Role of inserting an InGaN strain release interlayer in AlGaN growth

AlGaN grown on a GaN template usually suffers tensile stress, and the accumulated tensile stress may cause formation of cracks. In this paper, a method to reduce the tensile stress during AlGaN growth by inserting an InGaN interlayer is proposed. Although InGaN has a larger in-plane lattice constant, it will not cause the subsequent growth of AlGaN to be subject to greater tensile stress if InGaN is coherently grown on AlGaN. On the contrary, due to the low thermal expansion coefficient of InGaN, the subsequent growth of AlGaN will suffer less tensile stress through an asymmetric temperature varying process. The validity of this method was verified by in-situ curvature monitor, reciprocal space mapping and temperature-dependent Raman spectral observation. In addition, it is found by atomic force microscopy and scanning electron microscopy that the insertion of InGaN interlayer introduces V-shaped pits into the AlGaN structure which can be refilled by later AlGaN growth. It is inferred that they may play additional role in stress release similar to what the patterned substrate usually does.