This PDF file contains the front matter associated with SPIE Proceedings Volume 11291, including the Title Page, Copyright Information, Table of Contents, Author and Conference Committee lists.

Bright fiber-coupled single photon sources are essential components for practical quantum network. In this work, we present a bright single photon source based on an InAs/InP quantum dot emitting at telecom wavelengths. We designed a nanobeam with a photonic crystal mirror at the other end and a tapered coupler at the other end enabling both directional emission and gaussian-like far-field profile. We detected fiber-coupled single photon count rate of 1.1 MHz with 40 MHz pumping rate. Considering losses from optics and spectral filters, we achieved collection efficiency into first lens of 68% and a total fiber collection efficiency of 8.2%.

We are studying here the heterogeneously coupled Submonolayer (SML) on Stranski-Krastanov (SK) quantum dot (QD) heterostructures. The consolidation in SML on SK heterostructure has been observed by varying growth rate as 0.05 and 0.1 ML/sec. The barrier thickness between SK and SML QDs has also been varied as 5, 7.5, and 10 nm. Pphotoluminescence(PL) study shows transition of carriers with dot size distribution. The peak from SK QDs is prominent in PL spectra of both growth rate samples. The absence of SML peak from the PL might be due to the tunnelling of carriers from SML to SK QDs, which follows the SK ground energy states for recombination. SML peak is visible only in low growth rate sample for barrier thickness of 10 nm, as with higher barrier thickness there is reduction in the probability of tunnelling of carriers. Samples with lower growth rate shows bimodal dot size distribution at barrier thickness 7.5nm, whereas higher growth rate samples shows monomodal dot size distribution. Compressive strains were extracted from high-resolution X-Ray diffraction (HRXRD) measurement. From the HRXRD measurement, it has been found that the strain decreases with increasing barrier thickness. Low growth rate samples have less strain as compared to high growth rate samples. In the lower growth rate samples, PL peak is red shifted as compared to higher growth rate samples due to less strain in the heterostructures and larger size QDs. Therefore, this study will be useful for advanced optoelectronic applications.

Self-assembled InAs quantum dot (QD) based heterostructures have been emerged as a potential candidate for optoelectronic device application over last decade due to the three dimensional carrier confinement. Here, we qualitatively demonstrate the effect of growth rate of both QD and capping layer on the photoluminescence (PL) result of MBE grown InAs/GaAs QD heterostructures. The investigated samples are having 2.7 monolayer (ML) near-surface InAs QDs. The InAs QDs in samples A and B are grown with growth rates of 0.2 and 0.1 ML/sec respectively, whereas growth rate of the GaAs capping layer is kept constant (0.62 μm/hr) in both samples. In sample C, QD and capping layer are grown at 0.2 ML/sec and 1.13 μm/hr, respectively. Sample B exhibited lower full-width half maximum of ground peak (36 nm) as compared to sample A (40 nm). This indicates better homogeneity in dot size distribution in sample B, which has a lower growth rate of QDs. Moreover, sample C with higher growth rate of capping layer showed red-shift in PL as compared to sample A. It can be inferred that the growth rate of capping layer affects the composition of QDs by suppressing In diffusion from QDs towards the capping layer. However, sample C showed decrement in PL intensity and it could be attributed to the dissolution of dots due to higher growth rate of capping layer. There is trade-off in optimization of growth rate variabilities of both QDs and capping layer.

Laser interference lithography is used to directly pattern the growing surface during molecular beam epitaxy growth of self-assembled InAs quantum dots on GaAs (100) substrates. Arrays of few-monolayer high nano-islands are formed prior to InAs quantum dot growth, which we believe result from the surface diffusion promoted by transient photothermal gradients. The deposition of InAs on such a surface leads to the nucleation of quantum dots solely at the island sites. The number of dots per site is determined by the island size which varies with the laser energy intensity. We are able to achieve highly ordered dense arrays of quantum dots with a single nanosecond laser pulse exposure. InAs quantum dots formed in this fashion show bright narrow photoluminescence with a peak at 1.04 eV at 88 K.

This Conference Presentation, "Ultrafast photodetectors based on high-mobility indium gallium antimonide nanowires," was recorded at Photonics West 2020 held in San Francisco, California, United States.

A key application of metallic nanostructures is enhancement of the radiative decay rates of quantum emitters. In this contribution we investigate control of emission dynamics of semiconductor quantum dots (QDs) using combination of both metal oxides and plasmonic effects of gold thinfilms. Different metal oxides, including Cu, Ag and Al oxides are investigated. We show how such oxides can dramatically change the decay of QDs via photocatalytic processes in the absence and presence of plasmonic fields. The outcomes show the distinct impact of such oxides, ranging from total annihilation of QD emission to their plasmonic revival via Purcell effect.

Sn-containing group IV semiconductors (Si)GeSn represent a versatile platform to implement a variety of Si-compatible photonic, optoelectronic, and photovoltaic devices. This class of semiconductors provides two degrees of freedom, strain and composition, to tailor the band structure and lattice parameter thus laying the groundwork to implement novel heterostructures and low-dimensional systems on a Si substrate. In this presentation, we will discuss the recent progress in controlling and understanding the opto-electronic properties of metastable (Si)GeSn semiconductor nanowires and heterostructures. We will shed new light on the basic mechanisms governing their epitaxial growth and thermal stability. We will also discuss the opto-electronic properties and present strategies to integrate these material systems in the fabrication of short wavelength infrared (SWIR) and mid-infrared (MIR) detectors and light emitting devices.

Perovskite nanocrystals of the form FAPbBr₃ display significant promise in the field of optoelectronics. In particular, these nanocrystals could bridge the `green gap' of LED technology, and also serve to down-convert ultraviolet light for harvesting using silicon-based photovoltaic cells. To remain competitive with traditional devices, optimising the energy transfer between the nanocrystal and the device is crucial, however very little investigation has been performed into this subject.

Here, we characterise the energy transfer dynamics of FAPbBr₃ nanocrystals on a silicon substrate using time resolved photoluminescence. We also use deposited `spacer layers' to vary the displacement of the nanocrystals from the silicon in order to observe the effect on the energy-transfer dynamics. We find that the overall photo luminescent lifetime increases when reducing the distance between between the nanocrystals and the silicon layer, which runs counter to the expected behaviour. This suggests that the presence of an optically-active substrate suppresses photo luminescent lifetime and, further, suggests that nanocrystal-to-nanocrystal transfer is highly efficient.

GaAsP nanowires (NWs) containing a range of different heterostructures are shown to be a highly promising system for the fabrication of efficient and novel ultra-small light emitters. NWs containing GaAs radial quantum wells (QWs) have emission with high thermal stability, due to both large electron and hole confinement potentials. A structure containing three QWs exhibits very low threshold lasing at low temperatures. Within the GaAsP central region of the same NW, the formation of quantum wires (QWRs) on three of the six vertices is observed, these QWRs are aligned parallel to the NW axis. The presence of twins causes a 180° rotation of the crystal about the growth axis, breaking the QWRs into short sections which may act as quantum dots (QDs). Optical studies of the NWs support the formation of optically active QWRs and QDs. In a second type of NW, during growth of the GaAsP NW core the introduction of a short GaAs section forms a QD. The inclusion of up to 50 QDs with high structural and optical quality is shown to be possible; indicating the potential for the fabrication of QD lasers. A structure with only one QD exhibits a single sharp emission line and behavior consistent with single exciton recombination. The addition of passivation layers, grown as a shell on the NW core, is shown to be essential in obtaining good optical properties. Our studies hence demonstrate that GaAsP-GaAs NWs containing heterostructures have significant potential for a range of novel light emitting applications.

III-V semiconductor nanowires allow easy hetero-integration of optoelectronic components onto silicon due to efficient strain relaxation, well-understood design approaches and scalability. However continuous room temperature lasing has proven elusive. A key challenge is performing repeatable single-wire characterization { each wire can be different due to local growth conditions present during bottom-up growth. Here, we describe an approach using large-scale population studies which exploit inherent inhomogeneity to understand the complex interplay of geometric design, crystal structure, and material quality. By correlating nanowire length with threshold for hundreds of nanowire lasers, this technique reveals core-reabsorption as the critical limiting process in multiple-quantum-well nanowire lasers. By incorporating higher band-gap nanowire core, this effect is eliminated, providing reflectivity dominated behavior.

Graphene is gaining importance due to its unique properties following initial isolation and characterization in 2004. Graphene’s reported applications in electronics and medical disciplines are numerous and expanding. Accordingly, graphene quantum dots (GQDs) are gaining significance for their unique optical and electronic properties including characteristic photoluminescence when excited by UV light. Because GQDs are chemically inert and contain low levels of toxicity, they are attractive for in-vivo and intra-operational cancer imaging and diagnostic applications. GQDs can be formed through the bottom-up method of pyrolysis of non-toxic organic acids such as citric acid and L-glutamic acid. In this paper, GQDs formed from L-aspartic acid using a simple, bottom-up method are studied in detail for the first time. Absorption characteristics are studied using spectroscopic techniques. Results and future efforts are then discussed.

Multilayer strain-coupled P-i-P quantum dot infrared photodetectors (QDIPs) with different configurations are studied. Photoluminescence (PL) and photoluminescence excitation (PLE) measurements are carried out to investigate the improvement in the optical performance of these proposed devices. The samples are grown with a different growth strategy to minimize the dot size dispersion compared to the conventional QDIPs. Also, the effect of In_0.15Ga_0.85As strain reducing layer (SRL) in the proposed samples are analyzed. We report a monomodal PL spectrum and reduction of 28 meV in full-width half maximum (FWHM) of the ground state (GS) peak for the proposed structure in comparison with the conventional one. The monomodal behavior of the structures is confirmed by mapping deconvoluted PL peaks and PLE results. The GS peak of the conventional QDIP is observed at 1.2 eV, whereas the same for the proposed sample is at 1.18 eV. Further redshift in the peak position is achieved (1.14 eV) through the introduction of SRL, which also has a lesser FWHM than the conventional sample. A difference of 69 meV and 73 meV between GS and the first excited state (ES1) peak is observed in the PLE spectra of the conventional and proposed structure, respectively. However, two resolved excited state peaks (ES1 and ES2) are visible in the case of SRL-incorporated structure, which are 69.6 meV and 138 meV away from the GS peak. The proposed QD heterostructures with applied growth strategy and P-i-P configurations are expected to perform better at higher temperatures along with improved absorption efficiency.

Strain in the heterostructure plays a vital role in the characteristics of Quantum Dot (QD) based optoelectronic devices. Optimization of the number of dot layers to be strain-coupled is analyzed here to attain QD infrared photodetectors with higher efficiency. Heterostructures are grown in a molecular beam epitaxy (MBE) system with two (Bi), three (Tri), five (Penta) and seven (Hepta) strain-coupled QD layers, to observe the variation in the optical properties. The effect of thin In0.15Ga0.85As Strain Reducing Layer (SRL) over these coupled structures is also analyzed. Photoluminescence (PL) and Photoluminescence Excitation (PLE) spectroscopy are carried out on the grown structures. Low-temperature Power Dependent PL and PLE revealed the discrete energy states in the dots. The ground state (GS) peaks are found at 1.16 eV, 1.18 eV, 1.195 eV, and 1.194 eV for Bi-, Tri-, Penta-, and Hepta-layer structures. The corresponding peaks redshifted to 1.12 eV, 1.14 eV, 1.154 eV, and 1.152 eV, with the incorporation of 2 nm SRL. It is observed from the PLE results that the excited state peaks of Bi-to-Heptalayer structures are 68 meV, 70 meV, 74 meV, and 72 meV away from the GS peak. However, the differences obtained for the samples with In_0.15Ga_0.85As SRL are 59 meV, 66 meV, 68 meV, and 70 meV. It is seen that the GS PL peaks of Penta-layer samples with both kinds of structures have the highest intensity. The study shows the importance of strain-coupling and provides an optimum QD heterostructure for better device performance.

Submonolayer (SML) quantum dots (QDs) have higher confinement than conventional Stranski- Krastanov (SK) QDs. Moreover, hole-transport based QD infrared photodetectors (QDIPs) are anticipated to perform better at a higher temperature than its counterparts (electron-transport based devices). Effects of different stacking configuration and monolayer (ML) coverage of InAs SML QDs in In_0.15Ga_0.85As matrix are studied here for the development of high temperature operable, hole-transport based QDIPs. We increased the number of dot layers in the matrix as 4, 6 and 8. The monolayer coverage is varied from 0.3 ML to 0.5 ML. Radiative recombination is captured by photoluminescence (PL) and PL excitation (PLE) to observe the energy states of the grown heterostructures. The PL results in case of 0.3ML QDs show a gradual red shift in the ground state (GS) emission when we stack more dot layers in the matrix (1.334 eV, 1.269 eV, and 1.244 eV). Increase in dot size is suspected as the reason behind this change. A decrease in the difference between GS and first excited state (ES1) confirms the enlargement of dots for these samples. However, the PL (multimodal) peak position with maximum intensity changes more interestingly (1.195 eV, 1.154 eV and 1.188 eV) for 0.5 ML QDs with the increase in stacking. This variation is expected to be associated with the relaxation of dots via out diffusion of In atoms from the dot.

In this research, we present selective and rapid growth method of MnO₂ nanostructures by laser. MnO₂ nanostructures directly grow on metal layered substrate under ambient conditions. The MnO₂ nanostructures grow through micro temperature field which is photothermally generated by continuous wave laser. Hemi-urchin shaped nanowire array grows about 5μm length and show 12.5 times faster than conventional hydrothermal method. We characterize analytically the growth mechanism of MnO₂ nanostructures according to the laser irradiation time. In addition, MnO₂ nanostructure shows different morphologies by adjusting laser powers and precursor concentrations.

Here, the hysteresis and negative photoconductivity (NPC) in arginine-doped tungsten disulfide (WS2) quantum dots (QDs) synthesized via microwave heating method were investigated and discussed. WS₂ solution and arginine were used as the QDs and dopant sources, respectively. The structure of arginine-doped WS₂ QDs was analyzed by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The synthesized arginine-doped WS₂ QDs displays a diameter of less than 10 nm and demonstrates an excitation-dependent photoluminescence (PL) behavior. The PL intensity of arginine-doped WS₂ QDs displayed an 18 folds increase compared to the pristine WS₂ QDs. The electrical transport demonstrated a p-type doping as a result of the introduction of arginine in WS₂ QDs. I-V measurements in varying environment and laser illumination were utilized to investigate the hysteresis and negative photoconductivity (NPC) phenomena in arginine-doped WS₂ QDs. Based on this analysis, the hysteresis and NPC are proposed to originate from the interaction of water and/or gas molecules adsorbed on the surface of arginine-doped WS₂ QDs. This optoelectronic study of WS₂ QDs is expected to contribute for the potential development and performance improvement of WS₂-QD-based devices.

Phase transitions are accompanied by sudden changes in physical properties of the material, which opens possibilities for a wide range of applications. Therefore, an in-depth understanding of their dynamics is crucial, especially for the novel, developing field of van der Waals materials. We present a method to spatially resolve states during the metal-insulator phase transition in tantalum disulfide. Unlike other techniques, it allows to study the influence of microscopic laser illumination on the whole, macroscopic sample. The measurements are complemented by numerical simulations.

Heterogeneously coupled SK-SMLQuantum Dot (QD) heterostructures has superior characteristics compared to homogeneously coupled SK QDs in terms of dot density, cumulative strain and absorption efficiency. Here, we have carried out a comparative analysis between heterogeneously coupled SK on SML and SML on SK QDs heterostructures. The barrier thickness between SK and SML QDs, in both structures, has been varied as 5, 7.5 and 10 nm. The tunnelling of carriers from one type of QD (SK/SML) to another type of QD (SML/SK)has been explicated through photoluminescence (PL) study. The appearance of SML peak along with the SK peak for higher barrier thickness has been observed in case of SK on SML QD heterostructure. This might be due to decrease in tunnelling probability of carriers and thereby, transition takes place from both SK and SML QDs. However, this phenomenon has not been observed in SML on SK QD heterostructures. The reason might be the reduced average barrier thickness between SML and SK QDs, which allowed tunnelling of all the carriers. Thus, SML peak was absent in all three SML on SK QD heterostructures. Moreover, strain distribution in all the heterostructures have been investigated through high resolution X-ray diffraction (HRXRD) measurements. The significant modification in structural morphology of QDs, can be obtained fromHRXRD, clearly demonstrates variation in strain with respect to barrier thickness. This comparative analysis would help the research community to choose the optimized heterostructure for desired optoelectronic applications.

Self-assembled III-V compound semiconductor quantum dots (QDs) on silicon (Si) substrate is much explored topic for optoelectronic devices. Here, we have investigated the optical and structural behavior of InAs QDs grown on (001)- oriented Si substrate. The heterostructure has been grown without Si-Ge buffer/graded layer and without Migration Enhanced Epitaxy layer which might reduce the anti-phase domain and dislocation propagation towards the active region. The heterostructure grown on Si (sample A) consists of a thick GaAs buffer layer which was followed by AlAs/GaAs super-lattice buffer layer and three consecutive layers of 2.7 ML InAs QDs with 50 nm GaAs capping. A heterostructure with similar active layers was grown on GaAs substrate (sample B). Samples were characterized using photoluminescence (PL) and high resolution X-ray diffraction (HRXRD) measurements. Sample A exhibited blue shifted PL peak as compared to sample B, which might be due to the formation of smaller dots. Moreover, from the power-dependent PL analysis, a multimodal and bimodal dot size distribution was observed in sample A and B respectively. HRXRD measurements showed the poor crystalline quality in sample A as compared to sample B. However, PL of sample A exhibited a higher intensity in comparison to sample B. In addition, sample A provided higher activation energy of 290 meV, whereas it was 198 meV in case of sample B. This indicates better confinement of charge carriers, which might improve the device performance. The optoelectronic performances could be enhanced by further optimizing this growth strategy through optimizing the dot layer periodicity, capping material, and capping thickness.

Semiconductor nanowires are important materials for quantum transport experiments and are used in research on qubits. Extended arrays of nanowires can be grown bottom-up by Molecular Beam Epitaxy (MBE). The full process involves several steps. When fabricating nanowires, a common practice is to follow a well-established recipe and only characterize the finalized materials. If the final wires are found to be flawed, the process must be repeated with new parameters. It is therefore desirable to have a characterization method to monitor the process before and after each fabrication step. Conventional characterization techniques such as SEM are time-consuming and, in some cases, damage the samples, e.g. before and after an electron beam lithography process. Scatterometry is fast, accurate, non-destructive and is already used in the semiconductor industry. In this work, it is demonstrated that the imaging scatterometry technique is capable of monitoring the MBE fabrication process of InAs-nanowire arrays during the different process steps. Relevant parameters such as thin film thickness, hole depth, and diameter, etc., are found with nm precision for a macroscopic area in a few minutes. Using this approach, we demonstrate that errors can be caught early in the process and ultimately save resources while assuring a high quality of the final material.

Hybrid nanostructures that couple plasmon and exciton resonances generate hybridized energy states, which may result in unusual light-matter interactions. In our work we studied island films from the inhomogeneous ensemble of gold nanoparticles obtained by thermal vacuum deposition, spin-coated with a molecular layer of cyanine dye, in which Jaggregates were formed. The influence of the cyanine dye length chain of conjugation and the thickness of the island film on the optical properties of the hybrid structure was studied. The increase of the molecule absorption is observed for pseudoisocyanine, in comparison with mono- and dicarbocyanine dyes. The transparency in the absorption spectrum of a hybrid film with pseudoisocyanine was observed at a wavelength of 583 nm corresponding to the maximum of the Jaggregate band, which can be explained by the strong coupling of the exciton transition in the J-aggregate with the plasmon resonance of nanoparticles.