Progress and challenges of GaN-based microwave HEMTs, amplifiers and novel spin

AlGaN/GaN high electron mobility transistors are extremely promising for microwave power generation from S band up to Ka band. The list of potential applications includes commercial wireless base stations, phased array radar, satellite-based communication systems, digital radio and power flow control. Results to date show excellent power performance, with densities>10W.mm_-1 and high efficiency. In this paper we give a brief overview of the field, report on use of single-crystal oxide layers to provide effective surface passivation for HEMTs and then discuss some new spin-based GaN devices that may have a role in expanding the functionality of nitride electronics and photonics.