Elimination of Rotational Domain in AlN Layers Grown from Ga–Al Flux and Effects of Growth Temperature on the Layers

Abstract

We have been investigating crystal growth of AlN on nitrided sapphire substrates, and have grown c-axis oriented AlN layers using liquid phase epitaxy (LPE) with Ga–Al fluxes. However, rotational domains having 1-deg difference around the c-axis exist in the AlN layers. One of the purposes of this study is to eliminate the rotational domains. To do so, an annealing process at elevated temperatures was attempted before the LPE process. Then, its effectiveness was discussed. The origin of the rotational domain was explained using distortion of O²⁻ ions arrangement in (0002) sapphire surface. The mechanism of the eliminating the domains was discussed using the lattice vibration of the sapphire at elevated temperatures. Secondly, effects of growth temperature on the AlN layers were investigated in terms of the growth rate, surface morphology and crystal quality. The growth rate of the LPE AlN layer increased concomitantly with increasing growth temperature at 1373–1673 K. The growth rate attained at 1673 K was 0.52 µm·h⁻¹. Crystal quality is almost independent of the growth temperature in that temperature range.