Papers by Author: Robert F. Davis

Abstract: A paradigm shift in the development and utilization of power semiconductor switch technology is proposed. This new "top down" approach begins with the field-reliability of a power semiconductor switch in a power converter circuit is subjected to long-term repetitive-switching under stressful field-operating conditions. This approach is derived from extensive field-reliability data collected on state-of-the-art silicon power MOSFETs in compact computer/telecom power supplies that clearly suggests that power MOSFET field-failures were primarily caused by bulk material defects. A careful survey of power switch technologies reported to-date in Silicon Carbide (SiC) and Gallium Nitride (GaN) further suggests that excessive bulk material defects have predominantly hindered the development and commercialization of cost-effective, high-performance, and reliable high-power devices. A reliability-driven approach is likely to "unlock" the vast potential of SiC (and GaN for moderate power levels) power device technology for high-voltage and high-power switching electronics in order to impact transformative changes.

Abstract: Strain relaxation in the GaN/AlN/6H-SiC epitaxial system grown by vicinal surface epitaxy (VSE) is investigated and compared with that in on-axis epitaxy. High resolution x-ray diffraction (HRXRD) measurements show that GaN films grown by VSE have improved crystalline quality. High resolution transmission electron microscope (HRTEM) studies reveal that there are two types of misfit dislocations (MDs) at AlN/6H-SiC interfaces: 60˚ complete dislocations along <1120 > directions with Burgers vector 1/3<1120 > and 60˚ Shockley partials along <10 10 > directions with Burgers vector 1/3<10 10 >. The latter are usually geometrical partial misfit dislocations (GPMDs) that are dominant in VSE to accommodate the lattice mismatch and stacking sequence mismatch simultaneously. In VSE, it is the high-density GPMDs formed at the vicinal surface steps that facilitate rapid strain relaxation at the initial stage of deposition and hence lead to superior crystalline quality of the subsequently grown GaN films.