Research On Current Collapse Of AlGaN/GaN HEMT

Due to the excellent properties of GaN,such as wide band gap,high electron mobility,high saturation speed and high breakdown electric field,GaN-based High Electron Mobility Transistors(HEMTs)deliver highly promising performance in the fields of high power,radio frequency,and high temperature applications.However,they are still subject to the influence of current collapse which strangle its promotion.Based on TCAD,the characteristics and current collapse of AlGaN/GaN HEMT are studied in this dissertation.Firstly,the properties of GaN and the characteristics of GaN HEMT are introduced.The progress and existing problems at present research are analyzed at the same time.Secondly,the 2DEG in AlGaN/GaN heterojunctions and its influencing factors are studied,and the mechanism of AlGaN/GaN HEMT is analyzed.The output characteristics,transfer characteristics and transconductance characteristics of the device are studied.Besides,the effects of barrier thickness and Al fraction on 2DEG concentration,mobility and characteristics are analyzed.Then,DC method and transient pulse method are investigated to simulate the current collapse.The influence of buffer layer trap concentration and its energy level on the current collapse are also discussed at the same time.Research result shows that the peak electric field is a key factor in the current collapse of the AlGaN/GaN HEMT.In order to minimize the current collapse,the value of this electric field needs to be reduced.Finally,a new AlGaN/GaN HEMT with a grooved AlGaN barrier layer is proposed.The electric field peak is reduced and the current collapse effect is improved by the grooved barrier layer.Research result shows that the inhibition effect of the new structure on current collapse is increased by at least 22.30%.The optimized design of the length and height of the groove in the new structure shows that when the length of the groove is 0.8μm-1.2μm and the height is 10nm-13 nm,the current collapse of HEMT and its performance are significantly improved.