Investigation and characterization of aluminum gallium nitride/gallium nitride device structures and the effects of material defects and processing on device performance

The III-Nitride material system has proven extremely valuable for semiconductor device applications. The ability to grow high quality AlGaN/GaN that can be used for RF device applications is largely due to the commercial success of the implementation of p-type doping in GaN for optical devices. Even high quality GaN has relatively large defect densities. GaN devices are still able to achieve impressive performance, but not consistently. The variation in material quality, including deep-level defects and nonuniformities introduced by processing and growth, have deleterious effects on microwave device performance. These variations and the inability to control them reduce yield and reliability thus making AlGaN/GaN devices difficult to produce commercially. The purpose of this work is to characterize and contribute to the understanding of defects in AlGaN/GaN device systems and their effects on microwave device performance both DC and RF. The effects of device fabrication and surface processing on these defects have also been characterized.; Low Energy Electron-Excited Nano-luminescence (LEEN) Spectroscopy has been used to characterize radiative defects in the AlGaN/GaN material system on a microscopic scale and compare them with electrical measurements on HEMT's and TLM structures. Salient features commonly observed in the LEEN spectra include donor-bound excitons in GaN at ∼3.43 eV, donor-acceptor pair transitions (DAP) at ∼3.30 eV, yellow luminescence (YL) centered at ∼2.20 eV, AlGaN donor-bound exciton emission, and associated phonon replicas. These measurements have been used to successfully correlate contact and sheet resistance with DAP, YL, and AlGaN near-band edge emission spectral features within a given wafer and between wafers. The effects of ultrahigh vacuum processing with Argon sputtering and rapid thermal annealing on defects observed with LEEN spectra have been documented. Microscopic LEEN analysis has also been performed on working microwave devices and correlated to electrical measurements of frequency response, gain, and gate capacitance. Spectroscopic studies of working and failed microwave devices show that the surface and device processing changes have significant effects on device performance. These results show that it is possible to characterize and predict device performance in terms of deep level defects with non-destructive luminescence techniques on a very localized scale.