Effect of gate orientation on dc characteristics of Si-doped, nonpolar AlGaN/GaN metal-oxide semiconductor high electron mobility transistors

Sc 2 O 3 / AlGaN / GaN metal-oxide-semiconductor (MOS) high electron mobility transistors were fabricated on ( 11 2 ¯ 0 ) a -plane, Si-doped epitaxial layers grown by metal organic chemical vapor deposition on ( 1 1 ̱ 20 ) r -plane sapphire substrates. The gate finger direction was varied from parallel to the in-plane c -axis [0001] to the m -axis [ 1 0 1 ̱ 0 ] direction perpendicular to the observed striations in surface morphology. The [0001] gate devices show lower drain-source current, mobility, and transconductance than their [ 1 0 1 ̱ 0 ] counterparts, with a systematic dependence on gate finger direction. The symmetrical gate current-voltage characteristics and low gate current ( ∼ 3 × 10 − 9 A at ±5 V) confirm the effectiveness of the MOS gate, which is an attractive approach for these structures containing heavily Si-doped AlGaN.