Partial strain relaxation effects on polarization anisotropy of semipolar (11 2 ̄ 2) InGaN/GaN quantum well structures

Partial strain relaxation effects on polarization anisotropy of semipolar (11 2 ̄2) InGaN/GaN quantum well (QW) structures were investigated using the multiband effective-mass theory. In the case of strain relaxation of ε x ′ x ′ along x ′-axis, the polarization ratio gradually decreases with increasing strain relaxation. Also, with the strain relaxation by the same amount, the variation of the polarization ratio along x ′-axis is shown to be much larger than that along y ′-axis. However, the polarization switching is not observed even at a high In composition of 0.4 due to a small strain component (ε x ′ x ′ 0) with no strain relaxation. On the other hand, in the case of strain relaxation of ε y ′ y ′ along y ′-axis, the polarization switching is observed, and the optical anisotropy is found to change from positive to negative with increasing strain relaxation. Also, the absolute value of the polarization ratio gradually decreases with increasing carrier density. However, the polarization switching due to the carrier density is not observed. Thus, the polarization switching observed at high carrier density may be attributed to inhomogeneous strain distribution in the InGaN layer.