Influence of AlN barrier thickness on AlN/GaN heterostructure optical and transport properties

AlN/GaN heterostructures, with different AlN barrier thicknesses (3 and 6 nm), are characterized using atomic force microscopy, high-resolution transmission electron microscopy, photoluminescence, and Hall effect measurements. Based on the measured results, we suggest that with increased AlN barrier thickness, the tensile strain in the AlN barrier layer is relaxed by crack channels. In addition, the strain-induced cracking also greatly penetrated into the GaN buffer layer, and resulted in the relaxation of the compressive strain and the increase of the defects in the GaN buffer layer. This caused AlN/GaN heterostructure quality deterioration and introduced additional scattering.