This PDF file contains the front matter associated with SPIE Proceedings Volume 8996, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

We have investigated the molecular beam epitaxial growth and characterization of InN nanowires. Detailed optical and electrical transport studies confirm that nondoped InN nanowires can exhibit extremely low (< 10¹⁵ cm^-3) residual electron density. Furthermore, the near-surface Femi-level was measured to be 0.4 to 0.5 eV above the valence band maximum (VBM), suggesting the absence of Fermi-level pinning and surface electron accumulation. These features are fundamentally different from those of n-type degenerate InN nanowires or InN epilayers. The absence of surface electron accumulation was also observed in Mg-doped InN nanowires, where p-type conduction was directly measured via Mg-doped InN nanowire field-effect transistors. Furthermore, the near-surface Fermi-level can be tuned from 0.1 eV to 1 eV above the VBM, i.e., from p-type degenerate to n-type degenerate through controlled Mg and Si dopant incorporations, a first demonstration for any semiconducting nanowire structures.

The development of epitaxial technology for the fabrication of quantum dot (QD) gain material operating in the 1.55 μm wavelength range is a key requirement for the evolvement of telecommunication. High performance QD material demonstrated on GaAs only covers the wavelength region 1-1.35 μm. In order to extract the QD benefits for the longer telecommunication wavelength range the technology of QD fabrication should be developed for InP based materials. In our work, we take advantage of both QD fabrication methods Stranski-Krastanow (SK) and selective area growth (SAG) employing block copolymer lithography. Due to the lower lattice mismatch of InAs/InP compared to InAs/GaAs, InP based QDs have a larger diameter and are shallower compared to GaAs based dots. This shape causes low carrier localization and small energy level separation which leads to a high threshold current, high temperature dependence, and low laser quantum efficiency. Here, we demonstrate that with tailored growth conditions, which suppress surface migration of adatoms during the SK QD formation, much smaller base diameter (13.6nm versus 23nm) and an improved aspect ratio are achieved. In order to gain advantage of non-strain dependent QD formation, we have developed SAG, for which the growth occurs only in the nano-openings of a mask covering the wafer surface. In this case, a wide range of QD composition can be chosen. This method yields high purity material and provides significant freedom for reducing the aspect ratio of QDs with the possibility to approach an ideal QD shape.

In this study, we have investigated metal-organic vapor phase epitaxial nano-patterned selective area growth of InGaAs/InP on non-planar (001) InP surfaces. Due to high etching resistance and the small molecular size of negative tone electron beam HSQ resist, the protection mask formed in HSQ has small feature sizes in ten nanometers scale and allow realization of in-situ etching. As was observed in the SAG regime, in-situ etching of InP by carbon tetrabromide leads to formation of self-limited structures. By altering etching time, the groove shape can be changed from a triangular trench to a trapeze. Another appealing aspect of in situ etching is that the shape of InGaAs can be tuned from a crescent to a triangular or a line by varying growth parameters. Quantum well wires can be fabricated by growing directly in the bottom of V-shaped groove. In addition, changes of mask orientations lead to anistropic or isotropic character of etching. The investigated technique of nano-patterned selective area growth allows obtaining different profiles of structures and different quantum structures such as quantum well or wires in the same growth run. To investigate the shape and crystalline quality of the active material, the cross-sectional geometry was observed by field emission scanning electron microscopy and scanning transmission electron microscopy. The optical properties were carried out at room temperature using micro-photoluminescence setup. The results showed different deposition rates for openings oriented along [0-11] and [0-1-1] directions with higher rate along [0-1-1]. The fabricated active material was incorporated into photonic crystal waveguides.

In order to understand the structural and electronic properties of semiconductor nanowires, scanning tunneling microscopy is an appealing technique that can supplement transmission electron microscopies and conventional electrical characterization techniques. It is able to probe the surface of semiconductor materials at the atomic scale and can be successfully applied to study the nanofaceting morphology, the atomic structure and the surface composition of oxide-free nanowire sidewalls. Based on the advantages provided by the unique geometry of semiconductor nanowires for a low-cost and efficient integration into nanoscale devices, additional characterization schemes performed with multiple probe scanning tunneling microscopy are also presented to get a deeper understanding of their transport properties.

GaAs nanostructures are used in different optoelectronic applications including solar cells, LEDs and fast electronics. Although GaAs shows outstanding optical properties, it suffers from surface states and consequently high surface recombination velocity. The surface depletion effects lead to semi-insulating behaviors in GaAs devices. Passivation of GaAs nanostructures (AlGaAs or ionic liquid) lead to surface stability and improvement in optoelectronic properties. We provide a systematic study to compare the optical and electrical improvement after passivation (AlGaAs or ionic liquid) of GaAs nanostructure including nanowires and nanosheets. Both room temperature and low temperature photoluminescent (PL) spectra indicate increase in optical activity of GaAs nanostructures after passivation. Electron beam induced current (EBIC) measurements reveal the diffusion length of carries in different GaAs nanostructures.

The incorporation of metal nano particles affects the efficiency of OPVs in both positive and negative ways. In our previous work, we demonstrated that by appropriately inserting AuNPs in the OPV device, the efficiency can be increased by 30%. In this work we show that AuNPs not only contribute to the increase in the total conversion efficiency of the OPVs by increasing the absorption rate of the active layer, but their plasmonic resonance also changes the characteristics of their surrounding medium. In this work we focus on the electrical properties of PEDOT: PSS and how they change due to AuNPs’ increased E-field and temperature. Further, the incorporation of AuNPs changes the workfunction and thus the exciton dissociation rate of the OPVs.

The objective of this study is to optimize the absorption in the active region of InAs/GaSb T2SL photodetectors for the realization of high-performance MWIR devices. Two sets of MWIR (λ_{100% cut-off} ~ 5.5μm at 77K) T2SL detectors were realized; one set with varied detector absorber thickness, the other set with varied T2SL period. The T2SL material quality was evaluated on the basis of room temperature photoluminescence (RTPL) and the high-resolution X-ray diffraction (HRXRD) data. Then the device performance was compared using spectral response, dark current and responsivity measurements. Finally, quantum efficiency was calculated and employed as a metric for the definition of the optimal T2SL period and active region thickness. For the first part of the study, a homojunction pin architecture based on 8 monolayers (MLs) InAs/8MLs GaSb T2SL was used. The thickness of the non-intentionally doped absorber layers were 1.5μm, 2.5μm, and 3.5μm. For the second part of the study, unipolar barrier (pBiBn) devices were grown. The thickness of the absorber region and the T2SL constituent InAs layer thicknesses were kept the same (1.5 μm and 8 MLs, respectively) whereas the T2SL constituent GaSb thickness was varied as 6 MLs, 8 MLs, and 10 MLs. We have found that the pin detector with 2.5 μm thick absorber and the pBiBn detector with 8 ML InAs/ 8 ML GaSb T2SL composition are, within the scope of this study, optimal for the realization of MWIR single-element devices and FPAs with corresponding architectures.

Siliceous frustules were extracted from a representative fresh water diatom species (Cyclotella sp.) by treating with aqueous hydrochloric (HCl) acid. The structural characterizations of cleaned frustules were examined by scanning electron microscope (SEM). The microscopy images showed that the diatoms have a regular circular shape and are of almost equal size (average length is 9μm and average width is 3 μm). From energy dispersive X –ray spectroscopy (SEM-EDS) spot analysis it was confirmed that the frustules isolated from diatoms are composed mainly of silicon in the form of amorphous silica (SiO2). The bond information of chemical substances of diatom frustules was carried out at ambient temperature by means of Fourier Transform Infrared (FTIR) Spectroscopy. FTIR spectrum as recorded in transmittance mode showed the characteristic peaks for diatom biosilica, including for Si-O-Si stretching vibration at 1057 and 776 cm^-1. Photoluminescence (PL) measurements of diatom frustules were performed at room temperature and it was observed that they emitted strong blue PL centered at 440nm when excited with ultraviolet (UV) radiation.

The behaviour of the plasmonic modes of supported strongly coupled silver nanocubes is studied. Silver nanocube monolayers with controlled particle density were fabricated via the Langmuir-Blodgett technique and deposited on substrates with varying refractive indices. Substrates include glass, thin films of silicon, and titanium oxide on glass. The dipolar and bonded dipolar modes are red shifted with increasing refractive index of the substrate. Surface-enhanced Raman spectroscopy (SERS) is used as a tool to probe the electric field enhancements of the silver nanocube monolayers. SERS enhancement of silver nanocube monolayers is found to be highly substrate dependant, typically decreasing with increasing refractive index of the underlying substrate. This work aims to find the source of this enhancement decrease, and distinguishes between effects related electromagnetic enhancement and effects caused by the optics of the Raman spectroscopy system itself.

The present work investigates the plasmonic properties and behaviour of silver nanocube monolayers deposited on thin gold films. Monolayers were deposited via the Langmuir-Blodgett method using a phospholipid as a passive spacer. Interparticle coupling was minimized by depositing at low surface pressures. The interaction of the nanocube monolayers with the gold films was mediated by utilizing polyelectrolyte layering to generate a passive spacer to control the distance between the cubes and substrate. Silver nanocubes were characterized by UV-Visible spectroscopy and transmission electron microscopy, and the monolayers were characterized by UV-Vis, and atomic force microscopy.

Fast imaging plasma plume study have been carried out on vanadium-oxygen plasma generated using 248 nm, 25 ns pulses from an excimer KrF laser under oxygen atmosphere. The plume expansion dynamics of an ablated VO₂ target was investigated using a fast-imaging technique. The free expansion, splitting, sharpening and stopping of the plume were observed during these oxygen pressures, 0.01, 0.05, 0.10 and 0.20 mbar. The influence of the plume dynamics study on the properties of the obtained vanadium oxide thin films were examined using X-Ray Diffraction method. A vanadium dioxide phases were deposited at 0.05 mbar oxygen pressure for target-substrate distance of 40 mm and 50 mm. Mixed phases of vanadium oxide were deposited at 0.01, 0.10 and 0.20 mbar oxygen pressure for target-substrate distance of 40 mm. Transition temperatures of around 60.9^oC have been measured from sample deposited at 0.05 mbar oxygen pressure for target-substrate distance of 50 mm. We observe mixed nanostructures for thin film prepared at 0.05 mbar for target-substrate distance of 40 mm, while the thin film prepared at 0.05 mbar for target-substrate of 50 mm shows an uniform nanostructure film.