Intellectual Merit: A lack of sufficient knowledge on traps, which are present in bulk, at surface, and at heterojunction interfaces is one of the main obstacles for the progress of high-power III-nitride compound semiconductor microwave devices. The proposed basic research is aimed at identifying the traps (i.e. finding their energy in the bandgap with respect to a band edge, their capture cross-section and origin), which profoundly effect the device characteristics such as: drain current collapse, gain compression, gate and drain lag, frequency dispersion of transconductance and drain conductance of MBE-grown III-nitride GaN MESFETs, AlGaN/GaN HEMTs, and AlInGaN/InGaN HEMTs. Identification of traps in these device structures is very important for optimizing the device design, growth, and processing conditions and consequently for maximizing high-power microwave performance. The AlInGaN/InGaN HEMTs are projected to yield record power performance once their design, growth, and processing conditions are optimized.
A series of sets of samples will be fabricated, with only one growth/processing condition (growth temperature, surface passivation etc.) or a device design feature (alloy composition, layer thickness etc.) varied in each set keeping all the remaining conditions same. All devices will be characterized first for their DC, and pulsed drain current-drain voltage-gate voltage performance including the gate-lag and drain-lag; output power, gain and power added efficiency performance as a function of input power at various bias conditions and frequencies; and then for traps in the device structure. The traps will be studied by drain-current and gate capacitance deep level transient spectroscopy, photoionization spectroscopy, and transconductance and output-admittance frequency dispersion measurements. Energy location of the traps with respect to the band edges, their capture cross-section and concentration will be determined by analyzing the experimental data. Trap measurements also will be performed on devices subjected to short and long-term bias stress. For each set of samples the device performance and trap measurements results, and the extent of change in growth/processing/design parameter in that set of samples will be correlated to identify the trap/traps responsible for deterioration of a specific device performance quantity; origin of the trap/traps; and the growth, processing and design conditions, which can minimize the trap concentration.
Broader Impacts: The proposed work is a careful, detailed basic research, which requires careful experimentation and analysis. Results of this work will have an immediate impact on advancing high-power microwave III-nitride compound semiconductor device technology, by providing optimum growth and processing conditions, and device design features required for obtaining maximum device performance.
This work will be performed in collaboration with III-nitride device research group at Naval Research Laboratory (NRL). The PI has been successfully collaborating with NRL scientists, for more than 15 years, on NSF supported projects. This project offers an excellent opportunity for students for gaining hands-on experience on using state-of-the-art device growth, processing and characterization equipment in a prestigious government laboratory on an important research topic. This experience prepares students well for pursuing careers in industry and government. Both graduate and undergraduate students will participate on the proposed research.