| Electronics is a cornerstone of modern information society and technological advancement,playing an integral role in a range of fields.Among its essential components,power devices play a crucial role in the control and modulation of energy properties.As the "heart" of electronic devices,power electronic devices are vital energy control components utilized for the modulation of voltage and current properties across four types of application scenarios:inverters(DC-AC),rectifiers(AC-DC),converters(DC-DC),and frequency converters(AC-AC).They are widely used in power equipment for energy conversion and circuit control.The rise of a new energy revolution,including large-scale deployment of new energy sources such as wind power and solar energy,has led to increasingly higher requirements for energy efficiency,environmental protection,and reliability.Rapid growth of downstream markets,such as new energy vehicles,photovoltaics,and rail transportation,has resulted in a corresponding increase in demand for power semiconductor devices.As such,power semiconductor devices are poised to become one of the fastest-growing devices in the future.As the bottleneck of traditional silicon materials becomes increasingly prominent,the development of wide bandgap semiconductors has gradually been recognized and applied in high-power fields.β-Ga2O3,as a type of ultra-wide bandgap(～4.8 eV)semiconductor material,has a breakdown field strength of 8 MV/cm and a power quality factor of 3444 MW/cm2.It is an optimal material for the next-generation ultrahigh-power and extreme environment(high voltage,high temperature,strong radiation,etc.)power electronic devices,following gallium nitride and silicon carbide.The use ofβ-Ga2O3 power devices will bring advantages such as energy saving,smaller size,lighter weight,and faster speed compared to silicon-based devices,and can strengthen energy conservation and emission reduction,accelerate the promotion of green and sustainable development,and conform to the concept of "dual carbon".Power fieldeffect transistors are important components commonly used in power switches,electric vehicle driving motors,power amplifiers,and other electronic devices that require highpower control.Their main advantages are high switch speed,low switch loss,and high efficiency.The development of β-Ga2O3 field-effect transistors is limited because of the lack of p-type doping technology,and their performance is relatively backward compared toβ-Ga2O3 diode devices.This thesis proposes solutions to the incompatibility between enhancement process and device performance,and the difficulty of designing and implementing enhancement-type devices and improving their performance,the following achievements were made:(1)From the perspective of overall performance,based on the control and design of the doping concentration of the β-Ga2O3 channel itself,an enhancement-modeβ-Ga2O3 MOSFET structure with variation of lateral channel doping concentration was proposed.Through TCAD simulation,the variation of lateral doping technology inβ-Ga2O3 transistors was explored,i.e.,changing the doping concentration gradient in the channel structure of the β-Ga2O3 channel(especially the drift region).It was found that the transistor with variation of lateral doping has an enhancement-mode operation,an excellent conduction performance,and a significantly superior channel electric field distribution.To better demonstrate the optimized performance of the proposed new structure,we compared the performance of the transistor of variation of lateral doping channel with that of the transistor with uniform doping channel,demonstrating the excellent characteristics of the variation of lateral doping transitor.Specifically,compared with the uniform doping transistor,their conduction resistance is almost the same,and the transconductance of the laterally graded transistor is three times higher than that of the uniform doping transistor,reaching 30 mS/mm.The breakdown voltage of the uniform doping transistor is 1161 V,while the device with variation of lateral doping structure can achieve a higher breakdown voltage of 1832 V,which is 1.58 times higher than that of the uniform doping transistor,and the PFOM value is 2.5 times higher than that of the uniform doping transistor.We also optimized the concentration of the three regions in the drift region one by one and described the entire optimization process,obtaining the best PFOM of 332.7 MW/cm2.This work simultaneously considers the implementation of enhancement mode operation and the improvement of overall device performance,The work simultaneously addresses the implementation of the enhancement mode and the improvement of overall device performance,providing a new solution to the incompatibility between enhancing mode issues and device performance enhancement.(2)Regrowth technology was developed using 300 nm SiO2 as the regrowth mask.A combination of RIE dry etching and wet etching with BOE solution was used for patterning the shape of SiO2,and HF solution was used to remove the unwanted regrowth regions,resulting in an ideal regrowth region.This method was applied to the regrowth step in the ohmic contact region during device fabrication,which helped improve device performance and avoided the use of costly methods such as ion implantation.p-NiO was introduced into the β-Ga2O3 HJFET,combining pNiO/β-Ga2O3 heterojunction and gate trench processes to develop an enhanced β-Ga2O3 heterojunction FET structure.This structure preserves the thick β-Ga2O3 channel,which retains the transistor’s on-state characteristics while achieving enhanced mode operation.The β-Ga2O3 channel was grown using MOCVD,producing high-quality thin films.A low etching power(RF power of 10 W)ICP gate trench etching technology was developed to reduce damage to the channel during dry etching.Wet etching and hightemperature annealing were used to repair the etched channel lattice.The contact resistance was extracted using the transmission line model,which was found to be 10.5Ω·mm.The subthreshold swing and transconductance were 73 mV/dec and 14.8 mS/mm,respectively.The device had a saturation current of 11 mA/mm at a gate voltage of 2.5 V,an on-resistance of 151.5 Ω·mm,and a breakdown voltage of 980 V.(3)Considering the huge potential of vertical devices for high-current applications,a new technology was developed.Firstly,the effects of oxygen atmosphere annealing on gallium oxide were studied using techniques such as positron annihilation,photoluminescence spectroscopy,X-ray photoelectron spectroscopy,and capacitancevoltage measurements,and the necessary parameters for device f-abrication were determined.A current-blocking layer type β-Ga2O3 vertical trench gate field-effect transistor structure based on high-temperature oxygen atmosphere annealing technology was proposed.By annealing β-Ga2O3 in an oxygen atmosphere at high temperature,a high-resistance layer is formed on the surface instead of a p-type doped layer.Through the exploration of high-temperature oxygen annealing process,the annealing temperature and device basic structural parameters were determined,and aβ-Ga2O3 UMOSFET was successfully fabricated.The electrical characteristics of the fabricated device showed that the semi-insulating layer formed by oxygen annealing is an effective CBL,and its conductivity can be modulated by the side gate.The transistor device achieved the enhancement mode and obtained a threshold voltage of 11.5 V.The maximum on-state current was 11 A/cm2,and the current on/off ratio was 6 × 104.Despite being an initial attempt at a new principle device,this work has opened up a new preparation scheme for β-Ga203 high-voltage and high-current transistors,and is an important exploration achievement in the field of vertical β-Ga2O3 devices. |
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