Abnormal polarization switching phenomenon in a-plane Al(x)Ga(1-x)N

Abstract

The optical polarization properties of a-plane Al(x)Ga(1-x)N films have been investigated by polarization-dependent photoluminescence (PL). The degree of polarization decreased with increasing the Al composition, and the main optical polarization direction switched from epsilon perpendicular to c to epsilon // c at about x = 0.07 due to the valence band switching, representing that the optical transition energy of epsilon // c is surpassing that of epsilon perpendicular to c. However, with the Al composition larger than x = 0.1, the higher energy optical transitions of epsilon // c exhibited the stronger PL intensity, opposite to the normal situations that higher energy states commonly have weaker PL intensity than the lower energy states. We utilized the 6 x 6 k.p model and the lambertian-like radiation pattern assumption to explain this abnormal optical polarization switching behavior in the a-plane Al(x)Ga(1-x)N layers and obtained good agreement with the experimental results. (C) 2010 Optical Society of America