Sidegating effect of GaN MESFETs grown on sapphire substrate

A GaN metal semiconductor field effect transistor (MESFET) with 2 μm gate-length and 200 μm gate-width has been fabricated on a sapphire substrate. The electron mobilities for the n-GaN layer were 585 cm²/V·s with a carrier concentration of 1.1×10 ¹⁷ cm^-3 at 300 K, and 1217 cm²/V·s with 2.4×10¹⁶ cm^-3 at 77K. A GaN MESFET showed a transconductance of 31mS/mm and a drain-source current of 288 mA/mm. The sidegating effect was observed when the negative bias was applied to the sidegate electrode