Research On Normally-off Power Devices Based On P-GaN Gate

As the third-generation semiconductor material,GaN has excellent characteristics such as high critical breakdown electric field,large band gap,and fast electron saturation drift speed.At the same time,due to the polarization effect,GaN can form a two-dimensional electron gas channel with high area density and high mobility with materials such as AlGaN,so that AlGaN/GaN HEMT can simultaneously obtain high breakdown voltage and low on-resistance.It is considered to be the most promising power device.However,due to the lattice mismatch between GaN and AlGaN,reliability issues exist in AlGaN/GaN HEMT devices.In addition,AlGaN/GaN HEMT also has problems such as the electric filed crowding effect and the buffer layer leakage current,which makes the device breakdown in advance and fail to give full play to the high withstand voltage characteristics of GaN materials.Based on the above problems,this paper proposes two types of enhanced GaN-based power devices with p-type gates,and studies the mechanisms,structural parameters,and electrical characteristics.1.In order to solve the reliability problem of traditional AlGaN/GaN HEMT devices,the InAIN barrier layer with an In composition of 17%was used instead of the AlGaN barrier layer.Due to the strong spontaneous polarization effect of the InAlN/GaN heterojunction,a channel with a high concentration of 2DEG is finally achieved,which greatly improves the current density of the device.In order to improve the breakdown voltage of InAlN/GaN HEMT devices,the high relative dielectric constant passivation layer technology was studied,and the TiO2 passivation layer was used instead of the traditional Si3N4 passivation layer.The final design of the p-GaN gate InAlN/GaN HEMT device has an on-resistance of 2.6 mQ·cm2,a saturation output current of 1.22 A/mm,and a breakdown voltage of 1026 V.Compared with the p-GaN gate AlGaN/GaN HEMT device,the p-GaN gate InAlN/GaN HEMT device has reduced on-resistance by 23%,the saturation output current has increased by 52.5%,and the breakdown voltage has increased by 31.5%.2.Aiming at the shortcomings of traditional lateral AlGaN/GaN HEMT devices:current collapse effect,difficult to increase breakdown voltage,and large size,the vertical GaN-based power devices were studied.Based on the superjunction structure vertical GaN-based power device proposed by the researchers,the gradient doping superjunction vertical GaN-based power device is proposed,which can effectively improve the trade-off relationship between breakdown voltage and on-resistance.The designed new device has a breakdown voltage of 2610 V and an on-resistance of 2.81 m?·cm2.Compared with the superjunction structure vertical GaN-based power device,the breakdown voltage of the new device has increased by 30.5%,while the on-resistance has been reduced by 11.2%.