Recent developments in materials, architectures and processing of AlGaN/GaN HEMTs for future RF and power electronic applications: A critical review

This article critically reviews the architectural novelties, emerging materials (substrate, buffer, barrier & contact materials), technological advancements, processing techniques adopted, geometrical influences & challenges during fabrication, and driving reliability aspects of AlGaN/GaN high electron mobility transistors (AG-HEMTs) that are gaining rapid & progressive adoption as a semiconductor device of outrival choice for high power & RF frequency applications, due to exceptional material-properties of the heterostructure. The device has matured in the last decade reaching ID(drain current) up to 1940 mA/mm, gm(transconductance) up to 556 mS/mm, fT(cut-off frequency) up to 200 GHz, fmax (maximum oscillation frequency) up to 308 GHz and Vbr (breakdown voltage) up to 2900 V. The impact of various barrier and buffer materials, contact technologies, annealing process and temperature, passivation and etching techniques on the RF & DC performance of AG-HEMTs is presented in this paper. An assessment of the influence of irradiation effects, underlying degradation mechanisms, and associated reliability aspects is also included, which helps to exploit the potential of AG-HEMTs in space technology. AG-HEMTs stood a step ahead of conventional devices due to their exceptional material properties and enjoy a diverse range of applications like radar, satellite communication, telecommunication, sensors, space and aeronautics, microwave & millimeter-wave devices, and wireless infrastructures and many more.