Optical emission from InAs/InP self-assembled quantum dots: evidence for As/P intermixing

We have studied the optical properties of ultrathin InAs/InP quantum wells and Stranski-Krastanov nanostructures using photoluminescence and photoluminescence excitation experiments. For InAs epilayers thinner than 2.4 monolayers, the emission spectrum consists of a single peak and the ground-state exciton energy is in good agreement with predictions based on the tight-binding method for ultrathin quantum wells. Beyond this thickness, the photoluminescence spectra evolve to a multimodal emission indicative of the presence of families of quantum dots with small heights. The emission of these quantum dots is blue-shifted significantly (similar to 100 meV) from the predicted values. The discrepancy is explained by As/P intermixing that occurs during quantum dot formation.