Growth and characterization of thick GaN layers grown by halide vapour phase epitaxy on lattice-matched AlInN templates

We have investigated the feasibility to use GaN lattice-matched Al0.82In0.18N as a starting layer for growth of thick GaN using halide vapor phase epitaxy (HVPE). The buffer, which consisted of Al0.82In0.18N(0 0 0 1) on a 50-nm-thick TiN(1 1 1) seed layer, was grown by magnetron sputter epitaxy (MSE) on a 2″ Al2O3(0 0 0 1) substrate. It was found that the surface morphology of the GaN strongly depends on the choice of carrier gases. Using a mixture of hydrogen and nitrogen results in a rough morphology, while growth in pure nitrogen gives layers of good morphology and high transparency. For a 30-μm-thick GaN film, the threading dislocation (TD) density, as determined by cathodoluminescence, is about ∼3×108 cm−2. By transmission electron microscopy (TEM) , it was revealed that the threading dislocations originate from the buffer layer and the GaN/Al0.82In0.18N interface. The GaN/Al0.82In0.18N interface is roughened during growth due to a chemical incompatibility between the HVPE process and the Al0.82In0.18N layer. Additionally, the GaN layers are cracked due to tensile strain indicating initial growth of crystallites which eventually coalesce and hence build up a tensile stress in the film.