Origin of the radiative emission in blue-green light emitting diodes based on GaN/InGaN heterostructures

Phase separation effects induced by spinodal decomposition taking place in cubic In_xGa_1−xN epitaxial layers were investigated by means of resonant Raman scattering (RRS) and X-ray diffractometry (XRD) experiments. The alloy epilayers were grown by radio-frequency plasma-assisted molecular beam epitaxy on GaAs (001) substrates. Ab initio theoretical calculation of the alloy phase diagram predicts the formation of In-rich phases in the layers which is confirmed by the RRS and XRD experiments. Photoluminescence observed at room temperature and 30 K from the layers shows light emission in the blue-green region of the spectrum. RRS experiments demonstrated that the observed emission is directly linked to the In-rich separated phases (quantum dots) in the alloy. The results support the model that the origin of light emission in nitride-based light emitting diodes and laser diodes is related to quantum confinement effects taking place in quantum dots formed in the InGaN layers, active media of the devices.