Crystal Phase Quantum Dots in the Ultrathin Core of GaAs–AlGaAs Core–Shell Nanowires

Abstract

Semiconductor quantum dots embedded in nanowires (NW-QDs) can be used as efficient sources of nonclassical light with ultrahigh brightness and indistinguishability, needed for photonic quantum information technologies. Although most NW-QDs studied so far focus on heterostructure-type QDs that provide an effective electronic confinement potential using chemically distinct regions with dissimilar electronic structure, homostructure NWs can localize excitons at crystal phase defects in leading to NW-QDs. Here, we optically investigate QD emitters embedded in GaAs-AlGaAs core-shell NWs, where the excitons are confined in an ultrathin-diameter NW core and localized along the axis of the NW core at wurtzite (WZ)/zincblende (ZB) crystal phase defects. Photoluminescence (PL)-excitation measurements performed on the QD-emission reveal sharp resonances arising from excited electronic states of the axial confinement potential. The QD-like nature of the emissive centers are suggested by the observation of a narrow PL line width, as low as ~300 μeV, and confirmed by the observation of clear photon antibunching in autocorrelation measurements. Most interestingly, time-resolved PL measurements reveal a very short radiative lifetime <1 ns, indicative of a transition from a type-II to type-I band alignment of the WZ/ZB crystal interface in GaAs due to the strong quantum confinement in the ultrathin NW core.

Observing visible-range photoluminescence in GaAs nanowires modified by laser irradiation

“…Note, that similar structure may be used to design a single photon source, operating at room temperature. For example, recently developed single photon sources are based on GaAs 37 and InP 38 ZB/WZ superlattices.…”

Optical study of the band structure of wurtzite GaP nanowires

“…[1][2][3][4][5] Semiconductor nanowires (NWs) have shown excellent control of the growth of ZB-WZ phases, [6][7][8][9] allowing crystal structure band engineering. [10][11][12] Recently, the Auseeded growth of high purity WZ GaP nanowires via vaporliquid-solid (VLS) method was demonstrated, and the optical properties have been investigated. [13][14][15][16][17][18] Photoluminescence (PL) measurements on patterned arrays of WZ GaP wires showed optical emission at 2.09 eV with a short lifetime of $0.8 ns, indicating a direct band gap semiconductor.…”

Microscopic nature of crystal phase quantum dots in ultrathin GaAs nanowires by nanoscale luminescence characterization

“…Also, the type-II band alignment at the WZ/ZBinterface induces only indirect excitonic transitions with very long lifetimes (>several ns) due to the reduced overlap of electron and hole wave functions [4,14,[19][20][21][22]. Only very recently, first evidence was provided for bright and spectrally sharp single photon emitters from CPQDs in GaAs NWs with excitons confined in all three dimensions and with temporal characteristics exhibiting very fast lifetimes [23]. This was achieved by fabricating ultrathin, ∼10 nm wide GaAs-AlGaAs core-shell NWs with a random distribution of mixed WZ/ZB crystal phases, rotational twins and stacking defects [23,24].…”