Red Luminesecnce from Self-Assembled InAlAs/AlGaAs Quantum Dots with Bimodal Size Distribution

Red-emitting at about 640nm from self-assembled In_0.55Al_0.45As/Al_0.5Ga_0.5As quantum dots grown on GaAs substrate by molecular beam epitaxy are demonstrated. A doublepeak structure of photoluminescence (PL) spectra from quantum dots was observed, and a bimodal distribution of dot sizes was also confirmed by an atomic force micrograph (AFM) image for uncapped sample. From the temperature and excitation intensity dependence of PL spectra, it is found that the double-peak structure of PL spectra from quantum dots is strongly correlated to the two predominant quantum dot families. Taking into account the quantum-size effect on the peak energy, it is proposed that the high (low) energy peak results from a smaller (larger) dot family, and this result is identical to the statistical distribution of dot lateral size from the AFM image.