We develop a new, combined experimental and theoretical approach to make reliable predictions for the limiting case of surface reaction kinetics controlled growth. We solve the inverse problem of determining the growth velocity from observations of the evolution of the morphology of GaN islands grown by metalorganic chemical vapor deposition and make use of crystal symmetry and established theorems. We are able to predict the growth for both convex and concave surfaces, with faceted and curved features. We also give a general guideline for deducing growth velocities from experimental observations.

Ultraviolet light emitting diodes (LEDs) have been grown using metalorganic vapor phase epitaxy, while monitoring the 550 nm reflected light intensity. During nucleation of GaN on sapphire, the transition from three-dimensional (3D) grain growth to two-dimensional (2D) coalesced growth was intentionally delayed in time by lowering the NH3 flow during the initial high temperature growth. Initially, when the reflectance signal is near zero, the GaN film is rough and composed of partly coalesced 3D grains. Eventually, the reflected light intensity recovers as the 2D morphology evolves. For 380 nm LEDs grown on 3D nucleation layers, we observe increased light output. For LEDs fabricated on GaN films with a longer recovery time an output power of 1.3 mW at 20 mA current was achieved.

(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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