Photoreflectance study of GaN/AlGaN structures

In this paper we report on the results of photoreflectance spectroscopy (PR) of undoped GaN/AlGaN heterostructures used for fabrication of high electron mobility transistors (HEMTs). For proper operation of such devices a triangular quantum well created at the interface between GaN and AlGaN is required. Due to spontaneous and piezoelectric polarisation-induced electric fields in GaN/AlGaN heterostructures, free electrons are accumulated close to the interface forming a two dimensional electron gas (2DEG). Aluminium composition in AlGaN can be determined from PR and thus the obtained data allow for estimation of the shape of 2DEG confinement potential which is necessary for verification of design assumptions and control of growth process