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We report the optical spectroscopic results of a single self-assembled In0.75Al0.25As/Al0.3Ga0.7As quantum dot. The polarization-dependent shift of the Zeeman splitting in a single InAlAs QD has been observed. The induced Overhauser field is estimated to be ∼0.16 T in this InAlAs QD and the magnitude is shown to be controllable by the degree of circular polarization of excitation light.

We report the experimental demonstration of single-photon and cascaded photon pair emission in the infrared, originating from a single InAsP quantum dot embedded in a standing InP nanowire. A regular array of nanowires is fabricated by epitaxial growth on an electron-beam patterned substrate. Photoluminescence spectra taken on single quantum dots show narrow emission lines. Superconducting single photon detectors, which have a higher sensitivity than avalanche photodiodes in the infrared, enable us to measure auto and cross correlations. Clear antibunching is observed ͓g ͑2͒ ͑0͒ = 0.12͔ and we show a biexciton-exciton cascade, which can be used to create entangled photon pairs. © 2010 American Institute of Physics. ͓doi:10.1063/1.3506499͔Semiconductor quantum dot ͑QD͒ structures are attractive candidates for solid-state single photon and/or entangled-photon pair generation. 1-3 Nanowire QDs ͑NW-QDs͒ are promising candidates for such sources because of the controllability of doping, shape, and material freedom. 4,5 Fine structure splitting is predicted to be absent, which makes NW-QDs ideal for the creation of entangled photon pairs. 6 Single photon emission from a NW-QD has been shown at wavelengths shorter than 1000 nm. 7 However, a single photon NW-QD emitter at telecommunication wavelengths and a detailed study of its emission lines has not been reported, because until recently a single photon detector ͑SPD͒, with a high enough signal to noise ratio at infrared wavelengths and an adequate timing resolution was lacking. In this letter, we report on the fabrication and characterization of a regular array of InAsP QD embedded in an InP NW, emitting around 1.3 m and characterization of the QD photoluminescence ͑PL͒ using superconducting SPDs ͑SSPDs͒. We demonstrate controlled positioning of the NWs by growing them in a regular array. Control of the position is important for uniform growth, which is necessary for uniform QDs. SSPDs offer single photon detection with low dark counts, excellent timing resolution, and decent efficiency in the infrared, without the need for gating. In addition, SSPDs have very short dead times ͑10 ns͒ and no after pulsing. These characteristics enable us to perform auto and cross correlation experiments.Arrays of InAsP QDs embedded in InP NWs are synthesized by selective area metal organic vapor phase epitaxy ͑SA-MOVPE͒. 8 A metal catalyst is usually used ͑i.e., Au͒ to grow NW structures, however with SA-MOVPE a catalyst is not needed, preventing diffusion of the metal into the NW. A ͑111͒ InP wafer is covered by 30 nm of SiO 2 . By electron beam lithography and wet-etching, 40-60 nm diameter openings are created to form NW nucleation-sites. At a growth rate of 3 nm/s, first a 1 m long segment of InP is grown by adding trimethylindium and tertiarybutylphosphine ͑TBP͒ to the MOVPE reactor at 640°C. Subsequently the temperature is lowered to 580°C and arsine ͑AsH 3 ͒ is added to the reactor ͑V/III ratio 340, partial pressure TBP: AsH 3 3:1͒ to grow 8 to 10 nm InAsP to form the QDs. The ...