Malignant transformation in cultured hamster embryo cells produced by X-rays, 460-keV monoenergetic neutrons, and heavy ions.

Abstract

In this paper we present morphological, structural, optical and chemical characteristics of GaN homoepitaxial layers grown by MOCVD on Ga-polar (0001) substrates prepared using a novel reactive ion etching (RIE) procedure. The layers show microscopically featureless morphology and exhibit the step-flow growth mode with step heights of c/2 as evidenced by DIC optical and atomic force microscopy, respectively. Cross-sectional TEM illustrated the absence of threading defects. Low temperature (4.2 K) photoluminescence from this defect-free layer shows donor- and acceptor-bound exciton peaks with linewidth below 1 meV. Secondary ion mass spectroscopy revealed an abrupt change of the concentration of all the typical contaminants (O, C, Si, H) across the epilayer/substrate interface. The results indicate that the RIE process based on Ar–SiCl4–SF6 chemistry is the right tool for preparing Ga-polar GaN substrates for the growth of high quality homoepitaxial layers.