Degradation Mechanism And Suppression Methods Of AlGaN/GaN HEMT

Gallium nitride material has superior physical properties, such as wide bandgap, high saturation electron drift velocity and high thermal conductivity. It has great potential for application in high temperature, high power and microwaves fields. As a representative of GaN based device, AlGaN/GaN HEMT is widely used in space fields. However, AlGaN/GaN HEMT is usually applied under high voltage and radiation environment. The reliability of the device becomes a serious question. In this thesis, both experimental and theoretical studies on electrical stress degradation and proton radiation damage in AlGaN/GaN HEMT have been conducted.First, the degradation of AlGaN/GaN HEMT under electrical stress was studied. Three experiments were designed to independently analyze the main common three degradation mechanism models, such as channel hot electron model, gate electron injection model and inverse piezoelectric effect model. The floating-gate stress experiment was used to study channel hot electron effect, a bias voltage is applied between drain and source, in order to achieve an independent effect of channel hot electron injection degradation. The floating-source stress experiment was used to analyze gate electron injection mode, a bias voltage is applied between drain and gate, in order to gain an independent effect of gate electron injection degradation. The inverse piezoelectric effect model was studied by using a short-step stress test, and a step-increasing bias voltage with a short period between drain and gate was applied, in order to analyze an independent effect of inverse piezoelectric degradation. At last, some degradation suppression methods were presented .The proton radiation effect of the AlGaN / GaN HEMT was investigated by comparing IV characteristics. A acceptor–defect model was presented to explain the degradation of proton-radiation. Then AlGaN/GaN HEMT with AlGaN buffer layer was designed and fabricated to suppress the degradation, because AlGaN bake-barrier can block the injection of channel hot eletron and AlGaN has a higher property to withstand proton radiation. The experamental results show that the improved device has a higher property to withstand proton radiation.