The role of nucleation temperature in In-face InN-on-GaN(0001) growth by plasma-assisted molecular beam epitaxy

The nucleation of In-face InN films on GaN(0001) surfaces by plasma-assisted molecular beam epitaxy was investigated. Sustained growth of InN is possible for In/N flux ratio less than one and substrate temperature below 520 degreesC. However, under these conditions, nucleation of InN islands that grow with large height to width aspect ratios is observed. This is attributed to low N adatom mobility on the surface as well as to the significantly higher active nitrogen flux incident on the top surface of the islands as compared to the one incident on their lateral faces. Therefore the substrate temperature dependant nucleation density of the InN islands becomes the key factor determining their coalescence. Suppressed coalescence at high temperatures (450-500 degreesC) allows the growth of InN nano- and micro-columns and porous structures, while fast coalescence at low temperature (300-350 degreesC) results in InN templates suitable for overgrowth of continuous InN films. Strain relaxation by misfit dislocations proceeds faster in the case of continuous films. (C) 2004 Published by Elsevier Ltd.