GaN template layer strain effects were investigated on the growth of InGaN/GaN LED devices. Seven period InGaN/GaN multiple quantum well structures were deposited on 5µm and 15µm GaN template layers. It was found that the electroluminescence emission of the 15µm device was red-shifted by approximately 132meV. Triple-axis X-Ray Diffraction and Cross-Sectional Transmission Electron Microscopy show that the 15µm templay layer device was virtually unstrained while the 5µm layer experienced tensile strain. Dynamic Secondary Ion Mass Spectrometry depth profiles show that the 15µm template layer device had an average indium concentration of 11% higher than that of the 5µm template layer device even though the structures were deposited during the same growth run. It was also found that the 15µm layer device had a higher growth rate than the 5µm template layer device. This difference in indium concentration and growth rate was due to changes in thermodynamic limitations caused by strain differences in the template layers.

The evolution of nanoscale pores or dimples during ion etching of GaN was used to measure the magnitude of the curvature-dependent roughening. GaN(0001) surfaces were ion etched with glancing-incident, 300 eV Ar and nitrogen ions using a beam flux of 3.6×1014ionscm−2s−1. The samples were rotated during the etching, and the sample temperatures maintained between room temperature and 600 °C. This etch process smoothened the surface but left nanoscale dimples or pores with diameters between 30 and 800 nm. The density of these dimples remained constant during the etch process but the dimples were observed to grow larger in size until coalescence occurred. The formation of these ion-induced, nanoscale features was analyzed in terms of a continuum model that included a curvature-dependent roughening term and a smoothening term. The integral of the removed material was measured in order to directly determine the curvature dependence of the sputter yield. From the evolution of the dimple dimensions, we measured the roughening coefficient as 43±5 and 28±4nm2∕s at 460 and 315 °C, respectively, which are four orders of magnitude larger than that calculated using curvature-dependent sputtering alone. Preliminary measurements of the roughening coefficient versus temperature show a minimum at a temperature of about 365 °C.

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White sponge nevus (WSN) is one of a number of white lesions of the oral mucosa. It is an autosomal dominant disorder of wide variability and high penetrance. White sponge nevus is characterized by white, spongy lesions of the oral mucosa, although extraoral mucosae may also be affected. Onset is early in life, and both sexes are affected equally. There are no extramucosal lesions associated with WSN. The plaques of WSN are benign and may undergo alternate periods of remission and exacerbation. In two of our cases from an affected family, penicillin precipitated remission of the plaques.

Temperature-gradient metalorganic chemical vapor deposition (MOCVD) was used to deposit In x Ga 1-x N/GaN multiple quantum well (MQW) structures with a concentration gradient of indium across the wafer. These MQW structures were deposited on low defect density (2 ϫ 10 8 cm Ϫ2 ) GaN template layers for investigation of microstructural properties and V-defect (pinhole) formation. Room temperature (RT) photoluminescence (PL) and photomodulated transmission (PT) were used for optical characterization, which show a systematic decrease in emission energy for a decrease in growth temperature. Triple-axis x-ray diffraction (XRD), scanning electron microscopy, and cross-sectional transmission electron microscopy were used to obtain microstructural properties of different regions across the wafer. Results show that there is a decrease in crystal quality and an increase in V-defect formation with increasing indium concentration. A direct correlation was found between V-defect density and growth temperature due to increased strain and indium segregation for increasing indium concentration.