Characteristics of a GaN metal semiconductor field-effect transistor grownon a sapphire substrate by metalorganic chemical vapor deposition

Electron mobilities of an n-GaN layer on a sapphire substrate grown by meta lorganic chemical vapor deposition were 585 and 1217 cm(2)/V.s with electro n carrier concentrations of 1.1 x 10(17) and 2.4 x 10(16) cm(-3) at 300 and 77 K, respectively. A high current level of 281 mA/mm and a large transcon ductance (g(m)) of 33 mS/mm have been achieved for a GaN metal semiconducto r field-effect transistor (MESFET) with a gate length of 2 mu m and a width of 200 mu m at 25 degrees C. The GaN MESFET at high temperature showed deg raded characteristics: low g(m), gate leakage and poor pinch-off. However, the GaN MESFET at 25 degrees C, measured again after measurement at 400 deg rees C, showed the initial characteristic in spite of gate leakage. The GaN MESFET exhibited the sidegating effect, which was thought to be caused by the deep level in the undoped GaN layer beneath, the channel layer. The uni formity of thr sheet resistance seems to be insensitive to the high disloca tion density in the GaN layer.