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)Si_(3)N_(4) on the barrier layer,and the degree of decrease in sheet resistance R_(sh) is dependent on the Si_(3)N_(4) thickness.We choose 13 nm Si_(3)N_(4) as the gate insulator to decrease gate current and to improve the threshold voltage of devices.With selective etching of the passivation Si_(3)N_(4) 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 810 mA/mm and 190 mS/mm,respectively.The devices show a wide operation range of 4.5 V.