This PDF file contains the front matter associated with SPIE Proceedings Volume 10543, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

We present our recent progress in the monolithic integration and epitaxial gain control of GaAs-based nanowire (NW) lasers on Si photonic platform. First, we describe the challenges in realizing vertical-cavity NW lasers on Si and SOI-based waveguides based on the stringent requirements for high gain, low-loss wave-guiding and coupling efficiency as illustrated by detailed numerical simulations. Consequently, we discuss bottom-up, epitaxial schemes for site-selective integration of individual GaAs NW lasers on planar Si and non-planar Si ridge waveguides under different geometries, demonstrating vertical-cavity NW lasers with remarkably low lasing threshold (< 20 µJ/cm2) and high spontaneous emission coupling factor (B > 0.2) under pulsed optical excitation. First experiments of individual NW-lasers with direct coupling of lasing emission into the underlying Si-ridge waveguides are also shown. To further improve the threshold gain and lasing characteristics and achieve wavelength tunability, we further tailor the active gain media using low-dimensional systems embedded in the NW resonator cavity. Here, we particularly emphasize the challenges in the growth of GaAs-based cavities that incorporate coaxial GaAs-AlGaAs and InGaAs-AlGaAs multiple quantum well (MQW) heterostructures and illustrate even routes towards quantum-wire or quantum-dot based gain media. Finally, we provide a direct comparison of the lasing characteristics of 3D-bulk like GaAs NW lasers with coaxial NW-MQW heterostructure lasers, and show how the control of composition and structure of the MQW shifts the lasing emission to longer wavelengths.

Semiconductor nanowire (NW) lasers have recently attracted increasing attention as ultra-small, highly-efficient coherent light emitters in the fields of nanophotonics, nano-optics and nanobiotechnology. Although there have been several demonstrations of single NW lasers utilizing bulk materials, it is crucial to incorporate lower-dimensional quantum nanostructures into the NW in order to improve device performance with respect to threshold current, differential gain, modulation bandwidth and temperature sensitivity. The quantum dot (QD) is a useful and essential nanostructure that can meet these requirements. In this presentation, we will introduce our recent research progress in NWQD lasers with various device configurations. The NW cavities with multi-stacked In_0.2Ga_0.8As/GaAs QDs are grown on shallow (∼35 nm) GaAs core NWs and followed by GaAs/Al_0.1Ga_0.9As/GaAs core/shell/cap structures. Lasing oscillation have been so far achieved at room temperature by properly designing the NW cavity and tailoring the emission energy of each QD to enhance the optical gain. In this paper, several NWQD lasers with various device configurations are demonstrated and discussed; NWbased plasmonic QD lasers, free-standing NWQD lasers grown on DBRs/GaAs(111)B substrates, and NWQD lasers embedded in flexible substrates. Furthermore, we propose and demonstrate a growth scheme to reduce the lateral size of NWQDs by post-growth annealing to enhance their quantum confinement effect.

The integration of III-V optoelectronics on Si substrates is essential for next-generation high-speed communications. The major issue in the integration of III-V semiconductor on Si is the lattice mismatch between Si and the III-V semiconductor material at the interface. The strain induced by the lattice mismatch can be relaxed when a nanostructure, such as a nanopillar (NP), is grown on Si. In this work, we experimentally determine the lasing mode by optically pumping a single InGaAs nanopillar grown on Si on insulator (SOI). The lasing features of the InGaAs NP are characterized with different optical techniques. Power dependent photoluminescence (PL) at 7K is carried out to determine the lasing threshold by increasing the excitation power. The carrier dynamics below and above the threshold have been studied at 7K from time-resolved photoluminescence (TRPL) experiments at different excitation powers. We have measured a decrease in the carrier lifetimes with a rise in excitation power until the nanostructure starts lasing. The lifetime corresponding to the laser mode is on the order of the sensitivity of the streak camera (±1ps) indicating the extremely short laser lifetime. The InGaAs nanolaser shows a single longitudinal mode because of the small length dimensions (<1μm). The wavelength of the laser mode emission changes with each NP excited due to the slight differences in dimensions between NPs. In addition, the quality of the crystal grown has been studied with temperature-dependent PL. These results will contribute to further optimization of the InGaAs nanolaser for integration of III-V optoelectronics on Si substrates.

To characterize surface recombination of nanowires, time-resolved photoluminescence (TRPL) is commonly implemented to correlate measured lifetime with the nonradiative effect at surface. In this work, we develop a threedimensional transient model to perform a numerical analysis of surface recombination for InGaAs nanowires on GaAs substrates. By mimicking a complete TRPL measurement process, we computationally calculate optical generation and emission of InGaAs nanowires, and numerically probe the carrier dynamics inside nanowires. It is found that the TRPL spectra are determined by a complex convolution of surface recombination velocity and incident wavelengths. In addition, we show that due to the three-dimensional geometry of nanowire, using a typical analytical equation to extract surface recombination velocity might be no longer valid. We believe these results provide an alternative approach for the computational analysis of TRPL measurements and surface properties for three-dimensional nanostructured devices.

Recently, to sandwich InAs QDs with GaAs1-xSbx layers have attracted enormous attention. It is expected to achieve a transition from type-I to type-II band alignment at ~ x=12%. The type-II InAs/GaAs1-xSbx QDs are predicted to be one of the optimizing active region materials for achieving high efficient intermediate-band solar cells. We first investigate PL properties of InAs/GaAs1-xSbx QD structures of different Sb compositions (x=0, 0.15, and 0.25) in the GaAs1-xSbx capping layer. By capping the InAs QDs with GaAs0.85Sb0.15 and GaAs0.75Sb0.25 layer, we are able to gain type II QDs. These type II QDs exhibit a clear multi-peaks characteristic under increasing laser excitation intensity, which stems from different carriers recombination routes due to the combination of InAs QDs with GaAs1-xSbx capping layer. Time-resolved PL measurements further confirm our assignment for the mnulti-peaks in the PL spectra. We then study carrier coupling inside vertically aligned InAs/GaAs and InAs/GaAs1-xSbx QD pairs. The features of InAs/GaAs1-xSbx QD pairs are very different from the traditional InAs/GaAs QD-pairs. Again, clear multi-peaks characteristic are observed under stronng laser excitation intensity, which stems from different carriers recombination routes from the top InAs/GaAs1-xSbx QDs. Our investigations indicate that the optical behavior and carrier dynamics in type-II InAs/GaAs1-xSbx QDs and QD-pairs are much more complicated than the InAs/GaAs QDs counterparts. This study provide useful information for understanding the band structure and carrier dynamics of the InAs/GaAs1-xSbx QDs for high efficiency solar cell applications.

In this work, we investigated the effects of phosphorus ions implantation on InAs/GaAs QDs by varying the fluences from 8× 10¹¹ to 1×10¹³ ions/cm² at a fixed energy of 50 keV. Temperature dependent photoluminescence (PL) study shows a suppression of emission efficiency with the increase of fluence of implanted ions, attributed to the generation of defects/dislocations near around QDs acting as trapping centers for photocarriers. All the implanted samples demonstrated degradation in activation energy from 184 meV (as-grown) to 73 meV (highest fluence sample) indicating weaker carrier confinement in QDs. Implantation also resulted 40 nm blue shift in PL emission wavelength which is caused due to the atomic intermixing between QDs and surrounding materials. Rocking curves plotted from the double crystal X-ray diffraction study, depict a vanishing trend of satellite peaks with the increase of fluence of implanted ions, resulting from the loss of interface sharpness due to interdiffusion.

Silicon nanowires (Si NWs) array have emerged as a promising route on the road to achieve highly efficient solar cells (SCs). The NWs SCs can achieve highly efficient light trapping with reduced cost and material usage. However, it is difficult to fabricate NWs with smoothed surfaces due to the deficiency in the fabrication process. The surface roughness of SCs is an essential parameter of the optoelectronic performance of these devices. In this paper, the effect of surface roughness on the optical and electrical performance of the NW SCs is reported and analyzed. The optical absorption and the generation rates are calculated using 3D finite difference time domain (FDTD) method while the electrical characteristics are calculated using finite element method via Lumerical device software package. In this investigation, short circuit current density, open circuit voltage and power conversion efficiency (PCE) are numerically studied to quantify the electrical performance of the reported structure. The simulation results show that the Si NWs with 10% surface roughness has higher PCE than smoothed Si NWs counterpart by 8.33%. This is due to the multiple scattering between the SiNWs which increases the light absorption and hence the PCE.

Metal halide perovskite materials are emerging as highly promising materials for high performance optoelectronic devices thus triggered broad attention. Nanostructured perovskite materials have wide applications in nanoelectronics and nano-optoelectronics. Due to incompatibility of metal halide perovskite materials with conventional lithography techniques, it is preferable to achieve nano-perovskite material growth and assembly at the same time for further device applications. In our work, we have developed a chemical vapor deposition (CVD) process to grow ordered three-dimensional (3-D) metal halide nanowire (NW) arrays in nanoengineering templates. This unique CVD process utilizes metal nanoclusters at the bottom of vertical nanochannels to initiate high quality NW growth. As the nanochannels have largely controllable geometrical factors, namely, periodicity, diameter and depth, NW geometry can also be precisely nanoengineered. As the result, the ordered 3-D NW arrays can achieve ultra-high NW density in the range of ~109/cm2. The 3-D NW arrays are conspicuously promising for 3-D integrated nano-electronics/optoelectronics. To further demonstrate the technological potency of the perovskite NW arrays, they have been fabricated into photodetectors and proof-of-concept image sensors. Each image sensor consists of 1,024 photodiode pixels made of vertical perovskite NWs, and the imaging functionality has been verified by recognizing various optical patterns projected on the sensor. In addition, we have also discovered that the chemically and mechanically robust template can effectively protect perovskite NWs from water and oxygen invasion thus the material stability is significantly better than planar perovskite films confirmed by photoluminescence and photoelectric measurements.

The deep subwavelength confinement of infrared light offers exciting opportunities to manipulate photons, engineer thermal energy transport, and enhance molecular reactivity. Applications leveraging these phenomena will require constituent materials and devices that not only exhibit precisely controlled structural and compositional heterogeneity, but also can be produced at very large scales. Purely top-down fabrication techniques are unlikely to succeed in both regards. The bottom-up vapor-liquid-solid (VLS) mechanism – whereby a liquid seed particle collects precursor molecules from the vapor and directs crystallization of a nanowire – promises the requisite nanoscale programming of structure and composition while simultaneously being amenable to high-throughput manufacturing. This talk will describe our recent efforts to synthesize, understand, and engineer the infrared plasmonic properties of VLS-grown semiconductor nanowires. In particular, I will discuss (i) how programming of dopant profile along the nanowire length enables designer infrared spectral responses, (ii) that combining the dielectric properties of semiconductors and the 1-D geometry of nanowires leads to very strong near-field interactions, and (iii) that these interactions promise the efficient waveguiding of light and heat.

Nanowires show unique promise as nanoscale building blocks for a multitude of optoelectronic devices, ranging from solar cells to terahertz photonic devices. We will discuss the epitaxial growth of these nanowires in novel geometries and crystallographic phases, and the use of terahertz conductivity spectroscopy to guide the development of nanowire-based devices. As an example, we will focus on the development of nanowire-based polarization modulators for terahertz communications systems.

Foreign-catalyzed assisted grown nanowires deteriorate the performance of optoelectronic devices because of incorporation of foreign impurities into the nanowires. We report on growth self-catalyzed p-type GaAs nanowires (NWs) with pure zinc blende (ZB) structure, and the fabrication of single-NW-based photodetector. The carrier mobility and concentration of GaAs field effect transistor are characterized both at room temperature and at low temperature respectively. Due to the absence of stacking faults and single crystal phase of the NWs, the photodetector exhibits room-temperature high photo-responsivity over than 105 A W-1 and great specific detectivity, which outperforms previously reported NW-based photodetectors. These results demonstrate that these self-catalyzed pure-ZB GaAs NWs to be promising candidates for optoelectronics applications. In addition, optoelectronic properties of single quantum dots embedded in single nanowires will be represented with an applied magnetic field.

We give an overview on the present status of self-assembled quantum structure fabrication by using the local droplet etching (LDE) technique during semiconductor molecular-beam epitaxy (MBE). LDE functionalizes nanodroplets to drill spatially well separated nanoholes into semiconductor surfaces. The mechanisms, the influence of substrate and droplet materials, and the control of the nanohole shape and size by the process parameters is discussed. LDE nanoholes in AlGaAs are filled for the creation of strain-free GaAs quantum dots (QDs). LDE QDs demonstrate a tunable emission wavelength, narrow exciton peaks, a low exciton fine-structure splitting, and single-photon emission which suggests them for applications in quantum information processing. The QD shape can be varied by the process parameters from cone-like to a shape where the probability distributions of the charge carriers are concentrated on a cone shell. For the cone-shell QDs, we predict the controlled transformation of either the electron or the hole from a quasi zero-dimensional dot into a one-dimensional quantum ring by a gate-voltage. Furthermore, also coupled quantum systems can be fabricated by a self-aligned vertical stacking into a LDE nanohole. A first example are GaAs quantum dot molecules (QDMs) which are formed from two QDs. LDE QDMs exhibit indirect excitons and anti-crossings which indicates strong coupling. A second example are hybrids composed of a single QD and a plasmonic nanostructure. Here, first results establish that self-assembled metallic nanostructures can be filled into nanoholes and that LDE QDs can be located very close to metallic structures clearly within their optical near-field.

The self-assembly of epitaxial quantum dots on (001) surfaces, driven by compressive strain, is a widely used tool in semiconductor optoelectronics. In contrast, the growth of quantum dots on (111) and (110) surfaces has historically been a significant challenge. In most cases the strain relaxes rapidly via dislocation nucleation and glide before quantum dots can form. In this paper, we discuss a method for the reliable and controllable self-assembly of quantum dots on both (111) and (110) surfaces, where tensile strain is now the driving force. By showing that tensile-strained self-assembly is applicable to several material systems, we demonstrate the versatility of this technique. We believe that tensile-strained self-assembly represents a powerful tool for heterogeneous materials integration, and nanomaterial development, with future promise for band engineering and quantum optics applications.

Quantum dot nanostructures are one of the best practical examples of emerging nanotechnologies hence offering superior properties as compared to their quantum well counterparts. InAs/GaAs quantum dots allow producing energy- and cost-efficient devices with outstanding temperature stability, lowest threshold current, ultrafast gain dynamics, and low amplified spontaneous emission. This paper reports on the recent achievements in ultrafast and nonlinear dynamics properties of InAs/GaAs quantum dot lasers for radar systems, wireless communications and high-speed optical communications. Passive mode-locking is shown to exhibit a great potential for microwave, millimeter-wave and Terahertz signal generation with high repetition frequency tuning and jitter reduction. The optical feedback is also used to stabilize the pulse emission leading an integrated timing jitter as low as 90 fs without consuming additional power. Lastly, multimode optical feedback dynamics of InAs/GaAs QD lasers emitting on different lasing states is also studied. In particular, a chaos free operation is observed for the first time from the ground state lasing operation.

The absorption due to phonon vibrations in graphene oxide quantum dots (GO-QDs) has been modified by localized plasmons induced by Ag nanoparticles (NPS). The interference of phonons and plasmons results in coherent interaction that leads to the formation of "dark states" and "coherent population trapping" related to Fano like effect. The localized electric field effectively drives the phonons which in turn modifies the coherent interaction in exciton absorption states of graphene oxide. A quantum optical theory is used to qualitatively explain the differential absorption spectra measured using pump-probe spectroscopy demonstrating the formation of dark states.

Quantum dot(QD) based devices are capped with various strain reducing layers in order to improve quality of dots by low surface diffusion and increase detection to long wavelength infrared region(LWIR). We present a model for the effect of various strain reducing layers on quantum dot heterostructures and study the corresponding variation in optoelectronic properties viz. photoluminescence (PL), photoluminescence excitation (PLE) and device characteristics of the samples. Schrödinger equation was used in the concentration dependent model in order to calculate ground state and inter-sub band energy-levels. Three InAs QD (2.7 ML) samples with different capping GaAs (Sample A), 6 nm In_0.15Ga_0.85As (Sample B) and 6 nm In_0.15Ga_0.85As DWELL (Sample C with 2 nm pseudomorphic layer of In_0.15Ga_0.85As) were grown. Low temperature (8 K) PL spectra exhibits ground state peak at 1112.62, 1150 and 1166.93 nm for samples A, B and C, respectively. PLE measured at 8 K exhibited first and second excited state peaks at 1046.15 nm, 991.59 nm for Sample A, 1079nm and 1003nm for Sample B and 1095.55nm and 1034.51nm for Sample C. Highest absolute area measured using temperature dependent PL (photocurrent) was observed for sample B which can be justified by increment in quantum dots formation thus resulting higher quantum yield. Single pixel detectors were fabricated and sample B yielded lowest dark current density at 80 K. A multicolor spectral response was observed from sample B with corresponding peaks at 5.13 and 7.53 μm. The calculated energy levels are in good agreement with experimental results (PL and PLE). Spectral response peaks observed from all samples were successfully matched to the energy levels calculated from the simulation.

Quantum dots based devices suffer certain disadvantages like low quantum efficiency, smaller absorption co-efficient and high dark current. Dot-in-a- well heterostructures (DWELL) offers tuning of detection peak wavelength, low dark current and higher operating temperature with optimized quantum well thickness. In this report, we correlate the optoelectronics properties of 3 different DWELL structures namely samples A, B and C having SRL thickness of 4, 6 and 8 nm, respectively with concentration-dependent theoretical model. A blue shift of around 24 nm with a decrease in PL intensity is observed as the capping thickness increases above 6 nm. Full width at Half Maximum (FWHM) decreases from B to C. These are attributed to the presence of large number of defect states and the formation of InGaAs wells with dissolution of dots in C. Low temperature PL measurement at 2.54W/cm² and Photoluminescence Excitation (PLE) spectrum validate the presence of InGaAs wells peak at 1094.4nm for C. All samples exhibited peak spectral response at 7.56 μm. A concentration-dependent theoretical model using the Schrödinger equation was developed to calculate ground-state and inter-sub band energy-levels. The developed model shows great agreement with experimentally observed peaks from PL, PLE and spectral response. The same model was used to calculate the energy levels for InGaAs well. Based on the InGaAs experimental peak at 1.134 eV, average In concentration in the well was calculated to be around 30%.

The hydrostatic (ε_hy) and biaxial (ε_bi) strain in lateral (x) and growth (z) direction have been computed and compared for InAs quantum dot (QD) with different capping. The capping layers are: GaAs, InGaAs/GaAs, InAlGaAs/GaAs, InGaAs/InAlGaAs/GaAs, InAlGaAs/InGaAs/GaAs, and the total thickness is kept constant for all QD structures. The strain distribution is mainly confined within the dot and dies down towards the capping layer. The movement of conduction band edges is controlled by hydrostatic strain. QDs capped with InAlGaAs/InGaAs/GaAs and InAlGaAs/GaAs shows lower magnitude of ε_hy, which indicates better carrier confinement as compared to other capping. The electrostatic potential obtained for the InAlGaAs capped QDs is larger (~0.5 V) than other structures. The valence band splitting into the heavy hole and light hole depends on the biaxial strain. It is observed that GaAs and InAlGaAs/InGaAs/GaAs capping has the smallest and largest values of ε_bi respectively in the growth direction. The GaAs capped QD structure has a smaller ε_bi, which would increase the energy of the ground state hole, leading to blue shift in photoluminescence spectrum. However, the ground hole state has a lower energy due to larger ε_bi in InAlGaAs/InGaAs/GaAs capped QD, which results in a red shift in the photoluminescence spectrum (~1.35 μm at 300 K). Nonetheless, InAlGaAs capped QDs shows better results in the lateral direction also. Thus, based on the strain profile, QDs capped with InAlGaAs as the first capping layer is the optimized structure which can be useful for various optoelectronic applications.

The surface-enhanced Raman scattering (SERS) active substrates with high enhancement factor are required to detect trace concentration of biological or organic molecules by using SERS techniques. This work presents the results of the detection of trace concentration of pyridine by using silver nanotrees (AgNTs) that were deposited on silicon. The different densities of AgNTs were fabricated by electroless deposition on silicon wafer by using aqueous solution of HF and AgNO³ with changing etching time. It was observed that with increasing the time of etching the density of the fabricated AgNTs increased at room temperature. The morphology of the fabricated AgNTs was studied by using field emission scanning electron microscope (FESEM). The AgNTs with high branching gave the highest Raman spectrum of pyridine. In addition, the optical properties of the fabricated AgNTs at various etching time have been investigated by using a UV-vis- NIR spectrophotometer. The absorption increased with increasing the etching time due to increasing of branches of silver on silicon substrate.

Currently, silicon nanoparticles (SiNPs) are of great interest due to their potential applications in various fields such like optoelectronics, microelectronics, photonics, photovoltaics, chemical, and biologic sensors. SiNPs Become the most important and well-known semiconductor because Si-based devices have dominated microelectronics for many decades. Indeed, the production of smart SiNPs materials to enhance absorption and light scattering is currently the most convenient approach.

Recently, plasmonic fractal-like structures have been determined to enhance photovoltaic device performances; indeed, through an efficient coupling of the incident light at different frequency bands into both the surface plasmon modes and the cavity modes, a broadband absorption enhancement can be accomplished.

Silicon nanoparticles exhibit fluorescence deriving from Si quantum dot structures which are produced during chemical etching, and it can be synthesized with unique optical reflectivity spectra. These unique characteristics allow porous silicon to exhibit a signal that is affected in a expected way when exposed to environmental changes, presenting possibilities for the development of advanced functional systems that incorporate sensors for therapeutic functions or diagnostic.

In order to prevent rapid degradation after administration and to increase their blood half life, biocompatible polymers coating was performed on silicon nanoparticles. Different type of biocompatible polymers (chitosan, polylactic acid, PMMA, or dextran,) can be used.

However, several methods have been developed for the synthesis of silicon nanoparticles such as chemical etching, sol-gel technique, laser ablation, sputtering process; hot-wire synthesis, ball milling process, and microemulsion.

The main objective of this research is to develop a new technique for coating or encapsulation of Nanoparticles to modify their surface properties by using different polymers. Furthermore, polymers are non-toxic, non-flammable, relatively inexpensive and recyclable.

A simple, convenient and low cost chemical synthesis technique, chemical bath deposition, are used to deposit cadmium sulfide (CdS) and cadmium selenide (CdSe) quantum dots on glass substrates. Based our characterizations, high quality CdS and CdSe thin films have been deposited on the substrates. In order to synthsize CdS quantum dots on glass, we use cadmium sulfate (CdSO₄), ammonia water (NH₄OH) and thiourea (CS(NH₂)₂) as reaction agents. For CdSe thin films, we use cadmium acetate as cadmium ion source and sodium selenosulfate / thiourea as a selenium / sulfur ion sources. Aqueous ammonia is used as a complex reagent and also to adjust the pH of the final solution. The asdeposited thin films using this technique are optically transparent, adherent, homogeneous and yellowish for CdS and redish for CdSe without powdered precipitation. The deposition can be made at 60 – 70°C under magnetic stirring for all samples. The films have been characterized by X-ray diffraction, scanning electron microscope (SEM), and UV-Vis absorption. The SEM measurements show that the shapes of deposited CdSe nanoparticles on glass substrates can be controlled to exhibit different shapes under different reaction conditions.