Combined optical and electrical studies of the effects of annealing on the intrinsic states and deep levels in a self-assembled InAs quantum-dot structure

The effects of postgrowth rapid thermal annealing on the electronic states in a relatively long wavelength (∼1.3μm), self-assembled InAs∕GaAs quantum-dot structure are investigated. We combine optical and electrical experiments, i.e., photoluminescence (PL) and deep-level transient spectroscopy (DLTS) measurements, to identify the underlying physical processes responsible for the changes in the PL spectra at different annealing temperatures. Physical parameters of the intrinsic and deep-level states are quantitatively determined in the DLTS experiments. These include the thermal excitation energies, densities, and their changes with the annealing temperature. We observe that the densities of the deep levels that coexist in the quantum-dot layer decrease and a new deep level, about 0.62eV below the GaAs conduction band edge, is formed at elevated temperatures. Both effects explain the variations in the PL spectra. Moreover, beyond what can be revealed in the PL experiments, the DLTS spectra show a more complex electronic structure of both optically active and inactive states.