Bulk InAlAs(111)A as a novel material system for pure, single photon emission

Certain protocols for quantum cryptography rely on a single photon source.\footnote{Shields, Nat. Phot. 1, 215 (2007)} Semiconductor quantum dots (QDs) are an attractive candidate for single photon generation: QDs can be incorporated into scalable cavity/waveguide structures, and QD quantum key distribution has already been demonstrated.\footnote{Rau et al., New J. Phys. 16, 043003 (2014)} Growth of III-V QDs is well established, but very close control is required. QD density/size are dramatically affected by small changes in growth parameters, which is a challenge for QD uniformity. In contrast, we present a material system with a remarkably straightforward growth process, which delivers single photon emission. We see spectrally sharp emission lines from bulk InAlAs grown on InP(111)A. Via cross-sectional STM and $k\cdot p$ simulations, we identify excitons in indium-rich nanoclusters as the origin of these spectral features. In-rich regions form spontaneously during growth via nanoscale InAlAs phase-segregation. Nanocluster emission has median linewidth 137 eV, and fine structure splitting 28 eV. We confirm on-demand emission of pure, single photon emission, with 2nd-order correlation values $g^{(2)} = 0.05_{-0.05}^{+0.17}$ (CW), and $0.24 \pm 0.02$ (triggered).