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  • 1.
    Awan, Kashif Masud
    et al.
    KTH, School of Information and Communication Technology (ICT).
    Sanatinia, Reza
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Nanostructuring of GaAs with tailored topologies using colloidal lithography and dry etching2014In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 32, no 2, p. 021801-Article in journal (Refereed)
    Abstract [en]

    The authors report on the fabrication of GaAs nanopillars with different profiles/topologies using colloidal lithography and dry etching. GaAs nanopillars with different shapes and dimensions were successfully fabricated using inductively coupled plasma reactive ion etching. Two different etch chemistries CH4/H-2/Cl-2 and Ar/Cl-2 were investigated. The fabricated nanopillar arrays had a typical period of similar to 500 nm, and the depths could be varied from a few nanometers to 4 mu m. The CH4/H-2/Cl-2 chemistry with optimized gas flows and plasma powers is shown to produce nanopillars with smooth sidewalls compared to those fabricated with the Ar/Cl-2 chemistry. The GaAs nanopillar arrays have appreciably lower reflectivities in the measured wavelength range from 400 to 850 nm and are typically one order of magnitude lower compared to planar GaAs, which shows their potential for photovoltaic applications.

  • 2.
    De Luca, Eleonora
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Sanatinia, Reza
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Mensi, Mounir
    KTH, School of Information and Communication Technology (ICT).
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Swillo, Marcin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Modal phase matching in nanostructured zincblende semiconductors for second-harmonic generation2017In: Optics InfoBase Conference Papers, OSA - The Optical Society , 2017Conference paper (Refereed)
    Abstract [en]

    Gallium phosphide nanowaveguide arrays, designed to fulfill the phase matching conditions and field-overlap, are characterized by second-harmonic generation. The bandwidth of 30nm with maximum conversion efficiency of 10-3 is measured for 150fs optical pulses.

  • 3.
    De Luca, Eleonora
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Sanatinia, Reza
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Srinivasan, Anand
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Swillo, Marcin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Focused ion beam milling of gallium phosphide nanostructures for photonic applications2016In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 6, no 2, p. 587-596Article in journal (Refereed)
    Abstract [en]

    We report on the fabrication of gallium phosphide (GaP) nanowaveguides of controlled dimensions, as small as 0.03 μm and aspect ratio in excess of 20, using focused ion beam (FIB) milling. A known limitation of this fabrication process for photonic applications is the formation of gallium droplets on the surface. We demonstrate a post-fabrication step using a pulsed laser to locally oxidize the excess surface gallium on the FIB milled nanostructures. The process significantly reduces the waveguide losses. The surface optical quality of the fabricated GaP nanowaveguides has been evaluated by second-harmonic generation experiments. Surface and bulk contributions to second-order optical nonlinearities have been identified by polarization measurements. The presented method can potentially be applied to other III-V nanostructures to reduce optical losses.

  • 4.
    Dev Choudhury, Bikash
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Abedin, Ahmad
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Dev, Apurba
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Sanatinia, Reza
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Silicon micro-structure and ZnO nanowire hierarchical assortments for light management2013In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 3, no 8, p. 1039-1048Article in journal (Refereed)
    Abstract [en]

    We present fabrication and optical characterization of Si microstructure-ZnO nanowire (NWs) hierarchical structures for light management. Random and periodic hierarchical structures constituting Si micro pillar or micro pyramid arrays with overgrown ZnO NWs have been fabricated. Inexpensive colloidal lithography in combination with dry and wet chemical etching is used to fabricate Si microstructures, and ZnO NWs are grown by hydrothermal synthesis. The periodic Si micro pyramid-ZnO NWs hierarchical structure shows broadband antireflection with average reflectance as low as 2.5% in the 300-1000 nm wavelength range. A tenfold enhancement in Raman intensity is observed in this structure compared to planar Si sample. These hierarchical structures with enriched optical properties and high surface to volume ratio are promising for photovoltaic (PV) and sensor applications.

  • 5.
    Dev Choudhury, Bikash
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Sahoo, Pankaj Kumar
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA. Indian Institute of Technology, India.
    Sanatinia, Reza
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Andler, G.
    Stockholm University.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Swillo, Marcin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Surface second harmonic generation from silicon pillar arrays with strong geometrical dependence2015In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 40, no 9, p. 2072-2075Article in journal (Refereed)
    Abstract [en]

    We present experimental demonstration and analysis of enhanced surface second harmonic generation (SHG) from hexagonal arrays of silicon pillars. Three sets of Si pillar samples with truncated cone-shaped pillar arrays having periods of 500, 1000, and 2000 nm, and corresponding average diameters of 200, 585 and 1550 nm, respectively, are fabricated by colloidal lithography and plasma dry etching. We have observed strong dependence of SHG intensity on the pillar geometry. Pillar arrays with a 1000 nm period and a 585 nm average diameter give more than a one order of magnitude higher SHG signal compared to the other two samples. We theoretically verified the dependence of SHG intensity on pillar geometry by finite difference time domain simulations in terms of the surface normal E-field component. The enhanced surface SHG light can be useful for nonlinear silicon photonics, surface/interface characterization, and optical biosensing.

  • 6.
    Dhaka, Veer
    et al.
    Aalto University.
    Oksanen, Jani
    Aalto University.
    Jiang, Hua
    Aalto University.
    Haggren, Tuomas
    Aalto University.
    Nykänen, Antti
    Aalto University.
    Sanatinia, Reza
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Kakko, Joona-Pekko
    Aalto University.
    Huhtio, Teppo
    Aalto University.
    Ruokolainen, Janne
    Aalto University.
    Mattila, Marco
    Aalto University.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101).
    Kauppinen, Esko I
    Aalto University.
    Lipsanen, Harri
    Aalto University.
    Aluminum-Induced Photoluminescence Red Shifts in Core-Shell GaAs/AlxGa1-xAs Nanowires2013In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 13, no 8, p. 3581-3588Article in journal (Refereed)
    Abstract [en]

    We report a new phenomenon related to Al-induced carrier confinement at the interface in core-shell GaAs/AlxGa1-xAs nanowires grown using metal-organic vapor phase epitaxy with Au as catalyst. All AlxGa1-xAs shells strongly passivated the GaAs nanowires, but surprisingly the peak photoluminescence (PL) position and the intensity from the core were found to be a strong function of Al composition in the shell at low temperatures. Large and systematic red shifts of up to similar to 66 nm and broadening in the PL emission from the GaAs core were observed when the Al composition in the shell exceeded 3%. On the contrary, the phenomenon was observed to be considerably weaker at the room temperature. Cross-sectional transmission electron microscopy reveals Al segregation in the shell along six Al-rich radial bands displaying a 3-fold symmetry. Time-resolved PL measurements suggest the presence of indirect electron-hole transitions at the interface at higher Al composition. We discuss all possibilities including a simple shell-core-shell model using simulations where the density of interface traps increases with the Al content, thus creating a strong local electron confinement. The carrier confinement at the interface is most likely related to Al inhomogeneity and/or Al-induced traps. Our results suggest that a low Al composition in the shell is desirable in order to achieve ideal passivation in GaAs nanowires.

  • 7.
    Jaramillo-Fernandez, Juliana
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Chavez-Angel, Emigdio
    Sanatinia, Reza
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics. Harvard Univ, USA.
    Kataria, Himanshu
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. IRnova AB, Sweden.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Lourdudoss, Sebastian
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Sotomayor-Torres, Clivia M.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. CSIC, Spain; Barcelona Inst Sci & Technol, Spain; ICREA, Spain.
    Thermal conductivity of epitaxially grown InP: experiment and simulation2017In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 19, no 14, p. 1879-1887Article in journal (Refereed)
    Abstract [en]

    The integration of III-V optoelectronic devices on silicon is confronted with the challenge of heat dissipation for reliable and stable operation. A thorough understanding and characterization of thermal transport is paramount for improved designs of, for example, viable III-V light sources on silicon. In this work, the thermal conductivity of heteroepitaxial laterally overgrown InP layers on silicon is experimentally investigated using microRaman thermometry. By examining InP mesa-like structures grown from trenches defined by a SiO2 mask, we found that the thermal conductivity decreases by about one third, compared to the bulk thermal conductivity of InP, with decreasing width from 400 to 250 nm. The high thermal conductivity of InP grown from 400 nm trenches was attributed to the lower defect density as the InP micro crystal becomes thicker. In this case, the thermal transport is dominated by phonon-phonon interactions as in a low defect-density monocrystalline bulk material, whereas for thinner InP layers grown from narrower trenches, the heat transfer is dominated by phonon scattering at the extended defects and InP/SiO2 interface. In addition to the nominally undoped sample, sulfur-doped (1 x 10(18) cm(-3)) InP grown on Si was also studied. For the narrower doped InP microcrystals, the thermal conductivity decreased by a factor of two compared to the bulk value. Sources of errors in the thermal conductivity measurements are discussed. The experimental temperature rise was successfully simulated by the heat diffusion equation using the FEM.

  • 8.
    Jaramillo-Fernandez, Juliana
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Ordonez-Miranda, J.
    Ollier, E.
    Sanatinia, Reza
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Kataria, Himanshu
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Chavez-Angel, E.
    Volz, S.
    Sotomayor-Torres, Clivia M.
    Tuning of heat transport across thin films of polycrystalline AlN via multiscale structural defects2015In: ECS Transactions, Electrochemical Society, 2015, no 9, p. 53-64Conference paper (Refereed)
    Abstract [en]

    The effective thermal conductivity of nanocrystalline films of AlN with inhomogeneous microstructure is investigated experimentally and theoretically. This is done by measuring the thermal conductivity of the samples with the 3-omega method and characterizing their microstructure by means of electron microscopy. The relative effect of the microstructure and the interface thermal resistance on the thermal conductivity is quantified through an analytical model. Thermal measurements showed that when the thickness of an AlN film is reduced from 1460 to 270 nm, its effective thermal conductivity decreases from 8.21 to 3.12 WYm-1?K-1, which is two orders of magnitude smaller than its bulk counterpart value. It is shown that both the size effects of the phonon mean free paths and the intrinsic thermal resistance resulting from the inhomogeneous microstructure predominate for thicker films, while the contribution of the interface thermal resistance strengthens as the film thickness is scaled down. The obtained results demonstrate that the structural inhomogeneity in polycrystalline AlN films can be efficiently used to tune their cross- plane thermal conductivity. In addition, thermal conductivity measurements of epitaxially grown InP layers on silicon using Raman spectroscopy are reported.

  • 9.
    Naureen, Shagufta
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101).
    Rajagembu, Perumal
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101).
    Sanatinia, Reza
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101).
    Shahid, Naeem
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101).
    Li, Mingyu
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101).
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101).
    Nanostructuring of InP by colloidal lithography and ICP etching for photovoltaic applications2011In: Conference Proceedings - International Conference on Indium Phosphide and Related Materials, 2011Conference paper (Refereed)
    Abstract [en]

    We demonstrate a simple and cost effective method to fabricate InP nanopillars using silica particles as masks for etching InP. Oxygen plasma treatment of InP surfaces before dispersion of colloidal mask particles improved surface wettability significantly and helped in uniform coverage of the particles over large areas. Pillars with varied sizes were fabricated by dispersing colloidal SiO2 with different sizes on the sample and/or by reducing size of particles after dispersion. Nanopillars with different heights and shapes from near cylindrical to conical were obtained by varying etch process parameters and by progressive erosion of colloidal SiO 2 particle (mask). Pillars with aspect ratios in excess of 15:1 have been obtained. Investigations are also made on regular close packed hexagonal structures with wide area coverage. Size reduction of colloidal particles after dispersion is used to overcome the lag effect observed in the etching of close packed structures. The demonstrated nanostructuring method is attractive for producing photonic crystals and antireflecting surfaces in solar cells.

  • 10.
    Naureen, Shagufta
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Sanatinia, Reza
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Shahid, Naeem
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    High Optical Quality InP-Based Nanopillars Fabricated by a Top-Down Approach2011In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 11, no 11, p. 4805-4811Article in journal (Refereed)
    Abstract [en]

    Dense and uniform arrays of Top-based nanopillars were fabricated by dry etching using self-assembly of colloidal silica particles for masking. The pillars, both single and arrays, fabricated from epitaxially grown InP and InP/GaInAsP/InP quantum well structures :how excellent photoluminescence (PL) even at room temperature. The measured PL line widths are comparable to the as-grown wafer indicating high quality fabricated pillars. A stamping technique enables transfer with arbitrary densities of the nanopillars freed from the substrate by selectively etching a sacrificial InGaAs layer.

  • 11.
    Naureen, Shagufta
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Shahid, Naeem
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Sanatinia, Reza
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Top-Down Fabrication of High Quality III–V Nanostructures by Monolayer Controlled Sculpting and Simultaneous Passivation2013In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 23, no 13, p. 1620-1627Article in journal (Refereed)
    Abstract [en]

    In the fabrication of IIIV semiconductor nanostructures for electronic and optoelectronic devices, techniques that are capable of removing material with monolayer precision are as important as material growth to achieve best device performances. A robust chemical treatment is demonstrated using sulfur (S)-oleylamine (OA) solution, which etches layer by layer in an inverse epitaxial fashion and simultaneously passivates the surface. The application of this process to push the limits of top-down nanofabrication is demonstrated by the realization of InP-based high optical quality nanowire arrays, with aspect ratios more than 50, and nanostructures with new topologies. The findings are relevant for other IIIV semiconductors and have potential applications in IIIV device technologies.

  • 12.
    Sanatinia, Reza
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Ensemble and Individual III-V Semiconductor Nanopillars: Optical Properties and Applications2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Optical properties of semiconductor nanowires (NWs)/nanopillars (NPs), as individual or ensemble, have attracted significant research interest in recent years. Their potential applications range from solid-state lighting, photovoltaics, lasing and nonlinear optics to sensing and life sciences. Many of III-V NWs/NPs are particularly interesting for optoelectronic and photovoltaic applications, because of their direct band gap, high refractive index and superior electrical properties. These properties are beneficial for use in next generation solar cells by reducing the active cell thickness, while maintaining high efficiency. Furthermore, high second order nonlinearity coefficients of many III-V materials, for example GaAs and GaP, enhanced electric fields and tight confinement of optical modes make nanowaveguide geometries ideal for nonlinear effects.

    The focus of this thesis is on the fabrication of III-V NPs, their optical properties and applications. Different methods for fabrication of NPs (top-down approach) are proposed. The fabricated NPs show a broadband suppression of reflectance, which is particularly an interesting feature for photovoltaic applications. The effect of the shape and geometry of GaAs NPs on their reflectance spectra is investigated and the experimental data show a very good agreement with the simulations. In order to decrease surface recombination in the fabricated GaAs NPs, a sulfur-based chemical passivation method was used, resulting in the recovery of photoluminescence (PL) linewidth and enhancing the PL intensity for more than an order of magnitude. Moreover, a unique wafer-scale self-organization process for generation of InP NPs is demonstrated. As a proof of concept, the self-organized InP NPs were used to fabricate solar cell devices. For fabrication of InP NP solar cells, epitaxial overgrowth of NPs arrays was used to realize p-n junctions. A significant increase in the open circuit voltage (0.13 V) of the NP solar cell was obtained after surface passivation.

    Second-harmonic generation (SHG) was experimentally observed from GaP NP waveguides (single and in arrays) with vertical geometry. The generated second- harmonic light was analyzed with respect to the size of the NP waveguides and the corresponding effects of surface and bulk nonlinearities. In case of individual NPs, SHG was analyzed considering different modal excitations in GaP NPs. It was demonstrated that by varying the NP diameter and changing the pump polarization, it is possible to alter the field distribution of the radiated SHG light. The importance of tight confinement of the pump in the NP waveguides and consequently the longitudinal component of the electric field in this geometry is shown. A method was proposed to distinguish between surface and bulk contributions in SHG, which also addressed how to employ surface SHG to enhance the generated light. The proposed method was used to estimate the nonlinear coefficient and the effective thickness of the nonlinear region at the surface of GaP NP waveguides. Based on these findings, the corresponding nonlinear coefficient at the surface is estimated to be approximately 15 times higher, compared to the bulk. These findings, suggest that NPs/NWs (in this case GaP NPs) are potential alternatives for future nonlinear nanophotonic devices. Additionally, the SHG light from single GaP NPs are promising candidates for ultrafast light sources at nanoscopic scale, with potential applications in sensing, bio and single cell/ molecular imaging.

  • 13.
    Sanatinia, Reza
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Swillo, Marcin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Experimental quantification of surface optical nonlinearity in GaP nanopillar waveguides2015In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 2, p. 756-764Article in journal (Refereed)
    Abstract [en]

    We report on surface second-order optical nonlinearity in single GaP nanopillars (nanowaveguides). The relative contribution of optical nonlinearity from the surface and the bulk is resolved by mode confinement analysis and polarization measurements. By investigating the thickness of nonlinear region at the surface of nanopillars, we estimated the nonlinear coefficient to be similar to 15 times higher at the surface with respect to the bulk. The presented results are interesting both from the fundamental aspects of light-matter interaction and for future nonlinear nanophotonic devices with smaller footprint.

  • 14.
    Sanatinia, Reza
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Swillo, Marcin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Modal Engineering of Second-Harmonic Generation in Single GaP Nanopillars2014In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 14, no 9, p. 5376-5381Article in journal (Refereed)
    Abstract [en]

    We report on modal dispersion engineering for second-harmonic generation (SHG) from single vertical GaP nanopillars/nanowaveguides, fabricated by a top-down approach, using optical modal overlap between the pump (830 nm) and SHG (415 nm). We present a modal analysis for the SHG process in GaP nanopillars and demonstrate efficient utilization of the longitudinal component of the nonlinear polarization density. Our SHG measurements show quantitatively the presented model. We experimentally demonstrate that polarization beam shaping and field distribution modification of the radiated SHG light, at nanometer scale, can be achieved by tuning the pillar diameter and linear pump polarization. SHG from single pillars can be used as femtosecond nanoscopic light sources at visible wavelengths applicable for single cell/molecular imaging and interesting for future integrated nanophotonics components. While this work focuses on GaP nanopillars, the results are applicable to other semiconductor nanowire materials and synthesis methods.

  • 15.
    Sanatinia, Reza
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Awan, Kashif Masud
    KTH, School of Information and Communication Technology (ICT).
    Naureen, Shagufta
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Anttu, Nicklas
    Lund University.
    Ebraert, Evert
    KTH, School of Information and Communication Technology (ICT).
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    GaAs nanopillar arrays with suppressed broadband reflectance and high optical quality for photovoltaic applications2012In: Optical Materials Express, ISSN 2159-3930, Vol. 2, no 11, p. 1671-1679Article in journal (Refereed)
    Abstract [en]

    We report on fabrication and optical characterization of GaAs nanopillar (NP) arrays, obtained using a combination of low-cost mask generation by self-assembled silica particles (nanosphere lithography) and dry etching. Tapered structures (conical and frustum NP arrays) are fabricated by appropriate optimization of process parameters. Significant suppression of surface reflectance is observed for both geometries over a broad wavelength range. Simulations, based on finite difference time domain (FDTD) method, show good agreement with reflectivity measurements and serve as a guideline for design of NPs and understanding their interaction with light. A combination of wet chemical etching and sulfur-based passivation of GaAs NPs, results in more than one order of magnitude enhancement in PL intensity and recovery of PL line-width, which is very promising for photovoltaic applications.

  • 16.
    Sanatinia, Reza
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Berrier, Audrey
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA. Universität Stuttgart, Germany.
    Dhaka, Veer
    Aalto University.
    P. Perros, Alexander
    Aalto University.
    Huhtio, Teppo
    Aalto University.
    Lipsanen, Harri
    Aalto University.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Wafer-Scale Self-Organized InP Nanopillars with Controlled Orientation for Photovoltaic Devices2015In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 26, no 41, article id 415304Article in journal (Refereed)
    Abstract [en]

    A unique wafer-scale self-organization process for generation of InP nanopillars is demonstrated, which is based on maskless ion-beam etching (IBE) of InP developed to obtain the nanopillars, where the height, shape, and orientation of the nanopillars can be varied by controlling the processing parameters. The fabricated InP nanopillars exhibit broadband suppression of the reflectance, 'black InP,' a property useful for solar cells. The realization of a conformal p-n junction for carrier collection, in the fabricated solar cells, is achieved by a metalorganic vapor phase epitaxy (MOVPE) overgrowth step on the fabricated pillars. The conformal overgrowth retains the broadband anti-reflection property of the InP nanopillars, indicating the feasibility of this technology for solar cells. Surface passivation of the formed InP nanopillars using sulfur-oleylamine solution resulted in improved solar-cell characteristics. An open-circuit voltage of 0.71 V and an increase of 0.13 V compared to the unpassivated device were achieved.

  • 17.
    Sanatinia, Reza
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Swillo, Marcin
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Surface Second-Harmonic Generation from Vertical GaP Nanopillars2012In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 12, no 2, p. 820-826Article in journal (Refereed)
    Abstract [en]

    We report on the experimental observation and analysis of second-harmonic generation (SHG) from vertical GaP nanopillars. Periodic arrays of GaP nanopillars with varying diameters ranging from 100 to 250 nm were fabricated on (100) undoped GaP substrate by nanosphere lithography and dry etching. We observed a strong dependence of the SHG intensity on pillar diameter. Analysis of surface and bulk contributions to SHG from the pillars including the calculations of the electric field profiles and coupling efficiencies is in very good agreement with the experimental data. Complementary measurements of surface optical phonons by Raman spectroscopy are also in agreement with the calculated field intensities at the surface. Finally, polarization of the measured light is used to distinguish between the bulk and surface SHG from GaP nanopillars.

  • 18.
    Sanatinia, Reza
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Swillo, Marcin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Srinivasan, Anand
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Second harmonic generation in GaP nanopillars2011In: 2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference, CLEO EUROPE/EQEC 2011, 2011Conference paper (Refereed)
    Abstract [en]

    Semiconductor nanopillars and nanowires (NWs) exhibit interesting optical nonlinear effects [1,2]. These properties are attributed to the geometrical and optical properties of nanopillars which define optical field confinement [3] and the field discontinuity that contributes to bulk and surface nonlinearity [4,5]. Potential applications for these nonlinear effects include probing of the surface in nanostructures and nonlinear scanning laser microscopy

  • 19.
    Sanatinia, Reza
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Westendorp, S.
    KTH, School of Engineering Sciences (SCI).
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Swillo, Marcin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Enhanced second-harmonic generation in GaP nanopillars arrays by modal engineering2014In: Optics InfoBase Conference Papers, 2014Conference paper (Refereed)
    Abstract [en]

    Second harmonic generation from GaP nanopillars with optimized mode field overlap is analyzed and experimentally demonstrated. We present dispersion engineering in arrays of nanopillars to satisfy modal phase matching.

  • 20.
    Swillo, Marcin
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Sanatinia, Reza
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Investigation of second order optical nonlinearity at the surface of GaP nanowaveguides2013In: 2013 Conference on Lasers and Electro-Optics Europe and International Quantum Electronics Conference, CLEO/Europe-IQEC 2013, IEEE Computer Society, 2013, p. 6800994-Conference paper (Refereed)
    Abstract [en]

    Nonlinear optical properties of semiconductor nanowaveguides/nanowires are determined by both their crystal symmetry and geometry. For diameters comparable to the wavelength, high contrast of refractive index between the nanostructure and surrounding air leads to strong optical anisotropy [1]. It has been shown that for nanowaveguides with certain diameters (depending on the wavelength), the effect of electric field with polarization normal to the surface becomes significant [2]. The induced surface effect can consequently be utilized for second harmonic generation (SHG) in nanowaveguide. Nonlinear optical susceptibility at the surface results from the material discontinuity and electric quadrupole contribution [3], whereas the bulk nonlinearity is defined by the crystal symmetry.

  • 21.
    Swillo, Marcin
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Sanatinia, Reza
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Surface Optical Nonlinearity in GaP Nanopillar Waveguides2012Conference paper (Refereed)
    Abstract [en]

    Second harmonic generation in GaP nanopillars is investigated by polarization measurements and light confinement analysis. Effective thickness of the nonlinear surface region is ~ 10nm and the corresponding nonlinear coefficient 20 times larger than in bulk.

1 - 21 of 21
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