Effects of different potential barriers on the structural and optical properties of GaN∕AlxGa1−xN∕GaN coupled multiquantum wells

Coupled multiquantum well structures, $\mathrm{Ga}\mathrm{N}∕{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ bounded by ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ barriers with varying Al content $x$ , are characterized by using high-resolution x-ray diffraction and photoluminescence measurements. It is clearly demonstrated that the structural and optical properties strongly depend on the Al content $x$ . Photoluminescence peaks continue to be redshifted with respect to the bulk GaN band gap with increasing $x$ up to 0.5, but, in turn, become blueshifted beyond this value. This behavior is understood in terms of the different screening effects of the piezoelectric field induced by a strain with increasing Al content. It is found that the strain starts to be relatively relaxed around $x=0.5$ , leading to the reduction in the screening of the piezoelectric field.