Strain relaxation effects on TE-polarized light emission and in-plane polarization ratio in c-plane ultraviolet AlGaN/AlN quantum well structures

Strain relaxation effects on TE-polarized light emission and in-plane polarization ratio in c-plane ultraviolet (UV) Al_xGa_1−xN/AlN quantum well (QW) structures were investigated as a function of Al content. In the case of the strain relaxation along y(or x)-direction, the x (or y)-polarized light emission is shown to be larger than the y(or x-)polarized light emission, which can be explained by the topmost subband characteristics change from the HH1 subband to the admixture of HH1 and LH1 subbands by an anisotropic strain. In the case of ϵ_yy=0.4ϵ_yy ^o, the polarization ratio has values from 0.4 to 0.7 in an investigated range of Al content. In particular, the QW structure with the strain relaxation along x or y direction shows that the peak intensity is much larger than that for the convention AlGaN/AlN QW structure in a range of x<0.6.