Research And Design Of 600V GaN HEMT Device

As the third generation of semiconductor materials, gallium nitride (GaN) has advantages of wide energy band gap, large critical breakdown electrical field and high electron saturation velocity. Also, AlGaN/GaN hetero structure will generate two-dimensional electron gas (2DEG) of high density. All of these advantages make GaN HEMT be an attractive power device. However, conventional GaN HEMT is a depletion mode device and the breakdown voltage is low because of its large leakage current in GaN, so it is necessary to study enhancement mode GaN HEMT with high breakdown voltage for the application in power switch field.This thesis aims to design a 600V enhancement mode GaN HEMT with superior performance. Firstly, p-GaN gate GaN HEMT is adopted as the basic structure, the influences of the structure (including p-GaN layer, AlGaN barrier layer, distance between gate electrode and drift electrode, and AlGaN buffer layer) upon the tranfer characteristics, forward conduction characteristics, breakdown characteristics and capacitance characteristics have been analyzed by SILVACO simulations. In addition, because of the low threshold voltage of p-GaN gate GaN HEMT, a new GaN HEMT with buried insulated layer has been proposed to make the threshold voltage increased by 2.14 times.Besides, the current collapse effect of 600V enhancement mode GaN HEMT under high drain votage which is induced by defects in buffer layer has also been investigated. The study indicats that the electron will be injected into buffer layer and caparured by defects under the strong electric field besides gate, wihich is the primary cause of current collapse effect. Moreover, the current collapse will aggravate with high density and deep energy level defects. The number of electron injected into buffer layer has to be controled to decrease current collapse, so a new GaN HEMT with p buried layer is proposed, which can reduce the decrease of drain current from 11.0% to 5.12% and significantly restrain the current collapse effect.