Growth of low-defect AlGaN by lateral epitaxy over V-grooved sapphire substrates fabricated by wet chemical etching

Low-defect AlGaN films were grown by metal organic chemical deposition (MOCVD) over patterned sapphire substrates (PSS) with V-grooves fabricated by wet chemical etching based on a mixed solution of H2SO4 and H3PO4. Three high-temperature (HT) growth steps were performed on the wet-etched PSS. In the 1st HT-growth step, GaN layers with triangular cross-sections were grown on sapphire mesas of the surface of the wet-etched PSS. In the 2nd HT-growth step, the GaN layers were more grown in the lateral direction and coalescent at the bottom, but corrugated at the surface. Finally, in the 3rd HT-growth step, AlGaN layer was grown on the corrugated surface of GaN and coalesced completely into AlGaN layer with flat surface. By employing the corrugated surface of GaN grown on the wet-etched PSS as the initial surface for the growth of AlGaN layers, the tensile stress of AlGaN was remarkably reduced. Additionally, in order to completely eliminate the cracks of the AlGaN layer, a low-temperature (LT) AIN layer was inserted between the AlGaN layer and the GaN layer with the corrugated surface. By inserting the LT-AIN interlayer, no crack did generate in the AlGaN film, and the density of threading dislocations in the film was remarkably decreased after the lateral epitaxy using the wet-etched PSS with V-grooves.