Tailoring the Geometry of Bottom-Up Nanowires: Application to High Efficiency Single Photon Sources

Abstract

For nanowire-based sources of non-classical light, the rate at which photons are generated and the ability to efficiently collect them are determined by the nanowire geometry. Using selective-area vapour-liquid-solid epitaxy, we show how it is possible to control the nanowire geometry and tailor it to optimise device performance. High efficiency single photon generation with negligible multi-photon emission is demonstrated using a quantum dot embedded in a nanowire having a geometry tailored to optimise both collection efficiency and emission rate.

The onset of tapering in the early stage of growth of a nanowire

“…Typical shapes are schematized in figure 1(a). While a pure cylinder shape appears most preferable for transport studies, a cone shape (tapered nanowire) allows a better extraction of the light from an embedded quantum dot [1][2][3][4], and the pencil shape, with a long thick cylinder and a strong tapering isolated near the nanowire tip [5] ('P' in figure 1(a)) may be preferable for a better light collection in photovoltaic devices [6,7]. Similar shapes and sizes have been demonstrated for different systems in spite of large differences in the material parameters, for instance ZnTe and InP with orders of magnitudes difference in the diffusion length along the nanowire [8].…”

“…1a. While a pure cylinder shape appears most preferable for transport studies, a cone shape (tapered nanowire) allows a better extraction of the light from an embedded quantum dot [1][2][3][4] , and the pencil shape, with a long thick cylinder and a strong tapering isolated near the nanowire tip 5 ("P" in Fig. 1a) may be preferable for a better light collection in photovoltaic devices 6,7 .…”

Quantitative analysis of the blue-green single-photon emission from a quantum dot in a thick tapered nanowire

“…10 of Refs. [16], no re-excitation is visible but the use of a logarithmic scale and the simultaneous measure of the decay curve would allow a better evaluation of the presence of a slow component (dark-exciton type) at the center of the correlation plot. A good example is Fig.…”

“…An attractive configuration for bright single-photon emission is that of a QD embedded in a waveguide [14], or even in a nanowire (NW) [15] which can be inserted in a photonic circuit [16]. The shell around the QD acts as a waveguide and it constitutes also an efficient environment akin to protect the QD from surrounding defects.…”

Unity yield of deterministically positioned quantum dot single photon sources

“…In the second growth step, the nanowire core was clad with a nm InP shell 33 which defines the photonic nanowire waveguide 7 into which the dot emits. For the shell growth, the temperature was increased by 20℃ to 450 C and the III/V ratio was adjusted to produce the tapered geometry 63 observed in Fig. 1 c in order to obtain a an emission profile suitable for efficient collection 64 , 65 .…”