Gallium nitride MOSFETs for high voltage switching applications

Gallium nitride (GaN) is of interest for high-voltage and high-temperature devices due to its large bandgap (3.4 eV) and corresponding low intrinsic carrier concentration (ni ≈ 10-10 cm-3) and high critical electric field (3 MV/cm). This work examines the capabilities of GaN lateral accumulation-mode MOSFETs for logic and high-voltage switching applications.; High-voltage, depletion-mode, lateral RESURF (REduced SURface Field) n-channel MOSFETs in GaN were designed using analytical expressions and two-dimensional numerical models for a target breakdown voltage of ≈450 V. These lateral GaN MOSFETs incorporate dopants in the RESURF region to support high lateral fields, unlike GaN HFETs which rely on polarization charges and a large density of surface states.; Self-aligned GaN MOSFETs on the GaN/Sapphire sample were normally-off with a pinchoff voltage of +4 V and a specific on-resistance of 2.4 mO-cm 2 for a gate length of 2 mum. Non-self-aligned devices on the GaN/AlGaN/SiC epilayer structure were normally-on with a pinchoff voltage of -3 V, and a subthreshold slope of 360 mV/decade, caused by a front-gate interface-state density of 1.5 x 1012 cm-2eV -1 and a back-gate Dit of 5.5 x 1011 cm-2eV-1.; GaN RESURF MOSFETs on the SiC substrate with a 9 mum RESURF length have a breakdown voltage of 180 V and a specific on-resistance of 150 mO-cm 2. Breakdown of devices on SiC is limited by tunneling through the AlGaN/6H-SiC junction.; Separation of the on-resistance components of the fabricated devices shows that the channel resistance does not dominate the on-resistance; instead, the source and drain resistance dominates at breakdown voltages below 600 V, and the RESURF region resistance dominates at higher breakdown voltages. Use of the self-aligned process reduces the source/drain resistance by a factor of seven to 120 O-mm. (Abstract shortened by UMI.)...