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Contact selected area regrowth of GaN was performed by metal organic chemical vapor deposition using a silicon nitride dielectric hard mask to define plasma etched recesses and to define source-drain regions. A low temperature regrowth process at 750–850°C was adopted to limit lateral overgrowth. High resolution electron microscopy images and selected area diffraction confirmed the regrowth selectivity and revealed that the low temperature regrown GaN is epitaxial and has a wurtzite crystal structure. I-V characteristics of the fabricated metal oxidesemiconductor field effect transistor show enhancement mode operation.

High state densities in the band gap of the SiC-SiO 2 interface significantly reduce the channel mobilities in SiC-based high-temperature/high-power microelectronics. Investigations of the nature of the interface defects are thus of great importance. While several possible defects including very small carbon clusters with up to four carbon atoms have been identified by first-principles theory, larger carbon clusters as possible defects have attracted less attention. Here, we report first-principles quantum-mechanical calculations for two larger carbon clusters, the C 10 ring and the C 20 fullerence, at the SiC-SiO 2 interface. We find that both carbon clusters introduce significant states in the band gap. The states extend over the entire band gap with higher densities in the upper half of the gap, thus accounting for some of the interface trap densities observed experimentally.

Silicon carbide is a wide bandgap semiconductor whose intrinsic properties make it suited for high-power, high-temperature, and high frequency applications. Additionally, SiC has potential for the fabrication of metal-oxide-semiconductor (MOS) power supplies because it forms a native oxide in the same manner as silicon. The structure of the interface between the native oxide (SiO 2 ) and SiC is not fully understood, yet it is suspected that this interface limits the utilization of MOS power supply applications due to an electron mobility loss. We use scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS), and ab initio calculations to characterize atomic structure and chemistry of the interface. High resolution STEM images with atomic resolution show that the atomically flat interface can be perfectly crystalline or show a disturbed crystalline transition layer at the SiC side depending on process parameters. EELS investigations of the interface indicate that the both sides of the interface are rich in carbon. This interface effect is studied using various annealing conditions in an effect to further quantify outcome. Our results indicate that a high oxidation rate is effectively driving carbon into the SiC and can cause an almost amorphous transition layer. The cumulative effect of the oxidation is an atomically sharp interface with carbon defects leading to electronic states within the bandgap.978-1-4244-1892-3/07/$25.00 ©2007 IEEE