Optical polarization anisoptopy in a-plane GaN/AlGaN quantum-well structures

Abstract

Optical anisotropy as a function of Al composition of the (11 {ie1192-1} 0) a-plane GaN/AlxGa1−xN quantum-well (QW) structures was investigated using a non-Markovian optical model. The energy spacing between the first two subbands is shown to increase with increasing Al composition x in the barrier. The QW structure with a larger x has a larger optical matrix element than that with a smaller x because the potential well becomes deeper for QW structures with a larger x. Hence, the peak intensity of the optical gain rapidly increases with increasing Al composition in the AlGaN barrier, and the rate of increase of the x′-polarized optical gain with increasing Al content is larger than that of the y′-polarized optical gain. As a result, the absolute value of the anisotropy is found to decrease greatly with increasing Al composition. The optical anisotropy values are 0.74 and 0.40 for x = 0.1 and 0.3, respectively.