Study on the growth of crack-free Al_xGa_1-xN (0.133≥x>0.1)/GaN heterostructure with low dislocation density

We have investigated the growth of crack-free Al_xGa_1-xN layer (0.133≤x>0.1) with low dislocation density using Al_xGa_1-xN/GaN heterostructure. From the wet-etched surfaces and transmission electron microscopy (TEM) images, the 2 μm underlying Al_xGa_1-xN layer with low AlN molar fraction is effective in preventing the formation of cracks in Al_xGa_1-xN surface. Although the number of defects in the underlying Al_xGa_1-xN layer grown on low-temperature GaN buffer are increased by the increase of AlN molar fraction, the use of the highly strained Al_xGa_1-xN/GaN/Al_xGa_1-xN heterostructure on the underlying layer is effective in reducing the number of defects near the surface. The possibility of the growth of crack-free Al_xGa_1-xN/GaN heterostructure with low dislocation density by controlling the AlN molar fraction and the misfit strain value is presented.