Dependence of the electronic structure of self-assembled InGaAs/GaAs quantum dots on height and composition

摘要

While electronic and spectroscopic properties of self-assembledIn_{1-x}Ga_{x}As/GaAs dots depend on their shape, height and alloycompositions, these characteristics are often not known accurately fromexperiment. This creates a difficulty in comparing measured electronic andspectroscopic properties with calculated ones. Since simplified theoreticalmodels (effective mass, k.p, parabolic models) do not fully convey the effectsof shape, size and composition on the electronic and spectroscopic properties,we offer to bridge the gap by providing accurately calculated results as afunction of the dot height and composition. Prominent results are thefollowing. (i) Regardless of height and composition, the electron levels formshells of nearly degenerate states. In contrast, the hole levels form shellsonly in flat dots and near the highest hole level (HOMO). (ii) In alloy dots,the electrons' ``s-p'' splitting depends weakly on height, while the ``p-p''splitting depends non-monotonically. In non-alloyed InAs/GaAs dots, both thesesplittings depend weakly on height. For holes in alloy dots, the ``s-p''splitting decreases with increasing height, whereas the ``p-p'' splittingremains nearly unchaged. Shallow, non-alloyed dots have a ``s-p'' splitting ofnearly the same magnitude, whereas the ``p-p'' splitting is larger. (iii) Asheight increases, the ``s'' and ``p'' character of the wavefunction of the HOMObecomes mixed, and so does the heavy- and light-hole character. (iv) In alloydots, low-lying hole states are localized inside the dot. Remarkably, innon-alloyed InAs/GaAs dots these states become localized at the interface asheight increases. This localization is driven by the biaxial strain present inthe nanostructure.