A new device-first low-temperature bonded gallium nitride (GaN)-on-diamondhigh-electronic mobility transistor (HEMT) technology with state-of-the-art,radio frequency (RF) power performance is described. In this process, thedevices were first fabricated on a GaN-on-silicon carbide (SiC) epitaxial waferand were subsequently separated from the SiC and bonded onto ahigh-thermal-conductivity diamond substrate. Thermal measurements showed thatthe GaN-on-diamond devices maintained equivalent or lower junction temperaturesthan their GaN-on-SiC counterparts while delivering more than three-times higherRF power within the same active area. Such results demonstrate that the GaNdevice transfer process is capable of preserving intrinsic transistor electricalperformance while taking advantage of the excellent thermal properties ofdiamond substrates. Preliminary step-stress and room-temperature, steady-statelife testing shows that the low-temperature bonded GaN-on-diamond device has noinherently reliability limiting factor. GaN-on-diamond is ideally suited towideband electronic warfare (EW) power amplifiers as they are the most thermallychallenging due to continuous wave (CW) operation and the reduced power-addedefficiency obtained with ultra-wide bandwidth circuit implementations.

In an effort to investigate the stability of the surface and hetero-interface of AlGaN/GaN HEMTs during high temperature device processing steps, AlGaN/GaN HEMT samples were subjected to temperatures from 650°C to 1150°C for a period of 30 seconds prior to processing. Hall and photoluminescence measurements were performed on samples before and after temperature stressing. The samples annealed at 700°C and 1150°C were then processed, and electrical parametric data were collected during and after processing. Large increases in HEMT Schottky gate diode reverse leakage current are observed at higher pre-process annealing temperatures, while the low-field mobility decreases.