Heat treatment method for improving optical performance of zinc selenide (ZnSe) single crystal

Abstract

The invention belongs to the technical field of crystal annealing, and discloses a heat treatment method for improving the optical performance of a zinc selenide (ZnSe) single crystal, which specifically comprises the following steps of: 1, polishing the ZnSe crystal grown by a moving heater method; 2, cleaning the heat-treated quartz tube and the quartz bracket; and 3, vertically placing the polished ZnSe crystal on a quartz support, then putting the quartz support into a heat treatment quartz tube, and carrying out vacuum-pumping sealing treatment. And 4, putting the sealed quartz tube into a three-section horizontal tube furnace, setting proper heat treatment process parameters, and carrying out heat treatment on the ZnSe crystal. The heat treatment method provided by the invention is simple and efficient, a PbCl2 flux inclusion in the ZnSe crystal grown by a moving heater method can be removed, and the infrared transmittance of the crystal is improved from 38% to 70%.

Description

Technical Field

[0001] The present invention relates to a heat treatment method for improving the optical properties of zinc selenide (ZnSe) single crystals, and specifically to a method for eliminating flux inclusions in ZnSe single crystals. Background Art

[0002] As an excellent optoelectronic material, zinc selenide (ZnSe) crystals exhibit important application values and broad development prospects in the optoelectronic field. This material has a wide light transmission range at room temperature, making it an ideal matrix material for optoelectronic devices in the mid-infrared band. It is worth noting that ZnSe crystals show excellent transmission characteristics (transmittance > 68%) in the blue-green band (450 - 550 nm) of the visible light region, which gives it unique advantages in the field of blue semiconductor lasers.

[0003] The growth methods of ZnSe single crystals include vapor phase method, melt method, and traveling heater method (THM). Due to the large vapor pressure between Zn and Se, it is difficult to control the growth of single crystals by the vapor phase method, and the size of single crystals is small. The melt method uses a high-temperature (1520 °C) and high-pressure growth environment, and there are phase changes during the cooling process, resulting in the formation of structural defects (twinning, dislocations, pores, etc.) in ZnSe crystals and contamination from the growth crucible, deteriorating the crystal quality. The traveling heater introduces a low-temperature flux (PbCl2), reducing the growth temperature by 500 - 600 °C. The low temperature overcomes many difficult problems in the melt method growth, reduces structural defects in the crystal, and is expected to significantly improve the crystal quality. However, due to the introduction of the flux, flux inclusions (PbCl2) are easily formed inside the crystal, deteriorating the optical properties of the crystal and hindering the development and application of crystal devices.

[0004] Aiming at the technical difficulties mentioned in the background art, the present invention provides a heat treatment method for ZnSe single crystals grown by the THM method to achieve the purpose of eliminating flux inclusions (PbCl2) in ZnSe single crystals and improving the optical properties of the crystals. Summary of the Invention

[0005] The present invention adopts the following technical solutions:

[0006] A heat treatment method for zinc selenide (ZnSe) single crystals, characterized by including the following steps:

[0007] S1. Select a ZnSe crystal grown by the THM method using PbCl2 as a flux, and perform polishing treatment;

[0008] S2. Clean the heat treatment quartz tube and the sample quartz support;

[0009] S3. Vacuum-pack the polished ZnSe crystal into the quartz tube;

[0010] S4. Heat-treat the ZnSe crystal;

[0011] S5. Polish the heat-treated ZnSe crystal;

[0012] S6. Test the distribution of flux inclusions and optical properties in the ZnSe crystal;

[0013] In step S1, successively polish with silicon carbide sandpapers of 5000# and 7000# meshes for 6 - 10 minutes, and then finely polish the crystal with a suspension prepared from magnesium oxide powder with a particle size of 20 - 30 nm and deionized water for 10 - 15 minutes until the crystal surface reaches mirror-level brightness or no scratches are observed under a 100-fold optical microscope.

[0014] In step S2, successively clean the ultrasonic wafer quartz bracket and the heat-treatment quartz tube with a diameter of 10 - 20 mm and a length of 150 - 200 mm with deionized water, acetone, and aqua regia, and then bake in a blast drying oven at 100 - 120 °C for 8 - 12 hours.

[0015] In step S3, vertically place the polished crystal on the quartz bracket, put the quartz bracket into the heat-treatment quartz tube, evacuate to below 1.0×10 -4 Pa, and then use a hydrogen-oxygen flame to seal the quartz tube orifice.

[0016] In step S4, put the sealed quartz tube into a three-zone horizontal tube furnace, set the heat-treatment program to ensure that the ZnSe wafer is at 550 - 750 °C, the temperature gradient is 10 - 20 °C, and the heat-treatment time is 24 - 72 hours. After the heat treatment, cool to room temperature at a cooling rate of 10 - 50 °C / h.

[0017] In step S5, take out the ZnSe crystal and polish the crystal using the polishing method described in the first step.

[0018] In step S6, observe the flux inclusions in the wafer using an infrared transmission microscope and perform optical property tests using a Fourier transform infrared spectrometer.

[0019] The beneficial effects of the present invention are as follows:

[0020] The present invention provides a heat treatment process for eliminating flux inclusions (PbCl2) in ZnSe crystals grown by the THM method. Based on the thermodynamic data of the ZnSe matrix and the flux inclusion PbCl2, the heat treatment process is optimized. The ZnSe crystal is heat-treated for 24 to 72 hours under the temperature field conditions of 550 to 750 °C and a temperature gradient of 10 to 20 °C / cm. In this way, not only is it ensured that the inclusion PbCl2 (melting point 501 °C) is in a molten state, and under the condition of a large temperature gradient, it is beneficial for its rapid thermal migration in the matrix ZnSe to the crystal surface and then removed by polishing, ultimately achieving the purpose of eliminating flux inclusions inside the crystal, but also the thermal decomposition of the ZnSe matrix (thermal decomposition temperature 800 °C) is avoided, the volatilization of components during the heat treatment process is inhibited, and non-stoichiometric defects are reduced, which is beneficial to improving the optical properties of the crystal. After heat-treating the ZnSe crystal grown by THM using the present invention, the flux inclusion PbCl2 in the crystal is successfully eliminated, the absorption and scattering of mid-infrared light are reduced, and the infrared transmittance is increased from 38% to 70%, and its optical properties are significantly improved. Brief Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions in the present invention, the following briefly introduces the solutions in the examples using the drawings.

[0022] Figure 1 Schematic diagram of the heat treatment device for ZnSe crystals.

[0023] Figure 2 Composition analysis of flux inclusions in ZnSe crystals grown by the THM method.

[0024] Figure 3 Infrared transmission microscope observation of flux inclusions in ZnSe crystals before and after heat treatment.

[0025] Figure 4 Infrared transmittance of ZnSe crystals before and after heat treatment. Detailed Embodiments

[0026] The following are specific example implementation schemes. The present invention can be better explained in combination with the drawings.

[0027] Example 1

[0028] First step: Polish the selected ZnSe crystal. Grind it with 5000# and 7000# silicon carbide sandpapers for 6 minutes in sequence, and then finely polish the crystal with a suspension prepared from magnesium oxide powder with a particle size of 20 - 30 nm and deionized water for 10 minutes until the crystal surface reaches mirror-level brightness or no scratches are observed under a 100-fold optical microscope. Second step: Clean the heat treatment annealing tube and quartz bracket. Clean the ultrasonic wafer quartz bracket and the heat treatment quartz tube with a diameter of 10 mm and a length of 150 mm successively with deionized water, acetone, and aqua regia, and then bake them in a blast drying oven at 100 °C for 8 hours. Third step: Vertically place the polished crystal on the quartz bracket, then place the quartz bracket into the heat treatment quartz tube, and evacuate to below 1.0×10 -4 Pa. When it reaches below this pressure, use a hydrogen-oxygen flame to seal the quartz tube mouth. Fourth step: Perform heat treatment on the ZnSe crystal. Place the sealed quartz tube into a three-zone horizontal tube furnace, set the heat treatment program to ensure that the ZnSe wafer is at 550 °C, the temperature gradient is 10 °C, and the heat treatment time is 72 hours. After the heat treatment is completed, cool it to room temperature at a cooling rate of 10 °C / h. Fifth step: Observe the flux inclusions in the wafer using an infrared transmission microscope and perform optical property tests using a Fourier transform infrared spectrometer.

[0029] Example 2

[0030] First step: Polish the selected ZnSe crystal. Grind it with 5000# and 7000# silicon carbide sandpapers for 8 minutes in sequence, and then finely polish the crystal with a suspension prepared from magnesium oxide powder with a particle size of 20 - 30 nm and deionized water for 12 minutes until the crystal surface reaches mirror-level brightness or no scratches are observed under a 100-fold optical microscope. Second step: Clean the heat treatment annealing tube and quartz bracket. Clean the ultrasonic wafer quartz bracket and the heat treatment quartz tube with a diameter of 15 mm and a length of 200 mm successively with deionized water, acetone, and aqua regia, and then bake them in a blast drying oven at 120 °C for 10 hours. Third step: Vertically place the polished crystal on the quartz bracket, then place the quartz bracket into the heat treatment quartz tube, and evacuate to below 1.0×10 -4 Pa. When it reaches below this pressure, use a hydrogen-oxygen flame to seal the quartz tube mouth. Fourth step: Perform heat treatment on the ZnSe crystal. Place the sealed quartz tube into a three-zone horizontal tube furnace, set the heat treatment program to ensure that the ZnSe wafer is at 600 °C, the temperature gradient is 15 °C, and the heat treatment time is 72 hours. After the heat treatment is completed, cool it to room temperature at a cooling rate of 30 °C / h. Fifth step: Observe the flux inclusions in the wafer using an infrared transmission microscope and perform optical property tests using a Fourier transform infrared spectrometer.

[0031] Example 3

[0032] First step: Polish the selected ZnSe crystal. Grind it with 5000# and 7000# silicon carbide sandpapers for 10 minutes in sequence, and then finely polish the crystal with a suspension prepared from magnesium oxide powder with a particle size of 20 - 30 nm and deionized water for 15 minutes until the crystal surface reaches mirror-level brightness or no scratches are observed under a 100-fold optical microscope. Second step: Clean the heat treatment annealing tube and quartz bracket. Clean the quartz bracket for the ultrasonic wafer and the heat treatment quartz tube with a diameter of 20 mm and a length of 200 mm with deionized water, acetone, and aqua regia in sequence, and then bake it in a forced-air drying oven at 120 °C for 12 hours. Third step: Vertically place the polished crystal on the quartz bracket, then put the quartz bracket into the heat treatment quartz tube, evacuate to below 1.0×10 -4 Pa, and use a hydrogen-oxygen flame to seal the quartz tube orifice. Fourth step: Perform heat treatment on the ZnSe crystal. Put the sealed quartz tube into a three-zone horizontal tube furnace, set the heat treatment program to ensure that the ZnSe wafer is at 650 °C, the temperature gradient is 15 °C, and the heat treatment time is 48 hours. After the heat treatment is completed, cool it to room temperature at a cooling rate of 30 °C / h. Fifth step: Observe the flux inclusions in the wafer using an infrared transmission microscope, and perform optical property tests using a Fourier transform infrared spectrometer.

[0033] Example 4

[0034] First step: Polish the selected ZnSe crystal. Grind it with 5000# and 7000# silicon carbide sandpapers for 10 minutes in sequence, and then finely polish the crystal with a suspension prepared from magnesium oxide powder with a particle size of 20 - 30 nm and deionized water for 15 minutes until the crystal surface reaches mirror-level brightness or no scratches are observed under a 100-fold optical microscope. Second step: Clean the heat treatment annealing tube and quartz bracket. Clean the quartz bracket for the ultrasonic wafer and the heat treatment quartz tube with a diameter of 20 mm and a length of 200 mm with deionized water, acetone, and aqua regia in sequence, and then bake it in a forced-air drying oven at 120 °C for 12 hours. Third step: Vertically place the polished crystal on the quartz bracket, then put the quartz bracket into the heat treatment quartz tube, evacuate to below 1.0×10 -4 Pa, and use a hydrogen-oxygen flame to seal the quartz tube orifice. Fourth step: Perform heat treatment on the ZnSe crystal. Put the sealed quartz tube into a three-zone horizontal tube furnace, set the heat treatment program to ensure that the ZnSe wafer is at 700 °C, the temperature gradient is 20 °C, and the heat treatment time is 48 hours. After the heat treatment is completed, cool it to room temperature at a cooling rate of 50 °C / h. Fifth step: Observe the flux inclusions in the wafer using an infrared transmission microscope, and perform optical property tests using a Fourier transform infrared spectrometer.

[0035] Example 5

[0036] First step: Polish the selected ZnSe crystal. Grind it with silicon carbide sandpaper of 5000# and 7000# mesh for 8 minutes in sequence, and then finely polish the crystal with a suspension prepared from magnesium oxide powder with a particle size of 20 - 30 nm and deionized water for 10 minutes until the crystal surface reaches mirror-level brightness or no scratches are observed under a 100-fold optical microscope. Second step: Clean the heat treatment annealing tube and quartz support. Clean the ultrasonic wafer quartz support and the heat treatment quartz tube with a diameter of 20 mm and a length of 200 mm successively with deionized water, acetone, and aqua regia, and then bake it in a forced-air drying oven at 120 °C for 12 hours. Third step: Vertically place the polished crystal on the quartz support, then place the quartz support into the heat treatment quartz tube, and evacuate to below 1.0×10 -4 Pa, and then use a hydrogen-oxygen flame to seal the quartz tube opening. Fourth step: Conduct heat treatment on the ZnSe crystal. Place the sealed quartz tube into a three-zone horizontal tube furnace, set the heat treatment program to ensure that the ZnSe wafer is at 750 °C, the temperature gradient is 15 °C, and the heat treatment time is 24 hours. After the heat treatment is completed, cool it to room temperature at a cooling rate of 50 °C / h. Fifth step: Observe the flux inclusions in the wafer using an infrared transmission microscope and conduct optical property tests using a Fourier transform infrared spectrometer.

[0037] The above has specifically described this example in combination with the attached drawings. However, the present invention is not limited to the above embodiments. Any improvement or other form of improvement made by ordinary people in the art without departing from the principles of the present invention falls within the scope of the present invention.

Claims

1. A heat treatment method for improving the optical properties of zinc selenide (ZnSe) single crystals, characterized in that It includes the following steps: In the first step, polish the ZnSe crystal. Grind it with silicon carbide sandpaper of 5000# and 7000# mesh numbers for 6 - 10 minutes in sequence, and then finely polish the crystal with a suspension prepared from magnesium oxide powder with a particle size of 20 - 30 nm and deionized water for 10 - 15 minutes until the crystal surface reaches mirror-level brightness or no scratches are observed under a 100-fold optical microscope. In the second step, clean the heat-treatment quartz tube and quartz bracket. Clean the ultrasonic wafer quartz bracket and the heat-treatment quartz tube with a diameter of 10 - 20 mm and a length of 150 - 200 mm with deionized water, acetone, and aqua regia in sequence, and then bake it in a blast drying oven at 100 - 120 °C for 8 - 12 hours. Step 3: Vertically place the polished crystal on a quartz support, then place the quartz support into a heat treatment quartz tube. When the vacuum reaches below 1.0×10 -4 Pa, use a hydrogen-oxygen flame to seal the quartz tube opening. In the fourth step, place the sealed quartz tube into a three-zone horizontal tube furnace, set the heat-treatment program to ensure that the ZnSe wafer is at 550 - 750 °C, the temperature gradient is 10 - 20 °C, and the heat-treatment time is 24 - 72 hours. After the heat treatment is completed, cool it to room temperature at a cooling rate of 10 - 50 °C / h. In the fifth step, after the heat treatment is completed, take out the ZnSe crystal, polish the crystal using the polishing method described in the first step, observe the flux inclusions in the wafer, and conduct optical property tests.

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