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 2nm/5nm/1.5nm-thin GaN/AlGaN/AIN 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 Rsh 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 Id,max and the maximum transconductance are 810mA/mm and190mS/mm,respectively.The devices show a wide operation range of 4.5 V.