GOALI: Effects of Defects and Degradation Mechanisms in SiC and GaN Devices

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Intellectual Merit. This GOALI project at Arizona State University (ASU), in collaboration with our industrial partner Technologies and Devices International, Inc. (TDI), will investigate the effects of extended crystal defects on the performance of electronic devices fabricated from GaN, and identify the cause of the major degradation mechanisms in devices made from SiC. The high breakdown field, reasonable mobilities, and ability to form heterostructures (in the GaN case) of these materials has led to increasing interest in their use for high power, high temperature electronics applications. However, crystal defects and related degradation mechanisms currently limit these applications. The objective is to determine the fundamental causes of degradation mechanisms that currently affect SiC devices so that they can be eliminated, and to determine the effects of various classes of crystal defects on the electrical properties of junctions fabricated in GaN so that the most important defects can be targeted for elimination. SiC degradation mechanisms will be studied using in situ measurements by synchrotron based white-beam X-ray topography (SWBXT), to be performed at State University of New York-Stony Brook. Device fabrication, electrical characterization, optical Nomarski microscopy, electron beam-induced current (EBIC), and cathodoluminescence (CL) will be performed at ASU. The effects of defects in GaN diodes will be studied by fabricating high voltage diodes in either lateral or vertical geometries, using low defect density GaN starting material. This material will be grown at TDI, and provided to ASU. The diodes will be characterized electrically, and defects will then be studied by SWBXT, EBIC, and atomic force microscopy. Using small active area devices, we will establish the effects of each defect class on electrical performance. We will also search for luminescence signatures of various structural defects in GaN. Some TEM measurements of selected defects will be carried ASU. The results will be correlated to yield a comprehensive understanding of the influence of defects, and the results will be shared with TDI to help improve their growth processes.Broader Impacts. This project will educate two Ph.D. students in an industrially relevant research area. PowerPoint slides detailing the properties and applications of wide band gap semiconductors will be developed and made freely available to those teaching semiconductor device physics at the graduate and undergraduate levels. Undergraduate students will be involved through a senior design project based on the grant. Web pages aimed at high school students and the general public will be developed to explain the properties and applications of wide band gap semiconductors. Industrial interactions with TDI and another company in this area will be strengthened by this project. Solution of the technical problems limiting the application of these materials will lead to more efficient power switching devices, which could reduce losses in power systems and yield large savings in fossil fuels and pollution.