The goal of this project is to gain fundamental understanding of charged defects and leakage paths that ultimately degrade performance in GaN-based devices. Such defects may arise from bulk imperfections such as threading dislocations and inversion domains, or from surface states due to poor passivation. The approach includes HVPE (hydride vapor phase epitaxy) GaN film growth on sapphire, SiC, and GaN templates followed by surface science characterization with an emphasis on imaging defect features on a micron to nanometer-scale using techniques such as Surface-Contact-Potential Electric Force Microscopy (SCP-EFM) and Conductive Atomic Force Microscopy (C-AFM). The project will extend the imaging of active Modulation Doped Field Effect Transistors (MODFET's or HEMT's) based on AlGaN/GaN heterostructures. These imaging techniques will help elucidate how surface defects, strain, and polarization are related to device anomalies such as current lag that degrade high frequency behavior. The influence of surface passivation techniques and interface barriers will also be explored. These findings, which will enhance understanding of parasitic pathways to current conduction and charge transfer, will also be applicable to other GaN devices and will extend fundamental understanding of this important materials system. %%% The broad impact of this project includes advancement of a high technological impact research area along with training of graduate and undergraduate students in multidisciplinary research. The PI's are from departments of Electrical Engineering and Physics, and will collaboratively use their expertise in surface science imaging to address fundamental problems of electrically active defects in MODFET structures, as well as to fabricate and test prototype device structures. The project provides support for graduate and undergraduate students who will have unique research and educational opportunities working with sophisticated materials synthesis, processing, and characterization equipment along with device fabrication, testing, and analysis, while participating in interdisciplinary research in an environment of joint mentoring across materials science, physics, and electrical engineering. ***
