Growth of Strain Free GaN Layers on 6H‐SiC (0001) by Plasma‐Assisted Molecular Beam Epitaxy

Abstract

The strain state of the GaN/6H-SiC (0001) heterostructure is shown to depend on the AlN nucleation layer thickness and growth process. Using identical GaN growth conditions with different AlN buffer layer thickness, the GaN layers were found to be under different strain in the plane normal to the growth direction. The accomplishment of double-step AlN buffer (150 nm) grown at two different temperatures with a difference of 30–50 °C has lead into strain free growth of 1.2 μm thick GaN layers with improved structural and optical characteristics. The unstrained nature of the GaN layers was found from the lattice constants (a = 0.3191 nm and c = 0.5186 nm) of the GaN layer measured from the X-ray diffraction space mapping. Post growth cooling introduced tensile strain in the GaN layer is ineffective when nucleated on the double-step AlN buffer layers, whereas the compressive and tensile strain remains in the GaN layers when nucleated on the single-step thin AlN buffer layer and directly on SiC, respectively.