Gallium nitride films have been grown on 6H-SiC substrates employing a new form of selective lateral epitaxy, namely pendeo-epitaxy. This technique forces regrowth to start exclusively on sidewalls of GaN seed structures. Both discrete pendeo-epitaxial microstructures and coalesced single crystal layers of GaN have been achieved. Analysis by SEM and TEM are used to evaluate the morphology of the resulting GaN films. Process routes leading to GaN pendeo-epitaxial growth using silicon substrates have also been achieved and the preliminary results are discussed.

The lateral epitaxial overgrowth of GaN on Si(111) substrates was achieved using an extension of our standard LEO process on GaN/Al2O3 substrates, and the reduction of the dislocation density was demonstrated by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The growth on the Si(111) substrate was initiated with the deposition of a thin AlN buffer layer to avoid the formation of potentially detrimental silicon nitride at the interface. The wafers were then patterned with a SiO2 layer in which 5 micron wide opening separated by 35 microns were etched using buffered HF. After reloading the samples in the MOCVD chamber, the LEO growth was performed using our standard parameters. There are a few unresolved issues concerning the effect of the AlN buffer thickness and its chemical compatibility with the SiO2 mask layer, but after a basic optimization we were able to obtain 5 microns of lateral overgrowth with smooth sidewalls in a reproducible manner. We are currently investigating the use of mask materials other than SiO2 to achieve LEO on Si(111) over a wider range of process parameters.

We describe the effect of various growth parameters such as V/III ratio and temperature on the lateral epitaxial overgrowth of GaN by MOCVD. We also discuss the effect of the mask pattern geometry used as the "seed" template. Structural characterization (AFM, TEM) show that for suitable growth conditions the LEO GaN contains almost no threading dislocations (approx. 10 (exp 5)/sq cm). Based on these results we developed a 40 micrometers period LEO GaN template (containing essentially dislocation-free regions approx. 15 micrometers wide) that is suitable for the subsequent growth of device layer structures and device fabrication. Preliminary results showing the improved properties of AlGaN/GaN and InGaN/GaN heterostructures grown on these templates are then discussed.

The unique materials properties of GaN-based semiconductors havestimulated a great deal of interest in research and developmentregarding nitride materials growth and optoelectronic andnitride-based electronic devices. High electron mobility andsaturation velocity, high sheet carrier concentration atheterojunction interfaces, high breakdown field, and low thermalimpedance of GaN-based films grown over SiC or bulk AlN substratesmake nitride-based electronic devices very promising.

Group III-nitrides, and in particular, aluminum nitride (AIN), gallium nitride (GaN), and indium nitride (InN) make up a class of compound semiconductors with direct bandgaps ranging from 1.2 electron volts to 6.2 electron volts (eV). They afford a broad range of applications including light emitting diodes (LED's) and laser diodes (LD's) emitting from the visible to the ultraviolet (UV) portions of the electromagnetic spectrum, radiation detectors, and high power, high frequency electronic devices capable of operating at high temperatures, and in hostile chemical environments. Materials studied in this work were grown on silicon substrates, Si(111) by Molecular Beam Epitaxy (MBE) under a broad range of growth parameters and characterized using X-ray diffraction (XRD), Energy Dispersive Spectroscopy (EDS), Atomic Force Microscopy (AFM), Photoluminescence (PL), and four-point probe resistivity measurements. Growth began with deposition of 0.3 monolayer (ML) of Al on the Si(111)7x7 surface leading to fully passivated Si(111) [root of]3x[root of]3-Al surface. Next, an AIN buffer layer and then the GaN layers were deposited. X-ray measurements indicated growth of single-crystalline hexagonal GaN(001) while PL measurement demonstrated a peak position corresponding to bulk hexagonal-GaN. Sample morphology and resistivity showed a strong dependence on growth conditions. The layer RMS roughness increased with increasing thickness for samples grown with low atomic-nitrogen (N) to molecular N ratio while smoother layers were obtained at the highest atomic N concentrations. Un-intentionally doped layers were n-type. P-type doping was achieved by doping with Mg.