Self-driven X-ray detector based on LiGa0. 5In0. 5Se2 crystal and preparation method

Abstract

The invention relates to a self-driven X-ray detector based on LiGa0. 5In0. 5Se2 crystal and a preparation method thereof, the detector is of an MSM device structure, a c-surface LiGa0. 5In0. 5Se2 wafer is used as a semiconductor material, a metal material is used as an electrode, and self-driven X-ray detection can be realized under zero bias voltage; the preparation method of the self-driven X-ray detector comprises the following steps: (1) preparing a LiGa < 0.5 > In < 0.5 > Se < 2 > crystal; (2) directionally processing the LiGa < 0.5 > In < 0.5 > Se < 2 > wafer on the c surface; (3) polishing the upper surface and the lower surface of the LiGa0. 5In0. 5Se2 wafer, and carrying out surface passivation treatment; and (4) metal electrodes are evaporated on the upper surface and the lower surface of the LiGa0. 5In0. 5Se2 wafer. The self-driven X-ray detector is prepared by utilizing a body photovoltaic effect generated by a non-centrosymmetric structure of LiGa0. 5In0. 5Se2, the device is simple in structure, and meanwhile, due to the fact that LiGa0. 5In0. 5Se2 crystals have high resistivity, the prepared device has low dark current, and high-sensitivity X-ray detection can be achieved.

Description

Technical Field

[0001] The present invention relates to a LiGa based 0.5 In 0.5 The invention relates to a self-driven X-ray detector of Se2 crystal and a preparation method thereof, belonging to the technical field of X-ray detection. Technical Background

[0002] X-ray detectors are widely used in non-destructive testing, security inspection, medical diagnosis and other fields. The principle is that X-rays interact with the detection material to generate carriers, and the carriers move in a directional manner in the material to generate electrical signal responses. Self-driven X-ray detection means that electrical signals can be collected and detected without external bias, which has important application value in low-power and high-sensitivity X-ray detection.

[0003] The basic principles of self-driven X-ray detection include: bulk photovoltaic effect, heterojunction and PN junction. The preparation process of heterojunction and PN junction detectors is complex, while X-ray detection based on bulk photovoltaic effect uses the bulk photovoltaic effect of non-centrosymmetric materials under X-ray irradiation to generate photogenerated electron holes, and realizes effective separation under zero bias to achieve detection. Compared with traditional PN junction self-driven X-ray detectors, self-driven X-ray detectors based on bulk photovoltaic effect only require a single polarity material to achieve X-ray detection, avoiding complex material interface engineering, and have the advantages of simple device preparation, large photovoltage, fast response speed and high tolerance to material defects. It has important application potential in the field of self-driven X-ray detection.

[0004] At present, X-ray detectors based on perovskite materials have received widespread attention, but they have problems such as Pb toxicity, poor material stability, and weak bulk photovoltaic effect, which limit their application in the field of self-driven X-ray detection.

[0005] LiGaSe 0.5 In 0.5 Se2) crystal is a polar crystal with non-centrosymmetric structure, belonging to the orthorhombic system, Pna21 space group. This crystal has a suitable band gap (2.22eV), high resistivity (2.36×10 12 Ωcm), the intrinsic polar structure leads to a strong bulk photovoltaic effect, as well as excellent performance such as good stability, and the material itself does not contain Pb, which has the advantages of being non-toxic and environmentally friendly. 0.5 In 0.5 Se2 crystals can achieve self-driven X-ray detection with high sensitivity and low detection limit, and have great application prospects in the field of low-power X-ray detection.

[0006] However, there is no LiGa-based 0.5 In 0.5Specific application of Se2 crystal in self-driven X-ray detection. Summary of the invention

[0007] Aiming at the shortcomings of the current self-driven X-ray detection technology, such as low sensitivity and poor material stability, the present invention designs a LiGa based X-ray detection device with simple structure and high sensitivity and low detection limit. 0.5 In 0.5 Self-driven X-ray detector in Se2 crystal.

[0008] The present invention is based on LiGa 0.5 In 0.5 The self-driven X-ray detector of Se2 crystal adopts the following technical solutions:

[0009] The self-driven X-ray detector is an MSM device structure with c-plane LiGa 0.5 In 0.5 Se2 wafer is used as semiconductor material and metal material is used as electrode, which can realize self-driven X-ray detection under zero bias.

[0010] The direction of the current generated by the electrodes is parallel to the c-axis direction of the crystal.

[0011] The wafer size is 6×6 mm 2 -8×8mm 2 .

[0012] The wafer thickness is 1.5 mm to 2 mm.

[0013] The metal material is gold or silver.

[0014] The electrode thickness is 60nm-100mm.

[0015] Because LiGa 0.5 In 0.5 Se2 crystal is a polar crystal with a non-centrosymmetric structure and a large dipole moment in the c direction, which can produce a strong bulk photovoltaic effect and facilitate the realization of self-driven X-ray detection. 0.5 In 0.5 Se2 crystal has a suitable band gap (2.22eV) and high resistivity (2.36×10 12 Ωcm) and good stability. Therefore, based on LiGa 0.5 In 0.5 The self-driven X-ray detector based on Se2 crystal has high sensitivity and low detection limit, and can achieve high-performance self-driven X-ray detection.

[0016] The present invention is based on LiGa 0.5 In 0.5The method for preparing a self-driven X-ray detector of Se2 crystal comprises the following steps:

[0017] (1) Preparation of LiGa 0.5 In 0.5 Se2 crystals;

[0018] (2) Directional processing of c-plane LiGa 0.5 In 0.5 Se2 wafer;

[0019] LiGa 0.5 In 0.5 Se2 wafer size is 6×6mm 2 -10×10mm 2 , thickness is 1.5mm-2mm.

[0020] (3) LiGa 0.5 In 0.5 The upper and lower surfaces of the Se2 wafer are polished and surface passivated;

[0021] The process of surface passivation is to 0.5 In 0.5 The Se2 wafer is immersed in a 30% H2O2 solution at 80-85°C for 1-1.5 hours.

[0022] (4) In LiGa 0.5 In 0.5 Metal electrodes are evaporated on the upper and lower surfaces of the Se2 wafer.

[0023] In the step (1), LiGa 0.5 In 0.5 The process of Se2 crystal is:

[0024] ① The raw materials are mixed in a pre-treated graphite crucible according to the molar ratio of Li:Ga:In:Se=2:1:1:4, and then placed in a pre-treated quartz ampoule, evacuated and sintered to seal the tube;

[0025] ②Raise the temperature of the quartz ampoule in stages to allow the raw materials to fully react;

[0026] The staged heating firstly heats up to 200-250°C in 30-40 hours and keeps the temperature constant for 25-35 hours; then heats up to 600-650°C in 30-40 hours and keeps the temperature constant for 30-40 hours; finally heats up to 900-950°C and keeps the temperature constant for 40-50 hours.

[0027] ③After the reaction is completed, cool to room temperature;

[0028] The time for dropping to room temperature is 50 to 60 hours.

[0029] ④ Break the quartz ampoule and take out LiGa from the crucible 0.5 In 0.5 Se2 polycrystalline material, ground into LiGa 0.5 In 0.5 Se2 powder;

[0030] ⑤ The ground LiGa 0.5 In 0.5 Se2 powder is loaded into a pre-treated graphite crucible, and then placed in a pre-treated quartz ampoule, vacuumed, sintered and sealed;

[0031] ⑥ Melt the quartz ampoule at 850-900℃ for 30-40 hours, then lower it to 800-850℃ at a rate of 0.15-0.3mm / h, then lower it to room temperature at a rate of 1-2℃ / h, break the quartz ampoule, and take out LiGa from the crucible. 0.5 In 0.5 Se2 crystals.

[0032] The graphite crucible pretreated in ① and ⑤ is to grind the inner wall smooth, clean and dry.

[0033] The pre-treated quartz ampoule described in ① and ⑤ is to immerse the quartz ampoule in a dilute hydrochloric acid solution (mass fraction of 10%) for 20 hours, and then wash it with deionized water and anhydrous ethanol in turn.

[0034] The vacuum degree of the vacuum pumping in ① and ⑤ is ≤10 -4 Pa;

[0035] In step ⑥, the quartz ampoule is placed in the high temperature zone of the Bridgman furnace, and the temperatures of the high temperature zone and the low temperature zone of the Bridgman furnace are set to 850-900° C. and 650-700° C. respectively.

[0036] Because LiGa 0.5 In 0.5 Se2 crystals have a polar structure and a large dipole moment along the c-axis. 0.5 In 0.5 The detector made of Se2 wafer generates carriers when irradiated with X-rays. The photogenerated carriers move along the crystal polar axis c to reach both ends of the electrode, thereby generating photocurrent in the absence of bias and realizing self-driven X-ray detection.

[0037] The performance of the self-driven X-ray detector prepared above was tested using a semiconductor test system, using X-rays with 40keV photon energy and a dose rate of 2.944-7.429μGy / s. Under no bias, the sensitivity of the device was as high as 354μC Gy -1 cm -2, which is much higher than the sensitivity of commercial X-ray detectors based on α-Se (20 μC Gy -1 cm -2 ), the detection limit of the detector is as low as 125.5nGy / s. The performance of self-driven X-ray detectors based on other materials is shown in Table 1. Compared with detectors made of other materials, LiGa 0.5 In 0.5 Se2 crystal X-ray detector has outstanding performance advantages such as high sensitivity and low detection limit, see Table 1 for details.

[0038] Table 1 Comparison of self-driven X-ray detection performance of different materials

[0039]

[0040] The present invention utilizes LiGa 0.5 In 0.5 The bulk photovoltaic effect produced by the non-centrosymmetric polar structure of Se2 crystal is used to design and prepare a self-driven X-ray detector with simple device structure and high process stability. 0.5 In 0.5 Se2 crystal has a large resistivity, which is beneficial to reduce the dark current, so LiGa 0.5 In 0.5 Se2 crystal X-ray detectors can achieve high-sensitivity X-ray detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a structural schematic diagram of the self-driven detector of the present invention.

[0042] Figure 2 is the LiGa in Example 1 0.5 In 0.5 Photo of Se2 wafer.

[0043] Figure 3 The LiGa used in Example 1 0.5 In 0.5 High-resolution X-ray single crystal rocking curve of Se2 crystal.

[0044] Figure 4 This is the IV curve of the self-driven X-ray detector prepared in Example 1.

[0045] Figure 5 It is the It curve of the self-driven X-ray detector prepared in Example 1 under no bias.

[0046] Figure 6 This is the detection limit curve of the self-driven X-ray detector prepared in Example 1.

[0047] Among them: 1. Metal electrode, 2. LiGa0.5 In 0.5 Se2 wafer, 3. X-rays with photon energy of 40keV. DETAILED DESCRIPTION

[0048] The present invention aims to provide a highly sensitive self-driven X-ray detector based on polar crystals. 0.5 In 0.5 The device is composed of Se2 crystals and is designed as a metal-semiconductor-metal (MSM) structure. Based on the bulk photovoltaic effect generated by the intrinsic polar structure of the crystal, high-sensitivity X-ray detection is achieved. Figure 1 As shown, LiGa 0.5 In 0.5 Se2 crystals are used as semiconductor materials in LiGa 0.5 In 0.5 Metal electrodes 1 are deposited on the upper and lower surfaces of the Se2 wafer 2, and the device structure is a simple metal-semiconductor-metal (MSM) structure. The device can detect X-rays 3 with a photon energy of 40keV under zero bias.

[0049] Figure 2 The LiGa used in the self-driven X-ray detector of the present invention is given. 0.5 In 0.5 Optical photograph of Se2 crystal. Figure 3 The high-resolution X-ray single crystal rocking curve spectrum of the crystal is given.

[0050] The specific preparation process of the self-driven X-ray detection device based on bulk photovoltaic effect of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0051] The instruments used in each embodiment are: (1) graphite crucible; (2) single temperature zone pit furnace; (3) graphite crucible; (4) quartz ampoule; (5) Bridgman furnace, whose two temperature zones are independently controlled by a programmable temperature controller, and the temperatures of the high temperature zone and the low temperature zone are set to 850-900°C and 650-700°C, respectively; (6) glove box; (7) vacuum evaporation machine.

[0052] The graphite crucible is pre-treated as follows: the inner wall is polished smooth, cleaned and dried.

[0053] The quartz ampoule was pretreated as follows: the quartz ampoule was immersed in a dilute hydrochloric acid solution (mass fraction of 10%) for 20 hours, and then cleaned with deionized water and anhydrous ethanol in turn.

[0054] Example 1

[0055] This embodiment uses 6×6×2mm 3 LiGa 0.5 In0.5 Se2 crystal self-driven X-ray detector is prepared, the steps are as follows:

[0056] (1) In a glove box, the raw materials were mixed in a pre-treated graphite crucible according to the molar ratio of Li:Ga:In:Se = 2:1:1:4, and then placed in a pre-treated quartz ampoule and evacuated to ≤10 -4 After pa, sinter and seal the tube.

[0057] (2) The quartz ampoule was placed in a single-temperature zone pit furnace and a staged temperature increase program was adopted. First, the temperature was increased to 200°C in 30 hours and kept at a constant temperature for 35 hours; then, the temperature was increased to 600°C in 30 hours and kept at a constant temperature for 30 hours; finally, the temperature was increased to 900°C and kept at a constant temperature for 40 hours.

[0058] (3) After the reaction is completed, the furnace is cooled to room temperature for 60 hours and the quartz ampoule is taken out;

[0059] (4) Break the ampoule and take out the LiGa from the graphite crucible 0.5 In 0.5 Se2 polycrystalline material, ground into LiGa 0.5 In 0.5 Se2 powder.

[0060] (5) The ground LiGa 0.5 In 0.5 Se2 powder was loaded into a graphite crucible and then placed in a pre-treated quartz ampoule and evacuated to ≤10 -4 Pa is then sintered and sealed.

[0061] (6) Place the quartz ampoule in the high temperature zone of the Bridgman furnace (the high temperature zone and low temperature zone temperatures are set to 850°C and 700°C, respectively), melt at 850°C for 30 hours, then descend to 800°C at a rate of 0.15 mm / h, then cool to room temperature at a rate of 1°C / h, take out the quartz ampoule and break it, and take out the LiGa from the crucible. 0.5 In 0.5 Se2 crystals.

[0062] (7) LiGa 0.5 In 0.5 The Se2 crystal is oriented to determine the c-plane of the crystal.

[0063] (8) Cutting the c-shaped wafer, the wafer size is 6×6 mm 2 , thickness is 2mm.

[0064] (9) The cut c-shaped wafer is precisely polished, and the polished crystal is placed in a 30% concentration H2O2 solution, and then the solution is heated to 80°C and kept at a constant temperature for 1 hour for surface passivation treatment. The passivated crystal is washed with deionized water and anhydrous ethanol in turn, and then dried.

[0065] (10) The passivated crystals were subjected to thermal evaporation to prepare metal electrodes. Gold was selected as the electrode material and the electrode thickness was 60 nm.

[0066] Figure 4 The IV curve of the self-driven X-ray detector prepared in this embodiment is given, showing a large open circuit voltage and short circuit current, and a good linear relationship between voltage and current, which proves the good ohmic contact between the electrode and the material.

[0067] Figure 5 The It curve of the self-driven X-ray detector prepared in this embodiment without bias voltage is given, showing that at 0V, it shows good response to different dose rates of 40keV, and the sensitivity is as high as 354μC Gy -1 cm -2 , demonstrating its self-driven X-ray detection capability.

[0068] Figure 6 The detection limit measurement results of the self-driven X-ray detection device prepared in this embodiment are given. The detection limit of the device is as low as 125.5 nGy / s without bias.

[0069] Example 2

[0070] This embodiment uses 8×8×1.5mm 3 LiGa 0.5 In 0.5 Se2 crystal self-driven X-ray detector is prepared, the steps are as follows:

[0071] (1) In a glove box, the raw materials were mixed in a pre-treated graphite crucible according to the molar ratio of Li:Ga:In:Se = 2:1:1:4, and then placed in a pre-treated quartz ampoule and evacuated to ≤10 -4 After pa, sinter and seal the tube.

[0072] (2) The quartz ampoule was placed in a single-temperature-zone pit furnace and a staged temperature increase program was adopted. The temperature was first increased to 220°C over 35 hours and kept constant at that temperature for 25 hours; then, the temperature was increased to 630°C over 35 hours and kept constant at that temperature for 40 hours; and finally, the temperature was increased to 920°C and kept constant at that temperature for 42 hours.

[0073] (3) After the reaction is completed, the furnace is cooled to room temperature for 50 h and the quartz ampoule is taken out;

[0074] (4) Break the ampoule and take out the LiGa from the graphite crucible 0.5 In 0.5 Se2 polycrystalline material, ground into LiGa 0.5 In 0.5 Se2 powder.

[0075] (5) The ground LiGa 0.5 In 0.5 Se2 powder was loaded into a graphite crucible and then placed in a pre-treated quartz ampoule and evacuated to ≤10 -4 Pa is then sintered and sealed.

[0076] (6) Place the quartz ampoule in the high temperature zone of the Bridgman furnace (the high temperature zone and low temperature zone temperatures are set to 900°C and 700°C, respectively), melt at 880°C for 35 hours, then descend to 830°C at a rate of 0.3 mm / h, then cool to room temperature at a rate of 2°C / h, take out the quartz ampoule and break it, and take out the LiGa from the crucible. 0.5 In 0.5 Se2 crystals.

[0077] (7) LiGa 0.5 In 0.5 The Se2 crystal is oriented to determine the c-plane of the crystal.

[0078] (8) Cutting the c-shaped wafer, the wafer size is 8×8 mm 2 , thickness is 1.5mm.

[0079] (9) The cut c-shaped wafer is precisely polished, and the polished crystal is placed in a 30% concentration H2O2 solution, and then the solution is heated to 85°C and kept at a constant temperature for 1.5 hours for surface passivation treatment. The passivated crystal is cleaned with deionized water and anhydrous ethanol in turn, and then dried.

[0080] (10) The passivated crystals were subjected to thermal evaporation to prepare metal electrodes, silver was selected as the electrode material, and the electrode thickness was 80 nm.

[0081] Example 3

[0082] This embodiment uses 10×10×2mm 3 LiGa 0.5 In 0.5 Se2 crystal self-driven X-ray detector is prepared, the steps are as follows:

[0083] (1) In a glove box, the raw materials were mixed in a pre-treated graphite crucible according to the molar ratio of Li:Ga:In:Se = 2:1:1:4, and then placed in a pre-treated quartz ampoule and evacuated to ≤10 -4After pa, sinter and seal the tube.

[0084] (2) The quartz ampoule was placed in a single-temperature zone pit furnace and a staged temperature increase program was adopted. First, the temperature was increased to 250°C over 40 hours and kept constant for 20 hours; then, the temperature was increased to 650°C over 40 hours and kept constant for 35 hours; finally, the temperature was increased to 950°C and kept constant for 50 hours.

[0085] (3) After the reaction is completed, the furnace is cooled to room temperature for 55 h and the quartz ampoule is taken out;

[0086] (4) Break the ampoule and take out the LiGa from the graphite crucible 0.5 In 0.5 Se2 polycrystalline material, ground into LiGa 0.5 In 0.5 Se2 powder.

[0087] (5) The ground LiGa 0.5 In 0.5 Se2 powder was loaded into a graphite crucible and then placed in a pre-treated quartz ampoule and evacuated to ≤10 -4 Pa is then sintered and sealed.

[0088] (6) Place the quartz ampoule in the high temperature zone of the Bridgman furnace (the high temperature zone and low temperature zone temperatures are set to 860°C and 650°C, respectively), melt at 900°C for 40 hours, then descend to 850°C at a rate of 0.2 mm / h, then cool to room temperature at a rate of 1.5°C / h, take out the quartz ampoule and break it, and take out the LiGa from the crucible. 0.5 In 0.5 Se2 crystals.

[0089] (7) LiGa 0.5 In 0.5 The Se2 crystal is oriented to determine the c-plane of the crystal.

[0090] (8) Cutting the c-shaped wafer, the wafer size is 10×10 mm 2 , thickness is 2mm.

[0091] (9) The cut c-shaped wafer is precisely polished, and the polished crystal is placed in a 30% concentration H2O2 solution, and then the solution is heated to 82°C and kept at a constant temperature for 1.2 hours for surface passivation treatment. The passivated crystal is washed with deionized water and anhydrous ethanol in turn, and then dried.

[0092] (10) The passivated crystals were subjected to thermal evaporation to prepare metal electrodes, with gold being selected as the electrode material and the electrode thickness being 100 nm.

Claims

1. A LiGa-based 0.5 In 0.5 The self-driven X-ray detector of Se2 crystal is characterized by: The detector is a MSM device structure with c-plane LiGa 0.5 In 0.5 Se2 wafer is used as semiconductor material and metal material is used as electrode to realize self-driven X-ray detection under zero bias.

2. The LiGa-based 0.5 In 0.5 The self-driven X-ray detector of Se2 crystal is characterized by: The direction of the current generated by the electrodes is parallel to the c-axis direction of the crystal.

3. The LiGa-based 0.5 In 0.5 The self-driven X-ray detector of Se2 crystal is characterized by: The wafer size is 6×6 mm 2 -8×8mm 2 , the chip thickness is 1.5mm-2mm.

4. The LiGa-based 0.5 In 0.5 The self-driven X-ray detector of Se2 crystal is characterized by: The metal material is gold or silver.

5. The LiGa-based 0.5 In 0.5 The self-driven X-ray detector of Se2 crystal is characterized by: The electrode thickness is 60nm-100mm.

6. A LiGa-based nanostructured ... 0.5 In 0.5 The method for preparing a self-driven X-ray detector of Se2 crystal is characterized in that: The following steps are involved: (1) Preparation of LiGa 0.5 In 0.5 Se2 crystals; (2) Directional processing of c-plane LiGa 0.5 In 0.5 Se2 wafer; (3) LiGa 0.5 In 0.5 The upper and lower surfaces of the Se2 wafer are polished and surface passivated; (4) In LiGa 0.5 In 0.5 Metal electrodes are evaporated on the upper and lower surfaces of the Se2 wafer.

7. The LiGa-based 0.5 In 0.5 The method for preparing a self-driven X-ray detector of Se2 crystal is characterized in that: In the step (1), LiGa 0.5 In 0.5 The process of Se2 crystal is: ① The raw materials are mixed in a pre-treated graphite crucible according to the molar ratio of Li:Ga:In:Se=2:1:1:4, and then placed in a pre-treated quartz ampoule, evacuated and sintered to seal the tube; ②Raise the temperature of the quartz ampoule in stages to allow the raw materials to fully react; The staged heating is firstly to heat to 200-250°C in 30-40 hours and keep the temperature constant for 25-35 hours; then, to heat to 600-650°C in 30-40 hours and keep the temperature constant for 30-40 hours; finally, to heat to 900-950°C and keep the temperature constant for 40-50 hours; ③After the reaction is completed, cool to room temperature; ④ Break the quartz ampoule and take out LiGa from the crucible 0.5 In 0.5 Se2 polycrystalline material, ground into LiGa 0.5 In 0.5 Se2 powder; ⑤ The ground LiGa 0.5 In 0.5 Se2 powder is loaded into a pre-treated graphite crucible, and then placed in a pre-treated quartz ampoule, vacuumed, sintered and sealed; ⑥ Melt the quartz ampoule at 850-900℃ for 30-40 hours, then lower it to 800-850℃ at a rate of 0.15-0.3mm / h, then lower it to room temperature at a rate of 1-2℃ / h, break the quartz ampoule, and take out LiGa from the crucible. 0.5 In 0.5 Se2 crystals.

8. The LiGa-based 0.5 In 0.5 The method for preparing a self-driven X-ray detector of Se2 crystal is characterized in that: The graphite crucible pretreated in steps ① and ⑤ is polished smooth, cleaned and dried; the quartz ampoule pretreated in steps ① and ⑤ is soaked in a dilute hydrochloric acid solution for 20 hours, and then washed with deionized water and anhydrous ethanol in turn; the vacuum degree of the vacuum in steps ① and ⑤ is ≤10 -4 Pa; in the step ⑥, the quartz ampoule is placed in the high temperature zone of the Bridgman furnace, and the temperatures of the high temperature zone and the low temperature zone of the Bridgman furnace are set to 850-900°C and 650-700°C, respectively.

9. The LiGa-based 0.5 In 0.5 The method for preparing a self-driven X-ray detector of Se2 crystal is characterized in that: The time for decreasing to room temperature in the step ③ is 50 to 60 hours.

10. The LiGa-based 0.5 In 0.5 The method for preparing a self-driven X-ray detector of Se2 crystal is characterized in that: The surface passivation process in step (3) is to passivate LiGa 0.5 In 0.5 The Se2 wafer is immersed in a 30% H2O2 solution at 80-85°C for 1-1.5 hours.

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