Enhanced Gan High Electron Mobility Transistor

AlGaN/GaN high electron mobility transistors (HEMTs) show a high prospective in Microwave and power amplification with high bandgap, thermal conductivity and saturation mobility, while the reliability is up in the air and some trap mechanism is unclear until now. At the same time, in many applications, however, the employment of enhancement-mode (E-mode) GaN HEMTs is highly desirable for the simple single-polarity voltage supply and digital IC operation.In this thesis, trap behaviors in AlGaN/GaN heterostructures were characterized by the means of capacitance-voltage (C-V) technique for samples grown on sapphire and SiC substrates. Fluorine plasma treatment was carried out with appropriate time and power for further identification. The VGa-related defects in (Al)GaN bulk layers were responsible for the frequency-dependent capacitance dispersion in pinch-off region, while the surface status influenced the capacitance dispersion in pinch-on region directly.According to the flexible fluorine plasma treatment, GaN HEMTs are prepared with different threshold voltage and enhancement-mode GaN HEMT devices are realized with threshold voltage of 0.35V. And the enhancement-mode device exhibits a maximum output current (ID,max) of 650mA/mm with Vgs=4V. The current-gain cut-off frequency (fT) and maximum oscillation frequency (fmax) shows any regression after treatment as about 10.3GHz and 12.5GHz. And then E-mode GaN HEMTs with a gate length of 0.35μm are fabricated on S-I-SiC substrate. A fT of 40 GHz and fmax of 91 GHz are achieved. At 18 GHz, the fabricated enhancement-mode device exhibits a maximum continuewave output power density of 3.65 W/mm and a maximum PAE 42%. A device simulation is also carried out with fluorine treated as acceptorlike trap level and also increased the Schottky barrier, which is taken as a simple explanation for the threshold voltage affected by fluorine plasma treatment.