Step 6: Passivation and corrosion p + / n + Electrode holes: CdTe / ZnS double-layer passivation process is adopted; Positive photoresist was used to etch etching electrode holes in each injection hole and p-type region, and etching was performed in freezing point pure hydrochloric acid and hydrobromic acid. Step 7, metal electrode fabrication: Cr / Au electrodes with thicknesses of 50nm / 100nm were prepared using an electron beam evaporation device, then immersed in acetone, followed by metal stripping and removal of photoresist; Step 8, In pillar fabrication: In pillar fabrication areas are formed by photolithography with positive photoresist between the electrode holes and the common electrode in each injection area. UBM metal Cr / Au with thicknesses of 100nm / 100nm is first prepared by electron beam evaporation. Then, the In pillar is thermally evaporated on the UBM metal Cr / Au. After fabrication, it is immersed in acetone, and then the metal is stripped and the photoresist is removed. Step 9, Device flip-soldering: The structure fabricated in step 8 is interconnected with the external gemstone substrate via In-pillar flip-soldering; Step 10, Current-Voltage and Gain Multiplication Test: Use a variable temperature Dewar test system to test the light / dark current-voltage characteristics of devices with different areas.

2. The method for fabricating the mid-wave avalanche detector structure with fully depleted absorption region at high temperature according to claim 1, characterized in that: The interdiffusion annealing treatment is carried out at a temperature of 300-500℃ for 1-48 hours.

3. The method for fabricating the mid-wave avalanche detector structure with fully depleted absorption region at high temperature according to claim 1, characterized in that: The p+ type annealing treatment is performed at a temperature of 250-400℃ for 24-72 hours.

4. The method for fabricating the mid-wave avalanche detector structure with fully depleted absorption region at high temperature according to claim 1, characterized in that: The ion implantation aperture size ranges from 5μm to 50μm.

5. The method for fabricating the mid-wave avalanche detector structure with fully depleted absorption region at high temperature according to claim 1, characterized in that: The boron ion energy is 120-180 keV, and the dose is 1×10⁻⁶. 13 -1×10 15 cm -2 The beam current is 50-200μA.

6. The method for fabricating a mid-wave avalanche detector structure operating at high temperature with full depletion of the absorption region according to claim 1, characterized in that: The push-bonding annealing temperature is 150-250℃, and the time is 120-250s.

7. The method for fabricating a mid-wave avalanche detector structure operating at high temperature with full depletion of the absorption region according to claim 1, characterized in that: After the push-bonding annealing, n - The width of the multiplication region is 1-4 μm.

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