Coherent optoelectronic control of single excitons

Steffen J. Michaelis de VasconcellosPaderborn, Univ., Diss., 200

Quantum optics with single quantum dot devices

A single radiative transition in a single-quantum emitter results in the emission of a single photon. Single quantum dots are single-quantum emitters with all the requirements to generate single photons at visible and near-infrared wavelengths. It is also possible to generate more than single photons with single quantum dots. In this paper we show that single quantum dots can be used to generate non-classical states of light, from single photons to photon triplets. Advanced solid state structures can be fabricated with single quantum dots as their active region. We also show results obtained on devices based on single quantum dots.Peer Reviewe

InAs avalanche photodiodes

The ability to efficiently detect low-level light in the infrared above wavelengths of 1.7 μm is becoming increasingly important for many applications such as gas sensing, defence/geoscience ranging and clinical thermography. The III-V narrow gap semiconductor InAs, with a bandgap of 0.36 eV, is well known for its use as a conventional photodiode. The aim of this thesis was to design, build and test InAs devices for use as reverse biased avalanche photodiodes. In order to fabricate a lownoise detector, a passivation study was conducted. For the first time we report the achievement of high quality single crystal II-VI passivation layers on InAs mesa structures. Pre-growth surface oxide removal processes were developed to improve surface morphology of II-VI layers grown on InAs samples. ZnSe and ZnTe successfully terminate the InAs mesa devices preventing atmospheric oxidation. Low surface leakage currents are observed at low reverse bias and at room temperature for both materials. LIDAR at wavelengths greater than 2 μm was studied using these InAs mesa photodiodes, showing potential to take advantage of the low solar background at these wavelengths. For the first time, laboratory based LIDAR experiments, with ranges of around 0.5 metre stand-off distance, were performed with InAs n-i-p edge illuminated mesa photodiodes, used in linear multiplication mode. Time-of-flight measurements were demonstrated at wavelengths from 1.3 μm to 2.365 μm. A 6 mm ranging error was observed in these short range measurements

Near infrared heteronanocrystals with enhanced electro-optical properties : from synthesis to layer formation

Synthesis of nanocrystals actived in the near infrared and study of their opto-electronic properties

Design Rules for Obtaining Narrow Luminescence from Semiconductors Made in Solution

Solution-processed semiconductors are in demand for presentandnext-generation optoelectronic technologies ranging from displaysto quantum light sources because of their scalability and ease ofintegration into devices with diverse form factors. One of the centralrequirements for semiconductors used in these applications is a narrowphotoluminescence (PL) line width. Narrow emission line widths areneeded to ensure both color and single-photon purity, raising thequestion of what design rules are needed to obtain narrow emissionfrom semiconductors made in solution. In this review, we first examinethe requirements for colloidal emitters for a variety of applicationsincluding light-emitting diodes, photodetectors, lasers, and quantuminformation science. Next, we will delve into the sources of spectralbroadening, including "homogeneous" broadening fromdynamical broadening mechanisms in single-particle spectra, heterogeneousbroadening from static structural differences in ensemble spectra,and spectral diffusion. Then, we compare the current state of theart in terms of emission line width for a variety of colloidal materialsincluding II-VI quantum dots (QDs) and nanoplatelets, III-VQDs, alloyed QDs, metal-halide perovskites including nanocrystalsand 2D structures, doped nanocrystals, and, finally, as a point ofcomparison, organic molecules. We end with some conclusions and connections,including an outline of promising paths forward

Enhanced carrier multiplication in engineered quasi-type-II quantum dots

Sem informaçãoOne process limiting the performance of solar cells is rapid cooling (thermalization) of hot carriers generated by higher-energy solar photons. In principle, the thermalization losses can be reduced by converting the kinetic energy of energetic carriers into additional electron-hole pairs via carrier multiplication (CM). While being inefficient in bulk semiconductors this process is enhanced in quantum dots, although not sufficiently high to considerably boost the power output of practical devices. Here we demonstrate that thick-shell PbSe/CdSe nanostructures can show almost a fourfold increase in the CM yield over conventional PbSe quantum dots, accompanied by a considerable reduction of the CM threshold. These structures enhance a valence-band CM channel due to effective capture of energetic holes into long-lived shell-localized states. The attainment of the regime of slowed cooling responsible for CM enhancement is indicated by the development of shell-related emission in the visible observed simultaneously with infrared emission from the core.518Sem informaçãoSem informaçãoSem informaçãoC. M. C., L. A. P., K. A. V., I. R., J.M.P. and V. I. K acknowledge support of the Center for Advanced Solar Photophysics (CASP), an Energy Frontier Research Center (EFRC) funded by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES). N.S.M. is a CASP member supported by LANL Director's Postdoctoral Fellowship. Q. L. and H. L. are CASP affiliates supported by the New Mexico Consortium and Los Alamos National Laboratory