Research On Process And Novel Structure Of AlGaN/GaN Recessed-gate MISHEMT Device

With the development of semiconductor technology,silicon semiconductor technology has been developing continuously for decades,and has become the most mature technology in the semiconductor technology,but the silicon device is close to the theoretical limit in the field of power semiconductor.So it is very important to explore novel semiconductor materials and devices.GaN material has great potential for having larger band gap,higher breakdown electric field,greater electron mobility,faster electron saturation rate and can work can work well at higher temperatures compared with silicon material.Conventional AlGaN/GaN HEMT devices are depletion-mode devices because AlGaN/GaN heterojunction has two-dimensional electron gas with high concentration,How to change depletion-mode device to enhancement-mode device is a very important direction in the research field of GaN devices,this paper is dedicated to the research process and novel structure of AlGaN/GaN recessed-gate device.The main contents of this paper include:(1)The effects of different size of the device and the recessed gate depth on AlGaN/GaN HEMT devices,and the influence of different recessed gate depth,gate dielectric materials and gate dielectric thickness on AlGaN/GaN recessed-gate MISHEMT devices are studied by simulation.The results show that the saturation drain current and transconductance(gm)of HEMT devices decrease with the increase of the drain source distance,the gate length and the gate leakage distance.The threshold voltage(VT)and gm of MISHEMT devices increase with the recessed gate depth increase.And the VT increases with the increases of gate dielectric thickness and the decreases of dielectric constant increases.However,the gm decreases with the increases of gate dielectric thickness and the decreases of dielectric constant increases.(2)The technology of dry etching and wet etching for the fabrication of recessed gate were studied.By using the method of wet etching after thermal oxidation tcombined with dry etching,the recessed gate with a certain depth is obtained.And the RMS(root mean square)roughness of the recessed gate surface is only 0.198 nm.A new method for the fabrication of recessed gate by means of gate sinking was presented in this paper.(3)An enhanced-mode MISHEMT device with a VT of 3.2V was fabricated by using dry etching to achieve recessed gate,and an enhanced-mode MISHEMT device with a VT of 3.5V was fabricated by combining wet etching with dry etching to achive recessed gate.The wet etching made the threshold voltage hysteresis decreases from 0.7V to 0.1V.(4)A novel structure of AlGaN/GaN HEMT is fabricated by using gate sinking to achieve recessed gate,the VT is adjusted from-4.3V to-3V.