Unintentional indium incorporation into barriers of InGaN/GaN multiple quantum wells studied by photoreflectance and photoluminescence excitation spectroscopy

InxGa1–xN/GaN single and multi quantum well (MQW) structures with x ≈ 0.13 were investigated optically by photoreflectance, photoluminescence excitation spectroscopy, and luminescence. Clear evidence of unintentional indium incorporation into the nominal GaN barrier layers is found. The unintentional In content is found to be around 3%. Inhomogeneous distribution of In atoms occurs within the distinct quantum well (QW) layers, which is commonly described as statistical alloy fluctuation and leads to the characteristic S-shape temperature shift of emission energy. Furthermore, differences in emission energy between the first and the other QWs of a MQW stack are found experimentally. This effect is discussed with the help of model calculations and is assigned to differences in the confining potential due to unwanted indium incorporation for the upper QWs.