Normally‐on/off AlN/GaN high electron mobility transistors

We report on the novel normally-on/off AlN/GaN high electron mobility transistors (HEMTs) grown by plasma-assisted molecular beam epitaxy. With simple oxygen exposure, the threshold voltage can be tuned from -2.76 V to +1.13 V depending on the treatment time. The gate current was reduced and current-voltage curves show metal-oxide semiconductor diode-like characteristics after oxygen plasma exposure. The extrinsic transconductance of HEMTs decrease with increasing oxygen plasma exposure time due to the thicker Al oxide formed on the gate area. The unity current gain cut-off frequency, fT, and maximum frequency of oscillation, fmax, were 20.4 GHz and 36.5 GHz, respectively for an enhancement-mode HEMT with the gate dimension of 0.4 × 100 μm2. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)