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

Electron mobilities of an n-GaN layer on a sapphire substrate grown by metalorganic chemical vapor deposition were 585 and 1217 cm²/V·s with electron carrier concentrations of 1.1 × 10¹⁷ and 2.4 × 10¹⁶ cm^-3 at 300 and 77 K, respectively. A high current level of 281 mA/mm and a large transconductance (g_m) of 33 mS/mm have been achieved for a GaN metal semiconductor field-effect transistor (MESFET) with a gate length of 2 μm and a width of 200 μm at 25°C. The GaN MESFET at high temperature showed degraded characteristics: low g_m, gate leakage and poor pinch-off. However, the GaN MESFET at 25°C, measured again after measurement at 400°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 uniformity of the sheet resistance seems to be insensitive to the high dislocation density in the GaN layer.