Relaxation-induced lattice misfits and their effects on the emission properties of InAs quantum dots

Strain relaxation in InAs/InGaAs quantum dots (QDs) is shown to introduce misfits in the QD and neighboring GaAs bottom layer. A capacitance-voltage profiling shows an electron accumulation peak at the QD with a long emission time, followed by additional carrier depletion caused by the misfits in the GaAs bottom layer. The emission-time increase is explained by the suppression of tunneling for the QD excited states due to the additional carrier depletion. As a result, electrons are thermally activated from the QD states to the GaAs conduction band, consistent with observed emission energies of 0.160 and 0.068 eV which are comparable to the confinement energies of the QD electron ground and first-excited states, respectively, relative to the GaAs conduction band. This is in contrast to non-relaxed samples in which emission energy of 60 meV is observed, corresponding to the emission from the QD ground state to the first-excited state.