Modeling And Simulation Of Strain Model For Normally-off HEMTs With P-GaN Gate

As the primary representative of the third-generation semiconductor devices,GaN(gallium nitride)power devices are very suitable for high-temperature,high-pressure,high-power applications due to their superior material characteristics.Because the channel of the device kept turned on without extra turn-on voltage due to the twodimensional electron gas(2DEG)generated by the polarization effect,the GaN-based high-speed electron mobility transistors(HEMTs)is usually normally-off type.The misstarting caused by noise in the actual circuit and the additional power consumption caused by turning off the device with negative voltage promotes the need for normally-off devices,of which p-GaN HEMT devices are the research hotspots.There are still many factors that influence the large-scale applications of p-GaN HEMT devices,out of which stress is important.However,there is no systematic study on the effect of stress on the electrical characteristics of p-GaN HMET devices.Therefore,the impact of stress on the electrical performance of p-GaN HEMT devices is discussed in this paper.Firstly,the model of p-GaN HMET devices is derived theoretically;then the effect of stress on device reliability is studied.The main contents include the following parts:First,based on the energy band structure,the relationship between the device threshold voltage,the channel electron concentration,and the biaxial strain and stress relaxation of the barrier layer is derived;and the stress model of the p-GaN normally-off HEMT device is derived.With the help of Silvaco simulation software,the electrical characteristics of the gate Schottky contact p-GaN HEMT device were studied,and the effects of the p-GaN capping layer doping concentration,gate metal work function,and GaN buffer layer trap concentration on the DC performance are analyzed.The simulation results show that as the doping concentration of the p-GaN layer increases,the conduction band at the heterojunction will move up and a higher threshold voltage can be obtained.As the gate work function increases,the transfer characteristic curve will shift to the left,and the threshold voltage tends to decrease.As the concentration of acceptor traps in the GaN layer increases,the electrons of the channel are more likely to tunnel into the AlGaN barrier layer,resulting in a decrease in the concentration of electrons in the channel and lowering the drain saturation current.Secondly,the effect of external biaxial strain on the barrier layer(when the barrier layer is in a stress relaxation state)is studied.The simulation results show that when the biaxial strain applied to the barrier layer changes from-1 to 1(%),the threshold voltage can be increased by 0.145 V for each additional 1%;the drain saturation current can be increased by 0.075A;the breakdown voltage is reduced by 9.2V.Then,under the premise of fixing the Al composition in the AlGaN barrier layer,when the stress relaxation of the barrier layer is adjusted from 0.2 to 0.4,the threshold voltage will be decreased by 0.075V;the drain saturation current will be decreased by 0.06A;the breakdown voltage can be increased by 8.9V.By introducing a local biaxial strain to the gate edge of the drain side,the breakdown voltage can be increased from 802 V to 820 V without affecting other DC characteristics of the device.Finally,based on the stress model,the influence of the non-uniform strain of the barrier layer due to the inverse piezoelectric effect or the passivation layer on the electrical characteristics of the device was studied.The results show that the biaxial strain of Region-G(gate part)has the greatest influence on the threshold voltage and drain saturation current of the device.When the biaxial strain changes from-1(%)to 1(%),the threshold voltage can be increased by 8 %,The drain saturation current can be increased by 5%,and Region-GD(gate-drain part)has the greatest influence on the breakdown voltage of the device.When the biaxial strain changes from-1(%)to 1(%),the breakdown voltage will be reduced by 2%.Then,the influence of strain on the DC electrical characteristics of the gate ohmic contact device is analyzed.The simulation results show that the threshold voltage can be obtained by applying biaxial strain to the barrier layer,and the saturation current of the drain is increased,but the breakdown voltage is reduced.