Sandia National Labs FY20 LDRD Annual Report

FY20 ANNUAL REPORT

Mitigation of point defects in wide-bandgap semiconductors. Wide-bandgap (WBG) semiconductors represent today’s state-of-the-art materials for high-performance power electronics and are being developed for the electric grid and other critical applications. However, the performance of WBG devices, such as gallium nitride (GaN) vertical power diodes, is presently limited by native crystalline defects and impurities that incorporate during materials growth. This project demonstrated that above-bandgap, ultraviolet (UV) excitation of GaN during materials growth can significantly reduce the density of carbon impurities that limit device performance by compensating intentional dopants. This UV-induced reduction in compensating defects was shown to improve GaN electronic transport properties by increasing both electronic carrier densities and mobilities. Through defect-aware drift-diffusion modeling, the project predicted that compensating defects at the sample surface can be converted to benign defects by UV-induced electronic carriers over a reasonable range of growth parameter space, revealing a viable mechanism by which compensating defects are reduced. (PI: Mary Crawford) Compact solid-state high-voltage switch. Researchers at Sandia developed a semiconductor- based high-voltage switch, with experimental results showing potential for enhanced radiation hardness, for use in several power conversion applications. Gallium nitride (GaN) metal-oxide semiconductor field effect transistors (MOSFETs) were modeled using commercial and Sandia’s Charon software to understand their performance and for prediction of future device operation in radiation environments. Fabrication of the GaN MOSFETs required development of epitaxial materials growth using metal-organic chemical vapor deposition, design and fabrication of the

insulating gate structures using atomic layer deposition, and high- voltage edge termination designs. This technology laid the path to eventual replacement of traditional vacuum switches with GaN MOSFET switches for improved timing performance, lower cost, and faster redesign cycle time to accommodate evolving requirements. (PI: Gregory Pickrell) Prototype 4-finger GaN MOSFET chip before packaging and subsequent technology maturation. Current scaling would increase chip size to ~5.5 mm x 5.5 mm and would require a package size similar to a traditional vacuum switch for comparable performance.

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LABORATORY DIRECTED RESEARCH & DEVELOPMENT