Café com Física

Início

Agenda

29 de agosto de 2018
16h
Sala F-149 (LEF)

Stanko Tomić

University of Salford, Manchester, UK

Single Photon Sources Based on InGaN/GaN Single Quantum Dots

Proof-of-principle demonstrations with InAs/GaAs [1], GaN/AlN [2] and phosphide-compatible material systems have shown that solid-state quantum dots (QDs) can be near-ideal sources of quantum light, albeit covering narrow wavelength ranges. Radiative recombination from exciton (X) and biexciton (XX) states, confined in InGaN/GaN wurtzite quantum dots (QD), could potentially provide useful sources of visible quantum-light, targeting applications in the nascent field of quantum information, amongst others. To assess their potential, a theoretical methodology with which to calculate single-particle states was established, based on both symmetry exact strain-dependent envelope function Hamiltonian, with contributions from the spin-orbit interaction, crystal-field splitting, piezoelectric and spontaneous polarization all included. Excitonic states were found using the configuration interaction method that takes quantum mechanics effects of charge correlations and exchange explicitly [3], whilst taking into account the important second-order effect of piezoelectricity in this III-N material system [4]. The influence of mirror changes was eliminated with a Makov-Payne correction, adapted to wurtzite lattices. The optimal QD morphology for use in quantum light sources was determined by varying the aspect ratio, based on the optimization of the target function, which depends on the biexcitonic shift and optical dipole matrix element of the excitonic transition. The model established in this work is validated against experimental results on existing single GaN QD sources [2]. Further to this the model predicts that, with suitable variation of the In concentration within the QD, from 20 to 70%, it is possible to find morphologies that emit throughout the entire visible spectrum, i.e., from ~3 to 1.6 eV [5]. Within this range of In-concentrations conditions can be found for the formation bound biexcitons. [5] The competition between strong confinement in InGaN QDs and the internal electric field, generally reported in wurtzite III-N, was also investigated, as well as its effect on existence of bound biexcitons and a vanishing fine-structure spitting. The latter is a prerequisite for the on-demand generation of the entangled-photon pairs from InGaN-QD’s.

[1] R. M. Stephenson, R. J. Young, P. Atkinson et al. Nature 439, 179 (2006)

[2] S. Kako, C. Santori, K. Hoshino et al, Nature Materials 5, 887 (2006)

[3] S. Tomić and N. Vukmirović, Phys. Rev. B 79, 245330 (2009)

[4] J. Pal, G. Tse, V. Haxha, M. A. Migliorato, and S. Tomić, Phys. Rev. B 84, 085211 (2011)

[5] S. Tomić, J. Pal, M. Milgliorato, R.J. Young, N. Vukmirović, ACS Photonics 2, 958 (2015)