The Effects of Sapphire Surface Treatments and Nitridation on GaN Nucleation Grown using Hydride Vapor Phase Epitaxy

Abstract

We have studied the effects of sapphire surface treatments and nitridation on GaN nucleation grown using the hydride vapor phase epitaxy technique. The surface treatments used were airannealing at 1400°C, etching in pure H₂SO₄ at 250°C, and etching in a 3:1 mixture of H₂SO₄:H₃PO₄ solution at 250°C. A nitridation step was carried out using 20% NH₃ in N₂ gas mixture at 1100°C. GaN nucleation and the early stage s of growth was investigated by short time growth and quench experiments. Atomic force microscopy and double crystal x-ray diffraction were used to examine the sapphire surface morphology, GaN island density, and GaN island structure. A lower density of GaN islands was grown on the air-annealed sapphire compared to the H₂SO₄-etched and 3:1 H₂SO₄:H₃PO₄-etched sapphire. GaN islands grown on the 3:1 H₂SO₄:H₃PO₄-etched sapphire had a broad mosaic spread due to preferential growth on surface pits. Sapphire nitridation resulted in a higher GaN island density with a smaller mosaic spread. A high density and uniform nucleation of GaN islands is critical in producing high quality thick GaN films. The H₂SO₄-etched sapphire and nitridation resulted in a high density of uniform GaN islands.