We have studied the activation of Si ion implanted un-and Mg-doped gallium nitride (GaN) for the fabrication of reduced surface field (RESURF) metal-oxide-semiconductor field-effect transistors (MOSFETs). By annealing at 1260 C for 30 s by using rapid thermal annealing (RTA), the activation ratios of un-and Mg-doped GaN with Si doses of 3 Â 10 15 cm À2 were $100 and 73%, respectively. These values are sufficient for application some semiconductor devices. Hardly any diffusion of the Si atoms implanted in GaN was observed by secondary ion mass spectrometry (SIMS). The activation ratio between unand Mg-doped GaN was markedly different at low doses. The cause of the difference appears to be Mg compensation in GaN. In addition, we fabricated GaN MOSFETs with ion implanted RESURF zones. We also monitored the field-effect transitor (FET) operation and high breakdown voltage of the GaN MOSFETs. The threshold voltage was +2 V. An enhancement mode operation and a breakdown voltage higher 1500 V at a RESURF length of 20 mm were achieved.
We investigated normally off operation GaN metal-oxide-semiconductor field effect transistors (MOSFETs). The drain current of GaN MOSFETs with a gate width of 1 mm increased from 0.004 to 0.1 A by which the channel length decreased from 100 to 2 mm. However, the on-resistance was increased by shortening a channel length. In addition, the drain current of GaN MOSFETs with the channel length of 4 mm was increased from 0.08 A to more than 2.2 A, by which the channel width was increased from 1 to 16 mm. As a result, we achieved normally off operation GaN MOSFETs with the highest operation temperature of 250 C. The drain current was 2.2 A at V g ¼ þ14 V. The threshold voltage (V th ) was +3 V.
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