An Ultrathin AlGaN Barrier Layer MIS-HEMT Structure for Enhancement-Mode Operation

A GaN-based enhancement-mode (E-Mode) metal-insulator-semiconductor (MIS) high electron mobility transistor (HEMT) with a 2 nm/5 nm/1.5nm-thin GaN/AlGaN/AlN barrier is presented. We find that the formation of a two-dimensional electron gas (2DES) in the GaN/AlGaN/AlN/GaN heterostructure can be controlled by the presence of the plasma-enhanced chemical-vapor deposition (PECVD) Si₃N₄ on the barrier layer, and the degree of decrease in sheet resistance R_sh is dependent on the Si₃N₄ thickness. We choose 13 nm Si₃N₄ as the gate insulator to decrease gate current and to improve the threshold voltage of devices. With selective etching of the passivation Si₃N₄ under gate and over fluorine plasma treatment, the MIS-HEMT exhibits a high threshold voltage of 1.8 V. The maximum drain current I_d,max and the maximum transconductance are 810 mA/mm and 190 mS/mm, respectively. The devices show a wide operation range of 4.5 V.