Abstract
We demonstrate single-photon emission from self-assembled m-plane InGaN quantum dots (QDs) embedded on the side-walls of GaN nanowires. A combination of electron microscopy, cathodoluminescence, time-resolved microphotoluminescence (μPL), and photon autocorrelation experiments give a thorough evaluation of the QD structural and optical properties. The QD exhibits antibunched emission up to 100 K, with a measured autocorrelation function of g(2)(0) = 0.28(0.03) at 5 K. Studies on a statistically significant number of QDs show that these m-plane QDs exhibit very fast radiative lifetimes (260 ± 55 ps) suggesting smaller internal fields than any of the previously reported c-plane and a-plane QDs. Moreover, the observed single photons are almost completely linearly polarized aligned perpendicular to the crystallographic c-axis with a degree of linear polarization of 0.84 ± 0.12. Such InGaN QDs incorporated in a nanowire system meet many of the requirements for implementation into quantum information systems and could potentially open the door to wholly new device concepts.
Highlights
The ability to generate on-demand single photons is of vital importance to quantum information technology such as quantum cryptography, linear optical quantum computing, and quantum metrology.[1−3] Due to their high stability, good repetition rates, and practicable incorporation into cavities and electronically pumped structures,[4] quantum dots (QDs) are ideal candidates for the generation of, and interaction with, single photons
Due to their wurtzite crystal structure, the orientation of quantum well (QW) and QD nanostructures relative to the crystal axis is of great importance; most work in the nitrides features growth on the polar (0001) c-plane, causing large in-built fields across the heterostructures leading to decreased oscillator strengths of exciton transitions via the quantum-confined Stark effect (QCSE)
To gain further insight into the InGaN layer morphology, high-resolution transmission electron microscopy (TEM) imaging has been performed on cross-sectional lamella prepared by focused ion beam (FIB) milling
Summary
QD growth methods have not translated well onto m-plane substrates.[17]. While claims have been made for fabrication of mplane QDs,[18−20] only the formation of nanostructures on mplane facets has been demonstrated; there is currently no single-QD spectroscopy that shows optical emission from individual nanostructures, provides evidence of their QD-like behavior, or demonstrates their superior properties relative to c-plane QDs. These line widths are several times higher than many other reported values for InGaN QDs.[31,33,34] We have attributed the larger-than-expected ZPline width to the likely significant presence of spectral diffusion in the sample, given the probable high density of point defects associated with the Si dopants, which act as charge trapping sites in the regions in which QDs are formed, as discussed previously. QD formation, signal to background estimations, emission energy vs temperature, and temperature dependence of lifetimes and polarization (PDF)
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