Optical polarization switching in semipolar (20(2)over-bar1) InGaN multiple quantum wells induced by strain engineering

Semipolar (20 (2) over bar1) InGaN/AlGaN multiple quantum wells (MQWs) with a low In content (<0.05) were coherently grown on a partially relaxed AlxGa1-xN (0<X-Al<0.4) layer. As X-Al increased from 0.15 to 0.38, the degree of optical polarization measured by photoluminescence at 13K changed from 0.49 to -0.24, where (-) indicates the change in the dominant polarization direction from [11<(2)over bar>0] to [10 (14) over bar]. Regardless of X-Al 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 [10 (14) over bar] relative to [11 (2) over bar0]. These results demonstrate that the optical polarization switching in semipolar MQWs can be controlled by engineering the strain state of the underlying layer.