A method for suppressing the persistent photoconductive effect of gallium oxide and its application

Abstract

The present invention belongs to the field of semiconductor device technology and relates to a method and application for suppressing the persistent photoconductive effect of gallium oxide. The method comprises: providing a crystalline gallium oxide material and preheating the crystalline gallium oxide material; the preheating temperature is not lower than the melting point of metallic gallium; spreading liquid gallium in air, forming an amorphous gallium oxide film layer on the surface of the spread liquid gallium; while maintaining the liquid gallium in a liquid state, contacting the preheated crystalline gallium oxide material surface with the amorphous gallium oxide film layer on the surface of the liquid gallium, thereby transferring the amorphous gallium oxide film layer to the surface of the crystalline gallium oxide material; and nitriding, phosphatizing, or sulfiding the amorphous gallium oxide film layer on the surface of the crystalline gallium oxide material, thereby converting the amorphous gallium oxide film layer into a gallium nitride film layer, a gallium phosphate film layer, or a gallium sulfide film layer. The method provided by the present invention not only improves material performance but also significantly increases the response speed of the photodetector device.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor devices and relates to a method for suppressing the persistent photoconductive effect of gallium oxide and its application. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Gallium oxide (Ga2O3), an ultra-wide bandgap (4.2-5.1 eV) III-VI semiconductor material, has attracted significant attention in the field of photodetection due to its high optical absorption coefficient, excellent thermal and chemical stability, radiation resistance, and low cost. This material exhibits high transmittance in the ultraviolet to visible light range, making it suitable for solar-blind ultraviolet detection. It is widely used in military and civilian fields such as ultraviolet communications, missile warning, biomedical testing, fire monitoring, and high-voltage power equipment status monitoring. However, practical applications of GaO-based optoelectronic devices are hampered by the persistent photoconductivity (PPC) phenomenon. The PPC effect, which arises from the long-term capture of photogenerated carriers by internal defects in the material, significantly prolongs the photocurrent response recovery time, severely degrading the device's temporal resolution and dynamic detection performance, thus hindering the practical application of GaO photodetectors. Summary of the Invention

[0004] In order to address the shortcomings of the existing technology, the purpose of the present invention is to provide a method and application for suppressing the persistent photoconductive effect of gallium oxide. The method provided by the present invention not only improves the material performance, but also greatly improves the response speed of its photoelectric detection device. At the same time, it can achieve low energy consumption or even detection effect without external energy. In this way, the response band can also be broadened, which can be used for wide-spectrum detection, and is particularly suitable for the field of photoelectric detection.

[0005] In order to achieve the above object, the technical solution of the present invention is:

[0006] In a first aspect, a method for suppressing the persistent photoconductive effect of gallium oxide comprises the following steps:

[0007] Providing a crystalline gallium oxide material and preheating the crystalline gallium oxide material; the preheating temperature is not lower than the melting point of metallic gallium;

[0008] Spreading liquid gallium in air, and forming an amorphous gallium oxide film layer on the surface of the spread liquid gallium;

[0009] While keeping the liquid gallium in a liquid state, bringing the preheated surface of the crystalline gallium oxide material into contact with the amorphous gallium oxide film layer on the surface of the liquid gallium, so that the amorphous gallium oxide film layer is transferred to the surface of the crystalline gallium oxide material;

[0010] The amorphous gallium oxide film layer on the surface of the crystalline gallium oxide material is nitrided, phosphated or sulfided, so that the amorphous gallium oxide film layer is converted into a gallium nitride film layer, a gallium phosphate film layer or a gallium sulfide film layer.

[0011] The present invention first forms an amorphous gallium oxide film layer on a crystalline gallium oxide material, and then converts the amorphous gallium oxide film into a gallium nitride film layer, a gallium phosphate film layer or a gallium sulfide film layer through nitridation, phosphation or sulfidation, thereby constructing a heterojunction to form a built-in electric field. The built-in electric field can significantly suppress the persistent photoconductivity effect of the crystalline gallium oxide.

[0012] The present invention forms an amorphous gallium oxide film on the surface of liquid gallium metal and transfers it to the surface of a crystalline gallium oxide material by pressure dipping while maintaining the liquid gallium in a liquid state. This method utilizes a thin amorphous gallium oxide film on the surface of the liquid gallium metal, which has good density, uniformity, and flexibility. This allows for better construction of a built-in electric field after transfer to the surface of the crystalline gallium oxide material, and the process is simple, reducing costs. Furthermore, by increasing the number of transfers, the thickness of the amorphous gallium oxide film can be accumulated, thereby enabling the thickness of the amorphous gallium oxide film to be controlled.

[0013] However, the present invention has experimentally found that when transferring an amorphous gallium oxide film layer to the surface of a crystalline gallium oxide material by simple pressing and dipping, problems such as discontinuity and cracking of the transferred film layer usually occur, which reduces the success rate of completely transferring the amorphous gallium oxide film layer to the surface of the crystalline gallium oxide material. Therefore, the present invention further performs a hydrophilic treatment on the surface of the crystalline gallium oxide material and preheats the hydrophilic treated crystalline gallium oxide material. After the hydrophilic treatment, there are more polar groups or groups that can form hydrogen bonds on the surface, such as hydroxyl (-OH) and carbonyl (C=O). These groups can form strong chemical adsorption with gallium (Ga) atoms or oxygen (O) atoms in the amorphous gallium oxide, which is beneficial to improve the integrity of the transfer of the amorphous gallium oxide film layer, thereby improving the problems of discontinuity and cracking of the transferred film layer, and improving the success rate of completely transferring the amorphous gallium oxide film layer to the surface of the crystalline gallium oxide material.

[0014] In a second aspect, an application of the above-mentioned method for suppressing the persistent photoconductive effect of gallium oxide in the preparation of crystalline gallium oxide-based photoelectric devices.

[0015] The beneficial effects of the present invention are:

[0016] 1. This invention transfers an amorphous gallium oxide film from the surface of liquid gallium to the surface of a crystalline gallium oxide material by dipping and pressing, while maintaining the liquid gallium in a liquid state. Due to the plasticity of liquid metal gallium, the amorphous gallium oxide film can be applied to any desired surface, making it universally applicable to the preparation of crystalline gallium oxide in various forms. Furthermore, the amorphous gallium oxide film is nitrided, phosphated, or sulfurized, and a built-in electric field is formed by creating a heterojunction. This significantly suppresses the persistent photoconductivity effect of gallium oxide, improving the device performance of gallium oxide while constructing a self-powered photodetector, further expanding its application in advanced optoelectronic devices.

[0017] 2. The present invention enhances the adsorption capacity of the amorphous gallium oxide film on the surface of the crystalline gallium oxide material by hydrophilizing the surface of the crystalline gallium oxide material. This makes it easier for the amorphous gallium oxide film to be completely transferred to the surface of the crystalline gallium oxide material, thereby improving the success rate of complete transfer of the amorphous gallium oxide film to the surface of the crystalline gallium oxide material. Furthermore, by partially modifying the surface of the crystalline gallium oxide material and then transferring the amorphous gallium oxide film to the non-hydrophobic modified portion of the crystalline gallium oxide material surface, a patterned amorphous gallium oxide film can be obtained on the surface of the crystalline gallium oxide material. This increases the flexibility of subsequent device design, eliminates the need for complex photolithography or etching processes, greatly simplifies the subsequent device preparation process, and promotes innovation in gallium oxide device structures.

[0018] 3. The heterojunction construction method adopted in the present invention has low cost, readily available raw materials, and is environmentally friendly. It can construct heterojunctions on a variety of semiconductor materials and meet the precursor requirements of a variety of devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0020] Figure 1 This is a component content diagram of the heterojunction obtained in Example 1.

[0021] Figure 2 3 is a comparison diagram of the response time before and after the formation of the heterojunction photodetector obtained in Example 1; wherein a is the normalized intensity diagram from 0 to 140 s, and b is the normalized intensity diagram from 0 to 1000 ms.

[0022] Figure 3 This is a component content diagram of the heterojunction obtained in Example 2.

[0023] Figure 43 is a comparison diagram of the response time before and after the formation of the heterojunction photodetector obtained in Example 2; wherein a is the normalized intensity diagram from 0 to 150 s, and b is the normalized intensity diagram from 0 to 1000 ms.

[0024] Figure 5 This is a graph of component contents of the failed heterojunction obtained in comparative example 1.

[0025] Figure 6 This is a response time diagram of the failed heterojunction photodetector obtained in comparative example 2.

[0026] Figure 7 This is the SEM image of the topmost gallium oxide amorphous film obtained in Comparative Example 3. DETAILED DESCRIPTION

[0027] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0029] In view of the fact that gallium oxide-based photoelectric devices have poor performance and are difficult to apply due to the persistent photoconductivity effect, the present invention proposes a method and application of suppressing the persistent photoconductivity effect of gallium oxide.

[0030] A typical embodiment of the present invention provides a method for suppressing the persistent photoconductive effect of gallium oxide, comprising the following steps:

[0031] Providing a crystalline gallium oxide material and preheating the crystalline gallium oxide material; the preheating temperature is not lower than the melting point of metallic gallium;

[0032] Spreading liquid gallium in air, and forming an amorphous gallium oxide film layer on the surface of the spread liquid gallium;

[0033] While keeping the liquid gallium in a liquid state, bringing the preheated surface of the crystalline gallium oxide material into contact with the amorphous gallium oxide film layer on the surface of the liquid gallium, so that the amorphous gallium oxide film layer is transferred to the surface of the crystalline gallium oxide material;

[0034] The amorphous gallium oxide film layer on the surface of the crystalline gallium oxide material is nitrided, phosphated or sulfided, so that the amorphous gallium oxide film layer is converted into a gallium nitride film layer, a gallium phosphate film layer or a gallium sulfide film layer.

[0035] In some embodiments, the surface of the crystalline gallium oxide material is subjected to a hydrophilic treatment, and the hydrophilic treated crystalline gallium oxide material is preheated. The hydrophilic treatment of the present invention can be performed by coating the surface of the crystalline gallium oxide material with a hydrophilic agent, such as by evaporation, spraying, or immersion, or by plasma treatment.

[0036] Liquid gallium is spread on a substrate. In some embodiments, the substrate on which the liquid gallium is spread is made of glass, quartz, or a silicon wafer with an oxide layer, etc. Such a material is conducive to the spreading of liquid gallium.

[0037] At the same time, the present invention can adjust the adsorption properties of the amorphous gallium oxide film layer and the surface of the crystalline gallium oxide material by performing a hydrophilic treatment or a hydrophobic treatment on the surface of the crystalline gallium oxide material, thereby achieving patterning processing.

[0038] The present invention performs a hydrophilic treatment on the surface of the crystalline gallium oxide material, then transfers the amorphous gallium oxide film layer on the surface of the liquid gallium to the hydrophilic portion of the crystalline gallium oxide surface. The present invention performs a hydrophobic treatment on the surface of the crystalline gallium oxide material, then transfers the amorphous gallium oxide film layer on the surface of the liquid gallium to the non-hydrophobic portion of the crystalline gallium oxide surface. Because the hydrophilic treatment enhances the adsorption properties of the amorphous gallium oxide film layer to the surface of the crystalline gallium oxide material, improving the efficiency and integrity of the transfer of the amorphous gallium oxide film layer to the surface of the crystalline gallium oxide material, the present invention preferably performs a hydrophilic treatment on the surface of the crystalline gallium oxide material to achieve patterning.

[0039] When performing the hydrophilic treatment or hydrophobic treatment step in the present invention, the hydrophilic agent or hydrophobic agent may be used to cover the surface of the crystalline gallium oxide material, or the plasma treatment may be used.

[0040] Specifically, the hydrophilic agent used in the hydrophilic treatment is maleic anhydride, acrylic acid or methacrylic acid.

[0041] Specifically, the hydrophobic agent used in the hydrophobic treatment is trimethylchlorosilane, silane solution, polytetrafluoroethylene (PTFE), polyolefin or olefin.

[0042] In some embodiments, a mask is used to perform hydrophilic treatment on a portion of the surface of the crystalline gallium oxide material. The mask can be in any shape, such as straight, curved, or wrinkled.

[0043] In some embodiments, the hydrophilic treatment or hydrophobic treatment is carried out by evaporation, spraying, or soaking.

[0044] In some embodiments, the liquid gallium is maintained in a liquid state by heating the substrate. Specifically, the substrate is heated to a temperature of 35-130°C. This removes old gallium oxide from the surface of the liquid gallium, exposing fresh liquid gallium. In air, an amorphous gallium oxide film forms on the surface of the fresh liquid gallium.

[0045] In some embodiments, the crystalline gallium oxide material is preheated after the surface is hydrophilized, and within 3.0 minutes, the hydrophilized surface of the crystalline gallium oxide material is brought into contact with the amorphous gallium oxide film on the surface of the liquid gallium. This condition is conducive to the transfer of the amorphous gallium oxide film.

[0046] In some embodiments, the contact time between the preheated crystalline gallium oxide material surface and the amorphous gallium oxide film layer on the liquid gallium surface is 0.01 to 10 seconds. This condition is conducive to the transfer of the amorphous gallium oxide film layer.

[0047] In some embodiments, after the amorphous gallium oxide film is transferred, the residual metallic gallium on the surface of the amorphous gallium oxide film is cleaned in boiling ethanol. Specifically, during cleaning, the force applied to the amorphous gallium oxide film is less than 2N to avoid damaging the amorphous gallium oxide film.

[0048] In some embodiments, the nitridation temperature is 600-900°C and the nitridation time is 30-120 minutes. Research has shown that under these conditions, a nitrogen source can react with an amorphous gallium oxide film to form a two-dimensional gallium nitride film, and the crystalline gallium oxide material is not affected by the nitridation.

[0049] In some embodiments, the nitrogen source used for nitridation is urea. Specifically, urea is evaporated and introduced into the crystalline gallium oxide material containing the amorphous gallium oxide film. More specifically, the urea evaporation temperature is 300-500°C. More specifically, the distance between the urea and the crystalline gallium oxide material containing the amorphous gallium oxide film is 10-15 cm. More specifically, the carrier gas used to transport the urea vapor is nitrogen.

[0050] In some embodiments, the sulfurization temperature is 500-800°C and the sulfurization time is 30-120 minutes. Studies have shown that under these conditions, a sulfur source can react with an amorphous gallium oxide film to form a two-dimensional gallium sulfide film, and the crystalline gallium oxide material is not affected by nitridation.

[0051] In some embodiments, the sulfur source used for sulfurization is sulfur. Specifically, the sulfur is vaporized and introduced into the crystalline gallium oxide material containing the amorphous gallium oxide film. More specifically, the sulfur vaporization temperature is 150-300°C. More specifically, the distance between the sulfur and the crystalline gallium oxide material containing the amorphous gallium oxide film is 12.5-15 cm. More specifically, the carrier gas for transporting the sulfur vapor is nitrogen.

[0052] In some embodiments, the phosphorylation temperature is 300-400°C and the phosphorylation time is 60-120 minutes. Studies have shown that under these conditions, the phosphorus source can react with the amorphous gallium oxide film to form a two-dimensional gallium phosphate film, and the crystalline gallium oxide material is not affected by nitridation.

[0053] In some embodiments, the phosphorus source for phosphorylation is phosphoric acid (H3PO4). Specifically, the phosphoric acid is evaporated and introduced into the crystalline gallium oxide material containing the amorphous gallium oxide film. More specifically, the phosphoric acid is evaporated at a temperature of 300-400°C. More specifically, the distance between the phosphoric acid and the crystalline gallium oxide material containing the amorphous gallium oxide film is 10-15 cm. More specifically, the carrier gas for delivering the phosphoric acid vapor is nitrogen.

[0054] In some embodiments, the following steps are preferred:

[0055] Step 1: Take a large piece of solid gallium metal with a purity of 99.9999% or higher, heat it on a hot plate at 90-130°C in an oxygen-free glove box to melt it, and then divide the melted gallium metal into 5-50ml plastic bottles for subsequent use. Store the divided plastic bottles containing the gallium metal in an oxygen-free environment. Use water, acetone, and ethanol to clean the crystalline gallium oxide material with a persistent photoconductive effect 1-3 times in sequence. Then, hydrophilize the surface of the crystalline gallium oxide material. If patterning is required, prepare a pre-designed template and mask the gallium oxide film. During the hydrophilic treatment, use evaporation, spraying, or immersion to pattern the crystalline gallium oxide material with a surfactant (maleic anhydride, acrylic acid, or methacrylic acid as a hydrophilic surfactant) so that the surface of the crystalline gallium oxide material that needs to be covered with an amorphous gallium oxide film layer is a hydrophilic area.

[0056] Step 2: Place the liquid gallium metal on a glass slide and spread it flat. Place the glass slide on a hot plate at 35°C-130°C. Use glass, quartz, silicon wafer, etc. to quickly scrape off the old liquid gallium on the surface of the gallium metal to expose fresh liquid gallium. Remove the mask from the hydrophilic treated surface of the crystalline gallium oxide material, preheat it, and quickly cover the hydrophilic treated surface of the crystalline gallium oxide material with the fresh liquid gallium surface within 3 minutes, and then quickly remove it within 10 seconds. If it is necessary to clean the residual gallium metal on the surface, use a cotton swab that does not shed lint in boiling alcohol to clean it. The force of the cotton swab in contact with the amorphous gallium oxide film should be less than 2N until the surface gallium metal is cleaned.

[0057] Step 3: Construct the required heterojunction according to the Fermi level and nitride, phosphate, and sulfide the top amorphous gallium oxide film. If nitridation is required, take urea (50mg-2g) and place it on an alumina boat in the lower temperature area of ​​the tube furnace. The urea particles can generate ammonia gas. The crystalline gallium oxide material covered with the amorphous gallium oxide film is placed upside down on the center of another alumina boat, with the distance between the two quartz boats being 10-15cm. Heat the urea to 300-500℃ and the temperature of the crystalline gallium oxide material to 600-900℃. The heating rate of both places is 10-15℃ / min. Nitrogen with a flow rate of 45-55sccm is used as the carrier gas. The holding time is 30-90min. After the synthesis is completed, cool naturally to room temperature. The patterned amorphous gallium oxide film reacts with ammonia to obtain a two-dimensional gallium nitride film.

[0058] If a gallium sulfide film is required for the surface to be covered, a crystalline gallium oxide material covered with an amorphous gallium oxide film can be placed upside down in the center of another alumina boat. 50mg-1g of sulfur powder should be added, and the sulfur powder should be approximately 12.5-15cm away from the crystalline gallium oxide material. The evaporation temperature of the sulfur powder is approximately 150-300°C. The crystalline gallium oxide material is heated to 500-800°C. To maintain product uniformity and optimal results, a heating rate of 5-10°C / min is used. A nitrogen carrier gas with a constant flow rate of 45-55sccm is used, and the holding time is 30-90 minutes. This will produce a heterojunction with a patterned gallium sulfide surface.

[0059] If a GaPO4 film layer is required to be covered on the surface, phosphoric acid powder (50mg-2g) is used as the phosphorus source, and the crystalline gallium oxide material covered with the amorphous gallium oxide film is placed upside down in the center of the alumina boat, 10-15cm away from the phosphoric acid powder. Nitrogen is used as the carrier gas with a flow rate of 0.5-0.7 L / min. The crystalline gallium oxide material and the phosphoric acid powder are heated in the same temperature zone at 300-400℃ for 60-90min. A heterojunction with a surface covered with a patterned GaPO4 film can be obtained.

[0060] Another embodiment of the present invention provides an application of the above-mentioned method for suppressing the persistent photoconductive effect of gallium oxide in the preparation of a crystalline gallium oxide-based photoelectric device.

[0061] In some embodiments, the process also includes preparing electrodes. Specifically, the electrodes are located on the surface of the crystalline gallium oxide material and the surface of the gallium nitride film layer, the gallium phosphate film layer, or the gallium sulfide film layer. Specifically, the electrodes are prepared by vapor deposition. Specifically, the thickness of the electrodes is 50-500 nm.

[0062] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0063] Example 1:

[0064] 1. Selection and processing of raw materials

[0065] 1.1. Take a large block of solid gallium metal with a purity of 99.9999%. Preheat the hot plate in the glove box to 100°C in an oxygen-free environment. Melt the gallium metal on the preheated hot plate. Dispense the melted gallium metal into 5 mL plastic bottles for subsequent use. Place the plastic bottles containing the gallium metal in a vacuum chamber and store them in a vacuum environment.

[0066] 1.2. Clean the gallium oxide wafer with persistent photoconductivity effect using water, acetone, and ethanol in sequence, using each solvent for three cleaning cycles.

[0067] 1.3. Prepare the designed mask in advance and mask the gallium oxide wafer. Use a spray method to perform a patterned hydrophilic treatment on the masked gallium oxide wafer using maleic anhydride solution.

[0068] 2. Heterojunction construction process

[0069] 2.1. Place a glass sheet on a hot plate at 35°C, place metal gallium on the glass sheet, and heat the hot plate to melt the metal gallium and make the liquid metal gallium spread out flat.

[0070] 2.2. Use glass to quickly scrape off the old gallium oxide on the surface of the liquid metal gallium in step 2.1 to expose fresh gallium droplets.

[0071] 2.3. Remove the mask from the hydrophilized gallium oxide wafer surface patterned in step 1.3 and preheat it on a 40°C hot plate. Within 3 minutes, quickly cover the hydrophilized surface of the gallium oxide wafer with the fresh gallium droplet obtained in step 2.2. Then, quickly remove the gallium oxide wafer within 10 seconds, leaving the hydrophilized surface covered with the patterned amorphous gallium oxide film. Use a lint-free cotton swab to clean any remaining gallium metal in boiling alcohol, applying a force of 1 N.

[0072] 2.4. Place 50 mg of urea on an alumina boat in the lower temperature zone of a tube furnace. Place a gallium oxide wafer covered with a patterned amorphous gallium oxide film upside down in the center of another alumina boat (with the amorphous gallium oxide film on top of the wafer), with a distance of 10 cm between the two boats. Heat the urea to 300°C and the gallium oxide wafer to 600°C at a heating rate of 10°C / min for both locations, using nitrogen as the carrier gas at a constant flow rate of 50 sccm. Hold the mixture at this temperature for 30 minutes, then cool naturally to room temperature after synthesis. The patterned amorphous gallium oxide film reacts with ammonia to produce a two-dimensional gallium nitride film.

[0073] Using a mask, 100nm thick titanium was evaporated on both the gallium oxide wafer and the two-dimensional gallium nitride film layer as electrodes to construct a photodetector.

[0074] The element content of the upper two-dimensional gallium nitride film layer and the element content of the lower gallium oxide wafer obtained in this embodiment were tested at two locations, such as Figure 1 As shown. Figure 1 It can be seen that the purity of the heterojunction obtained in this embodiment is very high, and the underlying gallium oxide wafer is not nitrided. Figure 2 It can be seen that after the heterojunction is constructed, the persistent photoconductivity effect of the photodetector constructed in this embodiment is significantly suppressed compared to the case where only the gallium oxide wafer is used before the construction.

[0075] Example 2:

[0076] 1. Selection and processing of raw materials

[0077] 1.1. Take a large block of solid gallium metal with a purity of 99.9999%. Preheat the hot plate in the glove box to 100°C in an oxygen-free environment. Melt the gallium metal on the preheated hot plate. Dispense the melted gallium metal into 10ml plastic bottles for subsequent use. Place the plastic bottles containing the gallium metal in a vacuum chamber and store them in a vacuum environment.

[0078] 1.2. Clean the gallium oxide wafer with persistent photoconductivity effect using water, acetone, and ethanol in sequence, using each solvent for three cleaning cycles.

[0079] 1.3. Prepare the designed mask in advance, mask the gallium oxide wafer, and use acrylic acid to perform patterned hydrophilic treatment on the masked gallium oxide wafer by evaporation.

[0080] 2. Heterojunction construction process

[0081] 2.1. Place a glass sheet on a 45°C hot plate, place metal gallium on the glass sheet, and heat the hot plate to melt the metal gallium and make the liquid metal gallium flat.

[0082] 2.2. Use glass to quickly scrape off the old gallium oxide on the surface of the liquid metal gallium in step 2.1 to expose fresh liquid gallium.

[0083] 2.3. Remove the mask from the hydrophilized gallium oxide wafer surface patterned in step 1.3 and preheat it on a 40°C hot plate. Within 3 minutes, quickly cover the hydrophilized surface of the gallium oxide wafer with the fresh gallium droplet obtained in step 2.2. Then, quickly remove the gallium oxide wafer within 10 seconds, leaving the hydrophilized surface covered with the patterned amorphous gallium oxide film. Clean the amorphous gallium oxide film with a lint-free cotton swab in boiling alcohol, applying a force of 1 N.

[0084] 2.4. Place 50 mg of sulfur powder on an alumina boat in the lower temperature zone of a tube furnace. Place a gallium oxide wafer covered with an amorphous gallium oxide film upside down in the center of another alumina boat. The distance between the sulfur powder and the gallium oxide wafer is approximately 12.5 cm. The evaporation temperature of the sulfur powder is approximately 150°C. Heat the gallium oxide wafer to 500°C. Use a heating rate of 5°C / min. Use nitrogen as the carrier gas at a constant flow rate of 50 sccm and hold the temperature for 30 minutes. The patterned amorphous gallium oxide film reacts with the sulfur vapor to produce a two-dimensional gallium sulfide film. This results in a heterojunction with a surface covered with a patterned gallium sulfide film.

[0085] Using a mask, titanium metal with a thickness of 100nm was evaporated on the gallium oxide wafer and the two-dimensional gallium sulfide film layer to construct a photodetector.

[0086] The element content of the upper two-dimensional gallium sulfide film layer and the element content of the lower gallium oxide wafer obtained in this embodiment were tested at two locations, such as Figure 3 As shown. Figure 3 It can be seen that the purity of the heterojunction obtained in this embodiment is very high, and the underlying gallium oxide wafer is not sulfurized. Figure 4 It can be seen that after the heterojunction is constructed, the persistent photoconductivity effect of the photodetector constructed in this embodiment is significantly suppressed compared to when only gallium oxide is used before construction.

[0087] Example 3:

[0088] 1. Selection and processing of raw materials

[0089] 1.1. Take a large block of solid gallium metal with a purity of 99.9999%. Preheat the hot plate in the glove box to 100°C in an oxygen-free environment. Melt the gallium metal on the preheated hot plate. Dispense the melted gallium metal into 10ml plastic bottles for subsequent use. Place the plastic bottles containing the gallium metal in a vacuum chamber and store them in a vacuum environment.

[0090] 1.2. Use water, acetone, and ethanol in sequence to clean the gallium oxide crystals with persistent photoconductivity effect.

[0091] 1.3. Prepare the designed mask in advance and mask the gallium oxide wafer. Use methacrylic acid solution to spray the masked gallium oxide wafer to perform a patterned hydrophilic treatment.

[0092] 2. Heterojunction construction process

[0093] 2.1. Place a glass sheet on a hot plate at 50°C, and place metal gallium on the glass sheet. Heat the hot plate to melt the metal gallium and make the liquid metal gallium spread out flat.

[0094] 2.2. Use glass to quickly scrape off the old gallium oxide on the surface of the liquid metal gallium in step 2.1 to expose fresh gallium droplets.

[0095] 2.3. Remove the mask from the hydrophilized gallium oxide wafer surface patterned in step 1.3 and place it on a 40°C hot plate for preheating. Within 3 minutes, quickly cover the hydrophilized surface of the gallium oxide wafer with the fresh gallium droplet obtained in step 2.2. Then, quickly remove the gallium oxide wafer within 10 seconds, leaving the hydrophilized surface covered with the patterned amorphous gallium oxide film. Clean the gallium metal from the surface with a cotton swab that does not shed lint in boiling alcohol. The contact force between the cotton swab and the amorphous gallium oxide film should be 1N.

[0096] 2.4. Place 50 mg of phosphoric acid powder on an alumina boat in the lower temperature zone of a tube furnace. Place a gallium oxide wafer covered with a patterned amorphous gallium oxide film upside down in the center of another alumina boat (i.e., the amorphous gallium oxide film is located above the gallium oxide wafer). Keep a distance of 10 cm between the gallium oxide wafer and the phosphoric acid powder. Heat the gallium oxide wafer and phosphoric acid powder in the same temperature zone at 300°C for 60 minutes, using nitrogen as the carrier gas at a flow rate of 0.6 L / min. The patterned amorphous gallium oxide film reacts with phosphorus vapor to form a two-dimensional GaPO4 film. This results in a heterojunction with a patterned GaPO4 film covering the surface.

[0097] Using a mask, titanium metal with a thickness of 100nm was evaporated on the gallium oxide wafer and the two-dimensional GaPO4 film layer to construct a photodetector.

[0098] The elemental content of the upper two-dimensional GaPO4 film and the lower gallium oxide wafer obtained in this example were tested at two locations. The test results showed that the purity of the heterojunction obtained in this example was very high, and the lower gallium oxide wafer was not phosphorylated. The results of photodetection response time testing showed that the persistent photoconductivity effect of the photodetector constructed in this example was significantly suppressed.

[0099] Example 4:

[0100] 1. Selection and processing of raw materials

[0101] 1.1. Take a large block of solid gallium metal with a purity of 99.9999%. Preheat the hot plate in the glove box to 90°C in an oxygen-free environment. Melt the gallium metal on the preheated hot plate. Dispense the melted gallium metal into 10ml plastic bottles for subsequent use. Place the plastic bottles containing the gallium metal in a vacuum chamber and store them in a vacuum environment.

[0102] 1.2. Clean the gallium oxide wafer with persistent photoconductivity effect using water, acetone, and ethanol in sequence, using each solvent for three cleaning cycles.

[0103] 1.3. Prepare the designed mask in advance, mask the gallium oxide wafer, and use maleic anhydride solution to perform patterned hydrophilic treatment on the masked gallium oxide wafer by spraying.

[0104] 2. Heterojunction construction process

[0105] 2.1. Place a glass sheet on a hot plate at 50°C, and place metal gallium on the glass sheet. Heat the hot plate to melt the metal gallium and make the liquid metal gallium spread out flat.

[0106] 2.2. Use glass to quickly scrape off the old gallium oxide on the surface of the liquid metal gallium in step 2.1 to expose fresh liquid gallium.

[0107] 2.3. Remove the mask from the hydrophilized gallium oxide wafer surface patterned in step 1.3 and preheat it on a 40°C hot plate. Within 3 minutes, quickly cover the hydrophilized surface of the gallium oxide wafer with the fresh gallium droplet obtained in step 2.2. Then, quickly remove the gallium oxide wafer within 10 seconds, leaving the hydrophilized surface covered with the patterned amorphous gallium oxide film. Use a lint-free cotton swab to clean any remaining gallium metal in boiling alcohol, applying a force of 1 N.

[0108] 2.4. Place 70 mg of urea on an alumina boat in the lower temperature zone of a tube furnace. Place a gallium oxide wafer covered with an amorphous gallium oxide film upside down on the center of another alumina boat, with a distance of 10 cm between the two boats. Heat the urea to 400°C and the gallium oxide wafer to 700°C at a heating rate of 15°C / min for both locations, using nitrogen as the carrier gas at a flow rate of 50 sccm. Hold the mixture at this temperature for 60 minutes, then cool naturally to room temperature. The patterned amorphous gallium oxide film reacts with ammonia to produce a two-dimensional gallium nitride film.

[0109] Using a mask, 100nm thick titanium was evaporated on the gallium oxide wafer and the two-dimensional gallium nitride film as electrodes to construct a photodetector.

[0110] The elemental content of the upper two-dimensional gallium nitride film and the underlying gallium oxide wafer obtained in this embodiment were tested at two locations. The results showed that the purity of the heterojunction obtained in this embodiment was very high, and the underlying gallium oxide wafer was not nitrided. The results of photodetection response time testing showed that the persistent photoconductivity effect of the photodetector constructed in this embodiment was significantly suppressed.

[0111] Example 5:

[0112] 1. Selection and processing of raw materials

[0113] 1.1. Take a large block of solid gallium metal with a purity of 99.9999%. Preheat the hot plate in the glove box to 100°C in an oxygen-free environment. Melt the gallium metal on the preheated hot plate. Dispense the melted gallium metal into 5 mL plastic bottles for subsequent use. Place the plastic bottles containing the gallium metal in a vacuum chamber and store them in a vacuum environment.

[0114] 1.2. Use water, acetone, and ethanol in sequence to clean the gallium oxide wafer with persistent photoconductivity effect.

[0115] 1.3. Prepare the designed mask in advance and mask the gallium oxide wafer. Use acrylic acid to perform a patterned hydrophilic treatment on the masked gallium oxide wafer using evaporation.

[0116] 2. Heterojunction construction process

[0117] 2.1. Place a glass sheet on a hot plate at 50°C, and place metal gallium on the glass sheet. Heat the hot plate to melt the metal gallium and make the liquid metal gallium spread out flat.

[0118] 2.2. Use glass to quickly scrape off the old gallium oxide on the surface of the liquid metal gallium in step 2.1 to expose fresh gallium droplets.

[0119] 2.3. Remove the mask from the hydrophilized gallium oxide wafer surface patterned in step 1.3 and preheat it on a 40°C hot plate. Within 3 minutes, quickly cover the hydrophilized surface of the gallium oxide wafer with the fresh gallium droplet obtained in step 2.2. Then, quickly remove the gallium oxide wafer within 10 seconds, leaving the hydrophilized surface covered with the patterned amorphous gallium oxide film. Clean the gallium oxide film in boiling alcohol with a lint-free cotton swab, applying a force of 1 N to the amorphous gallium oxide film.

[0120] 2.4. Place 50 mg of sulfur powder on an alumina boat in the lower temperature zone of a tube furnace. Place a gallium oxide wafer covered with an amorphous gallium oxide film upside down in the center of another alumina boat. The distance between the sulfur powder and the gallium oxide wafer is approximately 15 cm. The evaporation temperature of the sulfur powder is approximately 200°C. Heat the gallium oxide wafer to 600°C. Use a heating rate of 5°C / min. Use nitrogen as the carrier gas at a constant flow rate of 50 sccm and hold the temperature for 60 minutes. The patterned amorphous gallium oxide film reacts with the sulfur vapor to produce a two-dimensional gallium sulfide film. This results in a heterojunction with a patterned gallium sulfide surface coating.

[0121] Using a mask, titanium metal with a thickness of 100nm was evaporated on the gallium oxide wafer and the two-dimensional gallium sulfide film layer to construct a photodetector.

[0122] The elemental content of the upper two-dimensional gallium sulfide film and the underlying gallium oxide wafer obtained in this example were tested at two locations. The results demonstrated high purity of the heterojunction obtained in this example, and the underlying gallium oxide wafer was not sulfurized. Photodetection response time measurements also demonstrated that the persistent photoconductivity effect of the photodetector constructed in this example was significantly suppressed.

[0123] Example 6:

[0124] 1. Selection and processing of raw materials

[0125] 1.1. Take a large block of solid gallium metal with a purity of 99.9999%. Preheat the hot plate in the glove box to 90°C in an oxygen-free environment. Melt the gallium metal on the preheated hot plate. Dispense the melted gallium metal into 10ml plastic bottles for subsequent use. Place the plastic bottles containing the gallium metal in a vacuum chamber and store them in a vacuum environment.

[0126] 1.2. Use water, acetone, and ethanol in sequence to clean the gallium oxide crystals with persistent photoconductivity effect.

[0127] 1.3. Prepare the designed mask in advance and mask the gallium oxide wafer. Use methacrylic acid solution to spray the masked gallium oxide wafer to perform a patterned hydrophilic treatment.

[0128] 2. Heterojunction construction process

[0129] 2.1. Place a glass sheet on a hot plate at 100°C, and place metal gallium on the glass sheet. Heat the hot plate to melt the metal gallium and make the liquid metal gallium spread out flat.

[0130] 2.2. Use glass to quickly scrape off the old gallium oxide on the surface of the liquid metal gallium in step 2.1 to expose fresh gallium droplets.

[0131] 2.3. Remove the mask from the hydrophilized gallium oxide wafer surface patterned in step 1.3 and place it on a 40°C hot plate for preheating. Within 3 minutes, quickly cover the hydrophilized surface of the gallium oxide wafer with the fresh gallium droplet obtained in step 2.2. Then, quickly remove the gallium oxide wafer within 10 seconds, leaving the hydrophilized surface covered with the patterned amorphous gallium oxide film. Clean the gallium metal from the surface with a cotton swab that does not shed lint in boiling alcohol. The contact force between the cotton swab and the amorphous gallium oxide film should be 1N.

[0132] 2.4. Place 1g of phosphoric acid powder on an alumina boat in the lower temperature zone of a tube furnace. Place a gallium oxide wafer covered with a patterned amorphous gallium oxide film upside down in the center of another alumina boat (with the amorphous gallium oxide film on top of the wafer). Keep the gallium oxide wafer and phosphoric acid powder 12cm apart. Heat the wafer and phosphoric acid powder at 300°C in the same temperature zone for 90 minutes using nitrogen as the carrier gas at a flow rate of 0.6L / min. The patterned amorphous gallium oxide film reacts with phosphorus vapor to form a two-dimensional GaPO4 film. This results in a heterojunction with a surface covered with a patterned GaPO4 film.

[0133] Using a mask, 100nm of titanium metal was evaporated on the gallium oxide wafer and the two-dimensional GaPO4 film layer to construct a photodetector.

[0134] The elemental content of the upper two-dimensional GaPO4 film and the lower gallium oxide wafer obtained in this example were tested at two locations. The test results showed that the purity of the heterojunction obtained in this example was very high, and the lower gallium oxide wafer was not phosphorylated. The results of photodetection response time testing showed that the persistent photoconductivity effect of the photodetector constructed in this example was significantly suppressed.

[0135] Example 7:

[0136] 1. Selection and processing of raw materials

[0137] 1.1. Take a large block of solid gallium metal with a purity of 99.9999%. Preheat the hot plate in the glove box to 100°C in an oxygen-free environment. Melt the gallium metal on the preheated hot plate. Dispense the melted gallium metal into 10ml plastic bottles for subsequent use. Place the plastic bottles containing the gallium metal in a vacuum chamber and store them in a vacuum environment.

[0138] 1.2. Clean the gallium oxide wafer with persistent photoconductivity effect using water, acetone, and ethanol in sequence, using each solvent for three cleaning cycles.

[0139] 1.3. Prepare the designed mask in advance, mask the gallium oxide wafer, and use maleic anhydride solution to perform patterned hydrophilic treatment on the masked gallium oxide wafer by spraying.

[0140] 2. Heterojunction construction process

[0141] 2.1. Place a glass sheet on a hot plate at 50°C, and place metal gallium on the glass sheet. Heat the hot plate to melt the metal gallium and make the liquid metal gallium spread out flat.

[0142] 2.2. Use glass to quickly scrape off the old gallium oxide on the surface of the liquid metal gallium in step 2.1 to expose fresh gallium droplets.

[0143] 2.3. Remove the mask from the hydrophilized gallium oxide wafer surface patterned in step 1.3 and preheat it on a 40°C hot plate. Within 3 minutes, quickly cover the hydrophilized surface of the gallium oxide wafer with the fresh gallium droplet obtained in step 2.2. Then, quickly remove the gallium oxide wafer within 10 seconds, leaving the hydrophilized surface covered with the patterned amorphous gallium oxide film. Use a lint-free cotton swab in boiling alcohol to remove any remaining gallium metal.

[0144] 2.4. Place 200 mg of urea on an alumina boat in the lower temperature zone of a tube furnace. Place a gallium oxide wafer covered with a patterned amorphous gallium oxide film upside down in the center of another alumina boat (with the amorphous gallium oxide film on top of the wafer), with a distance of 10 cm between the two boats. Heat the urea to 500°C and the gallium oxide wafer to 800°C at a heating rate of 10°C / min for both locations, using nitrogen as the carrier gas at a flow rate of 50 sccm. Hold the mixture at this temperature for 90 minutes, then cool naturally to room temperature. The patterned amorphous gallium oxide film reacts with ammonia to produce a two-dimensional gallium nitride film.

[0145] Using a mask, 100nm thick titanium was evaporated on the gallium oxide wafer and the two-dimensional gallium nitride film as electrodes to construct a photodetector.

[0146] The elemental content of the upper two-dimensional gallium nitride film and the underlying gallium oxide wafer obtained in this embodiment were tested at two locations. The results showed that the purity of the heterojunction obtained in this embodiment was very high, and the underlying gallium oxide wafer was not nitrided. The results of photodetection response time testing showed that the persistent photoconductivity effect of the photodetector constructed in this embodiment was significantly suppressed.

[0147] Example 8:

[0148] 1. Selection and processing of raw materials

[0149] 1.1. Take a large block of solid gallium metal with a purity of 99.9999%. Preheat the hot plate in the glove box to 100°C in an oxygen-free environment. Melt the gallium metal on the preheated hot plate. Dispense the melted gallium metal into 10ml plastic bottles for subsequent use. Place the plastic bottles containing the gallium metal in a vacuum chamber and store them in a vacuum environment.

[0150] 1.2. Use water, acetone and ethanol in sequence to clean the gallium oxide film with persistent photoconductivity effect.

[0151] 1.3. Prepare the designed mask in advance, mask the gallium oxide wafer, and use acrylic acid to perform patterned hydrophilic treatment on the masked gallium oxide wafer by evaporation.

[0152] 2. Heterojunction construction process

[0153] 2.1. Place a glass sheet on a hot plate at 100°C, and place metal gallium on the glass sheet. Heat the hot plate to melt the metal gallium and make the liquid metal gallium spread out flat.

[0154] 2.2. Use glass to quickly scrape off the old gallium oxide on the surface of the liquid metal gallium in step 2.1 to expose fresh liquid gallium.

[0155] 2.3. Remove the mask from the hydrophilized gallium oxide wafer surface patterned in step 1.3 and preheat it on a 40°C hot plate. Within 3 minutes, quickly cover the hydrophilized surface of the gallium oxide wafer with the fresh gallium droplet obtained in step 2.2. Then, quickly remove the gallium oxide wafer within 10 seconds, leaving the hydrophilized surface covered with the patterned amorphous gallium oxide film. Clean the gallium oxide film in boiling alcohol with a lint-free cotton swab, applying a force of 1 N to the amorphous gallium oxide film.

[0156] 2.4. Place 100 mg of sulfur powder on an alumina boat in the lower temperature zone of a tube furnace. Place the gallium oxide sample covered with an amorphous gallium oxide film upside down in the center of another alumina boat, with the sulfur powder approximately 12.5 cm away from the gallium oxide wafer. The sulfur powder has an evaporation temperature of approximately 250°C. Heat the gallium oxide wafer to 700°C. Use a heating rate of 5°C / min. Use nitrogen as the carrier gas at a constant flow rate of 50 sccm, and hold the temperature for 90 minutes. The patterned amorphous gallium oxide film reacts with the sulfur vapor to produce a two-dimensional gallium sulfide film. This results in a heterojunction with a surface covered with a patterned gallium sulfide film.

[0157] Using a mask, titanium metal with a thickness of 100nm was evaporated on the gallium oxide wafer and the two-dimensional gallium sulfide film layer to construct a photodetector.

[0158] The elemental content of the upper two-dimensional gallium sulfide film and the underlying gallium oxide wafer obtained in this example were tested at two locations. The results demonstrated high purity of the heterojunction obtained in this example, and the underlying gallium oxide wafer was not sulfurized. Photodetection response time measurements also demonstrated that the persistent photoconductivity effect of the photodetector constructed in this example was significantly suppressed.

[0159] Comparative Example 1

[0160] The sulfurization process was as described in Example 2, except that in step 2.4, 3 g of sulfur powder was used, and the distance between the sulfur powder and the gallium oxide wafer was approximately 5 cm. The evaporation temperature of the sulfur powder was approximately 300°C. The sample was heated to 1100°C and held at this temperature for 3 hours.

[0161] Since the heating time is too long and the temperature is too high, the reaction will affect the gallium oxide wafer, making it impossible to obtain a heterojunction. Figure 6 shown.

[0162] Comparative Example 2

[0163] As described in Example 6, except that: during the sulfurization process in step 2.4, the distance between the gallium oxide wafer and the phosphoric acid powder was 20 cm, nitrogen was used as the carrier gas with a flow rate of 0.6 L / min, and the gallium oxide wafer and the phosphoric acid powder were heated in the same temperature zone at 200°C for 30 min.

[0164] Since the heating time is too short and the temperature is too low, the upper amorphous gallium oxide film layer cannot be fully phosphated, so the heterojunction cannot be obtained. The obtained heterojunction has no obvious light response. The photodetector responds to light with a wavelength of 254nm as shown below. Figure 6 shown.

[0165] Comparative Example 3

[0166] The process was as described in Example 7, except that the scraping off of old gallium oxide in step 2.2 was not performed.

[0167] At this time, the inherent gallium oxide layer on the surface is wrinkled and partially broken, so it is impossible to obtain a gallium oxide amorphous film with a smooth surface. Figure 7 shown.

[0168] Comparative Example 4

[0169] As described in Example 8, except that the temperature of the gallium oxide wafer is heated to 300° C. and the holding time is 20 minutes.

[0170] Since the reaction time available for sulfurization is too short and the temperature cannot reach the conversion temperature, a heterojunction cannot be prepared and the persistent photoconductivity effect in the photodetector cannot be effectively suppressed.

[0171] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for suppressing the persistent photoconductive effect of gallium oxide, characterized in that: The steps include: Providing a crystalline gallium oxide material, performing a hydrophilic treatment on the surface of the crystalline gallium oxide material, and preheating the hydrophilic treated crystalline gallium oxide material; the preheating temperature is not lower than the melting point of metallic gallium; Spreading liquid gallium in air, and forming an amorphous gallium oxide film layer on the surface of the spread liquid gallium; While keeping the liquid gallium in a liquid state, bringing the preheated surface of the crystalline gallium oxide material into contact with the amorphous gallium oxide film layer on the surface of the liquid gallium, so that the amorphous gallium oxide film layer is transferred to the surface of the crystalline gallium oxide material; Performing nitriding, phosphating or sulfiding on the amorphous gallium oxide film layer on the surface of the crystalline gallium oxide material, so that the amorphous gallium oxide film layer is converted into a gallium nitride film layer, a gallium phosphate film layer or a gallium sulfide film layer; The hydrophilic agent used in the hydrophilic treatment is maleic anhydride, acrylic acid or methacrylic acid.

2. The method according to claim 1, wherein: The substrate for spreading liquid gallium is made of glass, quartz or a silicon wafer with an oxide layer.

3. The method according to claim 1, wherein: The liquid gallium is kept in a liquid state by heating the substrate.

4. The method according to claim 1, wherein: After the surface of the crystalline gallium oxide material is hydrophilically treated, preheating is started, and within 3.0 minutes after preheating, the surface of the crystalline gallium oxide material after the hydrophilic treatment is brought into contact with the amorphous gallium oxide film layer on the surface of the liquid gallium.

5. The method according to claim 1, wherein: The contact time between the preheated crystalline gallium oxide material surface and the amorphous gallium oxide film layer on the liquid gallium surface is 0.01 to 10 seconds.

6. The method according to claim 1, wherein: After the amorphous gallium oxide film layer is transferred, the metal gallium remaining on the surface of the amorphous gallium oxide film layer is cleaned in boiling ethanol.

7. The method according to claim 1, wherein: The nitriding temperature is 600-900℃ and the nitriding time is 30-120min; Alternatively, the nitrogen source used in nitridation is urea; Alternatively, the vulcanization temperature is 500-800°C and the vulcanization time is 30-120 minutes; Alternatively, the sulfur source used in the vulcanization is sulfur; Alternatively, the phosphorylation temperature is 300-600°C and the phosphorylation time is 60-120 min; Alternatively, the phosphorus source for phosphorylation is phosphoric acid.

8. Use of the method according to any one of claims 1 to 7 in preparing a crystalline gallium oxide-based optoelectronic device.

9. The use according to claim 8, characterized in that: It also includes the process of preparing electrodes.

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