.algan / Gan Hemt Current Collapse Mechanism Study

Wide bandgap semiconductors are extremely attractive for the gamut of power electronics applications from power conditioning to microwave transmitters for communications and radar. Of the various materials and device technologies, the AlGaN/GaN high-electronmobility transistor (HEMT) seems the most promising.However, the performace of AlGaN/GaN HEMT is limited for the reasons related to material, process, and reliability, such as Ohmic contact and current collapse.In this thesis, the basic characteristics of AlGaN/GaN heterojuntion have been analyzed. Then fabrication of AlGaN/GaN HEMT and current collapse are investigated. Ti/Al/Ni/Au ohmic contact to low doping GaN film is studied. The contact resistance reduces to the minimum level of 6.6×10-6Ω.cm2 after annealing for 1min at 900℃;The deposition of Ni/Au on AlGaN is demonstrated for a good Schottky contact performance, the leakage current is at a low level of 10-8A. then, AlGaN/GaN HEMTs without mesa isolation and passivation is formed.Base on the measurement of pulse output characteristics, the origin of current collapse is discussed. The current collapse is attributed to surface states, which traps electrons from gate, then the surface with a negative potential makes the channel depleted, follows the current getting small. Meanwhile, gate lag results show that the recovery time of surface potential is dominated by relaxation time of lossy dielectric on surface. At last, comparison of gate-drain and gate-source surface states effects on current collapse is made, saturation of pulse output characteristics is attributed to gate-source surface states, while knee voltage increasing to gate-drain surface states.