A process for improving uniformity of large-area cadmium zinc telluride thin films by substrate annealing
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NORTHWESTERN POLYTECHNICAL UNIV
- Filing Date
- 2026-03-10
- Publication Date
- 2026-07-03
Smart Images
Figure CN122340934A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of II-VI group-based ternary compound semiconductor epitaxial film preparation technology, specifically involving a near-space sublimation process for improving the uniformity of large-area zinc cadmium telluride thin films through substrate air-firing treatment. Background Technology
[0002] Cadmium zinc telluride (CdZnTe, or CZT for short) belongs to the II-VI group of compound semiconductor materials. With its high atomic number, wide bandgap that can be continuously adjusted from 1.4 to 1.6 eV, excellent carrier mobility lifetime product (μτ value), and low electron-hole ionization energy, it has become an ideal material for preparing room temperature X-ray and gamma-ray detectors.
[0003] Compared to traditional amorphous selenium (a-Se) detectors, cadmium zinc telluride (CdT) thin films offer higher radiation absorption efficiency, faster response speed, and superior imaging resolution. They also operate stably at room temperature, significantly reducing energy consumption and system complexity, making them irreplaceable in fields such as precise medical imaging diagnosis, industrial non-destructive testing, and real-time nuclear radiation monitoring. Furthermore, the application potential of CdT thin films in areas such as solar cell heterojunction substrates and infrared detectors has also attracted widespread attention. Compared to CdT single crystals, CdT thin films offer advantages such as good growth repeatability, low preparation cost, and shorter processing time, demonstrating extremely broad application prospects.
[0004] Near-space sublimation (CSS) is a core technology for the preparation of cadmium zinc telluride (CZT) epitaxial films. It achieves single-crystal thick-film epitaxial growth through gas-phase transport and boasts advantages such as fast growth rate, low preparation cost, and the ability to grow large-area CZT epitaxial films. Compared to the traditional melt method, CSS is simpler, less expensive, and allows for large-area film formation, effectively addressing the drawbacks of the melt method, such as low ingot utilization and dense defect formation caused by sidewall nucleation.
[0005] However, due to factors such as uneven beam density in different regions of the growth source, unbalanced temperature field distribution within the furnace, uneven distribution of cadmium zinc telluride nucleation sites on the gallium arsenide substrate, and localized inhomogeneities in gas phase transport dynamics, cadmium zinc telluride epitaxial films still face the prominent problem of poor fabrication uniformity. The resulting large-area films exhibit significant differences in thickness and morphology across different regions, leading to limited usable area and low overall utilization. This inhomogeneity introduces localized stress and various defects, thereby reducing carrier mobility and lifetime. This results in problems such as decreased energy resolution and increased leakage current in the final X-ray detectors, severely hindering the development and practical application of high-performance, large-area detector arrays.
[0006] Therefore, how to improve the uniformity of film growth during the growth process has become a core issue in promoting the transition of zinc cadmium telluride films from the laboratory research and development stage to large-scale mass production. Summary of the Invention
[0007] The purpose of this invention is to address the shortcomings of the current near-space sublimation method for preparing zinc cadmium telluride (CdT) films, which suffers from poor macroscopic morphological uniformity. Instead, it provides a near-space sublimation process that improves the uniformity of large-area CdT films by subjecting to air-firing treatment. This method is suitable for the high-uniformity preparation of large-area semiconductor epitaxial films for X-ray imaging.
[0008] To achieve the above objectives, the technical solution provided by this invention is:
[0009] A near-space sublimation process for improving the uniformity of large-area zinc cadmium telluride thin films through substrate air-firing is characterized by the following steps:
[0010] Step 1: Pretreatment, including pretreatment of the growth source and pretreatment of the substrate.
[0011] Pretreatment of growth source refers to the air-firing treatment of CdZnTe polycrystalline growth source;
[0012] Substrate pretreatment refers to the air-firing process performed on the gallium arsenide substrate, and the steps are as follows:
[0013] The GaAs substrate is ultrasonically cleaned and dried in a vacuum environment to ensure that the deposits are removed before air burning, so that the surface of the GaAs substrate is free from contaminants. The GaAs substrate is purchased directly from the market. It has low resistivity and is polished on both sides. The current GaAs substrate is a GaAs (100) substrate, on which zinc zinc cadmium (100) single crystals can be epitaxially grown. This orientation is easier to grow and easier to grow into single crystals.
[0014] After cleaning and drying, the GaAs substrate with the growth surface (one side can be marked as the growth surface, and subsequent growth will be carried out on this surface) is placed with the growth surface facing upward in a near-space sublimation furnace for air firing. During air firing, the temperature of the upper heating stage and the lower heating stage is kept consistent, both set to 620-680 ℃, preferably 650 ℃.
[0015] After the air burn-in was completed, the GaAs substrate was removed and ultrasonically cleaned, and then dried in a vacuum environment to obtain the pretreated GaAs substrate.
[0016] Step 2: Epitaxial growth of CdZnTe thin films
[0017] The GaAs substrate and CdZnTe polycrystalline growth source after the first step of pretreatment were placed in a near-space sublimation furnace to perform epitaxial growth of CdZnTe thin films, resulting in large-area cadmium zinc telluride thin films with improved uniformity.
[0018] Furthermore, the specific process of substrate pretreatment in step one is as follows:
[0019] The GaAs substrate was ultrasonically cleaned sequentially in anhydrous ethanol (or acetone) and deionized water, and then dried in a vacuum environment.
[0020] Place the GaAs substrate in a near-space sublimation furnace, set the air-firing process parameters, close the exhaust solenoid valve, and turn on the water cooler and vacuum pump. When the vacuum level in the near-space sublimation furnace chamber drops below 40 Pa, turn on the molecular pump. When the vacuum level in the furnace reaches 1 Pa, start heating in the near-space sublimation furnace. Turn off the molecular pump and vacuum pump, fill the chamber with argon for protection, and wait for the near-space sublimation furnace to heat up to the set temperature at a heating rate of 1 °C / s (this heating rate is used to ensure uniform and sufficient heating). Hold the temperature for 10 mins, and then cool it down to room temperature with the help of water cooling. Turn off the water cooler, open the exhaust solenoid valve, and open the chamber.
[0021] Remove the GaAs substrate after air burning, wipe the growth surface with a lint-free cloth and acetone to remove residual deposits, then ultrasonically clean it in anhydrous ethanol and deionized water, and dry it in a vacuum environment.
[0022] Furthermore, the air-firing process parameters during the pretreatment of the growth source in step one are as follows:
[0023] The temperature of both the upper and lower heating stages was set to 500℃, the heating rate was set to 1℃ / s, and the holding time was set to 5mins. The purpose of dry burning of the growth source is to remove some contaminants and polishing damage layers from the surface of the growth source. 500℃ is a commonly used temperature in the laboratory, which can ensure that the dry burning is thorough and does not waste energy.
[0024] The CdZnTe polycrystalline growth source can be cut and spliced during the pretreatment of the growth source to meet the large-area size requirements of the CdZnTe thin film. For example, if a 6-inch thin film needs to be prepared, several qualified 3-inch CdZnTe growth sources with no obvious pores and uniform surface color can be selected to achieve higher economic efficiency. 0.9 Zn 0.1 Te polycrystalline source blocks are cut and spliced to meet the requirements of 6-inch thin film growth. After cutting the growth source, the edges of the cut growth source are first polished to facilitate splicing. Then, the cut growth source is polished until the thickness of the growth source is 2.5mm. Finally, the surface of the growth source is finely polished to remove the oxide layer. The polished growth source is then ultrasonically cleaned in deionized water to remove surface impurities and dried with N2 gas (other drying methods can also be used to avoid introducing impurities and contaminants). Subsequently, it is placed in a near-space sublimation furnace for air burn-in treatment. The air burn-in treatment operation is the same as the aforementioned substrate air burn-in treatment operation.
[0025] Furthermore, the process parameters for the epitaxial growth of the CdZnTe thin film in step two are as follows:
[0026] During the heat preservation stage, the temperatures of both the upper and lower heating stages were set to 300℃, with a heating rate of 1℃ / s and a holding time of 10 mins. During the growth stage, the temperatures of the upper heating stage and the lower heating stage were set to 500℃ and 700℃, respectively, with a heating rate of 2℃ / s and a growth time of 30 mins. Following these process parameters ensures more uniform temperature changes during growth.
[0027] Before epitaxial growth, all components in the near-space sublimation furnace (such as the upper heating stage support, lower heating stage support, AlN tray, and unsealed graphite frame) are subjected to air burn-in. The temperature of both the upper and lower heating stages is set to 650°C for 30 minutes to evaporate any residual zinc cadmium telluride on the previous film growth components, ensuring the components remain clean and will not affect subsequent film growth. After air burn-in, the 3mm glass plate, AlN tray, pretreated CdZnTe growth source, splicing mask, and unsealed graphite frame are sequentially placed into the lower heating stage support, and the pretreated GaAs substrate and 2mm glass plate are sequentially placed into the upper heating stage support. The chamber is then closed. The specific assembly method is known to those skilled in the art. The lower heating stage of the near-space sublimation furnace controls the temperature of the growth source, and the upper heating stage controls the temperature of the substrate. Because the temperature in the lower temperature zone is high, a 3mm glass plate is used in the lower temperature zone and a 2mm glass plate is used in the upper temperature zone to ensure uniform heat conduction.
[0028] Set the growth parameters according to the above process parameters, then close the exhaust solenoid valve and open the gate valve. Once the gate valve stops rotating, turn on the vacuum pump. When the vacuum level in the chamber drops below 40 Pa, turn on the molecular pump. The molecular pump speed will rapidly increase. When the speed reaches 350 Hz, click stop, and then the molecular pump speed will slowly decrease. When the molecular pump speed reaches 0, the vacuum level will reach below 1 Pa as required by the experiment. Turn on the water cooling, and the upper and lower heating stages will begin to heat up. Since the upper and lower heating stages have different temperatures, a temperature gradient exists during heating. The sublimated atoms from the growth source will reach the substrate surface under the drive of the concentration gradient, depositing to form a CdZnTe thin film. After the thin film growth is complete, wait for the chamber temperature to drop to room temperature due to water cooling, then turn off the main control contactor and water cooling. First, open the exhaust solenoid valve, then open the chamber for sampling.
[0029] Furthermore, it also includes:
[0030] Step 3: Scribing of CdZnTe thin films
[0031] The quartz glass substrate and the CdZnTe film prepared in step two are placed on a flat heating stage, and the temperature is set to 150℃. When the temperature of the flat heating stage reaches 120℃, paraffin wax is evenly applied to the quartz glass substrate. After the paraffin wax melts evenly, the CdZnTe film is fixed onto the quartz glass substrate. Paraffin wax is solid at room temperature and needs to be heated to melt it before being evenly applied to the quartz glass substrate. In this way, the CdZnTe film and the quartz glass substrate will firmly adhere together after cooling without damaging the film. The quartz glass substrate with the CdZnTe film is then placed in a cross clamp and cut to the required size (e.g., 10×10mm) using a laser cutter. 2 The CdZnTe thin film sample was diced (using an area block). After dicing, it could be removed simply by heating again to melt the paraffin. The grown CdZnTe epitaxial film was diced to allow for a series of characterizations, including surface morphology.
[0032] Furthermore, the laser cutting machine has a cutting speed of 2000 mm / s, a processing number of 40 times, and a frequency of 20 kHz.
[0033] Meanwhile, the present invention also provides a zinc cadmium telluride thin film prepared by the above-described near-space sublimation process, and an X-ray detector using the zinc cadmium telluride thin film as a detection material.
[0034] Advantages of this invention:
[0035] To address the issue of poor epitaxial film uniformity caused by varying bonding abilities between cadmium zinc telluride (CZT) diffused onto the gallium arsenide (GaAs) substrate and different regions of the substrate, as well as differences in lattice mismatch and interface defect density, leading to varying nucleation capabilities during near-space sublimation preparation of CZT epitaxial films, this invention significantly improves the physical and chemical state of the GaAs substrate surface by subjecting it to air-firing at a predetermined temperature. This effectively removes the oxide layer and adsorbed contaminants from the substrate surface and promotes atomic reconstruction, forming an atomically flat surface with more stable stoichiometry. This clean and regular surface provides uniform nucleation sites for the heteroepitaxial growth of CZT, significantly reducing the tendency for island-like growth patterns caused by inhomogeneous nucleation and varying nucleation capabilities, and promoting two-dimensional layered epitaxy. Meanwhile, the optimized substrate surface reduces stress concentration caused by interface state density and lattice mismatch, effectively suppressing defect propagation into the thin film. This significantly improves the thickness uniformity and morphological uniformity of the cadmium zinc telluride epitaxial film on a macroscopic scale, providing a reliable foundation for fabricating large-area, highly uniform radiation detector thin film materials. It also significantly improves the utilization rate of large-area cadmium zinc telluride thin films and reduces commercial costs. Furthermore, in this invention, the optimal effect on improving film uniformity is achieved when the substrate surface changes from a mirror-like finish to a uniform matte finish after being air-fired at 650°C.
[0036] This invention employs a substrate-air-firing method to improve the surface condition of gallium arsenide substrates, achieving highly uniform growth of zinc cadmium telluride epitaxial films. The resulting large-area zinc cadmium telluride epitaxial films significantly reduce morphological differences in different areas, with smooth and flat edges and no mound defects on the surface, thus significantly increasing the actual usable area of the zinc cadmium telluride thin film, which is beneficial for the commercial fabrication of large-area radiation detector thin film materials. Attached Figure Description
[0037] Figure 1 These are partial images of gallium arsenide substrates after being air-fired at 650°C, without air-fired, air-fired at 620°C, and air-fired at 680°C in Examples 1, 1, 2, and 3 of the present invention, respectively; wherein, a is the gallium arsenide substrate of Example 1 after air-fired at 650°C, b is the gallium arsenide substrate of Comparative Example 1 without air-fired treatment, c is the gallium arsenide substrate of Example 2 after air-fired at 620°C, and d is the gallium arsenide substrate of Example 3 after air-fired at 680°C.
[0038] Figure 2 These are photographs taken under an atomic force microscope of gallium arsenide substrates after being subjected to air-firing at 650°C, without air-firing, air-firing at 620°C, and air-firing at 680°C in Examples 1, 2, and 3 of this invention, respectively; wherein, a is the gallium arsenide substrate of Example 1 after air-firing at 650°C, b is the gallium arsenide substrate of Comparative Example 1 without air-firing treatment, c is the gallium arsenide substrate of Example 2 after air-firing at 620°C, and d is the gallium arsenide substrate of Example 3 after air-firing at 680°C.
[0039] Figure 3 These are photographs taken under an optical microscope of gallium arsenide substrates after being air-fired at 650°C, without air-fired, air-fired at 620°C, and air-fired at 680°C in Examples 1, 2, and 3 of this invention, respectively; wherein, a is the gallium arsenide substrate of Example 1 after air-fired at 650°C, b is the gallium arsenide substrate of Comparative Example 1 without air-fired treatment, c is the gallium arsenide substrate of Example 2 after air-fired at 620°C, and d is the gallium arsenide substrate of Example 3 after air-fired at 680°C.
[0040] Figure 4 These are cadmium zinc telluride epitaxial films grown on gallium arsenide substrates after air sintering at 650°C, without air sintering, air sintering at 620°C, and air sintering at 680°C, as described in Examples 1, 1, 2, and 3 of this invention. Specifically, a is the cadmium zinc telluride epitaxial film grown on a gallium arsenide substrate after air sintering at 650°C in Example 1; b is the cadmium zinc telluride epitaxial film grown on a gallium arsenide substrate without air sintering in Comparative Example 1; c is the cadmium zinc telluride epitaxial film grown on a gallium arsenide substrate after air sintering at 620°C in Example 2; and d is the cadmium zinc telluride epitaxial film grown on a gallium arsenide substrate after air sintering at 680°C in Example 3.
[0041] Figure 5 This is a diagram showing the division of the test areas for zinc cadmium telluride epitaxial films in all embodiments and comparative examples of the present invention;
[0042] Figure 6 These are photographs taken under an optical microscope of different regions I, II, and III of the zinc zinc cadmium epitaxial film grown on a gallium arsenide substrate that has been air-fired at 650°C in this Example 1.
[0043] Figure 7 These are photographs taken under an optical microscope of different regions I, II, and III of the zinc zinc cadmium epitaxial film grown on a gallium arsenide substrate without air burn-in treatment, as shown in Comparative Example 1.
[0044] Figure 8 These are photographs taken under an optical microscope of different regions I, II, and III of the zinc cadmium telluride epitaxial film grown on a gallium arsenide substrate that has been air-fired at 620°C in Example 2.
[0045] Figure 9 These are photographs taken under an optical microscope of different regions I, II, and III of the zinc cadmium telluride epitaxial film grown on a gallium arsenide substrate that has been air-fired at 680°C in Example 3.
[0046] Figure 10 These are photographs taken under a scanning electron microscope of different regions I, II, and III of the zinc cadmium telluride epitaxial film grown on a gallium arsenide substrate that has been air-fired at 650°C in Example 1.
[0047] Figure 11 These are photographs taken under a scanning electron microscope of different regions I, II, and III of the zinc zinc cadmium epitaxial film grown on a gallium arsenide substrate without air burn-in treatment in Comparative Example 1.
[0048] Figure 12 These are photographs taken under a scanning electron microscope of different regions I, II, and III of the zinc cadmium telluride epitaxial film grown on a gallium arsenide substrate that has been air-fired at 620°C in Example 2.
[0049] Figure 13 These are photographs taken under a scanning electron microscope of different regions I, II, and III of the zinc zinc cadmium epitaxial film grown on a gallium arsenide substrate that has been air-fired at 680°C in Example 3. Detailed Implementation
[0050] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:
[0051] Example 1:
[0052] Step 1: Air-firing treatment of gallium arsenide substrate:
[0053] A double-polished GaAs (100) substrate was selected and ultrasonically cleaned sequentially in anhydrous ethanol and deionized water, then dried in a vacuum drying oven. The cleaned and dried GaAs substrate was placed on a graphite frame in a near-space sublimation furnace. The upward-facing surface during the dry-firing process was designated as the growth surface, and subsequent growth was performed on this surface. The dry-firing process parameters for the near-space sublimation furnace were set, ensuring the upper and lower heating stages maintained the same temperature at 650℃ with a heating rate of 1℃ / s. The exhaust solenoid valve was closed, and the gate valve was opened. When the gate valve stopped rotating, the water cooling and vacuum pump were turned on. When the vacuum level in the chamber dropped below 40 Pa, the molecular pump was turned on, and its speed increased rapidly. When the chamber vacuum level reached 1 Pa, the near-space sublimation furnace heating was initiated. The molecular pump and vacuum pump are turned off, and the chamber is filled with argon gas for protection. After the near-space sublimation furnace reaches the specified temperature, it is held for 10 minutes. After the holding time is completed, the chamber temperature drops to room temperature under the action of water cooling. Then, the water cooling is turned off, the exhaust solenoid valve is opened, and the chamber is opened. The GaAs substrate that has been air-burned is taken out and the marked growth surface is wiped with a lint-free cloth and acetone to remove some of the residual deposits on the surface. Then, it is ultrasonically cleaned in anhydrous ethanol and deionized water for 10 minutes in sequence, and then dried in a vacuum environment. This completes the air-burning process of the substrate.
[0054] Step 2: Pretreatment of CdZnTe growth source:
[0055] Based on the required film size, select several qualified 3-inch Cd films with no obvious pores and uniform surface color. 0.9 Zn 0.1 Te polycrystalline sources were individually cut using a diamond pen for easy assembly. After cutting, the edges of the cut growth sources were first polished with 400-grit coarse sandpaper to ensure perfect assembly. Then, the upper surface of the cut small growth sources was polished with 400-grit coarse sandpaper until the thickness of the growth source was 2.5 mm. Finally, the surface of the growth source was finely polished with 2000-grit fine sandpaper to remove the oxide layer. The polished growth sources were then ultrasonically cleaned in deionized water for 10 minutes to remove surface impurities. Finally, the cleaned CdZnTe polycrystalline sources were dried with N2 gas and placed in a near-space sublimation furnace (CSS furnace) for hollow firing to remove the mechanical damage layer on the surface of the CdZnTe polycrystalline sources. The temperature of both the upper and lower heating stages of the near-space sublimation furnace was set to 500℃, the heating rate was 1℃ / s, and the holding time was set to 5 minutes.
[0056] Step 3: Epitaxial growth of CdZnTe thin films:
[0057] The upper heating stage support, lower heating stage support, AlN tray, and graphite frame were placed into the quartz cavity of the near-space sublimation furnace. The temperatures of both the upper and lower heating stages were set to 650℃ and air-fired for 30 minutes. After air-firing, a 3mm glass plate, AlN tray, pretreated CdZnTe growth source, splicing mask, and unsealed graphite frame were sequentially placed into the lower heating stage support; the GaAs substrate and 2mm glass plate were sequentially placed into the upper heating stage support. The lower heating stage of the near-space sublimation furnace controlled the temperature of the growth source, while the upper heating stage controlled the substrate temperature. The sublimation furnace growth process parameters were set. First, the holding stage parameters were set: the temperatures of both the upper and lower heating stages were set to 300℃, the heating rate was 1℃ / s, and the holding time was 10 minutes. During the growth stage, the upper heating stage temperature was set to 500℃, the lower heating stage temperature was set to 700℃, the heating rate was 2℃ / s, and the growth time was set to 30 minutes. The upper and lower heating stage supports were then placed into the furnace sequentially, and the cavity was closed. Then, close the exhaust solenoid valve and open the gate valve. Once the gate valve stops rotating, start the vacuum pump. When the vacuum level in the chamber drops below 40 Pa, start the molecular pump. The pump speed will rapidly increase, reaching 350 Hz. Stop the pump at this point, and then allow it to slowly decrease. When the pump speed reaches zero, the vacuum level will be below 1 Pa, as required by the experiment. Turn on the water cooling and start the near-space sublimation furnace. The upper and lower heating stages have different temperatures, creating a temperature gradient during heating. Atoms sublimated from the growth source will reach the substrate surface under the influence of this concentration gradient, depositing and forming a CdZnTe thin film. After film growth is complete, wait for the chamber temperature to drop to room temperature due to water cooling. Then, close the main control contactor and water cooling, first open the exhaust solenoid valve, and then open the chamber for sampling.
[0058] Step 4: Scribing of CdZnTe thin films:
[0059] The quartz glass block and the CdZnTe thin film sample were placed on a flat heating stage, and the temperature was set to 150℃. When the stage temperature reached 120℃, paraffin wax was evenly applied to the quartz glass block. After the paraffin wax melted evenly, the CdZnTe thin film sample was fixed onto the quartz glass block. The quartz glass block containing the CdZnTe thin film sample was then placed in a cross-shaped clamp, and the CdZnTe thin film sample was diced using a laser cutter at a cutting speed of 2000 mm / s, 40 cuts, and a frequency of 20 kHz, cutting the CdZnTe thin film sample into 10×10 mm pieces. 2 Area block.
[0060] Comparative Example 1:
[0061] To demonstrate the practical effect of air-firing substrate treatment on improving the uniformity of large-area cadmium zinc telluride epitaxial films, this comparative example was established. This comparative example is based on Example 1, but without air-firing the gallium arsenide substrate; that is, step one of Example 1 is omitted, while other steps remain unchanged. Epitaxial growth is directly performed on a cleaned and dried gallium arsenide substrate using the treated cadmium zinc telluride growth source to compare the effect of the air-firing substrate treatment on uniformity improvement. The specific steps are as follows:
[0062] Step 1: Pretreatment of CdZnTe growth source:
[0063] Based on the required film size, select several qualified 3-inch Cd films with no obvious pores and uniform surface color. 0.9 Zn 0.1 Te polycrystalline sources were individually cut using a diamond pen for easy assembly. After cutting, the edges of the cut growth sources were first polished with 400-grit coarse sandpaper to ensure perfect assembly. Then, the upper surface of the cut small growth sources was polished with 400-grit coarse sandpaper until the thickness of the growth source was 2.5 mm. Finally, the surface of the growth source was finely polished with 2000-grit fine sandpaper to remove the oxide layer. The polished growth sources were then ultrasonically cleaned in deionized water for 10 minutes to remove surface impurities. Finally, the cleaned CdZnTe polycrystalline sources were dried with N2 gas and placed in a near-space sublimation furnace (CSS furnace) for hollow firing to remove the mechanical damage layer on the surface of the CdZnTe polycrystalline sources. The temperature of both the upper and lower heating stages of the near-space sublimation furnace was set to 500℃, the heating rate was 1℃ / s, and the holding time was set to 5 minutes.
[0064] Step 2: Epitaxial growth of CdZnTe thin films:
[0065] The upper heating stage support, lower heating stage support, AlN tray, and graphite frame were placed into the quartz cavity of the near-space sublimation furnace. The temperatures of both the upper and lower heating stages were set to 650℃ and air-fired for 30 minutes. After air-firing, a 3mm glass plate, AlN tray, pretreated CdZnTe growth source, splicing mask, and unsealed graphite frame were sequentially placed into the lower heating stage support; the GaAs substrate and 2mm glass plate were sequentially placed into the upper heating stage support. The lower heating stage of the near-space sublimation furnace controlled the temperature of the growth source, while the upper heating stage controlled the substrate temperature. The sublimation furnace growth process parameters were set. First, the holding stage parameters were set: the temperatures of both the upper and lower heating stages were set to 300℃, the heating rate was 1℃ / s, and the holding time was 10 minutes. During the growth stage, the upper heating stage temperature was set to 500℃, the lower heating stage temperature was set to 700℃, the heating rate was 2℃ / s, and the growth time was set to 30 minutes. The upper and lower heating stage supports were then placed into the furnace sequentially, and the cavity was closed. Then, close the exhaust solenoid valve and open the gate valve. Once the gate valve stops rotating, start the vacuum pump. When the vacuum level in the chamber drops below 40 Pa, start the molecular pump. The pump speed will rapidly increase, reaching 350 Hz. Stop the pump at this point, and then allow it to slowly decrease. When the pump speed reaches zero, the vacuum level will be below 1 Pa, as required by the experiment. Turn on the water cooling and start the near-space sublimation furnace. The upper and lower heating stages have different temperatures, creating a temperature gradient during heating. Atoms sublimated from the growth source will reach the substrate surface under the influence of this concentration gradient, depositing and forming a CdZnTe thin film. After film growth is complete, wait for the chamber temperature to drop to room temperature due to water cooling. Then, close the main control contactor and water cooling, first open the exhaust solenoid valve, and then open the chamber for sampling.
[0066] Step 3: Scribing of CdZnTe thin films:
[0067] The quartz glass block and the CdZnTe thin film sample were placed on a flat heating stage, and the temperature was set to 150℃. When the stage temperature reached 120℃, paraffin wax was evenly applied to the quartz glass block. After the paraffin wax melted evenly, the CdZnTe thin film sample was fixed onto the quartz glass block. The quartz glass block containing the CdZnTe thin film sample was then placed in a cross-shaped clamp, and the CdZnTe thin film sample was diced using a laser cutter at a cutting speed of 2000 mm / s, 40 cuts, and a frequency of 20 kHz, cutting the CdZnTe thin film sample into 10×10 mm pieces. 2 Area block.
[0068] Example 2:
[0069] To illustrate the optimal substrate burn-in temperature for maximizing the uniformity of large-area cadmium zinc telluride epitaxial films, this embodiment is specifically formulated. The difference between this embodiment and Embodiment 1 is that the substrate burn-in temperature in step one is set to 620°C, while all other steps remain unchanged. The specific details of step one are as follows:
[0070] Step 1: Air-firing treatment of gallium arsenide substrate:
[0071] A double-polished GaAs (100) substrate was selected and ultrasonically cleaned sequentially in anhydrous ethanol and deionized water, then dried in a vacuum drying oven. The cleaned and dried GaAs substrate was placed on a graphite rack in a near-space sublimation furnace. The upward-facing surface during the dry-firing process was designated as the growth surface, and subsequent growth was performed on this surface. The dry-firing process parameters for the near-space sublimation furnace were set, ensuring the upper and lower heating stages maintained the same temperature at 620℃ with a heating rate of 1℃ / s. The exhaust solenoid valve was closed, and the gate valve was opened. When the gate valve stopped rotating, the water cooling and vacuum pump were turned on. When the vacuum level in the chamber dropped below 40 Pa, the molecular pump was turned on, and its speed increased rapidly. When the chamber vacuum level reached 1 Pa, the near-space sublimation furnace heating was initiated. The molecular pump and vacuum pump are turned off, and the chamber is filled with argon gas for protection. After the near-space sublimation furnace reaches the specified temperature, it is held for 10 minutes. After the holding time is completed, the chamber temperature drops to room temperature under the action of water cooling. Then, the water cooling is turned off, the exhaust solenoid valve is opened, and the chamber is opened. The GaAs substrate that has been air-burned is taken out and the marked growth surface is wiped with a lint-free cloth and acetone to remove some of the residual deposits on the surface. Then, it is ultrasonically cleaned in anhydrous ethanol and deionized water for 10 minutes in sequence, and then dried in a vacuum environment. This completes the air-burning process of the substrate.
[0072] Example 3:
[0073] To illustrate the optimal substrate burn-in temperature for maximizing the uniformity of large-area zinc cadmium telluride epitaxial films, this embodiment is specifically formulated. The difference between this embodiment and Embodiment 1 is that the substrate burn-in temperature in step one is set to 680°C, while all other steps remain unchanged. The specific details of step one are as follows:
[0074] Step 1: Air-firing treatment of gallium arsenide substrate:
[0075] A double-polished GaAs (100) substrate was selected and ultrasonically cleaned sequentially in anhydrous ethanol and deionized water, then dried in a vacuum drying oven. The cleaned and dried GaAs substrate was placed on a graphite rack in a near-space sublimation furnace. The upward-facing surface during the dry-firing process was designated as the growth surface, and subsequent growth was performed on this surface. The dry-firing process parameters for the near-space sublimation furnace were set, ensuring the temperatures of the upper and lower heating stages remained consistent at 680℃, with a heating rate of 1℃ / s. The exhaust solenoid valve was closed, and the gate valve was opened. When the gate valve stopped rotating, the water cooling and vacuum pump were turned on. When the vacuum level in the chamber dropped below 40 Pa, the molecular pump was turned on, and its speed increased rapidly. When the vacuum level in the chamber reached 1 Pa, the near-space sublimation furnace heating was initiated. The molecular pump and vacuum pump are turned off, and the chamber is filled with argon gas for protection. After the near-space sublimation furnace reaches the specified temperature, it is held for 10 minutes. After the holding time is completed, the chamber temperature drops to room temperature under the action of water cooling. Then, the water cooling is turned off, the exhaust solenoid valve is opened, and the chamber is opened. The GaAs substrate that has been air-burned is taken out and the marked growth surface is wiped with a lint-free cloth and acetone to remove some of the residual deposits on the surface. Then, it is ultrasonically cleaned in anhydrous ethanol and deionized water for 10 minutes in sequence, and then dried in a vacuum environment. This completes the air-burning process of the substrate.
[0076] To verify the effect of substrate air-firing on film uniformity in this invention, the results of Examples 1-3 and Comparative Example 1 were compared as follows:
[0077] from Figure 1 As can be seen from the macroscopic images of the substrates, the surface of the gallium arsenide substrate after being air-fired at 650°C in Example 1 exhibits a uniform matte finish; the surface of the substrate without air-fired finish in Comparative Example 1 is originally smooth and mirror-like; the surface of the gallium arsenide substrate after being air-fired at 620°C in Example 2 shows a slight light white change; and the surface of the gallium arsenide substrate after being air-fired at 680°C in Example 3 shows uneven changes and varying degrees of matte finish.
[0078] from Figure 2 The substrate images taken under an atomic force microscope show that the surface of the gallium arsenide substrate after being air-fired at 650°C in Example 1 becomes rougher; the surface of the substrate without air-fired in Comparative Example 1 is smoother and has lower roughness; the surface roughness of the gallium arsenide substrate after being air-fired at 620°C in Example 2 changes little; and the surface roughness of the gallium arsenide substrate after being air-fired at 680°C in Example 3 is larger.
[0079] from Figure 3The substrate images taken under an optical microscope show that, in Example 1, the surface of the gallium arsenide substrate after being air-fired at 650°C appears granular, indicating a change in surface condition; in Comparative Example 1, the surface of the substrate without air-fired is smooth; in Example 2, the surface of the gallium arsenide substrate after being air-fired at 620°C shows little change and remains relatively smooth under an optical microscope; in Example 3, the surface of the gallium arsenide substrate after being air-fired at 680°C shows significant change, exhibiting obvious and dense granular texture under an optical microscope, indicating a substantial change in surface condition.
[0080] from Figure 4 As can be seen from the macroscopic images of the thin films, the cadmium zinc telluride epitaxial film grown on the gallium arsenide substrate after air calcination at 650°C in Example 1 is macroscopically very uniform, with a smooth and clean surface across the entire area. In Comparative Example 1, the cadmium zinc telluride epitaxial film grown on the substrate without air calcination shows better growth in the central area, but poorer growth around the edges. In Example 2, the cadmium zinc telluride epitaxial film grown on the gallium arsenide substrate after air calcination at 620°C is generally good, but the growth effect in the central local area needs improvement. In Example 3, the cadmium zinc telluride epitaxial film grown on the gallium arsenide substrate after air calcination at 680°C shows good growth in most areas, but local defects still exist around the edges.
[0081] according to Figure 5 As shown, the grown zinc cadmium telluride film is divided into three regions from the inside out. The uniformity of the film from the inside out is demonstrated by taking samples from the three regions for microscopic characterization.
[0082] from Figures 6-9 Images of the thin films taken under an optical microscope show that, in Example 1, the cadmium zinc telluride epitaxial film grown on a gallium arsenide substrate after air calcination at 650°C is smooth and clean in all three regions from the inside to the outside, with no macroscopic defects, and the film has good uniformity. In contrast, the cadmium zinc telluride epitaxial film grown on the substrate without air calcination in Comparative Example 1 has obvious mound defects in all three regions from the inside to the outside, with the outer edges being too dense and the middle region having many growth pits, resulting in poor surface morphology of the grown film. In Example 2, the cadmium zinc telluride epitaxial film grown on a gallium arsenide substrate after air calcination at 620°C has obvious mound defects in the transition region and still has many growth pits. In Example 3, the cadmium zinc telluride epitaxial film grown on a gallium arsenide substrate after air calcination at 680°C has a small number of mound defects in the outer and center, and its condition is relatively good.
[0083] from Figures 10-13Images of the thin films taken under a scanning electron microscope show that, in Example 1, the cadmium zinc telluride epitaxial film grown on a gallium arsenide substrate after air calcination at 650°C exhibits smooth and clean surfaces in all three regions from the inside to the outside, indicating good uniformity across the entire film. In contrast, the cadmium zinc telluride epitaxial film grown on the substrate without air calcination in Comparative Example 1 shows mound-like defects in all three regions from the inside to the outside, and polycrystalline structures appear at the periphery, indicating that the complete fabrication of a large-area single-crystal thin film was not achieved. In Example 2, the cadmium zinc telluride epitaxial film grown on a gallium arsenide substrate after air calcination at 620°C has mound-like defects in the central region, and numerous growth pits in the periphery and transition region. In Example 3, the cadmium zinc telluride epitaxial film grown on a gallium arsenide substrate after air calcination at 680°C has a small number of growth pits and anti-evaporation pits in the periphery and center, which to some extent affect the overall morphology of the film.
[0084] In summary, the substrate air-firing method of the present invention can significantly improve the uniformity of the macroscopic morphology of the thin film and achieve highly uniform growth of the thin film, especially when the air-firing treatment is performed at 650°C.
[0085] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.
Claims
1. A near-space sublimation process for improving the uniformity of large-area zinc cadmium telluride thin films through substrate air-firing treatment, characterized in that, Includes the following steps: Step 1: Pretreatment, including pretreatment of the growth source and pretreatment of the substrate. Pretreatment of growth source refers to the air-firing treatment of CdZnTe polycrystalline growth source; Substrate pretreatment refers to the air-firing process performed on the gallium arsenide substrate, and the steps are as follows: The GaAs substrate was ultrasonically cleaned and then dried in a vacuum environment. After cleaning and drying, the GaAs substrate with the growth surface facing up was placed in a near-space sublimation furnace for air firing. During air firing, the temperature of the upper heating stage and the lower heating stage remained the same, both set to 620-680 ℃. After the air burn-in was completed, the GaAs substrate was removed and ultrasonically cleaned, and then dried in a vacuum environment to obtain the pretreated GaAs substrate. Step 2: Epitaxial growth of CdZnTe thin films The GaAs substrate and CdZnTe polycrystalline growth source after the first step pretreatment were placed in a near-space sublimation furnace for epitaxial growth of CdZnTe thin films, resulting in large-area cadmium zinc telluride thin films with improved uniformity.
2. The near-space sublimation process for improving the uniformity of large-area zinc cadmium telluride thin films by substrate air-firing treatment according to claim 1, characterized in that, The specific process of step one substrate pretreatment is as follows: The GaAs substrate was ultrasonically cleaned sequentially in anhydrous ethanol and deionized water, and then dried in a vacuum environment. Place the GaAs substrate in a near-space sublimation furnace, set the air burn process parameters, close the exhaust solenoid valve, and turn on the water cooling and vacuum pump. When the vacuum level in the near-space sublimation furnace chamber drops below 40 Pa, turn on the molecular pump. When the vacuum level in the furnace reaches 1 Pa, start heating in the near-space sublimation furnace. Turn off the molecular pump and vacuum pump, fill the chamber with argon for protection, and hold the near-space sublimation furnace at a heating rate of 1℃ / s until it reaches the set temperature. Then, cool it to room temperature with water cooling, turn off the water cooling, open the gas outlet solenoid valve, and open the chamber. Remove the GaAs substrate after air burning, remove any residual deposits on the growth surface, then ultrasonically clean it in anhydrous ethanol and deionized water, and finally dry it in a vacuum environment.
3. The near-space sublimation process for improving the uniformity of large-area zinc cadmium telluride thin films by substrate air-firing treatment according to claim 2, characterized in that: The air-firing process parameters during the pretreatment of the growth source in step one are as follows: The temperature of both the upper and lower heating stages is set to 500℃, the heating rate is set to 1℃ / s, and the holding time is set to 5mins.
4. The near-space sublimation process for improving the uniformity of large-area zinc cadmium telluride thin films by substrate air-firing treatment according to any one of claims 1-3, characterized in that, The process parameters for the epitaxial growth of the CdZnTe thin film in step two are as follows: During the heat preservation stage, the temperature of both the upper and lower heating platforms was set to 300℃, the heating rate was 1℃ / s, and the heat preservation time was 10mins. During the growth stage, the temperature of the upper heating platform was set to 500℃, the temperature of the lower heating platform was set to 700℃, the heating rate was 2℃ / s, and the growth time was set to 30min.
5. The near-space sublimation process for improving the uniformity of large-area zinc cadmium telluride thin films by substrate air-firing treatment according to claim 1, characterized in that, Also includes: Step 3: Scribing of CdZnTe thin films Place the sample-bearing quartz glass block and the CdZnTe thin film prepared in step two on a flat heating stage and set the temperature to 150°C. When the temperature of the flat heating stage reaches 120°C, apply paraffin wax evenly to the sample-bearing quartz glass block. After the paraffin wax melts evenly, fix the CdZnTe thin film onto the sample-bearing quartz glass block. Place the sample-bearing quartz glass block with the CdZnTe thin film inside a cross clamp and use a laser cutter to scribe the CdZnTe thin film sample according to the required product size.
6. The near-space sublimation process for improving the uniformity of large-area zinc cadmium telluride thin films by substrate air-firing treatment according to claim 5, characterized in that: The laser cutting machine has a cutting speed of 2000 mm / s and a frequency of 20 kHz.
7. A zinc cadmium telluride thin film, characterized in that: It is prepared using the near-space sublimation process described in any one of claims 1-6.
8. An X-ray detector, characterized in that: The zinc cadmium telluride thin film prepared by the near-space sublimation process described in any one of claims 1-6 is used as the detection material.