| Summary: | 碩士 === 國立清華大學 === 材料科學工程學系 === 93 === ABSTRACT
In this thesis, recent results on GaAs MESFET and MOSFET were discussed; including MBE growth of GaAs:Si channel layer, deposition of Ga2O3(Gd2O3), device processing and characteristics. For the fabrication of n-channel GaAs MESFET, the planar processing steps were adopted. The device of 1 x 50 �慆2 shows a high transconductance gm of 180mS/mm and a maximum current density of 160 mA/mm (at Vg=0.5V and Vd=4V). The effective channel-layer thickness of the device, estimated from the measured saturation current (Id,sat) and pinch-off voltage (Vp), is thinner than the nominal grown channel layer. The difference is mainly caused by the gate depletion, with a small portion of that being influenced by the defects- induced depletion or electrical measurement discrepancy.
A depletion-mode MOSFET, with a size of 1.6 x 100 �慆2, Ga2O3(Gd2O3) 480 Å thick as a gate oxide, and a channel 1000 Å thick of a 4E17 cm-3 doping, shows a maximum current density of 330 mA/mm (at Vg=4V and Vd=4V) and a maximum gm of 130 mS/mm. The gate bias-voltage can be up to 4V, raising large accumulation current, which indicate the high quality of the interface of the oxide and the channel. The oxide breakdown field strength is about +6MV/cm for the positive sweep and at least -7MV/cm for the negative sweep. An unsymmetrical behavior in the gate leakage (from gate to source) is probably caused by the damage of gate dielectric during the processing, which has caused high gate leakage currents. The leakage, however, has been reduced with a forming gas annealing.
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