Wide Bandgap Semiconductor Materials and Devices

The research project proposed to DARPA in this document will investigate novel device structures for maximizing the linear power density of microwave and mmwave GaN HFET transistors by examining innovative device structures to improve thermal management. These innovative structures will include device layouts, epitaxial layer structures, and device fabrication processes. This investigation will involve theoretical evaluation of thermal and EM characteristics of innovative structures using state-of-the-art simulation tools. Innovative device structures, including both one- and two-dimensional arrays will be investigated to determine the most effective in minimizing the operating temperature differences of transistor elements in these arrays. EM simulations will be carried out on the device structures to assess limitations on operating frequency. After a clear assessment of the thermal management and operating frequency capability, innovative approaches to minimizing any limitations on operation at mmwave frequencies will be investigated, including novel biasing schemes. The primary objective of this Phase I proposal is to define device structures which afford the maximum linear power density at both microwave and mmwave frequencies for GaN HFET device technology. Phase I activities will be followed by experimental evaluation of the most promising approaches at L-, X-, and V-band for GaN HFET power transistors.