GaN-based MESFETs and DC-MOSFETs

We present experimental results, which show that GaN MESFET and MOSFET technology can demonstrate the performance comparable to that of GaN-AlGaN HFETs for highly doped narrow channel devices. The device structures were grown by low-pressure MOCVD over [0001] sapphire substrates. PECVD 10-15 nm thick SiO/sub 2/ was used as an insulating layer for doped channel GaN-based MOSFETs. The threshold voltage for MESFETs and DC-MOSFETs ranged from 1.5 V to 10 V, and from 4 V to 20 V, respectively. The maximum drain currents up to 300 mA/mm and transconductances up to 60 mS/mm were measured for 100 /spl mu/m wide devices. The Schottky gate turn-on voltage for MESFET devices was close to 1 V, which is approximately two times lower than for AlGaN-GaN HEMTs. The gate leakage current in DC-MOSFETs was more than three orders of magnitude lower than in MESFETs. The long-channel GaN MESFETs that we fabricated exhibited a cut-off frequency-gate length product of 11.6 GHz-/spl mu/m. This number is comparable with the 16.4 GHz-/spl mu/m value demonstrated recently for AlGaN-GaN MOS-HFETs on SiC substrates and 18.2 GHz-/spl mu/m demonstrated for AlGaN-GaN HFETs on sapphire substrates. The cut-off frequency improves with increasing channel doping. Experimental results and model predictions show that GaN MESFETs and GaN DC-MOSFETs might find applications for power devices in X-band and above.