A method for repairing the surface lattice constant of a cadmium zinc telluride single crystal substrate

Abstract

The application belongs to the technical field of crystal processing, and particularly discloses a method for repairing surface lattice constants of a cadmium zinc telluride (Cd 1‑x Zn x Te, CZT) single crystal substrate. The method comprises the following steps: placing the CZT single crystal substrate in a vacuum treatment chamber, and irradiating and treating the CZT single crystal substrate by using pulsed ultraviolet laser with a wavelength less than 300 nm and a pulse width less than 30 ns, so as to remove the surface oxidation layer and the strain layer, expose the body lattice of the CZT single crystal substrate, and repair the surface lattice constants. The method is a non-contact treatment method, the process is simple, and no chemical reagent is needed. The method can effectively repair the surface lattice constants of the CZT single crystal substrate, improve the lattice matching degree between the CZT single crystal substrate and mercury cadmium telluride (MCT), and further improve the quality of the epitaxially grown MCT. The method solves the problem of lattice mismatch between the surface lattice of the existing CZT single crystal substrate and the epitaxial layer of the MCT due to cutting, polishing and natural oxidation, and simultaneously avoids the problems of human body harm and environmental pollution caused by the use of toxic reagents in the traditional chemical mechanical polishing.

Description

Technical Field

[0001] The present invention relates to the technical field of cadmium zinc telluride crystal processing, in particular to a method for repairing the lattice constant of the surface of a cadmium zinc telluride single crystal substrate. Background Art

[0002] Cadmium zinc telluride (Cd 1-x Zn x Te, abbreviated as CZT, 0<x<1) is a II-VI group semiconductor material, which is a continuous solid solution formed by CdTe and ZnTe. When x = 0.1, CZT has a large atomic number, a high carrier mobility-lifetime product (μτ), high resistivity, and a band gap of about 1.57 eV (which can effectively inhibit the thermal excitation of carriers at room temperature), making it a room-temperature X / γ-ray detector material with excellent performance, and it has broad application prospects in the fields of medical imaging, nuclear detection, security inspection, nuclear industry, astronomical detection and other fields. In addition, when x = 0.04, since mercury cadmium telluride (Hg 1-y Cd y Te, abbreviated as MCT, 0<y<1) has perfect lattice matching with CZT, CZT single crystal substrates are the most ideal epitaxial growth substrates for the infrared detection material MCT.

[0003] Methods commonly used for epitaxial growth of MCT crystal materials include liquid phase epitaxy and molecular beam epitaxy. Epitaxial growth requires lattice matching between the substrate and the grown crystal material. When processing CZT crystals as MCT epitaxial growth substrate materials, the current commonly used process is: first performing orientation cutting, grinding, polishing, cleaning and other processes on the CZT ingot, and then performing back-end processing. However, stress and strain layers are inevitably generated during cutting, grinding and polishing, and exposure to air also easily forms an oxide layer on the surface. Both strain and the oxide layer will cause changes in the lattice constant of the CZT single crystal substrate, resulting in lattice mismatch with MCT. In order to epitaxially grow high-quality MCT crystals on the surface of a CZT single crystal substrate, it is necessary to remove the strain layer and oxides on the surface of the CZT single crystal substrate, repair the lattice constant of the CZT single crystal substrate, and then use it as a substrate for epitaxial growth of MCT crystals.

[0004] Traditional CZT single-crystal substrates require chemical mechanical polishing (CMP) to remove stress from the CZT crystal surface after cutting and the tellurium-rich layer formed during etching. T. Sheahan et al. improved the surface quality of CZT crystals using CMP, achieving low roughness, high cleanliness, and accurate stoichiometry. However, surface oxides were not completely removed, requiring etching to obtain a CZT single-crystal substrate suitable for MCT epitaxial growth. CMP is problematic because the chemicals used are often highly toxic and corrosive, posing a significant challenge to operators and the environment. Furthermore, the CZT single-crystal substrate surface is soft and easily scratched, leading to texturing. Reagent and abrasive residues are also present, and the process is cumbersome and difficult to operate.

[0005] Therefore, how to provide a method for removing oxides from the surface of CZT single crystal substrates without direct contact with chemical reagents, thus avoiding the harm to human health and the environment caused by the toxicity and corrosiveness of chemical reagents, is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] To address the problems of easy scratching and residue buildup during chemical mechanical polishing (CMP) of CZT single-crystal substrates due to their low hardness, the cumbersome and costly process, and the potential harm to human health and the environment caused by the toxicity and corrosiveness of chemical reagents, this invention provides a method for repairing the lattice constant of CZT single-crystal substrates. This method eliminates the need for direct contact, chemical reagents, and abrasives. It utilizes a short-wavelength laser with photon energy higher than the dissociation energy of chemical bonds in the CZT single-crystal substrate and its surface oxide layer. The short-wavelength laser irradiation causes the chemical bonds in the CZT and surface oxide layers to break, thereby peeling off the strained layer and oxide layer, exposing the bulk lattice of the CZT single-crystal substrate.

[0007] To achieve the above objectives, the present invention employs the following technical solution: a method for repairing the lattice constant of a zinc cadmium telluride substrate surface, comprising the following steps: S1. Place the zinc cadmium telluride substrate in a vacuum chamber; S2. Irradiate the cadmium zinc telluride substrate with a pulsed ultraviolet laser with a wavelength less than 300 nm and a pulse width less than 30 ns. The pulse energy density of the ultraviolet laser irradiating the substrate surface is 30–300 mJ·cm⁻¹. -2 The lattice constant of the cadmium zinc telluride single crystal substrate was repaired.

[0008] Further improvements to the method for repairing the lattice constant of cadmium zinc telluride substrates: Preferably, the vacuum level inside the vacuum chamber is 1×10⁻⁶. -5 Pa to 1 Pa.

[0009] Preferably, the repetition frequency of the pulsed ultraviolet laser is 1–20 Hz, and the number of pulses processed in a single session is 1–1000.

[0010] Preferably, the energy density of the ultraviolet laser pulse is 50 mJ·cm⁻¹. -2 .

[0011] Preferably, the repetition frequency of the pulsed ultraviolet laser is 5 Hz, and the number of pulses processed in a single session is 100. Those skilled in the art can determine the appropriate number of pulses within the range of 1-1000 pulses through conventional experiments, depending on the energy density.

[0012] Preferably, the wavelength of the pulsed ultraviolet laser is 193 nm, 248 nm or 266 nm.

[0013] Preferably, an ultraviolet-grade calcium fluoride single crystal window is provided above the vacuum cavity, through which pulsed ultraviolet laser light irradiates the zinc cadmium telluride single crystal substrate.

[0014] Preferably, the pulsed ultraviolet laser forms a flat-topped spot on the surface of the cadmium zinc telluride single crystal substrate, and the spot size can completely cover the area of ​​the cadmium zinc telluride single crystal substrate.

[0015] Preferably, the pulsed ultraviolet laser undergoes beam collimation, beam expansion, and beam homogenization in sequence to obtain a laser spot with uniform energy distribution and appropriate size.

[0016] Preferably, the spot size of the pulsed ultraviolet laser is 0.1 × 0.1 cm. 2 Up to 1.5 × 1.5 cm 2 .

[0017] The method of the present invention has the following technical effects and advantages: This invention provides a method for repairing the lattice constant of a CZT single-crystal substrate surface. This method is a non-contact, rapid surface modification technique that requires no chemical reagents, avoiding the harm to human health, corrosion of equipment, and environmental pollution caused by chemical reagents during chemical mechanical polishing, as well as mechanical damage (such as scratches and textures) to the CZT single-crystal substrate surface, ensuring no drug or reagent residue on the CZT single-crystal substrate surface. Laser surface treatment can be completed within seconds, with extremely fast processing speed. The equipment used in this invention is relatively inexpensive and easy to operate, offering significant cost advantages. X-ray photoelectron spectroscopy (XPS) testing confirms that surface oxides are effectively removed from the CZT single-crystal substrate surface after laser irradiation with appropriate parameters. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the process for repairing the lattice constant of the CZT single crystal substrate surface in this invention.

[0020] Figure 2 The images show XPS (Te 3d) patterns of CZT single crystal substrates, where (a) is before repair and (b) to (e) are XPS (Te 3d) patterns after repair in Examples 1 to 4, respectively.

[0021] Figure 3 XPS (Te 3d) images of the CZT single crystal substrate surface treated with air atmosphere laser surface treatment in Comparative Example 1. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0023] In this embodiment, the cadmium zinc telluride substrates are all CZT ingots grown using the Bridgman process, with a zinc content of x = 0.04, used as substrates for MCT epitaxial growth.

[0024] The smooth-surfaced CZT ingot was divided into 5×5×1 mm sections. 3 The small pieces are blown off by cold, dry air to remove the small particles generated on the surface due to cutting. Then, a small amount of acetone is used to remove the organic contamination on the surface and it is dried with cold, dry air to obtain the CZT single crystal substrate to be laser irradiated.

[0025] Example 1 This embodiment discloses a method for repairing the lattice constant of a CZT single-crystal substrate surface, such as... Figure 1 As shown, the specific steps include the following: S1. Place the CZT single crystal substrate in a vacuum processing chamber and use a vacuum pump to evacuate the gas pressure inside the chamber to 5 × 10⁻⁶. -5 Pa.

[0026] S2. Using a KrF excimer laser with a wavelength of 248 nm and a pulse width of 25 ns, the pulsed ultraviolet laser was collimated, expanded, and homogenized to obtain a sample with a size of 1.0 × 1.0 cm. 2The uniform light spot allows the laser to pass through the ultraviolet-grade calcium fluoride single crystal window and completely cover the entire CZT single crystal substrate.

[0027] The energy density of the laser pulse was adjusted to 30 mJ·cm⁻¹ -2 The CZT single crystal substrate was subjected to laser irradiation for 1000 pulses at a frequency of 20 Hz to obtain the repaired CZT single crystal substrate 1.

[0028] Example 2 S1. Place the CZT single crystal substrate in a vacuum processing chamber and use a vacuum pump to evacuate the air pressure inside the chamber to 3 × 10⁻⁶. -3 Pa.

[0029] S2. Using a KrF excimer laser with a wavelength of 248 nm and a pulse width of 20 ns, the pulsed ultraviolet laser was collimated, expanded, and homogenized to obtain a sample with a size of 1.0 × 1.0 cm. 2 The uniform light spot allows the laser to pass through the ultraviolet-grade calcium fluoride single crystal window and completely cover the entire CZT single crystal substrate.

[0030] The energy density of the laser pulse was adjusted to 50 mJ·cm⁻¹ -2 The CZT single crystal substrate was subjected to laser irradiation for 100 pulses at a frequency of 5 Hz to obtain the repaired CZT single crystal substrate 2.

[0031] Example 3 S1. Place the CZT single crystal substrate in a vacuum processing chamber and use a vacuum pump to evacuate the air pressure in the chamber to 1 Pa.

[0032] S2. Using a KrF excimer laser with a wavelength of 248 nm and a pulse width of 20 ns, the pulsed ultraviolet laser was collimated, expanded, and homogenized to obtain a sample with a size of 1.0 × 1.0 cm. 2 The uniform light spot allows the laser to pass through the ultraviolet-grade calcium fluoride single crystal window and completely cover the entire CZT single crystal substrate.

[0033] The energy density of the laser pulse was adjusted to 300 mJ·cm⁻¹ -2 The CZT substrate was subjected to laser irradiation for one pulse at a frequency of 1 Hz to obtain the repaired CZT single crystal substrate 3.

[0034] Example 4 S1. Place the CZT single crystal substrate in a vacuum processing chamber and use a vacuum pump to evacuate the gas pressure inside the chamber to 5 × 10⁻⁶. -2 Pa.

[0035] S2. Using a KrF excimer laser with a wavelength of 248 nm and a pulse width of 20 ns, the pulsed ultraviolet laser was collimated, expanded, and homogenized to obtain a sample with a size of 1.0 × 1.0 cm. 2 The uniform light spot allows the laser to pass through the ultraviolet-grade calcium fluoride single crystal window and completely cover the entire CZT single crystal substrate.

[0036] The energy density of the laser pulse was adjusted to 150 mJ·cm⁻¹ -2 The CZT substrate was subjected to laser irradiation for 10 pulses at a frequency of 10 Hz to obtain the repaired CZT single crystal substrate 4.

[0037] Comparative Example 1 S1. Place the CZT single crystal substrate in a vacuum processing chamber without evacuating the vacuum, i.e., the chamber pressure is 1×10⁻⁶ atmospheres. 5 Pa.

[0038] S2. Using a KrF excimer laser with a wavelength of 248 nm and a pulse width of 20 ns, the pulsed ultraviolet laser was collimated, expanded, and homogenized to obtain a sample with a size of 1.0 × 1.0 cm. 2 The uniform light spot allows the laser to pass through the ultraviolet-grade calcium fluoride single crystal window and completely cover the entire CZT single crystal substrate.

[0039] The energy density of the laser pulse was adjusted to 50 mJ·cm⁻¹ -2 The CZT substrate was subjected to laser irradiation for 100 pulses at a frequency of 5 Hz to obtain the repaired CZT single crystal substrate 1.

[0040] Performance testing: X-ray photoelectron spectroscopy (XPS) was used to analyze the elemental stoichiometry and oxide content on the surface of CZT single-crystal substrates. XPS measurements were performed using an ESCALAB 250xi spectrometer with monochromatic Al Kα rays (1486.6 eV) as the excitation source and a vacuum level of 7 × 10⁻⁶ eV in the analysis chamber. -9 mbar. Binding energy calibration was performed with reference to the C 1s peak (284.8 eV) of surface-adsorbed hydrocarbons. XPS characterization was performed on CZT single-crystal substrates before and after KrF excimer laser treatment. Since the surface oxide layer causes lattice mismatch, the removal of the oxide layer was assessed using the characteristic peaks of Te oxide in the Te 3d spectrum (Te...). 4+ The disappearance of ) is used to determine the outcome.

[0041] Figure 2 (a) shows the XPS (Te 3d) image of the CZT single crystal substrate before repair. Figure 2Images (b), (c), (d), and (e) are XPS (Te 3d) images after repair according to Examples 1, 2, 3, and 4, respectively. Figure 2 As shown in (a), in a CZT single crystal substrate that has not been laser irradiated, 3d 3 / 2 and 3D 5 / 2 Te 2- The binding energies are approximately 583.5 eV and 573.1 eV, respectively, for Te. 4+ 3D 3 / 2 and 3D 5 / 2 The binding energies are approximately 586.5 eV and 576.1 eV, respectively; Te 4+ A high peak intensity indicates the presence of a significant oxide layer on the substrate surface. For example... Figure 2 As shown in (b) to (e), after laser irradiation treatment according to Examples 1 (1000 pulses), 2 (100 pulses), 3 (1 pulse), and 4 (10 pulses), the Te values ​​of each sample... 4+ The corresponding characteristic peaks all disappeared completely, indicating that oxides on the surface of CZT single crystal substrates can be effectively removed under different combinations of laser parameters.

[0042] Table 1 further presents the quantitative analysis results of the stoichiometry of surface elements and oxide content of each sample.

[0043] Table 1. Stoichiometry and oxide content of CZT single crystal substrates

[0044] Table 1 shows that the (Cd+Zn) / Te ratio on the untreated CZT single crystal substrate surface is only 0.85, indicating the presence of a significant Te-rich oxide layer. After vacuum atmosphere pulsed ultraviolet laser treatment in Examples 1–4, the (Cd+Zn) / Te ratios on the surface of each sample recovered to 1.03, 1.01, 1.05, and 1.03, respectively, all close to the ideal stoichiometric ratio of 1.00. Meanwhile, the Te ratio also increased. 4+ / Te 2- The ratios all decreased to below 0.05, further confirming that the surface oxides had been effectively removed and the lattice constant had been restored. Among them, Example 2 (energy density 50 mJ·cm⁻¹) -2 After treatment with a frequency of 5 Hz and 100 pulses, the surface stoichiometry was closest to 1.00, and Te 4+ / Te 2- A ratio of 0 represents the optimal processing condition in each embodiment, achieving complete removal of the oxide layer and repair of the lattice parameters without damaging the crystal surface.

[0045] Figure 3The changes in the Te3d spectrum of the CZT single-crystal substrate in Comparative Example 1 before and after irradiation with a KrF excimer laser in an air atmosphere are shown. The results indicate that even when treated with the same laser parameters as in Example 2 in an air atmosphere, the Te3d spectrum... 4+ Although the characteristic peaks have weakened, they are still significantly present (Te). 4+ / Te 2- =0.64), indicating that the surface oxides were not completely removed. This confirms that a vacuum atmosphere is a necessary condition for the effective removal of surface oxides and the restoration of surface lattice parameters on CZT single crystal substrates.

[0046] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for repairing the lattice constant of a cadmium zinc telluride single crystal substrate, characterized in that, Includes the following steps: S1. Place the zinc cadmium telluride substrate in a vacuum chamber; S2. Irradiate the cadmium zinc telluride substrate with a pulsed ultraviolet laser with a wavelength less than 300 nm and a pulse width less than 30 ns. The pulse energy density of the ultraviolet laser irradiating the substrate surface is 30–300 mJ·cm⁻¹. -2 The lattice constant of the cadmium zinc telluride single crystal substrate was repaired.

2. The method for repairing the lattice constant of a cadmium zinc telluride single crystal substrate according to claim 1, characterized in that, The vacuum level inside the vacuum chamber is 1×10⁻⁶. -5 Pa to 1 Pa.

3. The method for repairing the lattice constant of a cadmium zinc telluride single crystal substrate according to claim 1, characterized in that, The repetition frequency of the pulsed ultraviolet laser is 1–20 Hz, and the number of pulses processed in a single session is 1–1000.

4. The method for repairing the lattice constant of a cadmium zinc telluride single crystal substrate according to claim 1, characterized in that, The energy density of the ultraviolet laser pulse is 50 mJ·cm⁻¹ -2 .

5. The method for repairing the lattice constant of a cadmium zinc telluride single crystal substrate according to claim 4, characterized in that, The pulsed ultraviolet laser has a repetition frequency of 5 Hz and processes 100 pulses per cycle.

6. The method for repairing the lattice constant of a cadmium zinc telluride single crystal substrate according to claim 1 or 5, characterized in that, The wavelength of the pulsed ultraviolet laser is 193 nm, 248 nm, or 266 nm.

7. The method for repairing the lattice constant of a cadmium zinc telluride single crystal substrate according to claim 1, characterized in that, An ultraviolet-grade calcium fluoride single crystal window is provided above the vacuum cavity, through which pulsed ultraviolet laser light irradiates the zinc cadmium telluride single crystal substrate.

8. The method for repairing the lattice constant of a cadmium zinc telluride single crystal substrate according to claim 1, characterized in that, The pulsed ultraviolet laser forms a flat-topped spot on the surface of the cadmium zinc telluride single crystal substrate, and the spot size can completely cover the area of ​​the cadmium zinc telluride single crystal substrate.

9. The method for repairing the lattice constant of a cadmium zinc telluride single crystal substrate according to claim 8, characterized in that, The pulsed ultraviolet laser is sequentially collimated, expanded, and homogenized to obtain a laser spot with uniform energy distribution and appropriate size.

10. The method for repairing the lattice constant of a cadmium zinc telluride single crystal substrate according to claim 8, characterized in that, The spot size of the pulsed ultraviolet laser is 0.1 × 0.1 cm. 2 Up to 1.5 × 1.5 cm 2 .

Images