Non-planar growth of high Al-mole-fraction AlGaN on patterned GaN platforms for mitigating strain-induced cracks beyond the critical layer thickness

Abstract

Non-planar growth of AlxGa1-xN epitaxial layers with an average alloy composition up to Al-mole-fraction of x ∼ 0.21 was performed on patterned c-plane GaN on (0001) sapphire substrates with stripe-shaped mesa structures. This approach successfully realized the growth of crack-free AlGaN layers on the top of mesas with layer thicknesses greater than the expected critical layer thickness by relaxing the in-plane stress on the top of the mesa. The effectiveness of the relaxation strongly depends on the width and depth of the stripe mesa. The relaxation of in-plane stress and resultant suppression of cracks in AlGaN layer are qualitatively discussed.