Photoconductive switch for phonon auxiliary absorption and pulse power system

Abstract

The invention belongs to the technical field of photoconductive switches, and particularly relates to a phonon auxiliary absorption photoconductive switch and a pulse power system. According to the invention, the main excitation path of electrons is changed, that is, the main path of electron excitation in a photoconductive switch (PCSS) is changed into phonon-assisted inter-band transition from impurity energy level-assisted transition, so that bulk excitation with high photon-generated carrier concentration on the PCSS is realized, a large number of photon-generated carriers are relatively uniformly distributed in a conducting channel of the PCSS, and the photoelectric conversion efficiency of the PCSS is improved. And the voltage conversion efficiency of the PCSS can be obviously improved. In addition, the method can be widely and universally used for the PCSS based on the semiconductor material, and the voltage conversion efficiency of the PCSS based on various semiconductor materials is improved.

Description

Technical Field

[0001] This invention belongs to the field of photoconductive switch technology, specifically relating to a photoconductive switch with phonon-assisted absorption and a pulsed power system. Background Technology

[0002] Photoconductive semiconductor switches (PSS), with their ultra-fast response speed, ultra-high output power, and strong resistance to electromagnetic interference, have become core components of modern defense equipment, playing a crucial role in advanced radar, directed energy weapons, high-power microwaves, and other fields.

[0003] Currently, besides traditional materials with narrow bandgap such as gallium arsenide (GaAs), ultra-wide bandgap semiconductor materials, due to their advantages such as higher breakdown electric field strength, excellent thermal conductivity, and ultra-short carrier lifetime, are expected to achieve greater output power density per unit channel width and have gradually become an important direction in PCSS research, aiming to improve the overall performance of devices. However, in the research of these photoconductive switches, to achieve uniform excitation of carriers in the semiconductor, researchers usually use a light source with photon energy much smaller than the material's bandgap as the excitation source, relying on impurity energy levels to achieve bulk excitation of the semiconductor material. Although this impurity energy level-based excitation method can achieve bulk excitation of the semiconductor material and avoid device damage caused by excessively high local carrier concentration, the excitation efficiency of this method is extremely low, resulting in low voltage conversion efficiency and weak output signal of PCSS based on this excitation method.

[0004] Current Ga2O3 PCSS research includes IEEE Trans. Electron Devices 71, 1535-1540 (2024), IEEE Trans. Electron Devices 72, 3638-3645 (2025), and High Power Lasers and Particle Beams 37, 065004 (2025). In these comparative studies, researchers have chosen longer wavelength light sources as excitation sources. For example, IEEE Trans. Electron Devices 71, 1535-1540 (2024) selected 355 nm, 532 nm, and 1064 nm pulsed lasers as excitation sources, IEEE Trans. Electron Devices 72, 3638-3645 (2025) selected 532 nm and 1064 nm pulsed lasers as excitation sources, and High Power Lasers and Particle Beams 37, 065004 (2025) selected a 532 nm pulsed laser as the excitation source. These light sources have low photon energies and primarily achieve photogenerated carrier excitation in PCSS through electronic transitions in impurity energy levels. The efficiency of photogenerated carrier excitation is low, leading to low voltage conversion efficiency in Ga2O3 PCSS. Specifically, the highest voltage conversion efficiency for Ga2O3 PCSS is only 0.195% in IEEE Trans. Electron Devices 71, 1535-1540 (2024), while the highest is only 0.562% in IEEE Trans. Electron Devices 72, 3638-3645 (2025), and only 18% in High Power Laser and Particle Beams 37, 065004 (2025) (with an excitation pulse energy of 150 mJ).

[0005] The existing technologies in the aforementioned comparative literature mainly utilize impurity energy levels within the material to excite photogenerated carriers. Taking Fe:Ga2O3 as an example, a schematic diagram of its electronic transition process based on impurity absorption is shown below. Figure 1As shown in the figure, due to the presence of impurity energy levels in Ga2O3, using lasers with wavelengths of 355 nm (photon energy approximately 3.5 eV), 532 nm (photon energy approximately 2.3 eV), and 1064 nm (photon energy approximately 1.2 eV) as excitation sources can still excite the charge carriers in Ga2O3, thereby enabling the Ga2O3 PCSS to turn on. Although this method can achieve bulk excitation of the material, allowing photogenerated charge carriers to be relatively uniformly distributed within the conductive channel of the PCSS, the low absorption efficiency of Ga2O3 for light in the aforementioned wavelength range results in a low charge carrier concentration, hindering the high-performance output of the PCSS. The excitation principles of other photoconductive switches based on materials such as GaN and Diamond are similar.

[0006] In summary, the carrier excitation methods used in the prior art limit the improvement of Ga2O3 PCSS output capability. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, this invention provides a phonon-assisted absorption photoconductive switch and pulsed power system. This invention changes the primary electron excitation pathway in the PCSS from impurity-assisted transitions to phonon-assisted interband transitions, achieving bulk excitation of the PCSS with a high concentration of photogenerated carriers. This results in a relatively uniform distribution of a large number of photogenerated carriers in the PCSS's conductive channel, significantly improving the PCSS's voltage conversion efficiency and enhancing its output signal. Furthermore, since this excitation method relies solely on phonon assistance, it eliminates the current PCSS's dependence on impurities, enabling its widespread and universal application in PCSS based on various semiconductor materials.

[0008] This invention focuses on iron-doped gallium oxide (Fe:Ga2O3) with a bandgap of 4.8 eV, constructing a Ga2O3 PCSS. Based on this, a pulsed power system is built. Phonon-assisted bulk excitation of the Ga2O3 PCSS is achieved using a 266 nm laser with a pulse energy of 1.98 mJ (photon energy hω is approximately 4.66 eV) as the excitation source, resulting in a voltage conversion efficiency approaching 99% and a maximum output power of 313 kW. Furthermore, compared with Ga2O3 PCSSs using other excitation methods, this invention demonstrates significant advantages over existing Ga2O3 PCSSs in terms of voltage conversion efficiency, reduced energy loss, and increased output power density.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of the present invention provides a photoconductive switch with phonon-assisted absorption, the photoconductive switch comprising a band gap of E gThe photoconductive switch comprises a crystal block and electrodes or conductive epitaxial layers located on both sides of the crystal block. The excitation source of the photoconductive switch is a pulsed laser that induces phonon-assisted absorption in the photoconductive switch. The photon energy of the pulsed laser is equal to the band gap E of the crystal block. g The pulsed laser excites the crystal block to generate phonon-assisted interband transitions, and the absorption of the pulsed laser by the crystal block is determined by variable-temperature photoluminescence spectroscopy to determine whether the absorption of the pulsed laser by the crystal block is assisted by phonons; the crystal block is a semiconductor material.

[0010] Furthermore, the crystal block is any one of gallium oxide, aluminum nitride, diamond, cubic boron nitride, or doped gallium oxide, aluminum nitride, diamond, or cubic boron nitride.

[0011] Furthermore, the crystal block is iron-doped gallium oxide.

[0012] Furthermore, the electrodes are two Rogowski electrodes with skewed planes located on both sides of the crystal block, and the Rogowski electrodes are metal layers deposited sequentially on the surface of the crystal block.

[0013] Furthermore, when the crystal block is an iron-doped gallium oxide crystal block, the method for fabricating the gallium oxide photoconductive switch is as follows: based on maskless photolithography, Rogowski electrode patterns are exposed and fabricated on two opposite surfaces of the iron-doped gallium oxide crystal block. Ti / Au / Ag / Au metal layers are sequentially deposited on the two surfaces using electron beam evaporation. Excess metal is removed by a lift-off process, and then the interface contact characteristics between the electrode and the crystal are optimized by annealing. Finally, a gallium oxide photoconductive switch with an off-plane misaligned Rogowski electrode structure is fabricated.

[0014] Furthermore, the minimum spacing between the two Rogowski electrodes is 1 mm.

[0015] Furthermore, the electrodes are a ring electrode on one side of the crystal block and a metal electrode on the other side, wherein the ring electrode and the metal electrode are metal layers deposited sequentially on the surface of the crystal block.

[0016] Furthermore, when the crystal block is an iron-doped gallium oxide crystal block, the method for fabricating the gallium oxide photoconductive switch is as follows: based on maskless photolithography, a circular pattern is exposed on one side of the iron-doped gallium oxide crystal block, a Ti / Au / Ag / Au metal layer is deposited on the surface using electron beam evaporation, excess metal is removed by a lift-off process, a Ti / Au / Ag / Au metal layer is deposited on the other side, and then the interface contact characteristics between the metal layer electrode and the crystal are optimized by annealing treatment, finally fabricating a gallium oxide photoconductive switch with a circular electrode on one side and a metal electrode on the other side.

[0017] Furthermore, the electrode is a conductive epitaxial layer located on one side of the crystal block and a metal electrode on the other side, wherein the metal electrode is a metal layer sequentially deposited on the surface of the crystal block.

[0018] Furthermore, when the crystal block is an iron-doped gallium oxide crystal block, the method for fabricating the gallium oxide photoconductive switch is as follows: a conductive epitaxial layer is grown on one side of the iron-doped gallium oxide crystal block, and a Ti / Au / Ag / Au metal layer is deposited on the other side using an electron beam evaporation method. Then, the interface contact characteristics between the metal layer electrode and the crystal are optimized by annealing treatment, and finally a gallium oxide photoconductive switch with a conductive epitaxial layer on one side and a metal electrode on the other side is fabricated.

[0019] A second aspect of the present invention provides a pulsed power system comprising the above-described photoconductive switch, the pulsed power system comprising a high-voltage power supply, a resistor, a capacitor, a gallium oxide photoconductive switch, a coaxial attenuator, and an oscilloscope. The high-voltage power supply charges the capacitor through the resistor and provides a bias voltage to the gallium oxide photoconductive switch through the capacitor. The iron-doped gallium oxide crystal block in the gallium oxide photoconductive switch is vertically irradiated by a pulsed laser, and the output terminal of the gallium oxide photoconductive switch is connected to the oscilloscope through the coaxial attenuator.

[0020] Furthermore, the pulsed laser is a 266 nm ultraviolet pulsed laser with a pulse width of 6 ns and an incident spot size of 1.2 mm.

[0021] Furthermore, the resistance value of the resistor is 10 MΩ, the load of the oscilloscope is 50Ω, the model of the oscilloscope is SIGLENT SDS5104X, and the gallium oxide photoconductive switch is packaged on a printed circuit board with a characteristic impedance of 50Ω, and epoxy resin is coated around the device to prevent air breakdown.

[0022] Basic concepts related to the light absorption process: 1. Impurity absorption Electrons or holes bound to impurity energy levels can also cause light absorption; this type of light absorption is called impurity absorption. Taking the process of an electron absorbing a photon and transitioning to a conduction band level as an example, assuming the ionization energy of an electron on the impurity is E1, the lowest photon energy hω0 that causes impurity absorption is equal to E1, and the long-wavelength absorption limit of the impurity absorption spectrum is ω0. Since the bound state does not have a definite quasi-momentum, the wave vector of the state after the electron transition is unrestricted; that is, the electron can transition to any conduction band level, thus causing a continuous absorption spectrum. Furthermore, the probability of an electron transitioning to a higher conduction band level gradually becomes very small as the energy level increases; therefore, the absorption spectrum is mainly concentrated near the absorption limit E1.

[0023] 2. Interband transition light absorption Optical absorption via interband transitions in semiconductors refers to the physical process by which electrons in the valence band absorb energy from photons and transition to the conduction band. Besides energy conservation, momentum conservation is also required for this interband transition process.

[0024] 2.1. Inter-band transition light absorption In addition to photons, this type of transition requires the participation of other quasi-particles (usually phonons) to achieve the requirement of momentum conservation. The indirect transition process is a two-step process in which electrons interact with photons and phonons simultaneously. In the physical picture and theoretical discussion, it is usually assumed that the electron first vertically transitions to a certain intermediate state, and then transitions to the vicinity of the lowest energy state of the conduction band through the process of emitting or absorbing phonons.

[0025] The absorption coefficient for the case of phonon absorption only is: The absorption coefficient for the case of phonon emission only is: The overall absorption coefficient of the indirect transition is the sum of the absorption coefficients of both the phonon emission and absorption processes, and its absorption coefficient is: 2.2 Direct interband transition optical absorption In this type of transition, an electron in the valence band absorbs photon energy and then directly transitions to the conduction band at the same wave vector position in k-space. Its core characteristic is that the change in the electron's wave vector before and after the transition is negligible (Δk≈0), and energy and momentum conservation can be satisfied simultaneously without the involvement of phonons. Taking direct bandgap materials as an example, the minimum light energy for light absorption during direct interband transitions is determined by the direct bandgap Eg; and intense absorption begins from this energy. If we only consider the light absorption process within a smaller energy range above the conduction band bottom and below the valence band top, its absorption coefficient is: Where A and B are constants, hω is the photon energy, and E g E represents the band gap width of the material. p For phonon energy, K B is Boltzmann's constant, and T is the absolute temperature.

[0026] Technical principle of this invention: For semiconductor materials at room temperature (300K), due to the different absorption principles of the materials to incident light, the absorption coefficient of the material as a function of the incident light wavelength can generally be classified as follows: Figure 2The three regions are shown. In region I, the main electronic transitions occurring within the material are impurity-assisted electronic transitions, resulting in an extremely low absorption coefficient. In region II, the main electronic transitions occurring within the material are phonon-assisted interband transitions, resulting in a relatively low absorption coefficient that is significantly affected by the number of phonons. In region III, the main electronic transitions occurring within the material are high-energy photons-induced interband transitions, resulting in a high absorption coefficient.

[0027] Currently, mainstream PCSS (Power Channel Switching) relies on Type I excitation. While this allows carriers to be distributed throughout the entire PCSS conductive channel, the resulting low carrier concentration leads to low voltage conversion efficiency, limiting the high-performance output of the PCSS. In contrast, this study employs Type II excitation, avoiding both the surface-only excitation of Type III and the excessively low carrier concentration of Type I. Furthermore, since it does not require the material to have impurity energy levels, PCSS excited using the Type II method can achieve higher breakdown voltage and lower turn-off current by using materials with lower impurity concentrations and higher quality. The following section uses the electron-to-photon absorption transition process as an example to elaborate on the above three types of excitation: For case I, the photon energy hω <E g -E p Electrons in the valence band cannot directly transition between bands by absorbing photons; only electrons bound to impurity energy levels can absorb photons and transition to the conduction band. Since the photon energy is much lower than the material's band gap, the material's response to photon energy hω... <E g -E p The light absorption coefficient is extremely low within this range, and the number of free carriers excited under the same incident light power is extremely low. Furthermore, since impurities are relatively uniformly distributed within the material, the absorption process permeates the entire material. Therefore, current photoconductive switches primarily use this excitation method to achieve bulk excitation of semiconductor materials.

[0028] In the Type II case, the semiconductor material contains a large number of phonons at room temperature (300K). As the photon energy continues to increase, until the photon energy hω > E... g -E pIn addition to the impurity absorption that may occur in Type I cases, electrons in the valence band can also undergo interband transitions by absorbing or emitting phonons when absorbing photons (this patent mainly discusses single-phonon-involved processes, but in reality, higher-order processes involving multiple phonons may occur). The absorption coefficient caused by this type of interband transition is described by formulas (1)-(3). It can be seen that the absorption coefficient in this case is significantly affected by the number of phonons, that is, the number of free carriers excited by incident light is significantly controlled by the number of phonons. In addition, since this excitation process depends on both photons and phonons, it is a second-order process. Although its absorption coefficient is significantly increased compared to Type I cases, it is relatively low compared to Type III cases. Therefore, it also has a longer excitation depth and can achieve bulk excitation of semiconductor materials.

[0029] In case III, for direct bandgap semiconductor materials, when the photon energy continues to increase until the photon energy hω>E g When the absorption coefficient of the material increases significantly, the main reason is that electrons absorb photons and undergo direct interband transitions. The absorption coefficient caused by such direct interband transitions follows formula (4). For indirect bandgap semiconductor materials, when the photon energy is greater than the difference between the conduction band and valence band energies in the same wave vector space, direct interband transitions may also occur after electrons absorb photons. The absorption coefficient caused by this process is significantly greater than that caused by interband transitions assisted only by phonons. Although the probability of electrons being excited into free carriers is extremely high in this case, because the absorption coefficient is much greater than that in the Type II case, almost all incident light is absorbed by the material within a short distance, and only surface excitation can be formed, which is not conducive to the uniform distribution of carriers in the PCSS electric field.

[0030] This invention presents schematic diagrams of semiconductor materials irradiated with light of different wavelengths (using a direct bandgap semiconductor as an example) to visually demonstrate the distribution of photogenerated carriers within the semiconductor material. Figure 3 As shown. When the photon energy hω of the incident light is less than E... g -E p Only electrons bound to impurity energy levels can absorb photons and transition to the conduction band. Although photogenerated carriers can still be distributed throughout the material, the concentration of photogenerated carriers inside the material becomes extremely low due to the material's very weak light absorption. Specifically, as shown... Figure 3 As shown in Figure Ⅰ. When the photon energy of the incident light satisfies E g -E p <hω<E g At this point, electrons mainly undergo interband transitions that absorb phonons. The material's absorption of light weakens, and the concentration of photogenerated carriers decreases, but they can still penetrate and distribute throughout the material, achieving bulk excitation. Specifically, as shown... Figure 3As shown in Figure II, with further increases in photon energy, electrons mainly undergo direct interband transitions, resulting in strong absorption of light by the material. Almost all incident light is absorbed near the material surface, and the concentration of photogenerated carriers is extremely high, but it is only distributed near the material surface, as shown in Figure II. Figure 3 As shown in section III.

[0031] Based on the above analysis, this invention takes Ga2O3, a direct bandgap material, as the object and selects a 266 nm pulsed laser with a photon energy of about 98% of the Ga2O3 bandgap as the excitation source. The influence of phonons on the excitation of free carriers in the type II case was verified through experiments, and a photoconductive switch with phonon-assisted excitation was constructed.

[0032] First, this invention prepares an iron-doped gallium oxide single crystal with suitable absorption at 266 nm light: The process involves three steps: crystal growth, cutting, and thinning.

[0033] Growth: Crystals are grown using methods such as the guided model method. High-purity gallium oxide raw materials are uniformly mixed with doped iron oxide and melted. Seed crystals are used to guide the crystal. By precisely controlling the temperature gradient and pulling rate, steps such as shoulder formation and constant diameter growth are completed in sequence to grow large-size, low-defect single crystals.

[0034] Cutting: The grown crystal is then cut. Due to the significant anisotropy and cleavage of gallium oxide crystals, and their poor thermal conductivity, traditional bonding methods are prone to causing crystal cracking due to thermal stress. Therefore, this gallium oxide crystal is directly clamped using a specialized jig to avoid heated bonding. During cutting, diamond wire cutting technology is commonly used. The cutting angle is adjusted according to the crystal orientation of the principal face, and optimized parameters are employed to effectively suppress the generation of cleavage cracks. Alternatively, a lateral thinning machine can be used with a resin-bonded diamond wheel and a specific coolant for thinning to prevent crystal cracking and improve surface quality.

[0035] Thinning: After dicing, the wafers finally undergo polishing to achieve an ultra-smooth, damage-free surface. The polishing process includes multiple steps such as surface pretreatment, main polishing, and precision polishing. After polishing, the wafers need to undergo multi-stage cleaning and possible oxygen atmosphere annealing to remove residues and repair surface defects.

[0036] After obtaining a single-chip wafer of a certain thickness using the above steps, the transmittance of gallium oxide was tested using an ultraviolet spectrophotometer. The transmittance was determined using the formula T=(1-R). 2 e -αdThe absorption coefficient of the gallium iron oxide (GaO) single crystal was calculated, and then the thickness of the single crystal wafer that could almost completely absorb 266 nm light was calculated. The crystal growth, cutting, and polishing process was repeated to obtain the GaO single crystal of the target thickness. In this invention, a GaO single crystal with a thickness of 0.55 mm after cutting and polishing was finally used.

[0037] The present invention performs transmittance tests on the above-mentioned iron-doped Ga2O3 with a thickness of 0.55 mm, and the test results are as follows. Figure 4 As shown. Based on the analysis of the test results, this invention uses a 266 nm (hω=4.66 eV) laser with an energy slightly less than the Ga2O3 bandgap (4.8 eV) as a type II excitation source. From Figure 4 As can be seen, the transmittance of the iron-doped Ga2O3 used in this invention for 266 nm light is 2.42%. This indicates that the iron-doped Ga2O3 has suitable absorption for 266 nm light, and can fully absorb the light source to generate a sufficient concentration of charge carriers under bulk excitation.

[0038] Methods for determining phonon-assisted absorption: To verify that 266 nm light can be used as an excitation source for type II cases, and to investigate the effect of phonons on the excited carriers in iron-doped Ga₂O₃ during the excitation process, this invention used 193 nm (hω=6.42 eV) and 266 nm (hω=4.66 eV) lasers as excitation sources to conduct variable-temperature photoluminescence (PL) experiments on iron-doped Ga₂O₃. The experimental results are as follows: Figure 5 As shown. Figure 5 Figure (a) shows the variation of the integrated intensity of the photoluminescence spectrum with temperature when a 193 nm laser is used as the excitation source. It can be seen that the integrated intensity of the photoluminescence spectrum decreases monotonically with increasing temperature. The Arrhenius formula, i.e., formula (5), is used to fit this result.

[0039] The fitting results show that the test results conform to the Arrhenius formula, meaning that the decrease in integrated intensity in the test results is due to the increased nonradiative recombination probability of charge carriers caused by the increase in temperature. This further verifies that under 193 nm light source excitation, the excitation probability of charge carriers inside iron-doped Ga2O3 remains constant and is not affected by the phonon number, that is, the main transition process under this excitation condition is direct interband transition. Figure 5(b) shows the temperature-dependent variation of the integrated intensity of the photoluminescence spectrum when using a 266 nm laser as the excitation source. The test results show that the integrated intensity of the photoluminescence spectrum first increases and then decreases with increasing temperature. Under this excitation condition, the increase in integrated intensity is due to the increased number of phonons at higher temperatures, leading to a higher probability of phonon-assisted electronic transitions, which in turn increases the integrated intensity of the photoluminescence spectrum. This result is consistent with the previous analysis, verifying the phonon-assisted interband transition process in type II, and also verifying that the 266 nm light source, as the excitation source for type II, can achieve phonon-assisted bulk excitation of iron-doped Ga₂O₃.

[0040] Compared with the prior art, the beneficial effects of the present invention are: This invention utilizes phonon-assisted interband transitions in semiconductor materials at room temperature to achieve bulk excitation of the photogenerated carrier system (PCSS) with a high concentration of photogenerated carriers. This results in a relatively uniform distribution of a large number of photogenerated carriers in the conductive channel of the PCSS, thereby improving the voltage conversion efficiency and enhancing the output signal of the PCSS. Furthermore, the superiority of this method has been verified through the Ga2O3 embodiment described in this invention.

[0041] Furthermore, compared to carrier excitation processes based on impurity energy levels, the phonon-assisted excitation process proposed in this invention does not depend on the presence of material impurity energy levels. It can be universally applied to PCSS based on other materials, and materials with lower impurity concentration and higher quality can be used when constructing PCSS, thereby obtaining higher withstand voltage and lower turn-off current. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the internal electron excitation principle of Ga2O3 PCSS based on existing technology.

[0043] Figure 2 This is a typical absorption coefficient curve for semiconductor materials.

[0044] Figure 3 To illustrate the distribution of photogenerated carriers inside semiconductor materials under different excitation light and the excitation principle.

[0045] Figure 4 The transmittance is the iron-doped Ga2O3 used in this invention.

[0046] Figure 5 The study investigates the changes in the integral intensity of the photoluminescence spectrum of iron-doped Ga2O3 under different excitation sources and the corresponding electronic transition processes.

[0047] Figure 6 This is a schematic diagram of the pulse power system of the present invention.

[0048] Figure 7The image shows the physical device and structural diagram of the Ga2O3 PCSS in Example 1.

[0049] Figure 8 The output signal of Ga2O3 PCSS is given by Example 1, where the pulsed laser energy is 1.98 mJ and the bias voltage is 50~4000 V.

[0050] Figure 9 The output signal of Ga2O3 PCSS is given when the pulsed laser energy is 1.98 mJ and the bias voltage is 4000 V in Example 1.

[0051] Figure 10 The changes in voltage conversion efficiency and peak output voltage of Ga2O3PCSS when the pulsed laser energy is 1.98 mJ and the bias voltage is increased from 50 V to 4000 V are shown in Example 1.

[0052] Figure 11 The changes in voltage conversion efficiency and peak output voltage of Ga2O3PCSS are shown in Example 1 when the bias voltage is 50 V, 300 V, 600 V, and the pulsed laser energy is 1.98 mJ, 2.44 mJ, and 3.02 mJ.

[0053] Figure 12 The image shows the physical device and structural diagram of the Ga2O3 PCSS in Example 2.

[0054] Figure 13 The output signal of Ga2O3 PCSS in Example 2 is given by a pulsed laser energy of 2.44 mJ and a bias voltage of 500~4000 V.

[0055] Figure 14 The output signal of Ga2O3PCSS is given when the pulsed laser energy is 2.44 mJ and the bias voltage is 4000 V in Example 2.

[0056] Figure 15 The changes in voltage conversion efficiency and peak output voltage of Ga2O3PCSS when the pulsed laser energy is 2.44 mJ and the bias voltage is increased from 500 V to 4000 V are shown in Example 2.

[0057] Figure 16 The voltage conversion efficiency and peak output voltage of Ga2O3PCSS are shown in Example 2 when the bias voltage is 500 V, 2000 V, 4000 V, and the pulse laser energy is 1.28 mJ, 1.98 mJ, 2.44 mJ, and 3.02 mJ.

[0058] Figure 17 The image shows the physical device and structural diagram of the Ga2O3 PCSS in Example 3.

[0059] Figure 18 The output signal of Ga2O3 PCSS in Example 3 is given by a pulsed laser energy of 3.02 mJ and a bias voltage of 500~4000 V.

[0060] Figure 19 The output signal of Ga2O3PCSS is given when the pulsed laser energy is 3.02 mJ and the bias voltage is 4000 V in Example 3.

[0061] Figure 20 The changes in voltage conversion efficiency and peak output voltage of Ga2O3PCSS when the pulsed laser energy is 3.02 mJ and the bias voltage is increased from 500 V to 4000 V are shown in Example 3.

[0062] Figure 21 The voltage conversion efficiency and peak output voltage of Ga2O3PCSS are shown in Example 3 when the bias voltage is 500 V, 2000 V, 4000 V, and the pulse laser energy is 0.75 mJ, 1.28 mJ, 1.98 mJ, and 3.02 mJ. Detailed Implementation

[0063] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0064] This invention provides a Ga2O3PCSS pulsed power system, such as... Figure 6 As shown, the high-voltage power supply charges the capacitor through a 10 MΩ resistor, and the capacitor provides the bias voltage to the Ga2O3 PCSS. The output of the Ga2O3 PCSS is connected to an oscilloscope (50 Ω load, model: SIGLENT SDS5104X) via a coaxial attenuator with a certain attenuation factor. Before testing, the Ga2O3 PCSS was packaged on a printed circuit board with a characteristic impedance of 50 Ω, and epoxy resin was coated around the device to prevent air breakdown. The trigger light source in this pulsed power system is a 266 nm ultraviolet pulsed laser with a pulse width of approximately 6 ns and an incident spot size of approximately 1.2 mm.

[0065] The main properties and calculation formulas of Ga2O3 PCSS are as follows: Peak output voltage: The peak value of the output voltage signal.

[0066] Voltage conversion efficiency: peak output voltage / bias voltage.

[0067] Peak output current: Peak output voltage / Load resistance.

[0068] Minimum on-resistance: Bias voltage / Peak output current - Load resistance.

[0069] Peak output power: Peak output voltage Peak output current.

[0070] Rise time: The time it takes for the output signal to rise from 90% to 10% of its maximum value.

[0071] Fall time: The time it takes for the output signal to drop from 90% to 10% of its maximum value.

[0072] First, the present invention prepared an iron-doped gallium oxide single crystal with suitable absorption at 266 nm light, which was used to fabricate Ga2O3 PCSS with different structures in the following embodiments.

[0073] The process involves three steps: crystal growth, cutting, and thinning.

[0074] Growth: Crystals are grown using methods such as the guided model method. High-purity gallium oxide raw materials are uniformly mixed with doped iron oxide and melted. Seed crystals are used to guide the crystal. By precisely controlling the temperature gradient and pulling rate, steps such as shoulder formation and constant diameter growth are completed in sequence to grow large-size, low-defect single crystals.

[0075] Cutting: The grown crystal is then cut. Due to the significant anisotropy and cleavage of gallium oxide crystals, and their poor thermal conductivity, traditional bonding methods are prone to causing crystal cracking due to thermal stress. Therefore, this gallium oxide crystal is directly clamped using a specialized jig to avoid heated bonding. During cutting, diamond wire cutting technology is commonly used. The cutting angle is adjusted according to the crystal orientation of the principal face, and optimized parameters are employed to effectively suppress the generation of cleavage cracks. Alternatively, a lateral thinning machine can be used with a resin-bonded diamond wheel and a specific coolant for thinning to prevent crystal cracking and improve surface quality.

[0076] Thinning: After dicing, the wafers finally undergo polishing to achieve an ultra-smooth, damage-free surface. The polishing process includes multiple steps such as surface pretreatment, main polishing, and precision polishing. After polishing, the wafers need to undergo multi-stage cleaning and possible oxygen atmosphere annealing to remove residues and repair surface defects.

[0077] After obtaining a single-chip wafer of a certain thickness using the above steps, the transmittance of gallium oxide was tested using an ultraviolet spectrophotometer. The transmittance was determined using the formula T=(1-R). 2 e -αdThe absorption coefficient of the gallium iron oxide (GaO) single crystal was calculated, and then the thickness of the single crystal wafer that could absorb 266 nm light almost completely was calculated. The crystal growth, cutting, and polishing process was repeated to obtain the GaO single crystal of the target thickness. In this invention, a GaO single crystal with a thickness of 0.55 mm after cutting and polishing was finally used, which had a transmittance of 266 nm light of 2.42%, indicating that it could absorb 266 nm light relatively sufficiently.

[0078] The following are specific examples of different Ga2O3 PCSS: Example 1: Ga2O3 PCSS based on two Rogowski electrodes with skewed orientations and its testing Based on maskless photolithography, in a size of 1×1 cm 2 Rogowski electrode patterns were fabricated on two opposing surfaces of an iron-doped Ga₂O₃ crystal by exposure. Subsequently, Ti / Au / Ag / Au metal layers were sequentially deposited on these surfaces using electron beam evaporation. Excess metal was removed by a lift-off process, and the interfacial contact characteristics between the electrodes and the crystal were optimized through annealing. Finally, an iron-doped Ga₂O₃ PCSS with an out-of-plane dislocation Rogowski electrode structure was successfully fabricated. The shortest distance between the two Rogowski electrodes in this device is 1 mm. A photograph of the device is shown below. Figure 7 As shown.

[0079] Figure 8 The output signal of Ga2O3 PCSS with a pulsed laser energy of 1.98 mJ and a bias voltage increased from 50 V to 4000 V is demonstrated. Experimental results show that the peak value of the Ga2O3 PCSS output signal increases with increasing bias voltage, and the device exhibits a nanosecond-level response speed.

[0080] Figure 9 The maximum output signal of the Ga2O3 PCSS measured under this test system is shown (laser energy of 1.98 mJ and bias voltage of 4000 V). Analysis of this signal yields the following maximum output performance of the Ga2O3 PCSS in this system: Peak output voltage: 3957.1 V Peak output current: 79.14 A; PCSS minimum resistance: 0.5421 Ω; Peak output power: 313.17 kW; Rise time: 6.82 ns; Fall time: 43.47 ns.

[0081] Figure 10The changes in voltage conversion efficiency and peak output voltage of the PCSS (Power Constraint System) are shown when the pulsed laser energy is 1.98 mJ and the bias voltage increases from 50 V to 4000 V. The figure shows that, under the same operating conditions, the output signal of the PCSS exhibits high stability. At a bias voltage of 50 V, the voltage conversion efficiency of the PCSS is approximately 47.5%. As the bias voltage increases, the voltage conversion efficiency also increases, reaching approximately 99% at a bias voltage of 4000 V. Furthermore, with the increase of the bias voltage, the peak output power of the device also increases significantly, reaching a maximum of 313.17 kW.

[0082] Figure 11 The graph shows the changes in voltage conversion efficiency and peak output voltage of the PCSS when the bias voltage is 50 V, 300 V, 600 V, and the pulsed laser energy is 1.98 mJ, 2.44 mJ, and 3.02 mJ. As can be seen from the graph, when the bias voltage is constant, the voltage conversion efficiency and peak output power of the PCSS increase with increasing pulsed laser energy. Similarly, when the pulsed laser energy is constant, the voltage conversion efficiency and peak output power of the PCSS increase with increasing bias voltage.

[0083] Example 2: Ga2O3 PCSS and testing based on a circular annular electrode on one side and a metal electrode on the other side. Based on maskless photolithography, in a size of 1×1 cm 2 A circular pattern was fabricated on one side of an iron-doped Ga₂O₃ crystal with a thickness of 0.55 mm by exposure. Subsequently, a Ti / Au / Ag / Au metal layer was deposited on this surface using electron beam evaporation. Excess metal was removed by a stripping process, and a Ti / Au / Ag / Au metal layer was deposited on the other side. Annealing was then performed to optimize the interfacial contact characteristics between the metal layer electrode and the crystal, ultimately producing a Ga₂O₃ PCSS with a circular electrode on one side and a large-area metal electrode on the other. An image of the fabricated material is shown below. Figure 12 As shown.

[0084] Figure 13 The output signal of Ga2O3 PCSS with a pulsed laser energy of 2.44 mJ and a bias voltage increased from 500 V to 4000 V is shown. Experimental results show that the peak value of the Ga2O3 PCSS output signal increases with increasing bias voltage, and the device exhibits a nanosecond-level response speed.

[0085] Figure 14The maximum output signal of the Ga2O3 PCSS measured under this test system is shown (laser energy of 2.44 mJ and bias voltage of 4000 V). Analysis of this signal yields the following maximum output performance of the Ga2O3 PCSS in this system: Peak output voltage: 3028.5 V; Voltage conversion efficiency: 75.71%; Peak output current: 60.57 A; PCSS minimum resistance: 16.04 Ω; Peak output power: 183.43 kW; Rise time: 5.57 ns; Fall time: 12.61 ns.

[0086] Figure 15 The changes in voltage conversion efficiency and peak output voltage of the PCSS (Power Constraint System) are shown when the pulsed laser energy is 2.44 mJ and the bias voltage increases from 500 V to 4000 V. The figure shows that, under the same operating conditions, the output signal of the PCSS exhibits high stability. At a bias voltage of 500 V, the voltage conversion efficiency of the PCSS is approximately 14.17%, while at a bias voltage of 4000 V, its voltage conversion efficiency reaches approximately 75.71%. It can be seen that the voltage conversion efficiency of the PCSS increases significantly with increasing bias voltage. Furthermore, with increasing bias voltage, the peak output power of the device increases significantly, reaching a maximum of 183.43 kW.

[0087] Figure 16 The figure shows the changes in voltage conversion efficiency and peak output voltage of the PCSS when the bias voltage is 500 V, 2000 V, 4000 V, and the pulsed laser energy is 1.28 mJ, 1.98 mJ, 2.44 mJ, and 3.02 mJ. As can be seen from the figure, when the bias voltage is constant, the voltage conversion efficiency and peak output power of the PCSS increase with increasing pulsed laser energy. When the pulsed laser energy is constant, the voltage conversion efficiency and peak output power of the PCSS increase with increasing bias voltage.

[0088] Example 3: Ga2O3 PCSS based on a conductive epitaxial layer on one side and a metal electrode on the other side and its testing In a size of 1×1 cm 2A 2 μm thick conductive epitaxial layer was grown on one side of an iron-doped Ga₂O₃ crystal with a thickness of 0.55 mm, and a Ti / Au / Ag / Au metal layer was deposited on the other side. Annealing was then performed to optimize the interfacial contact characteristics between the metal layer electrode and the crystal, ultimately fabricating a Ga₂O₃ PCSS with a conductive epitaxial layer on one side and a metal electrode on the other. A photograph of the actual product is shown below. Figure 17 As shown.

[0089] Figure 18 The output signal of Ga2O3 PCSS with a pulsed laser energy of 3.02 mJ and a bias voltage increased from 500 V to 4000 V is shown. Experimental results show that the peak value of the Ga2O3 PCSS output signal increases with increasing bias voltage, and the device exhibits a nanosecond-level response speed.

[0090] Figure 19 The maximum output signal of the Ga2O3 PCSS measured under this test system (laser energy of 3.02 mJ and bias voltage of 4000 V) is shown. Analysis of this signal yields the following maximum output performance of the Ga2O3 PCSS in this system: Peak output voltage: 2348.8 V; Voltage conversion efficiency: 58.72%; Peak output current: 46.98 A; PCSS minimum resistance: 35.15 Ω; Peak output power: 110.34 kW; Rise time: 4.33 ns; Fall time: 4.55 ns.

[0091] Figure 20 The changes in voltage conversion efficiency and peak output voltage of the PCSS (Power Constraint System) are shown when the pulsed laser energy is 1.98 mJ and the bias voltage increases from 500 V to 4000 V. The figure shows that, under the same operating conditions, the output signal of the PCSS exhibits high stability. At a bias voltage of 500 V, the voltage conversion efficiency of the PCSS is approximately 50%, while at a bias voltage of 4000 V, it reaches approximately 55.2%. It can be seen that the voltage conversion efficiency of the PCSS does not significantly increase with increasing bias voltage. Furthermore, with increasing bias voltage, the peak output power of the device increases significantly, reaching a maximum of 110.34 kW.

[0092] Figure 21The figure shows the changes in voltage conversion efficiency and peak output voltage of the PCSS when the bias voltage is 500 V, 2000 V, 4000 V, and the pulsed laser energy is 0.75 mJ, 1.28 mJ, 1.98 mJ, and 3.02 mJ. As can be seen from the figure, when the bias voltage is constant, the voltage conversion efficiency and peak output power of the PCSS increase with increasing pulsed laser energy. When the pulsed laser energy is constant, the voltage conversion efficiency of the PCSS does not change significantly, while its peak output power increases with increasing bias voltage.

[0093] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A photoconductive switch with phonon-assisted absorption, characterized in that, The photoconductive switch has a band gap of E. g The photoconductive switch comprises a crystal block and electrodes or conductive epitaxial layers located on both sides of the crystal block. The excitation source of the photoconductive switch is a pulsed laser that induces phonon-assisted absorption in the photoconductive switch. The photon energy of the pulsed laser is equal to the band gap E of the crystal block. g The absorption of pulsed laser light by the crystal block is 80% to 100%, and it is necessary to determine whether the absorption of pulsed laser light by the crystal block is assisted by phonons through variable temperature photoluminescence spectroscopy test. The crystal block is a semiconductor material.

2. The photoconductive switch with phonon-assisted absorption according to claim 1, characterized in that, The crystal block is any one of gallium oxide, aluminum nitride, diamond, cubic boron nitride, or doped gallium oxide, aluminum nitride, diamond, or cubic boron nitride.

3. The photoconductive switch with phonon-assisted absorption according to claim 2, characterized in that, The electrodes are two Rogowski electrodes with skewed planes located on both sides of the crystal block, and the Rogowski electrodes are metal layers deposited sequentially on the surface of the crystal block.

4. The photoconductive switch with phonon-assisted absorption according to claim 3, characterized in that, When the crystal block is an iron-doped gallium oxide crystal block, the method for fabricating the gallium oxide photoconductive switch is as follows: Based on maskless photolithography, Rogowski electrode patterns are exposed and fabricated on two opposite surfaces of the iron-doped gallium oxide crystal block. Ti / Au / Ag / Au metal layers are sequentially deposited on the two surfaces using electron beam evaporation. Excess metal is removed by a lift-off process, and then the interface contact characteristics between the electrode and the crystal are optimized by annealing. Finally, a gallium oxide photoconductive switch with an off-plane misaligned Rogowski electrode structure is fabricated.

5. The photoconductive switch with phonon-assisted absorption according to claim 2, characterized in that, The electrodes are a ring electrode on one side of the crystal block and a metal electrode on the other side, wherein the ring electrode and the metal electrode are metal layers deposited sequentially on the surface of the crystal block.

6. The photoconductive switch with phonon-assisted absorption according to claim 5, characterized in that, When the crystal block is an iron-doped gallium oxide crystal block, the method for fabricating the gallium oxide photoconductive switch is as follows: Based on maskless photolithography, a circular pattern is exposed on one side of the iron-doped gallium oxide crystal block, and a Ti / Au / Ag / Au metal layer is deposited on the surface using electron beam evaporation. Excess metal is removed by a lift-off process, and a Ti / Au / Ag / Au metal layer is deposited on the other side. Then, the interface contact characteristics between the metal layer electrode and the crystal are optimized by annealing. Finally, a gallium oxide photoconductive switch with a circular electrode on one side and a metal electrode on the other side is fabricated.

7. The photoconductive switch with phonon-assisted absorption according to claim 2, characterized in that, The electrode consists of a conductive epitaxial layer on one side of the crystal block and a metal electrode on the other side, wherein the metal electrode is a metal layer sequentially deposited on the surface of the crystal block.

8. The photoconductive switch with phonon-assisted absorption according to claim 7, characterized in that, When the crystal block is an iron-doped gallium oxide crystal block, the method for fabricating the gallium oxide photoconductive switch is as follows: a conductive epitaxial layer is grown on one side of the iron-doped gallium oxide crystal block, and a Ti / Au / Ag / Au metal layer is deposited on the other side by electron beam evaporation. Then, the interface contact characteristics between the metal layer electrode and the crystal are optimized by annealing. Finally, a gallium oxide photoconductive switch with a conductive epitaxial layer on one side and a metal electrode on the other side is fabricated.

9. A pulsed power system comprising the photoconductive switch according to any one of claims 1-8, characterized in that, The pulsed power system consists of a pulsed laser that induces phonon-assisted absorption in the crystal block, a high-voltage power supply, a resistor, a capacitor, a gallium oxide photoconductive switch, a coaxial attenuator, and an oscilloscope. The high-voltage power supply charges the capacitor through the resistor, and the capacitor provides a bias voltage to the gallium oxide photoconductive switch. The iron-doped gallium oxide crystal block in the gallium oxide photoconductive switch is vertically irradiated by the pulsed laser, and the output terminal of the gallium oxide photoconductive switch is connected to the oscilloscope through the coaxial attenuator.

10. The pulsed power system according to claim 9, characterized in that, The pulsed laser is a 266 nm ultraviolet pulsed laser with a pulse width of 6 ns and an incident spot size of 1.2 mm; the resistor has a resistance of 10 MΩ; the oscilloscope has a load of 50Ω and is a SIGLENT SDS5104X model; the gallium oxide photoconductive switch is packaged on a printed circuit board with a characteristic impedance of 50Ω and is coated with epoxy resin around the device to prevent air breakdown.

Images