Study Of AlGaN/GaN HEMT Characteristics And Suppressing Current Collapse

GaN has direct and wide bandgap, high electron saturation velocity, high breakdown field, high thermal conductivity, chemical stability, radiation resistance and so on. These fundamental electronic properties make GaN an ideal material for high-temperature, high-power and high-frequency devices. GaN High Electron Mobility Transistor is based on AlGaN/GaN heterostructure. AlGaN/GaN HEMT is of great interest for its potential in high power microwave devices and high temperature applications. But it has not realized commercialism, because AlGaN/GaN HEMT has current collapse which seriously impacts on device performance. It's necessary to study Two-Dimensional Electron Gas and suppress current collapse to enhance performance of AlGaN/GaN HEMT. In the dissertation, it is based on polarization effect of AlGaN/GaN to study HEMT devices in detail.The major work and achievements are listed.(1)Introduction of physical model of polarization effect studies change of band, Two-Dimensional Electron Gas density, electric field and other characteristics. This can accurately reflect the relationship between AlGaN barrier layer thickness,Al content, Schottky contact, ohmic contact and output characteristics;(2)Characteristics of different HEMT structures are studied. Introduction of GaN layer will reduce output current; Double heterojunction structure can increase output current, to change thickness of double heterostructure layer can increase or decrease output current; Wide band gap AlN barrier layer can improve barrier height and increase output current; Narrow band gap InGaN is not conducive to raising 2DEG density and output current;MOS gate structure can reduce gate leakage current without affecting drain and source output current;(3) Current collapse seriously affects application of HEMT devices.Through studying its formation mechanism and method of suppressing current collapse,a new method of suppressing current collapse is proposed, which is introduction of p-type doping in the upper part of the AlGaN layer.This layer will form pn junction with the layer in the lower part. Simulation results show this method can effectively reduce current collapse.