Energy level alignment of confined hole states in InAs1−x−ySbxPy asymmetric double quantum dots for single-photon energy up- and downconversion

We present a combined experimental and theoretical study of uncapped In(As, Sb, P) graded composition laterally coupled asymmetric double quantum dots (DQDs), suited for application in nanodiodes or single-photon nano-optical up- and downconverters in the mid-infrared spectral range. We provide details on the growth process using liquid-phase epitaxy and characterization using atomic-force microscopy and scanning electron microscopy (SEM). We find that most DQDs exhibit asymmetry such that the two quantum dots (QDs) of each pair have different dimensions, giving rise to correspondingly different quantum confinement of hole states localized in each QD. Based on these data, we have performed systematic simulations using an eight-band k·p model to identify the relationship between QD dimensions and the energy difference between corresponding confined hole states in the two QDs. Finally, we have determined the strength of an applied electric field required to energetically align the hole ground states of two QDs of different dimensions in order to facilitate hole tunneling to the next QD for further recombination and single-photon emission with a different wavelength.