Novel approach for augmented carrier transfer and reduced Fermi level pinning effect in InAs surface quantum dots

Abstract

The present work introduces an in-situ technique to tune the inter-dot coupling between vertically aligned InAs surface and buried quantum dots (SQD and BQD). Here, we utilize the self-assembly growth kinetics to get the most stable SQDs with lowest possible surface states. We vary the monolayer (ML) coverage of top SQD layer (from 2.2 ML to 1.6 ML), keeping monolayer coverage of BQD constant (2.7 ML). The reduced Fermi level pinning effect is observed through the monolayer coverage minimization, and the upshifting of energy level in the conduction band is obtained. The degeneracy between BQD and SQD energy levels is maximized in case of the 1.6 ML SQD and an enhanced coupling between the two QD families is observed through the photoluminescence (PL) result analysis. The type-II carrier distribution with effect of the Fermi level pinning is reduced in the 1.6 ML SQD structure, which claims the highest level of Coulomb coupling between the two QD families. Also, AFM images show lower dispersion in size and shape of the surface dot with 1.6 ML coverage. The proposed optimum QD heterostructure would promote a QD based sensor with high efficiency in effect with higher level of inter- dot carrier tunneling.