This PDF file contains the front matter associated with SPIE Proceedings Volume XXXX, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

This paper aims to investigate the effects of the temperature on the mode-locking capability of two section InAs/InP quantum nanostructure (QN) passively mode locked lasers. Devices are made with multi-layers of self-assembled InAs QN either grown on InP(100) (5 quantum dashes (QDashes) layers) or on InP (311)B (6 quantum dots (QDs) layers). Using an analytical model, the mode-locking stability map is extracted for the two types of QN as a function of optical absorption, cavity length, current density and temperature. We believe that this study is of first importance since it reports for the first time a systematic investigation of the temperature-dependence on the mode-locking properties of InAs/InP QN devices. Beside, a rigorous comparison between QDashes and QDs temperature dependence is proposed through a proper analysis of the mode-locking stability maps. Experimental results also show that under some specific conditions the mode-locking operation can be temperature independent.

The effect of low energy H^– ions implantation on the InAs/GaAs quantum dot infrared photodetectors had been studied. Light ion implantation was found to be an effective post growth technique which helped dark current density suppression by four orders in the implanted devices. In this study we had mainly concentrated on determining how the defect-related material and structural changes had an impact on dark current density reduction for InAs/GaAs quantum dot infrared photodetectors.

One of the grand challenges for future solid state lighting is the development of high efficiency, phosphor-free white light emitting diodes (LEDs). In this context, we have investigated the molecular beam epitaxial growth and characterization of nanowire LEDs on Si, wherein intrinsic white-light emission is achieved by incorporating selforganized InGaN quantum dots in defect-free GaN nanowires on a single chip. We have further demonstrated that, with the incorporation of p-type modulation doping and AlGaN electron blocking layer, InGaN/GaN dot-in-a-wire white LEDs can exhibit nearly zero efficiency droop and significantly enhanced internal quantum efficiency (up to ~57%) at room-temperature.

The optical properties of nanostructured metallic nanofilms have been extensively studied in last few years. It was observed, for a wide variety of structures an enhancement in the transmission that can be explained as resulting from surface plasmon polaritons (SPP) waves propagating at the interface between the metallic film and the surrounding dielectric and/or substrate. In this work we utilize confocal microscope images as a useful tool to characterize the optical response of a set of concentric nanorings in the presence of SPP waves. We show for the first time the influence of the metal thickness on the light intensity profile. Reflected and transmitted light for concentric nanorings were observed under excitation of different laser wavelengths (405-633nm) as well as white light. Microscopy imaging with polarized light showed not only the spatial pattern of the radiation transmitted through these apertures but also a significant dependence of these patterns on the film thickness. The behavior was theoretically analyzed via basic principles as well as numerical simulation with standard software. A possible explanation is describing each ring as a source of radiation formed by two dipole systems, one electric dipole aligned to the applied electric field and a second one, a magnetic dipole, associated to a loop-antenna having an azimuthally non-homogeneous current dependence. This preliminary model is an ongoing study which may be useful to explain the behavior of the transmitted light. Analysis also showed the potential of confocal microscope for imaging nanostructures as well as for quantitative information on SPP excitation.

Single QDs are desirable probe objects for studying near-field optical interactions with photonic structures, however, they are often very difficult to manipulate due to their small sizes. Here, we describe a technique for the manipulation of individual colloidal CdSe/ZnS quantum dots (QDs) with nanometer accuracy along a two dimensional surface. A microfluidic approach is described which provides two-dimensional positioning of single QDs with nanoscale accuracy. In addition, we discuss the engineering of a water-based fluid that provides localization of QDs to within 100 nm of the channel surface. Through a combination of surface localization and in plane manipulation, a setup is described where single QDs can be utilized as single emitter probes for studying local light-matter interactions in a planar geometry.

We examined the interdot energy transfer between monodisperse quantum dots under different degrees of plasmonic effects (plasmonic field enhancement and Forster energy transfer from quantum dots to metallic nanoparticles). For this we studied emission of CdSe/ZnS quantum dots deposited on substrates containing self-organized arrays of gold nanoislands with radially distributed sizes gradually reduced from the centers of the substrates to their sides. The results suggest how metallic nanoparticles can be used to enhance interdot energy transfer in monodisperse quantum dots and how this process can explain some of the spectral changes seen in the emission of quantum dots when they are close to the metallic nanoparticles.

We studied how deposition of a very thin layer of gold or chromium oxide on glass substrates can modify the way irradiation changes the fluorescence of CdSe/ZnS quantum dots. We found that the gold layer tends to shield the quantum dots from the substrate, preventing photoinduced fluorescence enhancement caused by the Coulomb blockage. In this case the emission of the quantum dots did not show also any broadening but rather a slight red shift, independent of the irradiation time. In the case of the chromium-oxide coated substrates we observed significant broadening and blue shift, indicating such oxide could enhance photo-oxidation of colloidal quantum dots significantly.

Ga(As)Sb quantum dots (QDs) are epitaxially grown in AlGaAs/GaAs in the Stranski-Krastanov mode. In the recent past we achieved Ga(As)Sb QDs in GaAs with an extremely high dot density of 9.8∙10¹⁰ cm^-2 by optimization of growth temperature, Sb/Ga flux pressure ratio, and coverage. Additionally, the QD emission wavelength could be chosen precisely with these growth parameters in the range between 876 and 1035 nm. Here we report a photoluminescence (PL) intensity improvement for the case with AlGaAs barriers. Again growth parameters and layer composition are varied. The aluminium content is varied between 0 and 90%. Reflectance anisotropy spectroscopy (RAS) is used as insitu growth control to determine growth rate, layer thickness, and AlGaAs composition. Ga(As)Sb QDs, directly grown in Al_xGa_1-xAs emit no PL signal, even with a very low x ≈ 0.1. With additional around 10 nm thin GaAs intermediate layers between the Ga(As)Sb QDs and the AlGaAs barriers PL signals are detected. Samples with 4 QD layers and Al_xGa_1-xAs/GaAs barriers in between are grown. The thickness and composition of the barriers are changed. Depending on these values PL intensity is more than 4 times as high as in the case with simple GaAs barriers. With these results efficient Ga(As)Sb QD lasers are realized, so far only with pure GaAs barriers. Our index-guided broad area lasers operate continuous-wave (cw) @ 90 K, emit optical powers of more than 2∙50 mW and show a differential quantum efficiency of 54% with a threshold current density of 528 A/cm².

A better understanding of structural properties and growth kinetics of Stranski-Krastanov (SK) quantum dots is necessary for applying dot potential in optical and electronic applications. In fact, We have recently demonstrated theoretically and experimentally, the ability of reflection high energy electron diffraction (RHEED) tool in quantitative analysis such as extracting average dot size, facet orientation and average dot density and real time monitoring of dot size during growth .As an extended study, in this work for the first time we present the experimental evidence on onset epitaxial quantum dot average shape evolution and theoretical predictions on QD facet orientations.

The stability of colloidal PbS quantum dot (QD) films deposited on various substrates including glass and GaAs was studied. Over a period of months, the QD film sample was re-tested after being left unprotected in air under ambient conditions. Despite exposure to 532 nm laser excitation and cooling to cryogenic temperatures, the initial photoluminescence (PL) remained stable between tests. We also retested a set of samples that had remained under ambient conditions for over 2 years. To track potential changes to the QDs over time, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), optical microscopy, UV-Vis-NIR spectrophotometry and atomic force microscopy (AFM) were employed. Evidence points towards oxidation enforced shrinking of the active QD volume causing a blue shift of the absorption and photoluminescence. The presented studies are important for reliability expectations of light emitters based on PbS QDs.

Energy transfer between CdSe/ZnS quantum dots of different sizes were studied through the Thermal Lens technique. It was possible to obtain the energy transfer efficiency and the individual luminescence quantum efficiency of systems containing two sets of quantum dots with different sizes.

The quantum dot infrared photodetector is an emerging technology for advanced imaging. Multi-color imaging technologies are favored as they extend the boundary of applications of the device. We report multi-spectral performance of MBE grown InGaAs/GaAs (device A) and InAs/GaAs (device B) based photodetector with In_0.21Al_0.21Ga_0.58As capping at 77K. Spectral response measurement of device A shows the presence of a strong photoresponse at 10.2μm. Device B exhibits a four color response (5.7, 9.0, 14.5, 17 and 20 μm) over a broad range (5-20μm) at very low bias voltage.