Investigation of off-cut angle of sapphire for epitaxial lateral overgrowth of AlN and fabrication of high-quality AlN template

Abstract

Using a metal–organic vapor phase epitaxy, the epitaxial lateral overgrowth (ELO) of AlN was performed by varying a vicinal off-cut angle from 0.15 to 2.0° of sapphire substrates oriented to the m-axis, i.e., the a-axis of AlN. During overgrowth, step bunching resulted in the efficient conversion of dislocations to elongated voids. The dislocations were terminated at the voids formed over the groove regions and the low and high etch pit density (EPD) regions were observed. The dislocation was reduced by increasing the off-cut angle of the sapphire substrates up to 0.8°; however, low-EPD region became small in the ELO. Thus, we have attempted to achieve a longer growth of the ELO-AlN layer on the sapphire substrate with the off-cut angle of 0.15°. As a result, the EPD decreased with the increasing thickness. The ELO-AlN layer with the thickness of 15.9 µm exhibited the EPD of 2.1 × 106 cm−2 in the low dislocation region.