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Ensemble and Individual III-V Semiconductor Nanopillars: Optical Properties and Applications
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.ORCID iD: 0000-0002-2069-2820
2014 (English)Doctoral 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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , xiii, 68 p.
Series
TRITA-ICT/MAP AVH, ISSN 1653-7610 ; 2014:14
Keyword [en]
nanopillar, nanowires, nanophotonics, nanofabrication, III-V semiconductors, photovoltaics, second-harmonic generation, top-down approach, colloidal lithography, antireflection, modal dispersion, polarization, nanowaveguide, indium phosphide, gallium arsenide, gallium phosphide
National Category
Nano Technology
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-155205ISBN: 978-91-7595-333-5 (print)OAI: oai:DiVA.org:kth-155205DiVA: diva2:760249
Public defence
2014-11-26, Sal/hall 205, Electrum, KTH-ICT, Kista, 10:00 (English)
Opponent
Supervisors
Note

QC 20141104

Available from: 2014-11-04 Created: 2014-11-03 Last updated: 2014-11-04Bibliographically approved
List of papers
1. Nanostructuring of GaAs with tailored topologies using colloidal lithography and dry etching
Open this publication in new window or tab >>Nanostructuring of GaAs with tailored topologies using colloidal lithography and dry etching
2014 (English)In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 32, no 2, 021801- p.Article in journal (Refereed) Published
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.

Keyword
Nanowire Solar-Cells, High Optical-Quality, 2nd-Harmonic Generation, Fabrication, Light, Nanopillars, Arrays
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-144958 (URN)10.1116/1.4862976 (DOI)000333560600046 ()
Funder
Swedish Research CouncilEU, FP7, Seventh Framework Programme
Note

QC 20140505

Available from: 2014-05-05 Created: 2014-05-05 Last updated: 2017-12-05Bibliographically approved
2. GaAs nanopillar arrays with suppressed broadband reflectance and high optical quality for photovoltaic applications
Open this publication in new window or tab >>GaAs nanopillar arrays with suppressed broadband reflectance and high optical quality for photovoltaic applications
Show others...
2012 (English)In: Optical Materials Express, ISSN 2159-3930, Vol. 2, no 11, 1671-1679 p.Article in journal (Refereed) Published
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.

Keyword
Solar-Cells, Efficiency, Absorption, Sulfide, Limit
National Category
Other Physics Topics Nano Technology
Identifiers
urn:nbn:se:kth:diva-104526 (URN)10.1364/OME.2.001671 (DOI)000310647500023 ()2-s2.0-84870370508 (Scopus ID)
Funder
Swedish Research CouncilEU, FP7, Seventh Framework Programme
Note

QC 20121210

Available from: 2012-11-05 Created: 2012-11-05 Last updated: 2014-11-04Bibliographically approved
3. High Optical Quality InP-Based Nanopillars Fabricated by a Top-Down Approach
Open this publication in new window or tab >>High Optical Quality InP-Based Nanopillars Fabricated by a Top-Down Approach
2011 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 11, no 11, 4805-4811 p.Article in journal (Refereed) Published
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.

Keyword
Semiconductor nanopillars, quantum well, reactive ion etching, nanosphere lithography, photoluminescence, total reflectivity
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-50319 (URN)10.1021/nl202628m (DOI)000296674700054 ()2-s2.0-80755125658 (Scopus ID)
Note
QC 20120119Available from: 2012-01-19 Created: 2011-12-05 Last updated: 2017-12-08Bibliographically approved
4. Wafer-Scale Self-Organized InP Nanopillars with Controlled Orientation for Photovoltaic Devices
Open this publication in new window or tab >>Wafer-Scale Self-Organized InP Nanopillars with Controlled Orientation for Photovoltaic Devices
Show others...
2015 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 26, no 41, 415304Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2015
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-155199 (URN)10.1088/0957-4484/26/41/415304 (DOI)000363433700008 ()26403979 (PubMedID)2-s2.0-84947475230 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, 248855Swedish Research Council, 349-2007-8664Swedish Research Council, 621-2014-5078
Note

Updated from manuscript to article in journal.

QC 20160203

Available from: 2014-11-03 Created: 2014-11-03 Last updated: 2017-12-05Bibliographically approved
5. Surface Second-Harmonic Generation from Vertical GaP Nanopillars
Open this publication in new window or tab >>Surface Second-Harmonic Generation from Vertical GaP Nanopillars
2012 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 12, no 2, 820-826 p.Article in journal (Refereed) Published
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.

Keyword
Nanopillars, nanoscopic light source, second-harmonic generation, surface SHG, surface phonons, gallium phosphide
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:kth:diva-92065 (URN)10.1021/nl203866y (DOI)000299967800049 ()2-s2.0-84856962962 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20120326Available from: 2012-03-26 Created: 2012-03-26 Last updated: 2017-12-07Bibliographically approved
6. Modal Engineering of Second-Harmonic Generation in Single GaP Nanopillars
Open this publication in new window or tab >>Modal Engineering of Second-Harmonic Generation in Single GaP Nanopillars
2014 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 14, no 9, 5376-5381 p.Article in journal (Refereed) Published
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.

Keyword
Nanopillar, second-harmonic generation, modal dispersion, polarization, nanowaveguide, gallium phosphide
National Category
Nano Technology Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-150121 (URN)10.1021/nl502521y (DOI)000341544500070 ()25157424 (PubMedID)2-s2.0-84914168992 (Scopus ID)
Note

QC 20140919

Available from: 2014-08-30 Created: 2014-08-30 Last updated: 2017-12-05Bibliographically approved
7. Experimental quantification of surface optical nonlinearity in GaP nanopillar waveguides
Open this publication in new window or tab >>Experimental quantification of surface optical nonlinearity in GaP nanopillar waveguides
2015 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 2, 756-764 p.Article in journal (Refereed) Published
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.

Keyword
Gallium alloys, Nanostructures, Confinement analysis, Light-matter interactions, Nanophotonic devices, Nonlinear coefficient, Optical nonlinearity, Polarization measurements, Relative contribution, Second order optical nonlinearity
National Category
Nano Technology Atom and Molecular Physics and Optics
Research subject
Physics; Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-155198 (URN)10.1364/OE.23.000756 (DOI)000349166100016 ()2-s2.0-84921719961 (Scopus ID)
Funder
Swedish Research Council, 349-2007-8664Swedish Research Council, 621-2013-5811EU, FP7, Seventh Framework Programme, 248855
Note

QC 20150312. Updated from manuscript to article in journal.

Available from: 2014-11-03 Created: 2014-11-03 Last updated: 2017-12-05Bibliographically approved

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