1. Introduction

Silicon has long been the dominant semiconductor of choice for high-voltage power electronics applications.1 ^,2 However, recently, wide bandgap semiconductors, particularly SiC and GaN, have attracted much attention because they are projected to have much better performance than silicon and the epi/substrate technology has matured to make device commercialization possible. ^{3 7} Compared to silicon, these wide bandgap semiconductors, SiC, GaN and InN can be categorized into one group while diamond, BN and AIN into another because the former has bandgaps of 2 3.5 eV and the latter 5.5 6.5 eV. Group IV or IV-IV semiconductors have indirect bandgaps whereas most of the Group III-nitrides are direct (except BN). The superior physical properties of these semiconductors offer a lower intrinsic carrier concentration (10 to 35 orders of magnitude), a higher electric breakdown field (4 20 times), a higher thermal conductivity (3 13 times), a larger saturated electron drift velocity (2 2.5 times), when compared to silicon (See Table 1). SiC has over 150 polytypes (which are different crystal structures with the same stoichiometry of a compound semiconductor). Also, only the 6H- and 4H-SiC polytypes are available commercially in both bulk wafers (up to 4" in diameter at present) and custom epitaxial layers (up to at least 100 ?m at present) while 3C-SiC is available as heteroepitaxial layers on large-diameter silicon substrates. Between the two polytypes, 4H-SiC has...