Growth of AlGaN and AlN on patterned AlN/sapphire templates

Maskless epitaxial overgrowth of AlGaN on structured AlN templates was performed and the impact of stripe orientation on the lateral growth of AlGaN was studied. AlN/sapphire templates were patterned into stripes with 1.5μm wide bars and a period of 3μm. AlGaN and AlN growths were performed on the patterned templates. Two stripe orientations were investigated: stripes parallel to the [11¯00] and parallel to the [112¯0] directions. Coalescence was achieved for both stripe orientations. AlGaN layers grown on stripes oriented along the [11¯00] direction show a flat and closed surface in contrast to overgrown stripes oriented along the [112¯0] direction where the surface is facetted and rough. The Al content is strongly dependent on the growth facet and varies between 25% at the sidewalls and 50% on the c-facet. The overgrowth of stripes parallel to the [11¯00] direction with AlN shows coalescence and flat surfaces. The X-ray rocking curve full width at half-maximum of the (101¯2) reflection is reduced from 1000 arcsec to 500 arcsec for the overgrown AlN. Temperature dependent photoluminescence measurements of AlGaN:Si grown on these coalesced AlN templates also indicate a dislocation density reduction via this method.