Photoluminescence study of non-polar m-plane InGaN and near strain-balanced AlGaN/InGaN superlattices*

We present the first detailed study of the temperature-dependence of photoluminescence (PL) from m-plane bulk In_xGa_1-xN (x<0.25) layers and near strain-balanced AlGaN/InGaN superlattices grown by plasma-assisted molecular-beam epitaxy on free standing m-plane GaN substrates. The experimental PL peak positions were found to deviate from inter-band transition energies calculated using structural parameters obtained from high-resolution x-ray diffraction. The effect is stronger for superlattices than for bulk InGaN films. The temperature dependence of PL suggests the discrepancy is due to localization centers in InGaN. The low-temperature PL linewidths are narrower than some published results for both In_xGa_1-xN (x<0.1) and Al_0.2Ga_0.8N/In_0.09Ga_0.91N superlattices indicating lower alloy inhomogeneity than previously reported. We also observed the PL intensity drops dramatically as temperature increases. This suggests the presence of a high-density of non-radiative defects. We will describe our efforts to optimize growth conditions to increase PL efficiency and reduce PL linewidth at room temperature.