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(Received s The density of threading dislocations (TD) in GaN grown directly on flat sapphire substrates *m is typically greater than 109/cm2. Such high dislocation densities degrade both the electronic so and photonic properties of the material. The density of dislocations can be decreased b~~@ orders of magnitude using cantilever epitaxy (CE), which employs prepattemed sapphire substrates to provide reduced-dmension mesa regions for nucleation and etched trenches ($)42 between them for suspended lateral growth of Gall or AIGaN. The substrate k prepattemed d~w ith narrow lines and etched to a depth that permits coalescence of laterally growing III-N~@ nucleated on the mesa stiaces before vertical growth fills the etched trench. Low a dislocation densities typical of epitaxial lateral overgrowth (ELO) are obtained in the cantilever regions and the TD density is also reduced up to 1 micrometer from the edge of the support regions.The great potential of wide-band-gap Group III nitrides (III-N) has been limited in many applications by the very high density of treading dislocations (TDs) that form when the III-N materials are grown on latticemismatched substrates [1]. Growth of GaN on a planar substrate of sapphire, SiC, orSi(111) produces TD areal densities on~e order of 108to 1010/cm2.Although such high TD densltles do not appear to seriously degrade light-emitting diode (LED) performance due to the vertical character of the TDs and the short minority carrier difision lengths found in III-nitrides, they cause unacceptably short lifetimes for laser diodes (LDs) and excessive leakage current under reverse bias for p-n junction devices such as field-effect transistors (FETs) and high-electron-mobility transistors (HEMTs). To solve these problems, a GaN substrate with <1OG TDs/cm2 will be required.Several approaches have achieved considerable success in reducing TD densities to the 106/cm2range in selected regions of a wafer, but these techniques are very time-consuming to implement. These include epitaxial lateral overgrowth (ELO or LEO) [2,3], pendeoepitaxy (PE) [4], and lateral overgrowth from trenches (LOFT) [5]. While each technique produces selective areas on a wafer that possess the low TD densities (

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Three important processes dominate the wet thermal oxidation of AlxGa1−xAs on GaAs: (1) oxidation of Al and Ga in the AlxGa1−xAs alloy to form an amorphous oxide, (2) formation and elimination of crystalline and amorphous elemental As and of amorphous As2O3, and (3) crystallization of the amorphous oxide film. Residual As can lead to strong Fermi-level pinning at the oxidized AlGaAs/GaAs interface, up to a 100-fold increase in leakage current, and a 30% increase in the dielectric constant of the oxide layer. Thermodynamically favored interfacial As may impose a fundamental limitation on the use of AlGaAs wet oxidation in metal-insulatorsemiconductor devices in the GaAs material system.