Theoretical studies on in-plane polarization characteristics of (11(2)over-bar0) nonpolar InGaN/GaN quantum-well structures grown on InGaN substrates

The in-plane polarization characteristics of nonpolar (11 (2) over bar0) InxGa1-xN/GaN (x = 0.2) quantum-well (QW) structures are investigated as a function of In content in InyGa1-yN substrates by using the multiband effective-mass theory. States constituting the topmost valence subband change from vertical bar Y' >-like to vertical bar Z' >-like as the In content in the InGaN substrate increases. In the case of the QW structure grown on a conventional GaN substrate (y = 0.0), the y'-polarized matrix element is much larger than the x'-polarized matrix element. However, the y'-polarized matrix element rapidly decreases with increasing y content in the InGaN substrate and becomes similar to the x'-polarized matrix element. As a result, the magnitude of the in-plane optical anisotropy becomes smaller for QW structures with higher substrate In content because both x'- and y' -polarized emission peaks are similar to each other.