Effect of interfacial states on the binding energies of electrons and holes in InAs/GaAs quantum dots

Abstract

The interface between an InAs quantum dot and its GaAs cap in ``self-assembled'' nanostructures is nonhomogeneously strained. We show that this strain can lead to localization of a GaAs-derived ${X}_{1c}$-type interfacial electron state. As hydrostatic pressure is applied, this state in the GaAs barrier turns into the conduction-band minimum of the InAs/GaAs dot system. Strain splits the degeneracy of this ${X}_{1c}$ state and is predicted to cause electrons to localize in the GaAs barrier above the pyramidal tip. Calculation (present work) or measurement (Itskevich et al.) of the emission energy from this state to the hole state can provide the hole binding energy, ${\ensuremath{\Delta}}_{\mathrm{dot}}^{(h)}.$ Combining this with the zero-pressure electron-hole recombination energy gives the electron binding energy, ${\ensuremath{\Delta}}_{\mathrm{dot}}^{(e)}.$ Our calculations show ${\ensuremath{\Delta}}_{\mathrm{dot}}^{(h)}\ensuremath{\sim}270\mathrm{meV}$ (weakly pressure dependent) and ${\ensuremath{\Delta}}_{\mathrm{dot}}^{(e)}\ensuremath{\sim}100\mathrm{meV}$ at $P=0.$ The measured values are ${\ensuremath{\Delta}}_{\mathrm{dot}}^{(h)}\ensuremath{\sim}235\mathrm{meV}$ (weakly pressure dependent) and ${\ensuremath{\Delta}}_{\mathrm{dot}}^{(e)}\ensuremath{\sim}50\mathrm{meV}$ at $P=0.$ We examine the discrepancy between these values in the light of wave-function localization and the pressure dependence of the hole binding energy.