Mg-doped gallium oxide light guide modulation microwave device and preparation method thereof

Abstract

The invention discloses an Mg-doped unipolar gallium oxide light guide modulation microwave device with hole conduction, and mainly solves the problems of low withstand voltage, low output power and low output signal frequency of the device in the prior art. The device comprises a semi-insulating substrate (1), a pair of ohmic electrodes (3), a pair of electrode thickening layers (4) and a trigger source (6), the semi-insulating substrate adopts an Mg-doped gallium oxide single crystal substrate, two symmetrical grooves (2) are formed in the upper part of the semi-insulating substrate, and the pair of ohmic electrodes and the pair of electrode thickening layers are positioned in each groove from bottom to top; and a high-resistance layer (5) formed through high-temperature annealing in an oxygen atmosphere is arranged in a region between the two grooves. Only hole carriers can be excited to participate in conduction under the irradiation of a trigger source, the working time of the device under high voltage is prolonged, the dark-state resistance of the device can be increased through the high-resistance layer, the on-state resistance of the device can be reduced through the high-resistance layer, the withstand voltage of the device can be improved, the output frequency can be increased, and the device can be used for generating high-frequency-band and tunable microwave output signals.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state high-power microwave technology, and in particular relates to a Mg-doped gallium oxide photoconductive modulated microwave device, which can be used to generate a high-frequency and tunable microwave output signal. Background Art

[0002] With the advent of the new generation of 5G communications and the information age of equipment, higher requirements are placed on high-power microwave technology. The reason why high-power microwave technology can play an important role in many fields is that it can generate large currents, high voltages and has a very fast response speed. The main contents of high-power microwave technology research usually include three aspects: energy storage, pulse formation and switching technology. Among them, the switch is the core component of the high-power microwave system. It connects the power supply system, energy storage system and load system into an organic whole and realizes energy conversion. Photoconductive switches have become the international frontier and hot spot of current research due to their simple structure, small size, high voltage resistance, fast response speed and low jitter.

[0003] Photoconductive switch device is a new type of device that uses fast laser pulses to generate a large number of photogenerated carriers in the semiconductor device body, controls the conductivity of the material, and thus realizes the conduction and shutdown of the device. Compared with common switch devices such as traditional spark gap switches, turn-off thyristors and metal oxide semiconductor field effect transistors, photoconductive switches have the advantages of fast closing time, small jitter time, high repetition frequency, no electromagnetic interference, miniaturization, etc., and can take into account both power capacity and repetition frequency. Semiconductor materials based on photoconductive switches usually include first-generation semiconductor Si and second-generation semiconductor GaAs. Wide bandgap and ultra-wide bandgap semiconductor materials are the basis for the rapid development of microwave devices in high performance and miniaturization in recent years, and thus have become ideal materials for the preparation of photoconductive switches. Gallium oxide materials have higher bandgap width, critical breakdown field strength and Johnson figure of merit than other wide bandgap materials, making them a popular material in the field of high-frequency and high-power devices.

[0004] Patent document with application number CN202110414332.4 discloses a gallium oxide-based high-power optically controlled microwave device, such as Figure 1 As shown in the figure, the structure of the device is to deposit metal cathode and anode on both sides of the gallium oxide single crystal substrate, and use the light-controlled gallium oxide photoconductive switch to achieve microwave output, improve the switching ratio of the device's photocurrent and dark current, and the device power can reach the megawatt level, achieving high-power light-controlled microwave output. However, since it uses a vertical structure to prepare electrodes, it is easy to affect the performance of the device due to alignment errors, and the preparation process is relatively complicated. And due to the characteristics of the vertical structure, it is difficult to generate high-frequency microwave signal output.

[0005] In the article published by the National University of Defense Technology (L. Wang, X. Chu, M. Yi, et al., "Vertical SiC photoconductive switch with axial optical internal reflection trap," IEEE Trans. Electron. Devices 69, 5028 (2022)), a vanadium-doped 4H-SiC photoconductive switch device based on a planar electrode structure is proposed. It is a total internal reflection light capture structure with a focusing lens. The device can generate a continuously adjustable microwave output signal from the P band to the L band. However, since the vanadium impurity doped in the silicon carbide material is a bipolar impurity that is both a donor and an acceptor, the carriers excited by light have both electrons and holes participating in the conduction. Therefore, the device uses this bipolar conduction mechanism. It is difficult to meet the requirements of the photoconductive switch for long-term operation under high withstand voltage; at the same time, since the device uses a total internal reflection light capture structure with a focusing lens, although it can improve the light energy utilization rate of the photoconductive switch, the structure is relatively cumbersome and complex, which increases the volume of the device, which is not conducive to the compactness and integration of the photoconductive switch device. Summary of the invention

[0006] The purpose of the present invention is to address the deficiencies of the above-mentioned prior art and propose a Mg-doped gallium oxide photoconductive modulated microwave device and a preparation method thereof, so as to improve the high withstand voltage time of the photoconductive switch, simplify the device structure, and easily output a high-frequency tunable signal, which is conducive to compact and integrated preparation.

[0007] The technical idea for achieving the purpose of the present invention is: a photoconductive switching device is prepared on a Mg-doped gallium oxide single crystal substrate by a planar groove electrode structure combined with an oxygen annealing process, the device is used to excite only holes to participate in conduction under light, thereby generating a high-frequency microwave output signal, and the Mg-doped gallium oxide material used in the device is used to reduce the oxygen vacancy content on the device surface after the oxygen annealing process, so as to increase the dark state resistance and improve the device's withstand voltage, while reducing the on-state resistance and increasing the photocurrent, thereby improving the device's output power.

[0008] According to the above ideas, the technical solutions of the present invention include the following:

[0009] 1. A Mg-doped gallium oxide photoconductive modulated microwave device, comprising a semi-insulating substrate, a pair of ohmic electrodes, a pair of electrode thickening layers and a trigger source, characterized in that:

[0010] The semi-insulating substrate adopts a Mg-doped gallium oxide single crystal substrate, so that only hole carriers are excited to participate in conduction under the irradiation of a trigger source; two symmetrical grooves are opened on the upper part of the substrate;

[0011] The pair of ohmic electrodes and the pair of electrode thickening layers are located inside each groove from bottom to top;

[0012] A high resistance layer is provided in the region between the two grooves to increase the dark resistance of the device and reduce the on-state resistance;

[0013] Preferably, the depth of each groove is less than the sum of each ohmic electrode and each electrode thickening layer to increase the photocurrent.

[0014] Preferably, the pair of ohmic electrodes is a double-layer structure formed by titanium with a thickness of 15nm to 25nm and gold with a thickness of 225nm to 235nm.

[0015] Preferably, the pair of electrode thickening layers are formed of a double-layer structure of titanium with a thickness of 15nm to 25nm and gold with a thickness of 395nm to 405nm.

[0016] Preferably, each groove has a length of 3 mm to 5 mm, a width of 1 mm to 3 mm, a depth of 355 nm to 365 nm, and a distance between two grooves of 0.5 mm to 1.5 mm.

[0017] Preferably, the high resistance layer is formed by annealing in an oxygen atmosphere, and has a length of 3 mm to 5 mm and a width of 0.5 mm to 1.5 mm.

[0018] Preferably, the trigger source is a laser source with a wavelength of 500nm to 564nm.

[0019] 2. A method for manufacturing a Mg-doped gallium oxide photoconductive modulated microwave device, characterized in that it comprises the following steps:

[0020] S1: cleaning the semi-insulating substrate;

[0021] S2: Spin-coating photoresist on the front side of the cleaned semi-insulating substrate;

[0022] S3: exposing and developing the semi-insulating substrate spin-coated with photoresist by a photolithography machine carrying a photoresist plate to form two rectangular groove areas;

[0023] S4: performing groove etching and cleaning on the front side of the semi-insulating substrate by using an etcher;

[0024] S5: Spin-coating photoresist on the front side of the etched semi-insulating substrate;

[0025] S6: overlaying, exposing, and developing the semi-insulating substrate spin-coated with photoresist by a photolithography machine carrying a photolithography plate to form two rectangular ohmic electrode regions;

[0026] S7: performing oxygen plasma treatment on the front side of the semi-insulating substrate and sputtering titanium and gold through a sputtering table, then cleaning after stripping, and then annealing in a nitrogen atmosphere to form an ohmic electrode;

[0027] S8: Spin-coating photoresist on the front side of the annealed semi-insulating substrate;

[0028] S9: overlaying, exposing, and developing the semi-insulating substrate spun with photoresist by a photolithography machine loaded with a photolithography plate to form two rectangular electrode thickening layer regions;

[0029] S10: performing oxygen plasma treatment on the front side of the semi-insulating substrate and sputtering titanium and gold through a sputtering table, and then cleaning after stripping to form an electrode thickening layer;

[0030] S11: Annealing in an oxygen atmosphere to form a high resistance layer, completing device preparation.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] Firstly, the present invention adopts a Mg-doped gallium oxide single crystal substrate, which can only excite one type of hole carrier to participate in conduction under the irradiation of a trigger source, thereby realizing unipolar conduction to improve the withstand voltage performance, and provides a new idea for solving the problem of difficulty in P-type doping in the current gallium oxide system; and gallium oxide, as a direct bandgap material, has higher quantum efficiency and is easier to grow than other materials. It is easier to dope when preparing a single crystal substrate by the pulling method, and it is easier to control the doping concentration that meets the design requirements, and the preparation cost is low.

[0033] Secondly, since the present invention has two symmetrical planar grooves on the upper side of the substrate, not only can the output signal from P to L bands be continuously adjusted, but the modulation degree in S band can reach more than 75%, thus achieving higher frequency tunability.

[0034] Thirdly, since the ohmic electrode and the electrode thickening layer are deposited from bottom to top inside the groove, and the depth of each groove is less than the sum of the ohmic electrode and the electrode thickening layer, the conduction area is increased and the photocurrent is improved.

[0035] Fourthly, the present invention reduces the oxygen vacancy content by annealing in an oxygen atmosphere so that a high-resistance layer is formed in the area between the two grooves, thereby increasing the dark state resistance and improving the withstand voltage level. More carriers can be excited to participate in conduction under light, thereby increasing the light absorption efficiency and improving the photocurrent. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic structural diagram of the Mg-doped gallium oxide photoconductive modulation microwave device of the present invention;

[0037] Figure 2is an energy level diagram of Mg-doped gallium oxide in the device of the present invention;

[0038] Figure 3 It is a characterization diagram of the surface oxygen vacancy content before and after the high resistance layer is formed in the device of the present invention;

[0039] Figure 4 It is a schematic diagram of the implementation process of preparing the device of the present invention. DETAILED DESCRIPTION

[0040] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0041] Reference Figure 1 The Mg-doped gallium oxide photoconductive modulated microwave device of the present invention comprises a semi-insulating substrate 1, two grooves 2, two ohmic electrodes 3, two electrode thickening layers 4, a high resistance layer 5 and a trigger source 6. Among them:

[0042] The semi-insulating substrate 1 is a Mg-doped gallium oxide single crystal substrate; its shape is a square with a side length of 9 mm to 11 mm and a thickness of 500 μm to 540 μm, and is used to excite only hole carriers to participate in conduction under the irradiation of the trigger source 6, thereby achieving unipolar conduction to improve the withstand voltage performance, and providing a new idea for solving the current problem of difficulty in P-type doping in the gallium oxide system; and gallium oxide, as a direct bandgap material, has higher quantum efficiency, and is easier to dope when preparing a single crystal substrate by the pulling method compared to other material growth, and it is easier to control the doping concentration that meets the design requirements, and the preparation cost is low.

[0043] The two grooves 2 are located on the upper part of the semi-insulating substrate 1 and are parallel. The length of each groove is 3mm to 5mm, the width is 1mm to 3mm, the depth is 355nm to 365nm, and the distance between the two grooves is 0.5mm to 1.5mm. The two grooves can not only continuously adjust the output signals from the P to L bands, but also the modulation degree in the S band can reach more than 75%, thereby achieving higher frequency tunability and improving the output frequency of the device.

[0044] The two ohmic electrodes 3 are respectively located at the lower part of each groove 2, and their lower surfaces are tightly combined with the bottom of the groove. They are 3mm to 5mm in length and 1mm to 3mm in width. The material is a composite metal layer composed of titanium and gold, wherein the thickness of titanium is 15nm to 25nm and the thickness of gold is 225nm to 235nm, and they are used to reduce the potential barrier between the metal electrode and the semi-insulating material.

[0045] The two electrode thickening layers 4 are respectively located at the upper part of each groove 2, and their lower surfaces are tightly combined with the upper surface of the ohmic electrode 3. Their length is 3mm to 5mm and their width is 1mm to 3mm. The material is a composite metal layer composed of titanium and gold, wherein the thickness of titanium is 15nm to 25nm and the thickness of gold is 395nm to 405nm, and they are used to connect each ohmic electrode to an external circuit.

[0046] The high resistance layer 5 is located in the area between the two grooves 2, and is formed by annealing in an oxygen atmosphere to reduce the oxygen vacancy content; the pure gallium oxide single crystal substrate is weakly n-type due to background impurities and oxygen vacancy defects, and the doped Mg element can be used as an acceptor to compensate for a small amount of background impurities and oxygen vacancy defects to form semi-insulation, and oxygen annealing can fill the oxygen vacancy defects to reduce the content of oxygen vacancy defects, resulting in the reduction of the reasons for the formation of the weak n-type gallium oxide single crystal substrate, thereby improving the insulation of the single crystal substrate and increasing the dark resistance. At the same time, in this high resistance layer, due to the reduction of the content of oxygen vacancy defects, the amount of Mg impurity elements compensating for oxygen vacancy defects is reduced, and more hole carriers can be generated under the irradiation of the trigger source 6 to participate in conduction, thereby increasing the light absorption efficiency and improving the photocurrent; its length is 3mm to 5mm, and the width is 0.5mm to 1.5mm, which is used to increase the dark resistance of the device, improve the withstand voltage level, and excite more carriers to participate in conduction under light, thereby increasing the light absorption efficiency and improving the photocurrent.

[0047] The trigger source 6 is a laser source irradiated on the high resistance layer 5, with a wavelength of 500nm to 564nm and a repetition frequency of 1GHz to 8GHz, which is used to excite holes on the Mg energy level in the semi-insulating substrate 1 to the top of the valence band to form carriers, thereby participating in conduction under the action of an external electric field.

[0048] Reference Figure 4 The present invention provides three embodiments for manufacturing Mg-doped gallium oxide photoconductive modulated microwave devices.

[0049] Example 1: A Mg-doped gallium oxide single crystal substrate is prepared, which has a square side length of 10 mm and a thickness of 520 μm; each groove has a length of 4 mm, a width of 2 mm, and a depth of 360 nm; each ohmic electrode has a length of 4 mm and a width of 2 mm; each electrode thickening layer has a length of 4 mm and a width of 2 mm; and a high resistance layer has a length of 4 mm and a width of 1.0 mm, to form a photoconductive modulated microwave device.

[0050] Step 1, select a Mg-doped gallium oxide single crystal substrate, such as Figure 4 (a).

[0051] Reference Figure 2There are some background impurities and oxygen vacancy defects in the gallium oxide crystal, among which Si is a shallow donor impurity with an energy level position 30meV below the bottom of the conduction band and can be excited to the bottom of the conduction band at room temperature, Ir is a deep donor impurity with an energy level position 2.3eV below the bottom of the conduction band, oxygen vacancy defects are deep donor impurities with an energy level position 1.3eV to 2.7eV from the bottom of the conduction band, and the doped Mg is an acceptor impurity with an energy level position 1.2eV above the top of the valence band; the band gap width of the gallium oxide material is 4.9eV, and due to the presence of background impurities and oxygen vacancy defects, it presents a weak n-type. In the dark state, the doped Mg impurities compensate for the background impurities and oxygen vacancy defects to form a semi-insulating state. Since the Mg energy level position is 3.7eV away from the bottom of the conduction band, the 532nm laser is not enough to excite the electrons on this energy level to reach the conduction band, but can excite the holes on this energy level to reach the valence band, forming a unipolar device with only holes conducting electricity. Therefore, the Mg-doped gallium oxide single crystal substrate 1 is selected in this step.

[0052] Step 2: Cleaning the obtained Mg-doped gallium oxide semi-insulating substrate.

[0053] The Mg-doped gallium oxide semi-insulating substrate 1 is first placed in acetone for ultrasonication for 5 minutes; then placed in isopropanol for ultrasonication for 5 minutes; and then placed in deionized water for rinsing for 5 minutes;

[0054] Finally, the cleaned substrate is blown dry with nitrogen.

[0055] Step 3, performing a first spin coating of photoresist on the front side of the cleaned substrate.

[0056] The substrate was baked using a temperature-controlled heating stage at a temperature of 200°C for 5 minutes;

[0057] Select AZ6130 photoresist, fix the substrate on the coating table, drop the photoresist on the substrate, and spin coat at 4000r for 30 seconds;

[0058] A temperature-controlled heating stage is used to pre-bake the substrate with photoresist to fix the photoresist on the substrate. The temperature is 100° C. and the time is 2 minutes.

[0059] Step 4, the photoresist fixed on the substrate is exposed and developed for the first time, such as Figure 4 (b).

[0060] The substrate with the photoresist fixed thereon is exposed for the first time for 12 seconds using a photolithography machine equipped with a photoresist plate;

[0061] The exposed substrate is immersed in a developer for 80 seconds;

[0062] The developed substrate was rinsed with deionized water for 3 minutes and dried with nitrogen gas;

[0063] The dried substrate was hardened using a temperature-controlled heating table to remove moisture from the substrate. The temperature of the heating table was 100° C. and the hardening time was 1 minute.

[0064] Step 5, the substrate after the water is removed is subjected to groove etching, such as Figure 4 (c).

[0065] The substrate after the water is removed is etched into a groove 2 in a plasma etcher, the gas atmosphere is a mixed gas of boron chloride, chlorine and argon, and the etching time is 15 minutes.

[0066] Step 6, cleaning the substrate after the groove is etched.

[0067] After etching the groove 2, the substrate was first placed in acetone for 5 minutes for ultrasonic treatment; then placed in a stripping solution heated to 60°C and immersed for 15 minutes; then placed in acetone for 5 minutes for ultrasonic treatment; then placed in isopropanol for 5 minutes for ultrasonic treatment; then rinsed in deionized water for 3 minutes and then dried with nitrogen.

[0068] Step 7, after cleaning and drying, the front side of the substrate is spin-coated with photoresist for the second time.

[0069] The cleaned and dried substrate is baked on a temperature-controlled heating platform at a temperature of 200°C for 5 minutes.

[0070] Select SF6 photoresist, fix the baked substrate on the coating table, drop the photoresist on the substrate, and spin coat at 2000r for 30 seconds;

[0071] The substrate after spin coating with SF6 photoresist was pre-baked using a temperature-controlled heating stage at a temperature of 200°C for 5 minutes.

[0072] Select the photoresist model EPI621, fix the pre-baked substrate on the coating table, then drop the photoresist on the pre-baked substrate, and spin-coat at a speed of 5000r for 30 seconds;

[0073] The substrate on which the EPI621 photoresist was spin-coated was pre-baked using a temperature-controlled heating stage to fix the photoresist on the substrate at a temperature of 90° C. for 1 minute.

[0074] Step 8, the photoresist fixed on the substrate is exposed and developed for the second time, such as Figure 4 (d).

[0075] The substrate with the photoresist fixed is exposed for the second time using a photolithography machine with a photoresist plate, and the exposure time is 19 seconds;

[0076] The exposed substrate was post-baked using a temperature-controlled heating stage at 110°C for 1 minute.

[0077] The post-baked substrate is immersed in a developer for 50 seconds.

[0078] The developed substrate was rinsed with deionized water for 3 minutes and dried with nitrogen.

[0079] Step 9, depositing an ohmic electrode on the dried substrate.

[0080] The dried substrate surface was bombarded in oxygen plasma for 5 minutes;

[0081] A magnetron sputtering station was used to deposit titanium on the substrate after oxygen plasma treatment, with a power of 75 W, a gas flow of 1.5 mTorr, a time of 400 seconds, and a thickness of 20 nm.

[0082] A magnetron sputtering station was used to deposit metal gold on metal titanium, with a power of 25 W, a gas flow of 3 mTorr, a time of 2300 seconds, and a thickness of 230 nm, to form an ohmic electrode 3 composite layer composed of titanium and gold.

[0083] Step 10, the substrate on which the ohmic electrode composite layer is deposited is stripped for the first time, such as Figure 4 (e).

[0084] The substrate on which the ohmic electrode 3 composite layer is deposited is first soaked in acetone for 10 hours;

[0085] Then sonicate in acetone for 5 minutes and blow with a plastic pipette for 5 minutes;

[0086] Then heat it to 60℃ in the stripping solution and soak it for 30 minutes;

[0087] Then ultrasonicate in acetone and isopropanol for 5 minutes each;

[0088] Rinse with deionized water for 5 minutes and then blow dry with nitrogen.

[0089] Step 11, performing ohmic annealing on the dried substrate.

[0090] The dried substrate was rapidly annealed at a high temperature of 470° C. for 1 minute in a nitrogen atmosphere.

[0091] Step 12, spin-coating photoresist on the front side of the annealed substrate for the third time.

[0092] The annealed substrate is baked using a temperature-controlled heating stage at a temperature of 200° C. for 5 minutes;

[0093] Select SF6 photoresist, fix the annealed substrate on the coating table, then drop the photoresist on the annealed substrate and spin coat at 2000r for 30 seconds;

[0094] The substrate after spin coating with SF6 photoresist was pre-baked using a temperature-controlled heating stage at a temperature of 200°C for 5 minutes.

[0095] Select the photoresist model EPI621, fix the pre-baked substrate on the coating table, then drop the photoresist on the pre-baked substrate, and spin-coat at a speed of 5000r for 30 seconds;

[0096] The substrate on which the EPI621 photoresist was spin-coated was pre-baked using a temperature-controlled heating stage to fix the photoresist on the substrate. The temperature was 90° C. and the time was 1 minute.

[0097] Step 13, the photoresist fixed on the substrate is exposed and developed for the third time, such as Figure 4 (f).

[0098] The substrate with the photoresist fixed thereon is exposed for the third time using a photolithography machine with a photoresist plate, and the exposure time is 19 seconds;

[0099] The exposed substrate was post-baked using a temperature-controlled heating stage at 110°C for 1 minute.

[0100] The post-baked substrate is immersed in a developer for 50 seconds.

[0101] The developed substrate was rinsed with deionized water for 3 minutes and dried with nitrogen.

[0102] Step 14, depositing an electrode thickening layer on the blow-dried substrate.

[0103] The dried substrate surface was bombarded in oxygen plasma for 5 minutes;

[0104] A magnetron sputtering station was used to deposit titanium on the substrate after oxygen plasma treatment, with a power of 75 W, a gas flow of 1.5 mTorr, a time of 400 seconds, and a thickness of 20 nm.

[0105] A magnetron sputtering station was used to deposit metal gold on metal titanium, with a power of 25 W, a gas flow of 3 mTorr, a time of 4000 seconds, and a thickness of 400 nm, to form an electrode thickened with 4 composite layers consisting of titanium and gold.

[0106] Step 15, the substrate on which the electrode thickened composite layer is deposited is peeled off for the second time, such as Figure 4 (g).

[0107] The substrate on which the ohmic electrode 4 composite layer is deposited is first soaked in acetone for 10 hours;

[0108] Then sonicate in acetone for 5 minutes and blow with a plastic pipette for 5 minutes;

[0109] Then heat it to 60℃ in the stripping solution and soak it for 30 minutes;

[0110] Then ultrasonicate in acetone and isopropanol for 5 minutes each;

[0111] Rinse with deionized water for 5 minutes and then blow dry with nitrogen.

[0112] Step 16, the dried substrate is subjected to oxygen annealing to form a high resistance layer, such as Figure 4 (h).

[0113] The principle of forming the high resistance layer 5 by oxygen annealing is as follows:

[0114] The pure gallium oxide single crystal substrate is weakly n-type due to background impurities and oxygen vacancy defects. However, oxygen vacancy defects can be filled by oxygen annealing to reduce the content of oxygen vacancy defects, thereby reducing the reasons for the gallium oxide single crystal substrate to form a weak n-type and improving the insulation of the single crystal substrate, thereby increasing the dark resistance and forming a high resistance layer 5.

[0115] In this example, the dried substrate is annealed in an oxygen atmosphere at a temperature of 470° C. for 30 minutes to form a high resistance layer 5, thereby completing device fabrication.

[0116] The high resistance layer 5 region between the two grooves 2 was characterized by using an X-ray photoelectron spectroscopy before and after oxygen annealing. The results are as follows: Figure 3 .in Figure 3 (a) is the result of peak fitting after O1s fine spectrum obtained by X-ray photoelectron spectrometer test and C1s calibration. Figure 3 (b) Quantitative representation of oxygen vacancy content after peak fitting.

[0117] from Figure 3 (a) It can be seen that the O1s fine spectrum in gallium oxide can be measured by X-ray photoelectron spectrometer, which can be decomposed into three different peaks after peak fitting after C1s calibration: peak OI originates from Ga-O bonding, peak OII is attributed to the oxygen-deficient region, and peak OIII corresponds to the presence of chemically adsorbed hydroxyl and carbonate substances. Among them, peak OII is caused by the presence of oxygen defects in gallium oxide, and the area ratio of peak OII to peak (OI+OII) can be used to qualitatively evaluate the relative proportion of oxygen vacancies in gallium oxide.

[0118] from Figure 3 (b) It can be seen that the oxygen vacancy content is reduced from 37.8% before oxygen annealing to 9.2%, indicating that the photoconductive switch prepared on the Mg-doped gallium oxide single crystal substrate has a reduced oxygen vacancy content in the middle region between the two electrodes after annealing in an oxygen atmosphere, which reduces the reason why the gallium oxide single crystal substrate forms a weak n-type, resulting in improved insulation of the single crystal substrate and increased dark state resistance, thereby forming a high resistance layer 5.

[0119] Example 2: Prepare a Mg-doped gallium oxide single crystal substrate with a square side length of 9 mm and a thickness of 500 μm; each groove has a length of 3 mm, a width of 1 mm, and a depth of 355 nm; each ohmic electrode has a length of 3 mm and a width of 1 mm; each electrode thickening layer has a length of 3 mm and a width of 1 mm; the high resistance layer has a length of 3 mm and a width of 0.5 mm, and a photoconductive modulated microwave device.

[0120] Step 1. Select a Mg-doped gallium oxide single crystal substrate and clean it. Figure 4 (a).

[0121] The implementation of this step is the same as step 1 and step 2 of embodiment 1.

[0122] Step 2. Perform the first spin coating of photoresist on the front side of the cleaned substrate.

[0123] Place the cleaned substrate on a temperature-controlled heating table, set the temperature to 180°C, and bake it for 6 minutes;

[0124] Select AZ4620 photoresist, drop it on the coating table with the substrate, and spin coat it at 3000r for 40 seconds;

[0125] The substrate spin-coated with AZ4620 photoresist was placed on a temperature-controlled heating table, and the temperature was set to 140° C. The substrate spin-coated with the photoresist was pre-baked for 1 minute to fix the first spin-coated photoresist on the substrate.

[0126] Step 3. Fix the first spin-coated photoresist on the substrate and then expose and develop it. Figure 4 (b).

[0127] The substrate on which the first photoresist is fixed is placed on a photolithography machine carrying a photoresist plate for exposure for 19 seconds; the exposed substrate is then placed in a developer for immersion development for 60 seconds;

[0128] Then, the substrate after immersion and development was placed in deionized water for 4 minutes and then dried with nitrogen gas;

[0129] The dried substrate was placed on a temperature-controlled heating table and the temperature was set to 90° C. for 2 minutes to harden the film to remove moisture from the substrate.

[0130] Step 4. Etch the hardened substrate into grooves, such as Figure 4 (c).

[0131] The hardened substrate was placed in a plasma etcher, and the groove 2 was etched for 14 minutes in a gas atmosphere of a mixed gas of boron chloride, chlorine and argon.

[0132] Step 5. Clean the substrate with the grooves etched therein according to the same operation as step 6 of embodiment 1.

[0133] Step 6. Spin-coat photoresist a second time on the front side of the cleaned substrate.

[0134] Place the cleaned substrate on a temperature-controlled heating table and bake it at 180°C for 6 minutes; then select SF6 photoresist, drop it on the coating table carrying the substrate, and spin-coat it on the substrate at a speed of 2000r for 30 seconds;

[0135] The substrate with the SF6 photoresist spin-coated thereon is then placed on a temperature-controlled heating table and pre-baked at 180° C. for 6 minutes to fix the SF6 photoresist on the substrate;

[0136] Select 49CP photoresist, drop it on the substrate coated with SF6 photoresist and place it on the coating table for spin coating at a speed of 4000r for 40 seconds;

[0137] The substrate with SF6 photoresist fixed on it and 49CP photoresist spin-coated on it is then placed on a temperature-controlled heating table and pre-baked at 90°C for 1 minute to fix the 49CP photoresist on the SF6 photoresist to form a composite double-layer photoresist consisting of SF6 photoresist and 49CP photoresist.

[0138] Step 7. Expose and develop the composite double-layer adhesive. Figure 4 (d).

[0139] The composite double-layer adhesive substrate with the second spin coating fixed was placed on a photolithography machine with a photoresist plate for exposure for 21 seconds; and the exposed substrate was placed on a temperature-controlled heating table and pre-baked at 100°C for 2 minutes;

[0140] The pre-baked substrate was placed in a developer for immersion development for 60 seconds; the immersed and developed substrate was then placed in deionized water for rinsing for 4 minutes and then dried with nitrogen.

[0141] Step 8. Deposit an ohmic electrode on the dried substrate.

[0142] The blow-dried substrate was placed in oxygen plasma for 4 minutes of surface bombardment;

[0143] The bombarded substrate was placed on a magnetron sputtering table, and a 15 nm thick titanium layer was deposited under the process conditions of 74 W power, 1.0 mTorr gas flow rate, and 300 seconds.

[0144] The substrate on which the titanium metal was deposited was placed on a magnetron sputtering table, and metal gold with a thickness of 225 nm was deposited under the process conditions of a power of 24 W, a gas flow of 2.5 mTorr, and a time of 2250 seconds to form an ohmic electrode 3 composite layer composed of titanium and gold.

[0145] Step 9. Peel off the substrate after depositing the ohmic electrode composite layer. Figure 4 (e).

[0146] The substrate on which the ohmic electrode 3 composite layer was deposited was placed in acetone for 10.5 hours of soaking; the soaked substrate was then placed in acetone for 4 minutes of ultrasonic treatment and blown with a plastic straw for 4 minutes;

[0147] Place the dried substrate in a stripping solution heated to 55°C and soak for 35 minutes;

[0148] The immersed substrate was then placed in acetone, isopropanol and deionized water in turn, ultrasonicated for 4 minutes each, and then dried with nitrogen.

[0149] Step 10. Place the dried substrate in a nitrogen atmosphere and set the temperature to 460° C. for 65 seconds of rapid annealing.

[0150] Step 11. Spin-coat photoresist for the third time on the front side of the annealed substrate.

[0151] The front side of the annealed substrate is placed on a temperature-controlled heating platform and baked at 180°C for 6 minutes; then a SF6 type photoresist is selected and dropped on a coating platform carrying the substrate, and spin-coated on the substrate at a speed of 2000r for 30 seconds; then the substrate spin-coated with the SF6 photoresist is placed on a temperature-controlled heating platform and pre-baked at 180°C for 6 minutes to fix the SF6 photoresist on the substrate;

[0152] Select 49CP photoresist, drop it on the substrate coated with SF6 photoresist and place it on the coating table for spin coating at a speed of 4000r for 40 seconds;

[0153] The substrate with SF6 photoresist fixed on it and 49CP photoresist spin-coated on it is then placed on a temperature-controlled heating table and pre-baked at 90°C for 1 minute to fix the 49CP photoresist on the SF6 photoresist to form a composite double-layer photoresist consisting of SF6 photoresist and 49CP photoresist.

[0154] Step 12. Expose and develop the composite double-layer adhesive formed in step 11. Figure 4 (f).

[0155] The composite double-layer adhesive substrate with the third spin coating fixed was placed on a photolithography machine with a photoresist plate for exposure for 21 seconds; and the exposed substrate was placed on a temperature-controlled heating table and pre-baked at 100°C for 2 minutes;

[0156] The pre-baked substrate was placed in a developer for immersion development for 60 seconds, and then the immersed and developed substrate was placed in deionized water for 4 minutes for rinsing and then dried with nitrogen.

[0157] Step 13: Deposit an electrode thickening layer on the blow-dried substrate.

[0158] The dried substrate was placed in oxygen plasma for surface bombardment for 4 minutes;

[0159] The bombarded substrate was placed on a magnetron sputtering table, and metal titanium with a thickness of 15 nm was deposited under the process conditions of 74 W of power, 1.0 mTorr of gas flow, and 300 seconds of time;

[0160] The substrate on which the titanium metal was deposited was placed on a magnetron sputtering table, and metal gold was deposited with a thickness of 395 nm under the process conditions of a power of 24 W, a gas flow of 2.5 mTorr, and a time of 3950 seconds to form an electrode thickened 4 composite layer composed of titanium and gold.

[0161] Step 14. Peel off the substrate on which the electrode thickened composite layer is deposited. Figure 4 (g).

[0162] The substrate on which the electrode thickening 4 composite layers were deposited in step 13 was placed in acetone for 10.5 hours of soaking; the soaked substrate was placed in acetone for 4 minutes of ultrasonication and then blown dry with a pipette;

[0163] The dried substrate was placed in a stripping solution and heated to 55°C and then immersed for 35 minutes;

[0164] The soaked substrate was placed in acetone, isopropanol, and deionized water in turn for 4 minutes each for ultrasonic treatment, and then dried with nitrogen gas;

[0165] Step 15. The dried substrate is subjected to oxygen annealing to form a high resistance layer, such as Figure 4 (h).

[0166] The implementation of this step is the same as step 16 of Example 1.

[0167] Example 3: Prepare a Mg-doped gallium oxide single crystal substrate with a square side length of 11 mm and a thickness of 540 μm; each groove has a length of 5 mm, a width of 3 mm, and a depth of 365 nm; each ohmic electrode has a length of 5 mm and a width of 3 mm; each electrode thickening layer has a length of 5 mm and a width of 3 mm; the high resistance layer has a length of 5 mm and a width of 1.5 mm, and a photoconductive modulated microwave device.

[0168] Step A. Select a Mg-doped gallium oxide single crystal substrate and clean it. Figure 4 (a).

[0169] The implementation of this step is the same as step 1 and step 2 of embodiment 1.

[0170] Step B: Spin-coating photoresist for the first time on the front side of the cleaned substrate.

[0171] B1) baking the cleaned front side of the substrate on a temperature-controlled heating table at a temperature of 220° C. for 4 minutes;

[0172] B2) dripping photoresist on the baked substrate and spin coating, wherein the photoresist is AZ1500 model, the rotation speed of the coating station is 4000r, and the spin coating time is 20 seconds;

[0173] B3) placing the substrate spun with AZ1500 photoresist on a temperature-controlled heating table for pre-baking, setting the temperature of the temperature-controlled heating table to 60° C. and the pre-baking time to 3 minutes to fix the first spun AZ1500 photoresist on the substrate.

[0174] Step C. Fix the first spin-coated photoresist on the substrate and then expose and develop it. Figure 4 (b).

[0175] C1) placing the substrate with the photoresist fixed thereon on a photolithography machine carrying a photoresist plate for exposure, with an exposure time of 21 seconds;

[0176] C2) placing the exposed substrate in a developer for development for 100 seconds;

[0177] C3) rinsing the developed substrate in deionized water and drying it with nitrogen gas;

[0178] C4) placing the blow-dried substrate on a temperature-controlled heating table for hardening to remove moisture from the substrate. The hardening temperature is 110° C. and the time is 0.5 minutes.

[0179] Step D: The hardened substrate is subjected to groove etching and cleaning, such as Figure 4 (c).

[0180] D1) placing the hardened substrate in a mixed gas consisting of boron chloride, chlorine and argon to etch the groove 2 for 16 minutes;

[0181] D2) Cleaning the substrate with the grooves etched therein according to the same operation as step 6 of embodiment 1.

[0182] Step E: Spin-coat photoresist twice on the front side of the cleaned substrate.

[0183] E1) baking the cleaned front side of the substrate on a temperature-controlled heating table at a temperature of 220° C. for 4 minutes;

[0184] E2) dripping photoresist on the baked substrate for the first time and performing spin coating, wherein the photoresist is SF6 type, the rotation speed of the coating station is 2000r, and the spin coating time is 30 seconds;

[0185] E3) baking the substrate on which the SF6 photoresist is spin-coated on a temperature-controlled heating stage to fix the SF6 photoresist on the substrate, the baking temperature being 220° C. for 4 minutes;

[0186] E4) dripping photoresist for the second time on the substrate fixed with SF6 photoresist and performing spin coating, wherein the photoresist is 14CP type, the rotation speed of the coating station is 5000r, and the spin coating time is 20 seconds;

[0187] E5) Pre-baking the 14CP photoresist spin-coated on the substrate on a temperature-controlled heating table to fix the 14CP photoresist on the SF6 photoresist to form a composite double-layer photoresist consisting of SF6 photoresist and 14CP photoresist. The pre-baking temperature is 110° C. and the time is 0.5 minutes.

[0188] Step F: Expose and develop the composite double-layer adhesive formed in step E. Figure 4 (d).

[0189] F1) placing the substrate with the composite double-layer adhesive fixed thereon on a photolithography machine carrying a photoresist for exposure, with an exposure time of 21 seconds;

[0190] F2) placing the exposed substrate on a temperature-controlled heating table for post-baking at a temperature of 100° C. for 2 minutes;

[0191] F3) placing the post-baked substrate in a developer for development for 100 seconds;

[0192] F4) Rinse the developed substrate in deionized water and then blow dry with nitrogen.

[0193] Step G: Depositing an ohmic electrode on the substrate after step F.

[0194] G1) placing the dried substrate in oxygen plasma for surface bombardment for 6 minutes;

[0195] G2) Placing the bombarded substrate on a magnetron sputtering table to first deposit metal titanium, and then deposit metal titanium to form an ohmic electrode 3 composite layer composed of titanium and gold, wherein:

[0196] The process conditions for depositing titanium metal are set as follows: power of 76 W, gas flow of 2.0 mTorr, deposition time of 500 seconds, and thickness of titanium metal of 25 nm;

[0197] The process conditions for depositing metal gold were set as follows: power of 26 W, gas flow of 3.5 mTorr, deposition time of 2350 seconds, and thickness of metal gold of 235 nm.

[0198] Step H: peel off the substrate after depositing the ohmic electrode composite layer. Figure 4 (e).

[0199] H1) soaking the substrate on which the ohmic electrode 3 composite layer is deposited in acetone for 11 hours;

[0200] H2) ultrasonicating the immersed substrate in acetone for 6 minutes, and then drying it with a pipette;

[0201] H3) soaking the dried substrate in a stripping solution heated to 65° C. for 25 minutes;

[0202] H4) The immersed substrate was ultrasonicated in acetone, isopropanol and deionized water in sequence for 6 minutes, and then dried with nitrogen.

[0203] Step I: Rapidly anneal the substrate dried in step H under a nitrogen atmosphere at a temperature of 480° C. for 55 seconds.

[0204] Step J: Spin-coat photoresist twice on the front side of the annealed substrate.

[0205] J1) baking the front side of the annealed substrate on a temperature-controlled heating table at a temperature of 220° C. for 4 minutes;

[0206] J2) dripping photoresist on the baked substrate for the first time and performing spin coating, wherein the photoresist is selected from SF6 type, the rotation speed of the coating station is 2000r, and the spin coating time is 30 seconds;

[0207] J3) baking the substrate on which the SF6 photoresist is spin-coated on a temperature-controlled heating table to fix the SF6 photoresist on the substrate at a baking temperature of 220° C. for 4 minutes;

[0208] J4) dripping photoresist for the second time on the substrate fixed with SF6 photoresist and performing spin coating, wherein the photoresist is selected to be 14CP type, the rotation speed of the coating station is 5000r, and the spin coating time is 20 seconds;

[0209] J5) Pre-bake the 14CP photoresist spin-coated on the substrate on a temperature-controlled heating table to fix the 14CP photoresist on the SF6 photoresist to form a composite double-layer photoresist consisting of SF6 photoresist and 14CP photoresist. The pre-bake temperature is 110° C. and the time is 0.5 minutes.

[0210] Step K: Expose and develop the composite double-layer adhesive formed in step J, such as Figure 4 (f).

[0211] K1) placing the substrate with the composite double-layer adhesive fixed thereon on a photolithography machine carrying a photoresist for exposure, with an exposure time of 21 seconds;

[0212] K2) placing the exposed substrate on a temperature-controlled heating table for post-baking at a temperature of 100° C. for 2 minutes;

[0213] K3) placing the post-baked substrate in a developer for development for 100 seconds;

[0214] K4) The developed substrate is rinsed in deionized water and then blown dry with nitrogen.

[0215] Step L: Depositing an electrode thickening layer on the substrate dried in step K.

[0216] L1) placing the dried substrate in oxygen plasma for surface bombardment for 6 minutes;

[0217] L2) Placing the bombarded substrate on a magnetron sputtering table to first deposit metal titanium, and then deposit metal titanium to form an electrode thickening 4 composite layer composed of titanium and gold, wherein:

[0218] The process conditions for depositing titanium metal are set as follows: power of 76 W, gas flow of 2.0 mTorr, deposition time of 500 seconds, and thickness of titanium metal of 25 nm;

[0219] The process conditions for depositing metal gold are set as follows: power is 26 W, gas flow rate is 3.5 mTorr, deposition time is 4050 seconds, and the thickness of metal gold is 405 nm.

[0220] Step M: peel off the substrate after depositing the electrode thickening composite layer, such as Figure 4 (g).

[0221] M1) Soaking the substrate on which the electrode thickening 4 composite layers have been deposited in acetone for 11 hours;

[0222] M2) ultrasonicating the immersed substrate in acetone for 6 minutes and drying it with a pipette;

[0223] M3) soaking the dried substrate in a stripping solution heated to 65° C. for 25 minutes;

[0224] M4) The immersed substrate was ultrasonicated in acetone, isopropanol and deionized water in sequence for 6 minutes, and then dried with nitrogen.

[0225] Step N: oxygen annealing the dried substrate to form a high resistance layer, such as Figure 4 (h).

[0226] The implementation of this step is the same as step 16 of Example 1.

[0227] The above descriptions are only a few specific examples of the present invention and do not constitute any limitation to the present invention. It is obvious that for professionals in this field, after understanding the content and principles of the present invention, it is possible to make various modifications and changes in form and details without departing from the principles and structures of the present invention. For example, the various parameters of the device can be expanded or reduced on this basis in addition to the parameter ranges in the above examples, but these modifications and changes based on the ideas of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A Mg-doped gallium oxide photoconductive modulated microwave device, comprising a semi-insulating substrate (1), a pair of ohmic electrodes (3), a pair of electrode thickening layers (4) and a trigger source (6), characterized in that: The semi-insulating substrate (1) is a Mg-doped gallium oxide single crystal substrate, so that only hole carriers are excited to participate in conduction under the irradiation of a trigger source (6); two symmetrical grooves (2) are opened on the upper part of the substrate; The pair of ohmic electrodes (3) and the pair of electrode thickening layers (4) are located inside each groove (2) from bottom to top; A high resistance layer (5) is provided in the region between the two grooves (2) to increase the dark resistance of the device and reduce the on-state resistance.

2. The device according to claim 1, characterized in that The depth of each groove (2) is less than the sum of each ohmic electrode (3) and each electrode thickening layer (4), so as to increase the photocurrent.

3. The device according to claim 1, characterized in that Each ohmic electrode (3) is made of titanium with a thickness of 15nm to 25nm and gold with a thickness of 225nm to 235nm, forming a double-layer structure.

4. The device according to claim 1, characterized in that Each electrode thickening layer (4) is made of titanium with a thickness of 15nm to 25nm and gold with a thickness of 395nm to 405nm, forming a double-layer structure.

5. The device according to claim 1, characterized in that The length of each groove (2) is 3 mm to 5 mm, the width is 1 mm to 3 mm, the depth is 355 nm to 365 nm, and the distance between the two grooves is 0.5 mm to 1.5 mm.

6. The device according to claim 1, characterized in that The high resistance layer (5) is formed by annealing in an oxygen atmosphere and has a length of 3 mm to 5 mm and a width of 0.5 mm to 1.5 mm.

7. The device according to claim 1, characterized in that The trigger source (6) adopts a laser source with a wavelength of 500nm to 564nm.

8. A method for manufacturing a Mg-doped gallium oxide photoconductive modulated microwave device, characterized in that: The steps include: S1: cleaning the semi-insulating substrate (1); S2: Spin-coating a photoresist on the front side of the cleaned semi-insulating substrate (1); S3: exposing and developing the semi-insulating substrate (1) spin-coated with photoresist by a photolithography machine carrying a photolithography plate to form two rectangular groove (2) regions; S4: etching and cleaning the groove (2) on the front side of the semi-insulating substrate (1) by using an etcher; S5: Spin-coating a photoresist on the front side of the etched semi-insulating substrate (1); S6: using a photolithography machine with a photolithography plate to perform overlay, exposure, and development on the semi-insulating substrate spin-coated with photoresist to form two rectangular ohmic electrode (3) regions; S7: performing oxygen plasma treatment on the front side of the semi-insulating substrate (1) and sputtering titanium and gold through a sputtering table, then stripping and cleaning, and then annealing in a nitrogen atmosphere to form an ohmic electrode (3); S8: Spin-coating a photoresist on the front side of the annealed semi-insulating substrate (1); S9: using a photolithography machine equipped with a photolithography plate to perform overlay, exposure, and development on the semi-insulating substrate (1) spin-coated with photoresist to form two rectangular electrode thickening layer (4) regions; S10: performing oxygen plasma treatment on the front side of the semi-insulating substrate (1) and sputtering titanium and gold through a sputtering table, and then cleaning after stripping to form an electrode thickening layer (4); S11: Annealing in an oxygen atmosphere to form a high resistance layer (5), completing device preparation.

9. The method according to claim 8, characterized in that: The semi-insulating substrate (1) is cleaned in step S1), step S4), step S7) and step S10) by ultrasonicating in acetone, isopropanol and deionized water for 4 to 6 minutes respectively, and then dried in a nitrogen atmosphere; In step S2), step S5) and step S8), the cleaned semi-insulating substrate is spin-coated with photoresist on the front side, which is first baked on a temperature-controlled heating table: the temperature is 180°C to 220°C, and the time is 4 to 6 minutes; then the photoresist is spin-coated: the rotation speed is 2000r to 5000r, and the time is 20 seconds to 40 seconds; finally, the temperature-controlled heating table is used for front baking: the temperature is 60°C to 140°C, and the time is 1 minute to 3 minutes; In step S3), step S6) and step S9), the semi-insulating substrate spun with photoresist is exposed and developed by a photolithography machine carrying a photoresist plate, and the exposure time is 8 seconds to 32 seconds; the development time is 60 seconds to 100 seconds, and it is rinsed with deionized water for 2 minutes to 4 minutes, blown dry with nitrogen, and then hardened for 0.5 to 2.0 minutes at a temperature of 90°C to 110°C using a temperature-controlled heating table.

10. The method according to claim 8, characterized in that: In the step S4), groove etching is performed on the semi-insulating substrate after spin coating by using an etcher; The etching gas atmosphere is boron chloride, chlorine and argon, and the etching time is 14 minutes to 16 minutes; In the step S7) and step S10), oxygen plasma treatment is performed on the front side of the semi-insulating substrate and titanium and gold are sputtered and peeled off by a sputtering table; the parameters are set as follows: The oxygen plasma treatment time is 4 to 6 minutes; The power of sputtering titanium is 74W~76W, the gas flow rate is 1.0mTorr~2.0mTorr, and the time is 300 seconds~500 seconds; the power of sputtering gold is 24W~26W, and the gas flow rate is 2.5mTorr~3.5mTorr; The stripping process is to soak in acetone for 10 to 11 hours, then ultrasonicate for 4 to 6 minutes, blow off the metal in the non-electrode area, and filter, then soak in a stripping solution at a temperature of 55 to 65 degrees Celsius for 25 to 35 minutes, and finally ultrasonicate in isopropanol for 4 to 6 minutes. In the step S7), annealing is performed in a nitrogen atmosphere at a temperature of 460° C. to 480° C. for a time of 55 seconds to 65 seconds; In the step S11), annealing is performed in an oxygen atmosphere at a temperature of 460° C. to 480° C. for 25 minutes to 35 minutes.

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