Optical polarization switching in semipolar (202¯1) InGaN multiple quantum wells induced by strain engineering

Abstract

Semipolar (202¯1) InGaN/AlGaN multiple quantum wells (MQWs) with a low In content (<0.05) were coherently grown on a partially relaxed AlxGa1−xN (0 < XAl < 0.4) layer. As XAl increased from 0.15 to 0.38, the degree of optical polarization measured by photoluminescence at 13 K changed from 0.49 to −0.24, where (−) indicates the change in the dominant polarization direction from [112¯0] to [1014¯]. Regardless of XAl and thickness, no polarization switching was observed if AlxGa1−xN was fully strained to the GaN substrate. Band structure modeling based on the k⋅p method implies that the polarization switching is associated with strong valence band mixing induced by the one-dimensional strain relaxation in AlGaN, which leads to a significantly stronger compressive strain in MQWs along [1014¯] relative to [112¯0]. These results demonstrate that the optical polarization switching in semipolar MQWs can be controlled by engineering the strain state of the underlying layer.