We derive a general relation between the fine-structure splitting (FSS) and the exciton polarization angle of self-assembled quantum dots under uniaxial stress. We show that the FSS lower bound under external stress can be predicted by the exciton polarization angle and FSS under zero stress. The critical stress can also be determined by monitoring the change in exciton polarization angle. We confirm the theory by performing atomistic pseudopotential calculations for the InAs/GaAs quantum dots. The work provides deep insight into the dot asymmetry and their optical properties and a useful guide in selecting quantum dots with the smallest FSS, which are crucial in entangled photon source applications.

Using atomistic pseudopotential and configuration-interaction many-body calculations, we predict a metal-nonmetal transition and an excitonic ground state in the InAs/InSb quantum dot (QD) system. For large dots, the conduction band minimum of the InAs dot lies below the valence band maximum of the InSb matrix. Due to quantum confinement, at a critical size calculated here for various shapes, the single-particle gap Eg becomes very small. Strong electron-hole correlation effects are induced by the spatial proximity of the electron and hole wavefunctions, and by the lack of strong (exciton unbinding) screening, afforded by the existence of fully discrete 0D confined energy levels. These correlation effects overcome Eg, leading to the formation of a bi-excitonic ground state (two electrons in InAs and two holes in InSb) being energetically more favorable (by ∼ 15 meV) than the state without excitons. We discuss the excitonic phase transition on QD arrays in the low dot density limit. The formation of excitons in semiconductors and insulators usually requires energy, e.g. photons, for one has to excite carriers across the single-particle band-gap E g . There is a special interest, however, in the possibility of forming excitons exothermically, i.e. an "excitonic ground state" as envisioned by Mott [1] and Keldysh et al. [2]. Indeed, the electron-hole system exhibits a rich range of phases [3,4] as a function of the carrier density and effective-mass ratio m e /m h , including various excitonic insulating states such as molecular solid, exciton liquid, Mott insulator, and also various metallic phases. The excitonic ground state is of fundamental interest in itself because excitons can be a better alternative to atoms for studying Bose-Einstein condensation [5,6] on account of the lighter excitonic mass, thus higher condensation temperature. It is natural to search for excitonic ground states in systems where E g is small, yet the screening is weak enough so as to prevent unbinding of the exciton. The search in bulk solids [7] has thus focused on indirect gap semiconductors and semimetals to reduce screening, but excitonic ground states have not been conclusively observed so far in such systems. Ground state excitons were also searched in nanostructures, specifically in spatially indirect quantum-wells [8,9], where electrons and holes are confined in different spatial regions. In "type II" systems such as GaInAs/InP or CdTe/CdSe, electrons are localized in the well, whereas holes are localized on the barrier, so screening is weak, but E g is finite. In contrast, in "type III" heterostructures such as [10] InAs/GaSb, the conduction band minium (CBM) of the InAs well is lower than the valence band maximum (VBM) of the GaSb barrier, so at certain a well thickness one can have E g →0 [10], as well as separation of electrons from holes. Thus, at this thickness, one could expect an excitonic ground state if the electron-hole correlation energy will be large enough to stabilize the complex. Recent experiments [11] show evid...