Research And Optimization Of Self-heating Effect Of ?-Ga₂O₃ Devices

?-Ga₂O₃ is a strong contender for future power devices such as Schottky barrier diodes and field-effect transistors(FETs)that are expected to deliver superior power switching capabilities at higher efficiencies than the incumbent Si,Si C and Ga N technologies due to its ultra-wide bandgap of 4.8 e V and corresponding high electrical breakdown field of 8MV/cm.However,self-heating effect in?-Ga₂O₃ MOSFET is exacerbated by the low thermal conductivity?of?-Ga₂O₃that ranges from 10?25 W/m·K at room temperature along the three principle crystallographic directions.Inefficient heat transport leads to higher temperature in the active region of?-Ga₂O₃ devices than for other technologies at comparable power dissipation.and thus severe self-heating effect,which becomes one of major challenges to realize its practical applications.An effective approach to mitigate the self-heating effect of?-Ga₂O₃ field-effect transistors(FETs)is to utilize a higher?substrate rather than the?-Ga₂O₃ native substrate through a potential wafer bonding technique.Therefore,this thesis investigates the mitigation self-heating effect theoretically by four kinds of substrates,Si,Al N,Si C,and diamond.Firstly,a structure is proposed,in which the semi-insulating?-Ga₂O₃ substrate is retained as an insulating layer between the?-Ga₂O₃ active layer and the substrate with high thermal conductivity.The output characteristics of this structure with four kinds of substrates are simulated by using Sentaurus TCAD,which demonstrate the optimization of high?substrates on the self-heating effect of?-Ga₂O₃ devices.Next,the performance of the?-Ga₂O₃MOSFET with native substrate is investigated by Sentaurus TCAD at elevated temperature.It is found that the resistivity of semi-insulating?-Ga₂O₃ substrate will greatly decrease at elevated temperature,which is the reason why the off-state current of?-Ga₂O₃MOSFET increases by several orders of magnitude.Therefore,the promising structure is using Al₂O₃ as the insulating layer rather than the semi-insulating?-Ga₂O₃.An accurate analytical model to estimate the peak temperature of?-Ga₂O₃ based devices at steady-state involving the temperature dependence and the anisotropy of thermal conductivity?is presented.A simple expression based on device geometry and material parameters has been derived.An excellent agreement has been obtained between the model and COMSOL numerical simulations.In addition,a single exponential function has been derived to predict the time which is needed to reach steady-state for?-Ga₂O₃ MOSFET.