Preparation method of Schottky contact for radiation detection based on cadmium telluride single crystal

Abstract

The invention provides a preparation method of a Schottky contact for radiation detection based on a cadmium telluride single crystal, and solves the problems of Fermi level pinning and uncontrollable interface morphology of the cadmium telluride Schottky contact prepared by the existing method. The Schottky contact is successfully prepared by adopting a transfer method, the metal electrode and the substrate are separated by utilizing polydimethylsiloxane and a tungsten steel gold-plated probe through a mechanical stripping method, then the metal electrode is directly lapped on the clean cadmium telluride surface, and the adhesion between the polydimethylsilane and the metal electrode is reduced through heating, so that the Schottky contact is prepared. Finally, separation of the polydimethylsilane and the metal electrode and preparation of the cadmium telluride surface metal electrode are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor materials, and particularly relates to a preparation method of a Schottky contact for radiation detection based on cadmium telluride single crystals. Background Art

[0002] Radiation detection is irreplaceably important in the fields of radiology, astronomical observation, high-energy physics, and industrial non-destructive monitoring. Semiconductor radiation detection materials can directly convert radiation signals into electrical signals, and have higher radiation detection accuracy compared with traditional scintillator materials. As a third-generation semiconductor radiation detection material, cadmium telluride material has the characteristics of high atomic number and good electrical transport performance, and can achieve high-precision radiation measurement at room temperature, and is one of the most concerned materials in the current radiation detection field. However, the intrinsic resistivity of cadmium telluride material is relatively small. To suppress the dark current during device operation, a high-barrier junction contact is generally introduced on the crystal surface, and the device is operated under reverse cut-off conditions to meet the requirements of high-precision radiation detection; but currently, the preparation of cadmium telluride radiation detection devices based on Schottky contacts generally has the problem of Fermi level pinning. The main reason is that there are a large number of interface defects, strains, disordered structures and metal diffusion at the cadmium telluride metal-semiconductor interface obtained by the thermal evaporation method, which leads to a large number of metal-induced gap states at the interface. Severe Fermi level pinning results in the Schottky barrier constructed on the cadmium telluride surface being much lower than the theoretical barrier height, and the effective suppression of dark current cannot be achieved under reverse bias, which limits the application of cadmium telluride in high-precision radiation detection at high voltages. Therefore, it is of great significance to propose a preparation process for Schottky contacts on the surface of cadmium telluride single crystals with a high barrier.

[0003] Document 1 "Kosyachenko, L.A. et al. Higher Voltage Ni / CdTe Schottky Diodes With Low Leakage Current. IEEE Trans. Nucl. Sci. 2009, 56, 1827–1834." reported that argon ion bombardment was used to bombard the surface of cadmium telluride to bend the energy band on the crystal surface downward, and then a Ni electrode was prepared on the surface of cadmium telluride by thermal evaporation to form a Ni-CdTe Schottky contact, realizing the improvement of the Schottky barrier between cadmium telluride and nickel; however, the surface of cadmium telluride was still damaged, and the problem of Fermi level pinning still existed, which limited the potential of cadmium telluride radiation detection devices.

[0004] Reference 2 “Takahashi, T. et al. High-resolution Schottky CdTe diode for hard X-ray and gamma-ray astronomy. Nuclear Instruments and Methods in Physics Research. 1999, 436, 111–119.” reported that indium electrodes were prepared on the surface of cadmium telluride by thermal evaporation to form Schottky contacts. However, the obtained Schottky contact barrier was significantly smaller than the theoretical value, which the author attributed to the reduction of the Schottky barrier caused by the surface oxide layer. The measured Schottky barrier height was 0.75 eV. The device had an energy resolution of 0.8% for the 22 Na source under the test conditions of 5 °C and 511 keV.

[0005] Reference 3 “Ayoub, M. et al. Electroless Contact Study on CdTe Nuclear Detectors: New Results and Element Deposition. IEEE Trans. Nucl. Sci. 59, 1497–1503 (2012).” reported that platinum, tungsten, molybdenum and other metal electrodes were prepared on the surface of cadmium telluride by electroless plating, showing the characteristics of Schottky contacts. Compared with the evaporation method, it showed an increase in the Schottky barrier, but the wet electrode preparation process had problems of poor stability and uncontrollable interface morphology.

[0006] The above references reported that Schottky contacts were formed on the surface of cadmium telluride using different metals by different methods, achieving a significant reduction in the dark current under reverse bias compared with Ohmic contacts. However, the Schottky contacts of cadmium telluride obtained by the above methods still faced the problems of Fermi level pinning or uncontrollable interface morphology, resulting in the inability to effectively suppress the dark current under high bias voltages, and even better radiation detection performance could only be obtained under low-temperature conditions, greatly limiting the application scenarios of cadmium telluride radiation detection devices. Therefore, it is necessary to explore a new method for preparing Schottky contacts on cadmium telluride. Summary of the Invention

[0007] The purpose of the present invention is to solve the problems of Fermi level pinning and uncontrollable interface morphology existing in the Schottky contacts of cadmium telluride prepared by existing methods, and to provide a method for preparing Schottky contacts for radiation detection based on cadmium telluride single crystals.

[0008] Concept of the present invention:

[0009] In view of the problems of Fermi level pinning and uncontrollable interface morphology existing in the current cadmium telluride Schottky contact, the present invention conducts in-depth exploration on this, and finds that traditional metallization methods such as evaporation and sputtering will introduce a large number of gap states, and the devices obtained by the foregoing methods lack good performance in the field of metal-semiconductor contact.

[0010] Schottky contact belongs to a type of van der Waals contact. Van der Waals contact has shown great potential in the field of metal-semiconductor contact. Devices with van der Waals contact can have a higher Schottky barrier. Therefore, in view of the various problems faced by cadmium telluride materials at present, the present invention chooses to prepare by introducing van der Waals contact. However, there are many methods to introduce van der Waals contact. For example, the van der Waals contact between graphene and gold prepared on the surface of cadmium telluride by the chemical sacrificial method reported in Document 4 "Brus, V. V. et al. Graphene / semi-insulating single crystal CdTe Schottky-type heterojunction X-and γ-Ray Radiation Detectors. Sci Rep 9, 1065 (2019).", in which, obvious junction contact characteristics are shown between graphene and cadmium telluride. However, the multi-layer structure of graphene itself and its easy oxidation at high temperature bring difficulties to subsequent flip-chip and electrode lead-out; at the same time, there are many uncontrollable factors in the chemical sacrificial method, and it is easy to have residues of intermediate products that affect the performance of the device, and the stability is poor; another example is the thermal sacrificial method successfully applied on many two-dimensional materials; however, none of these methods can obtain a metal electrode that meets the performance requirements and has a large area, uniform and high quality to form a Schottky contact. Therefore, the present invention hopes to explore a method that can stably and gently metallize the surface of cadmium telluride. As a low-energy and non-destructive surface electrode preparation process, the transfer method can avoid interface damage and lattice defects on the surface of cadmium telluride caused by metallization by transferring and laminating a metal electrode film on the surface of cadmium telluride. However, when transferring a metal electrode on the surface of cadmium telluride, problems such as interface adhesion and the selection of transfer media still need to be explored, and transfer process parameters that can transfer the metal electrode to the surface of cadmium telluride intact need to be explored.

[0011] Based on the above inventive concept, to achieve the above object, the technical solution provided by the present invention is:

[0012] A preparation method of a cadmium telluride Schottky contact, characterized by comprising the following steps:

[0013] Step 1: Pre-fabricate an electrode on a first substrate

[0014] The conductivity of the electrode is greater than 10 6S / M (greater than copper is acceptable), and the adhesion work between the prepared electrode and the surface of the first substrate is less than 0.05 J / m 2 , so as to avoid the subsequent inability to separate the electrode from the first substrate;

[0015] During the prefabrication of the electrode, the material of the first substrate cannot chemically react with the electrode material, including but not limited to combination reactions, redox reactions, etc.;

[0016] Step 2: Process the prefabricated electrode

[0017] Process the edge of the prefabricated electrode in Step 1 so that the height difference between the upper surface of the electrode and the upper surface of the first substrate within a 1-μm horizontal range at the electrode edge exceeds 30 nm but does not exceed 1000 nm. That is, by sharpening the electrode edge, make the height difference at the electrode edge as obvious as possible (it is best to form a cliff-like height difference rather than a gentle transition height difference). In this way, it can avoid the problem that there is a gap between the surface of the electrode edge and the subsequent adhesive substrate due to the unclear height difference at the interface, resulting in poor adhesion;

[0018] Sharpen the edge of the prefabricated electrode in Step 1, and within a 1-μm horizontal range at the contact interface between the electrode and the first substrate, the electrode layer is higher than the first substrate by more than 30 nm but not more than 1000 nm;

[0019] Generally, the edge of the electrode prepared by the hard mask method is relatively blurred and needs to be processed first, while the edge of the electrode prepared by the soft mask method is relatively sharp and can be directly separated;

[0020] Step 3: Separate the electrode from the substrate

[0021] Attach the adhesive substrate to the surface of the electrode and mechanically peel the electrode and the first substrate to obtain the adhesive substrate with the electrode attached;

[0022] The adhesive substrate is made of a composite of multiple materials and is mainly composed of an adhesive material and a second substrate. When selecting the size of the adhesive substrate, the larger the better. The adhesive substrate should meet the following conditions:

[0023] ① When the separation tip speed is greater than 0.1 mm / s and less than 0.5 mm / s, the adhesion work between the adhesive substrate and the electrode is greater than 0.2 J / m 2 ; when the separation tip speed is greater than 0.001 mm / s and less than or equal to 0.1 mm / s, the adhesion work between the adhesive substrate and the electrode is less than or equal to 0.2 J / m 2; Because the viscous material is elastic rather than completely rigid, the speed of the separation tip will continue to change as the entire separation process proceeds. Therefore, it is more appropriate to use the corresponding adhesion work size within different separation tip speed ranges as a constraint; the adhesion work between the electrode and the first substrate is smaller than the adhesion work between the viscous substrate and the electrode, ensuring that the electrode can be separated from the viscous substrate;

[0024] ② Due to the particularity of the transfer process, it is required that when the thickness of the viscous material of the viscous substrate is less than 1mm and the bending angle θ=180°, if elastic deformation occurs, its bending radius is less than 50% of the length of the viscous material; the elastic modulus of the viscous material is between 1-5GPM;

[0025] Step 4: Transferring the electrodes to the cadmium telluride wafer surface

[0026] Using the adhesive substrate to directly adhere the electrode to the surface of the pre-treated cadmium telluride wafer;

[0027] The pretreatment process of the cadmium telluride wafer is as follows:

[0028] S1. Mechanically polish the surface of the cadmium telluride wafer to remove macro defects; mechanical polishing can improve the overall flatness and reduce the uneven stress that may be generated during the electrode transfer process, thereby reducing the risk of electrode cracking or falling off due to stress concentration; however, there is a residual stress damage layer on the surface after mechanical polishing, so S2 is required;

[0029] S2. Chemically etch or plasma treat the surface of the mechanically polished cadmium telluride wafer to remove the stress damage layer, ensure that the surface is clean and active, and then clean it to remove residual contaminants such as etching solution (use solvents such as acetone, isopropyl alcohol and deionized water to thoroughly clean the surface to remove organic matter, dust and other contaminants on the surface), and ensure that the maximum height of the profile of the surface roughness of the cadmium telluride wafer is less than 100nm;

[0030] Finally, the pre-treated cadmium telluride wafer is a complete single crystal, without any macro defects such as grain boundaries, holes, cracks, inclusions, etc.

[0031] Step 5: Remove the adhesive substrate to obtain the CdTe Schottky contact

[0032] The cadmium telluride wafer with the electrode attached thereto is treated so that the adhesion work between the electrode and the adhesive substrate is smaller than the adhesion work between the electrode and the cadmium telluride wafer. The adhesive substrate is then removed, and the electrode is successfully left on the surface of the cadmium telluride wafer, thereby obtaining a cadmium telluride Schottky contact.

[0033] Further, in step 1, a metal hard mask is used to thermally evaporate and deposit a metal electrode on the surface of the first substrate; the first substrate is a clean Si wafer; if the electrode is prepared by magnetron sputtering, the first substrate material needs to be replaced with a material with a worse bonding ability to the electrode, such as glass, because if the Si wafer is still used as the substrate, the electrode material cannot be separated from the first substrate.

[0034] Further, in step 2, for the electrode with a blurred edge during prefabrication, a tungsten carbide gold-plated probe is used to cut along the electrode edge to separate the electrode with a thinner edge from the electrode with a uniform thickness in the middle (i.e., the main body part of the electrode), making its edge sharp.

[0035] Further, in step 3, the sticky substrate is obtained by integrating polydimethylsiloxane (i.e., PDMS, which can be directly purchased, generally with a 10% ratio) on a polycarbonate sheet (i.e., PC sheet).

[0036] Further, in the pretreatment process of the cadmium telluride wafer in step 4:

[0037] In S1, a magnesium oxide polishing agent is used to mechanically polish the surface of the cadmium telluride wafer to remove macroscopic defects;

[0038] In S2, 2.5 - 7.5% bromine methanol is used to chemically etch the surface of the mechanically polished cadmium telluride wafer.

[0039] Further, step 5 is specifically as follows:

[0040] The cadmium telluride wafer with the attached electrode is heated to 80 - 100 °C (under the heating condition, the adhesion work between the PDMS material and the electrode will decrease), and then the sticky substrate and the metal electrode are slowly separated to realize the preparation of the metal electrode on the cadmium telluride surface, obtaining a cadmium telluride Schottky contact.

[0041] Further, in step 5, a ceramic heating sheet is used for heating.

[0042] Further, in step 1, the metal electrode is a gold electrode.

[0043] In addition, the present invention also provides a cadmium telluride Schottky contact prepared by the above method and a radiation detector based on the cadmium telluride Schottky contact.

[0044] The principle of the present invention:

[0045] The present invention successfully prepared a Schottky contact by using the transfer method. The polydimethylsiloxane and tungsten steel gold-plated probes were used to separate the metal electrode and the substrate by mechanical peeling. Then, the metal electrode was directly lapped on the clean cadmium telluride surface, and the adhesion force between the polydimethylsilane and the metal electrode was reduced by heating. Finally, the separation of the polydimethylsilane and the metal electrode and the preparation of the metal electrode on the cadmium telluride surface were realized. During the transfer process, the research team focused on and analyzed the following two influencing factors:

[0046] First, the quality of the cadmium telluride (CdTe) crystal surface directly determines the bonding performance between the metal electrode and its surface. For the traditional evaporation method, the surface morphology of cadmium telluride only needs to meet the usage requirements. However, in the transfer method used in the present invention, a higher flatness requirement for the cadmium telluride surface is needed. Therefore, the present invention puts forward more stringent requirements for the processing of cadmium telluride crystals, requiring that the maximum height of the roughness profile of the cadmium telluride wafer surface after pretreatment < 100 nm to further ensure the uniformity of the transferred electrode. Any excessive surface undulation poses a risk of cracking and peeling of the transferred electrode;

[0047] Second, the adhesion of the transfer medium is of great significance for the transfer of the metal electrode on the cadmium telluride surface. Good adhesion performance ensures that the metal electrode adheres uniformly to the cadmium telluride surface during the transfer process, avoiding falling off or uneven deposition, thus ensuring stable contact between the metal electrode and the material; however, too strong adhesion will instead affect the complete separation of the transferred electrode, which is not conducive to the preparation of application devices. To sum up, the adhesion of the transfer medium directly determines the success and stability of the transfer of the metal electrode on the cadmium telluride surface, and is a key factor in improving the performance and reliability of the device. In the transfer process, how to select a suitable transfer medium and optimize its adhesion performance to ensure the successful transfer and long-term stable operation of the electrode is also the key to realizing the preparation of the transfer electrode on the cadmium telluride surface. Therefore, the requirement for the adhesion work in each step in the present invention is indispensable, and those skilled in the art know how to control the adhesion work within a certain range.

[0048] Advantages of the present invention:

[0049] 1. The present invention provides a preparation scheme for ultra-high-performance metal electrodes on the cadmium telluride surface. The present invention realizes the preparation of metal electrodes on the cadmium telluride surface by using the transfer method. During the preparation of the electrode contact, it is possible to avoid interface damage and lattice defects caused by the metallization of the cadmium telluride surface, reduce the gap states at the metal-semiconductor contact interface, effectively solve the problem of Fermi level pinning, and significantly improve the controllability of the preparation of metal electrodes on the cadmium telluride surface. The dark current under a 1000V bias voltage is reduced by nearly 10 times, and the height of the Schottky barrier between gold and cadmium telluride is increased by 15%, approaching the theoretical limit of the two.

[0050] 2. The method of the present invention can achieve the rapid preparation of metal electrodes on the surface of cadmium telluride. Compared with the common preparation process of the surface junction contact of cadmium telluride, the transfer method is simple and fast to operate. The entire transfer process can be completed within 10 minutes, and it has the potential for mass production of devices. Compared with the traditional evaporation method, which is limited by the requirements of vacuum degree and takes 1 hour or even longer to prepare the electrodes, the preparation efficiency of the transfer method far exceeds that of processes such as evaporation and magnetron sputtering. It is a very promising preparation process for cadmium telluride junction contacts.

[0051] 3. The improvement of the transfer method proposed in the present invention greatly improves the success rate of the transfer of the surface electrodes of cadmium telluride. The processing requirements for the edge morphology of the electrodes can effectively achieve the separation between the metal electrodes and the substrate, and the viscosity (adhesion work) between the PDMS and the metal electrodes is reduced by heating during the transfer process. These two process measures can effectively improve the integrity and stability of the preparation of cadmium telluride surface electrodes by the transfer method, and successfully increase the size of the electrodes from the micron (μm) level to the millimeter (mm) level, greatly expanding the application scope of the transfer method in the field of cadmium telluride materials.

[0052] 4. The present invention innovatively proposes a processing method for the shape of the electrodes. Using a metal probe to cut the metal electrodes can achieve the rapid preparation of electrodes of different sizes and shapes. Compared with the traditional mask processing method, the electrodes prepared by this method are more conducive to the preparation of transfer electrodes. At the same time, the processing cycle is shortened from several days to dozens of minutes, and the rapid preparation of electrodes with complex shapes can be achieved, which is of great significance for the rapid research on the electrical properties of transfer electrodes on the surface of cadmium telluride.

[0053] 5. The present invention adds processes such as heating and electrode processing during the preparation process of the transfer method, making the transfer process more controllable and successfully achieving the preparation of large-area, uniform, and high-quality metal electrodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 is a schematic diagram of the preparation process of cadmium telluride Schottky contact in Example 1 and Example 2 of the present invention;

[0055] Figure 2 is an optical microscope photograph of Sample No. 1 of the gold-cadmium telluride Schottky contact of the pixel array prepared in Example 1 of the present invention;

[0056] Figure 3 is the test result of the I-V curve of Sample No. 1 of the gold-cadmium telluride Schottky contact of the pixel array prepared in Example 1 of the present invention at different temperatures.

[0057] Figure 4 is an optical microscope photograph of Sample No. 2 of the large-area gold-cadmium telluride Schottky contact prepared in Example 2 of the present invention;

[0058] Figure 5 These are the I-V curve test results of the large-area gold-cadmium telluride Schottky contact No. 2 sample prepared in Example 2 of the present invention at different temperatures. Detailed implementation manners

[0059] The following further describes the content of the present invention in detail with reference to the accompanying drawings and specific embodiments:

[0060] The present invention provides a preparation method for high-quality cadmium telluride Schottky contacts. This preparation method uses a deterministic transfer technique to directly transfer and bond a metal electrode thin film onto the surface of cadmium telluride, realizing the construction of a high-quality cadmium telluride Schottky contact interface and further improving the energy resolution of cadmium telluride radiation detection devices under high voltages.

[0061] Example 1

[0062] Step 1: Using a metal hard mask, thermally evaporate and prepare a 5×5 array of gold electrodes with a size of 200×200 μm and a thickness of 80 nm on the surface of a clean Si wafer. The spacing between the electrodes is 200 μm; when preparing gold electrodes on the Si wafer using this method, the adhesion work between the electrode and the substrate is less than 0.05 J / m 2 ; 2 ;

[0063] Step 2: Use a tungsten steel gold-plated metal probe to cut along the edge of the gold electrode to separate the thinner electrode at the edge from the main body part of the electrode with uniform thickness in the middle; after cutting, the sizes of the gold electrodes are 180×180 μm 2 and are named sample No. 1;

[0064] Step 3: Use a polydimethylsiloxane (PDMS) sticky substrate to adhere to the surface of the cut gold electrode, and separate the gold electrode and the Si wafer by mechanical peeling;

[0065] This polydimethylsiloxane sticky substrate is obtained by integrating polydimethylsiloxane on a clean PC thin sheet. When the separation tip speed is greater than 0.1 mm / s and less than or equal to 0.5 mm / s, the adhesion work between the sticky substrate and the electrode is greater than 0.2 J / m 2 ; when the separation tip speed is greater than 0.001 mm / s and less than or equal to 0.1 mm / s, the adhesion work between the sticky substrate and the electrode is less than or equal to 0.2 J / m 2 meeting the requirements, and when the polydimethylsiloxane sticky material has a thickness less than 1 mm and a bending angle θ = 180°, if elastic deformation occurs, its bending radius is less than 50% of the length of the polydimethylsiloxane sticky material; the elastic modulus of the polydimethylsiloxane sticky material at room temperature is 3 GPM;

[0066] Step 4: Select a cadmium telluride wafer with a clean surface after mechanical polishing and chemical etching pretreatment in sequence, and directly attach the separated gold electrodes to the surface of the cadmium telluride wafer by using a dry transfer technique;

[0067] The pretreatment process of the cadmium telluride wafer is as follows:

[0068] S1. First, mechanically polish the surface of the cadmium telluride wafer with a magnesium oxide polishing agent to remove macroscopic defects;

[0069] S2. Chemically etch the surface of the mechanically polished cadmium telluride wafer with 7.5% bromine methanol to remove the stress damage layer, and then sequentially clean the surface with acetone and deionized water. After drying, a cadmium telluride wafer with a maximum height of the surface roughness profile < 100 nm is obtained;

[0070] Step 5: Heat the attached gold electrodes and cadmium telluride wafer to 80 °C to reduce the adhesion work between the polydimethylsiloxane sticky substrate and the gold electrodes, and then slowly separate the polydimethylsiloxane sticky substrate and the gold electrodes to achieve the transfer of the gold electrodes on the cadmium telluride surface; among them, the optical microscope photo of Sample 1 is as Figure 2 shown;

[0071] Step 6: Under the condition of room temperature air, use a Keithley 2450 ammeter to test the current-voltage characteristic curves of two coplanar transfer electrodes of the gold-cadmium telluride Schottky contact of the prepared pixel array under variable temperature in a dark field environment. The test results are as Figure 3 , through Figure 3 it can be seen that the dark current of the sample changes significantly with temperature and the height of the Schottky barrier can be fitted. The fitting result is 0.82 eV, which is significantly improved compared with the report in Document 1.

[0072] Example 2

[0073] Step 1: Use a metal hard mask to thermally evaporate and prepare gold electrodes with a diameter of 2.5 mm and a thickness of 80 nm on the surface of a clean Si wafer; use this method to prepare gold electrodes on the Si wafer, and the adhesion work between the electrodes and the substrate is less than 0.05 J / m 2 ;

[0074] Step 2: Use a tungsten steel gold-plated metal probe to cut along the edge of the gold electrode to separate the thinner electrode at the edge from the main body part of the electrode with uniform thickness in the middle; the sizes of the gold electrodes after cutting are 1000×2000 μm 2 named Sample 2;

[0075] Step 3: Attach a polydimethylsiloxane (PDMS) sticky substrate to the surface of the cut gold electrode, and separate the gold electrode and the Si wafer by mechanical peeling;

[0076] The polydimethylsiloxane sticky substrate is obtained by integrating polydimethylsiloxane on a clean PC sheet, satisfying that when the separation tip speed is greater than 0.1 mm / s and less than or equal to 0.5 mm / s, the adhesion work between the sticky substrate and the electrode is greater than 0.2 J / m 2 ; when the separation tip speed is greater than 0.001 mm / s and less than or equal to 0.1 mm / s, the adhesion work between the sticky substrate and the electrode is less than or equal to 0.2 J / m 2 requirements, and when the thickness of the polydimethylsiloxane sticky material is less than 1 mm and the bending angle θ = 180°, if elastic deformation occurs, its bending radius is less than 50% of the length of the polydimethylsiloxane sticky material; the elastic modulus of the polydimethylsiloxane sticky material at room temperature is 3 GPM;

[0077] Step 4: Select a cadmium telluride wafer with a clean surface after mechanical polishing and chemical etching pretreatment in sequence, and directly attach the separated gold electrode to the surface of the cadmium telluride wafer by using a dry transfer technique;

[0078] The pretreatment process of the cadmium telluride wafer is as follows:

[0079] S1. First, use magnesium oxide polishing agent to mechanically polish the surface of the cadmium telluride wafer to remove macroscopic defects;

[0080] S2. Use 2.5% bromine methanol to chemically etch the surface of the mechanically polished cadmium telluride wafer to remove the profit damage layer, and then use isopropyl alcohol and deionized water to clean the surface in sequence. After drying, a cadmium telluride wafer with a maximum height of the surface roughness profile < 100 nm is obtained;

[0081] Step 5: Heat the attached gold electrode and cadmium telluride wafer to 80 °C to reduce the adhesion work between the polydimethylsiloxane sticky substrate and the gold electrode, and then slowly separate the polydimethylsiloxane and the gold electrode to realize the transfer of the metal electrode on the cadmium telluride surface; then use the thermal evaporation method to prepare a 2000×2000 μm 2 , 80 nm thick gold electrode (this is the negative electrode, and the previously transferred electrode is the positive electrode for current testing); among them, the optical microscope photo of sample No. 2 is as Figure 4 shown;

[0082] Step 6: Under room temperature air conditions, use a Keithley 2450 ammeter to test the temperature-dependent current-voltage characteristic curve of sample No. 2 of the prepared large-area gold-cadmium telluride Schottky contact in a dark field environment. The test results of sample No. 2 are as Figure 5As shown in the figure, it can be seen that the Schottky barrier obtained by fitting the transfer electrode is 0.83 eV, and the Schottky barrier height obtained by evaporating the electrode is 0.78 eV. The Schottky barrier height of the evaporated electrode is consistent with the reports in References 1 and 2, while the electrode obtained by the transfer method obviously has a higher Schottky barrier height.

[0083] It can be seen from the above embodiments that the present invention can construct a large-area gold-cadmium telluride Schottky contact with a success rate of 100%.

[0084] If further practical applications are carried out, the sample can be annealed at a low temperature of 200 °C for 2 hours in a low-vacuum environment of 0.1 Pa.

[0085] As mentioned above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. A method for preparing a cadmium telluride Schottky contact, characterized in that: The following steps are involved: Step 1: Prefabricate electrodes on the first substrate The conductivity of the electrode is greater than 10 6 S / M, and the adhesion work between the prepared electrode and the first substrate surface is less than 0.05 J / m 2 ; Step 2: Processing the prefabricated electrode The edge of the electrode prepared in step 1 is processed so that the height difference between the upper surface of the electrode and the upper surface of the first substrate within a lateral range of 1 μm from the edge of the electrode exceeds 30 nm but does not exceed 1000 nm; Step 3: Separate the electrode from the substrate Laminating the adhesive substrate on the surface of the electrode, and mechanically peeling the electrode and the first substrate to obtain the adhesive substrate with the electrode adhered thereto; The adhesive substrate is integrated with the adhesive material and the second substrate and meets the following requirements: ① When the separation tip speed is greater than 0.1 mm / s and less than or equal to 0.5 mm / s, the adhesion work between the sticky substrate and the electrode is greater than 0.2 J / m 2 When the separation tip speed is greater than 0.001 mm / s and less than or equal to 0.1 mm / s, the adhesion work between the sticky substrate and the electrode is less than or equal to 0.2 J / m 2 ; and the adhesion work between the electrode and the first substrate is less than the adhesion work between the adhesive substrate and the electrode; ② When the thickness of the viscous material of the viscous substrate is less than 1 mm and the bending angle θ=180°, if elastic deformation occurs, the bending radius is less than 50% of the length of the viscous material; the elastic modulus of the viscous material is between 1-5 GPM; Step 4: Transferring the electrodes to the cadmium telluride wafer surface Using the adhesive substrate to directly adhere the electrode to the surface of the pre-treated cadmium telluride wafer; The pretreatment process of the cadmium telluride wafer is as follows: S1. Mechanically polishing the surface of the cadmium telluride wafer to remove macro defects; S2. Chemically etch or plasma treat the surface of the mechanically polished cadmium telluride wafer to remove the stress damage layer, and clean it to ensure that the maximum height of the profile of the surface roughness of the cadmium telluride wafer is less than 100nm; Step 5: Remove the adhesive substrate to obtain the CdTe Schottky contact The cadmium telluride wafer with the electrode attached thereto is processed so that the adhesion work between the electrode and the adhesive substrate is smaller than the adhesion work between the electrode and the cadmium telluride wafer, and then the adhesive substrate is removed to obtain the cadmium telluride Schottky contact.

2. The method for preparing a cadmium telluride Schottky contact according to claim 1, characterized in that: In step 1, a metal electrode is prepared by thermal evaporation on the surface of a first substrate using a metal hard mask; The first substrate is a clean Si wafer.

3. The method for preparing a cadmium telluride Schottky contact according to claim 1 or 2, characterized in that: In step 2, for electrodes with blurred edges during prefabrication, a tungsten steel gold-plated probe is used to cut along the electrode edge to separate the electrode with thinner edges from the electrode with uniform thickness in the middle, so as to sharpen its edges.

4. The method for preparing a cadmium telluride Schottky contact according to claim 3, characterized in that: In step 3, the adhesive substrate is obtained by integrating polydimethylsiloxane on a polycarbonate sheet.

5. The method for preparing a cadmium telluride Schottky contact according to claim 4, characterized in that: In the pretreatment process of the cadmium telluride wafer described in step 4: In S1, the surface of the cadmium telluride wafer is mechanically polished using a magnesium oxide polishing agent to remove macro defects; In S2, 2.5-7.5% bromomethanol is used to chemically etch the surface of the mechanically polished cadmium telluride wafer.

6. The method for preparing a cadmium telluride Schottky contact according to claim 5, characterized in that: Step 5 is as follows: The cadmium telluride wafer with the electrode attached is heated to 80-100° C., and then the adhesive substrate and the metal electrode are slowly separated to prepare the metal electrode on the surface of the cadmium telluride and obtain the cadmium telluride Schottky contact.

7. The method for preparing a cadmium telluride Schottky contact according to claim 6, characterized in that: In step 5, a ceramic heating plate is used for heating.

8. The method for preparing a cadmium telluride Schottky contact according to claim 7, characterized in that: In step 1, the metal electrode is a gold electrode.

9. A cadmium telluride Schottky contact, characterized in that: The method is prepared by any one of claims 1 to 8.

10. A radiation detector, characterized in that: The core detection component is a cadmium telluride Schottky contact prepared by the method described in any one of claims 1 to 8.

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