Theoretical study of optical absorption in nonpolar AlGaN/GaN step quantum well structures

Abstract

The linear and nonlinear intersubband optical absorption coefficients (OACs) of nonpolar AlGaN/GaN step quantum well structures (SQWs) were calculated theoretically for various geometrical structures, $$ \delta $$ doping schemes, and material compositions. The results revealed that the absorption frequency of such structures is obviously tunable by changing parameters such as the quantum well width, step barrier width, Al composition in the step barrier layer, and doping position. These characteristics can be attributed to non-polarization-related effects. The doping and Al composition were found to have remarkable effects on the position and magnitude of the peaks in the nonlinear optical absorption spectrum, whereas the geometric parameters of the SQWs, such as the well width and step barrier width, changed the magnitude of the peaks only very slightly. On the other hand, the nonlinear OACs of the SQWs were found to be strongly sensitive to the Al composition x and doping density in the step barrier layer. This study suggests that the step barrier layer in SQWs plays an important role in manipulating their intersubband optical absorption.