Strong optical polarization in nonpolar (1(1)over-bar00) AlxGa1-xN/AlN quantum wells

The optical polarization properties in nonpolar (1 (1) over bar 00) AlxGa1-xN/AlN quantum wells (QWs) are investigated over the full range of Al compositions. The k . p calculation predicts that the lowest energy optical transition in (1 (1) over bar 00) AlxGa1-xN layers pseudomorphically grown on unstrained AlN is dipole allowed for the electric field vector parallel to the [0001] direction, and that the degree of polarization is hardly affected by the AlxGa1-xN QW width regardless of the Al composition. Experimentally, AlxGa1-xN/AlN QWs (0 <= x <= 0.81) are homoepitaxially grown on AlN substrates. Photoluminescence spectroscopy reveals that the emissions of all QWs, including GaN/AlN QWs, are strongly polarized along the [0001] direction. This result agrees with the theoretical prediction. DOI: 10.1103/PhysRevB.87.041306