In(Ga)As/GaAs quantum dots grown on a (111) surface as ideal sources of entangled photon pairs

Abstract

Self-organized In͑Ga͒As/GaAs quantum dots ͑QDs͒ grown on ͑111͒ substrate are proposed as ideal sources for the generation of entangled photon pairs. Due to the threefold rotational symmetry of the ͑111͒ surface, QDs with C 3v symmetry or higher are expected to develop during growth. In contrast to QDs on ͑001͒-oriented substrates, the symmetry of the confinement potential of ͑111͒ QDs is not lowered by piezoelectric effects. As a result the excitonic bright splitting vanishes and the biexciton→ exciton→ 0 recombination cascade can be used for the generation of entangled photons. We evaluate the spectroscopic separability of excitonic and biexcitonic emissions as a function of QD size, shape, and composition using the configuration-interaction model in conjunction with eight-band k · p theory. The piezoelectric field in ͑111͒ QDs predominantly aligns along the growth direction and gives rise to vertical charge separation. First-and second-order piezoelectric fields are oriented in opposite directions. The In/Ga ratio inside the QD determines the leading contribution and can be employed to balance both terms in order to achieve a field-free situation with maximal electron-hole overlap. The biexciton binding energy depends on the net piezoelectric potential drop across the QD vertical extension and becomes maximal if the first-and second-order fields outweigh each other within the QD interior.

Magnetic field induced valence band mixing in [111] grown semiconductor quantum dots

“…15 This growth axis has the advantage of providing in principle quantum-dot shape of the higher C 3v point symmetry. Really, small fine structure splittings in as grown [111] quantum dot structures have been recently predicted 16,17 and observed [18][19][20][21] making such structures a very promising system for entangled photon pair emission.…”

Accurate defect levels obtained from the HSE06 range-separated hybrid functional

“…4͑b͒ and 4͑c͔͒. Recently, the theoretical works of R. Singh et al 25 and A. Schliwa et al 26 on C 3v symmetric QDs have come to our attention. The assignment of a set of dark and bright transitions made in Ref.…”

Excitonic fine structure splitting in type-II quantum dots

“…Using (111) substrates for the growth of InAs QDs reduced both structural asymmetry and piezoelectric contribution. 8 Another attempt involved strain-free GaAs/AlGaAs QDs with zero piezoelectric field, which, however, still exhibited a finite FSS due to structural elongation. 5,9 Post-growth annealing 10 of InAs QDs allowed to decrease FSS from 96 µeV to mere 6 µeV.…”