Failure Mechanism Research Of AlGaN/GaN HEMT Under Strong-electrical Stresses

AlGaN/GaN high-electron-mobility transistors (HEMTs) are of much value formicrowave power and high-voltage applications because of the high break-down feld,thermal conductance and also saturation velocity in group-III nitride alloysemiconductors. However, the reliability problem is one of the issues that remain to besolved in order to move toward commercially available devices.In this thesis, the investigation about the failure mechanism of AlGaN/GaNHEMTunder strong-electrical stresses is performed, starting from the potential factors ofconstraining device reliability. The main research results are summarized as follows.A complete set of AlGaN/GaN HEMT process flow is given and AlGaN/GaNHEMTs with good performance are produced on SiC substrate. Then the high-fieldstress degradation behaviors of GaN-based device are analyzed. Device degradationeffects under two typical stress conditions are studied in particular, and then, thedegradation rule of the device parameters with stress time is obtained. The thresholdvoltage shows a positive shift in the early stress, then turns to negative shift. Thenegative shift of threshold voltage seems to have a long recovery time. A model relatedwith the balance of electron trapping and detrapping induced by shallow donors anddeep acceptors is proposed to explain this degradation mode.A methodology is presented to study trapping characteristics in GaN HEMTswhich is based on current-transient measurements. Its uniqueness lies in it is suitable forreliability study of electric be long-term use of integration experiment. The details of themeasurement and analysis procedures are presented. With this method, we haveresearched the trapping and detrapping dynamics of GaN HEMTs. In particular, weexamined layer location and energy level. We have comfirmed several traps inside theAlGaN barrier layer or at the surface close to the gate edge and in the GaN buffer.