Growth conditions for AlN in two dimensional (2D) and three dimensional (3D) growth modes were explored on SiC using metal organic chemical vapor deposition. High quality AlN layers were obtained by alternating between 3D and 2D growth modes, referred to as modulation growth (MG). Long parallel atomic terraces without step terminations were observed in atomic force microscopy (AFM) scans of MG AlN, indicating a reduced dislocation density. X-ray diffraction rocking curves yielded full widths at half maximum (FWHM) of 86 and 363arcsec for the (002) and (102) reflections, respectively, giving further evidence of low dislocation density in the film. 3D-2D MG also releases some of the tensile strain in the AlN film, enabling the growth of thick, crack-free AlN on SiC substrates.

Native cation vacancies in Si-doped AlGaN studied by monoenergetic positron beamsIdentification of vacancy-oxygen complexes in oxygen-implanted silicon probed with slow positrons Vacancy-type defects in AlN grown by metal-organic vapor phase epitaxy ͑MOVPE͒ and lateral epitaxial overgrowth ͑LEO͒ using halide vapor phase epitaxy were probed by a monoenergetic positron beam. Doppler broadening spectra of the annihilation radiation were measured and compared to the spectra calculated using the projector augmented-wave method. For MOVPE-AlN, the concentration of vacancy-type defects was high near the interface between AlN and the GaN buffer layer, and the defect-rich region expanded from the interface toward the surface when the NH 3 flow rate increased. For the sample grown on the AlN buffer layer, however, the introduction of such defects was suppressed. For LEO-AlN, distinct deep emission peaks at 3-6 eV were observed in cathodoluminescence spectra. From a comparison between Doppler broadening spectra measured for LEO-AlN and computer simulated ones, an origin of the peaks was identified as complexes of Al vacancy ͑V Al ͒ and oxygen atoms substituting nitrogen sites such as V Al ͑O N ͒ n ͑n = 3 and 4͒.

Fully coalesced Al 0:93 Ga 0:07 N films were demonstrated by metalorganic chemical vapor deposition on deep grooved SiC substrates. Lateral Al 0:93 Ga 0:07 N growth was achieved at low V/III ratios during growth. The deep grooves enabled coalescence despite of parasitic growth in the trenches. Dislocation reduction in the overgrown regions of the films was observed by transition electron microscopy and atomic force microscopy.

No abstract

Field-effect transistors (FETs) were grown on both GaN and AlGaN buffers. X-ray reciprocal space mapping and ω-2θ scans showed that the AlGaN barriers grown on these two buffers had different Al compositions and growth rates, which was attributed to the compositional pulling effect. AlGaN/GaN/AlGaN double heterojunction FETs exhibited lower output conductance and better pinch-off due to the improved electron confinement resulting from the increase in the effective back-side barrier height. Thus, this device is promising for highly scaled transistors. This device also demonstrated a state-of-the-art power added efficiency of 53.5% and an associated power gain of 9.1 dB at a drain bias of 20 V at 30 GHz.