Spectral diffusion is a result of random spectral jumps of a narrow line as a result of a fluctuating environment. It is an important issue in spectroscopy, because the observed spectral broadening prevents access to the intrinsic line properties. However, its characteristic parameters provide local information on the environment of a light emitter embedded in a solid matrix, or moving within a fluid, leading to numerous applications in physics and biology. We present a new experimental technique for measuring spectral diffusion based on photon correlations within a spectral line. Autocorrelation on half of the line and cross-correlation between the two halves give a quantitative value of the spectral diffusion time, with a resolution only limited by the correlation set-up. We have measured spectral diffusion of the photoluminescence of a single light emitter with a time resolution of 90 ps, exceeding by four orders of magnitude the best resolution reported to date

We present a high-temperature single-photon source based on a quantum dot inside a nanowire. The nanowires were grown by molecular beam epitaxy in the vapor-liquid-solid growth mode. We utilize a two-step process that allows a thin, defect-free ZnSe nanowire to grow on top of a broader, cone-shaped nanowire. Quantum dots are formed by incorporating a narrow zone of CdSe into the nanowire. We observe intense and highly polarized photoluminescence even from a single emitter. Efficient photon antibunching is observed up to 220 K, while conserving a normalized antibunching dip of at most 36%. This is the highest reported temperature for single-photon emission from a nonblinking quantum-dot source and principally allows compact and cheap operation by using Peltier cooling.

We have carried out a detailed optical characterization of a single CdSe quantum dot embedded in a ZnSe nanowire. Exciton, biexciton, and charged exciton lines have been identified unambiguously using photon correlation spectroscopy. This technique has provided a detailed picture of the dynamics of this system. It has been found that the dark exciton has a strong influence on the optical properties. The most visible influence is the strongly reduced excitonic emission compared to the biexcitonic one. Temperature-dependent lifetime measurements have allowed us to measure a large splitting of ⌬E = ͑6.0Ϯ 0.2͒ meV between the dark and the bright exciton as well as the spin-flip rates between these two states. This type of semiconducting quantum dot turns out to be a very efficient single photon source in the visible. Its particular growth technique opens additional possibilities as compared to the usual self-assembled quantum dots.

We have studied spectral diffusion of the photoluminescence of a single CdSe quantum dot inserted in a ZnSe nanowire. We have measured the characteristic diffusion time as a function of pumping power and temperature using a recently developed technique [G. Sallen et al, Nature Photon. \textbf{4}, 696 (2010)] that offers subnanosecond resolution. These data are consistent with a model where only a \emph{single} carrier wanders around in traps located in the vicinity of the quantum dot

We report on the growth of ZnSe nanowires and nano-needles using molecular beam epitaxy (MBE). Different growth regimes were found, depending on growth temperature and the Zn-Se flux ratio. By employing a combined MBE growth of nanowires and nano-needles without any post-processing of the sample, we achieved an efficient suppression of stacking fault defects. This is confirmed by transmission electron microscopy and by photoluminescence studies.

ZnSe nanowire heterostructures were grown by molecular beam epitaxy in the vapour-liquid-solid growth mode assisted by gold catalysts. Size, shape and crystal structure are found to strongly depend on the growth conditions. Both, zinc-blende and wurtzite crystal structures are observed using transmission electron microscopy. At low growth temperature, cone-shaped nano-needles are formed. For higher growth temperature, the nanowires are uniform and have a high aspect ratio with sizes of 1-2 µm in length and 20-50 nm in width as observed by scanning electron microscopy. Growing a nanowire on top of a nano-needle allows us to obtain very narrow nanorods with a diameter less than 10 nm and a low density of stacking fault defects. These results allow us the insertion of CdSe quantum dots in a ZnSe nanowire. An efficient photon anti-bunching was observed up to 220 K, demonstrating a high-temperature single-photon source.An appealing application for semiconductor nanowires (NWs) is the inclusion of quantum dots (QDs) into the NW. Due to the narrow lateral size, NW QD heterostructures can be directly grown on defined positions and without the necessity of self-assembly. This is especially important for for II-VI materials, where selfassembled QD formation occurs only within narrow windows of growth conditions [1]. Recently, II-VI compound semiconductor NWs have been synthesized by Au-catalysed metal-organic chemical vapour deposition (MOCVD) and molecular-beam epitaxy (MBE) methods [2,3,4]. QD devices can be utilized as emitters for the effective and controlled generation of single-photon states. Single-photon emission from a GaAsP/GaP NW QD was reported before at cryogenic temperature in ref. [5]. High-temperature experiments from individual Stransky-Krastanov (SK) grown QDs were reported from CdSe/ZnSe QDs [6] and from GaN/AlN QDs [7]. Both experiments showed photon anti-bunching up to 200 K with normalized dip values of 81% and 53%, respectively. Other systems have demonstrated room temperature single photon emission: nanocrystals [8] have the drawback that they suffer from blinking effect [9]; colour centres in diamond [10,11] have shown very reliable operation but with a very broad spectrum. Anyways, neither nanocrystals nor colour centres in diamond offer the possibility of electrical excitation, which is a very realistic and very promising perspective for semiconducting nanowires [12].In this paper, we report MBE growth of ZnSe NWs on Si and GaAs substrates and insertion of CdSe QDs in these NWs. The growth process is based on the Aucatalyzed VLS method. The morphology of the NWs depending on the growth parameters was examined by * Corresponding author. E-mail: thomas.aichele@physik.huberlin.de; present address: Institut für Physik, Humboldt Universität zu Berlin, Hausvogteiplatz 5-7, 10117 Berlin, Germany scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). We found two different growth regimes, resulting in either narrow and uniform NWs, or cone-shape nano-needles. Wh...

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In this chapter, current trends in the development and application of quantum dots (QDs) inserted in semiconductor nanowires are reviewed. The epitaxial growth of nanowires is explained, based on the example of CdSe QDs included into defect‐free ZnSe nanowires. Finally, an overview is provided of the diverse applications in the life sciences, nanoelectronics and quantum optics, especially on their use as sources for single photons at high temperature.