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Top-down Fabrication Technologies for High Quality III-V Nanostructures
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

III-V nanostructures have attracted substantial research effort due to their interesting physical properties and their applications in new generation of ultrafast and high efficiency nanoscale electronic and photonic components. The advances in nanofabrication methods including growth/synthesis have opened up new possibilities of realizing one dimensional (1D) nanostructures as building blocks of future nanoscale devices. For processing of semiconductor nanostructure devices, simplicity, cost effectiveness, and device efficiency are key factors. A number of methods are being pursued to fabricate high quality III-V nanopillar/nanowires, quantum dots and nano disks. Further, high optical quality nanostructures in these materials together with precise control of shapes, sizes and array geometries make them attractive for a wide range of optoelectronic/photonic devices.

This thesis work is focused on top-down approaches for fabrication of high optical quality nanostructures in III-V materials. Dense and uniform arrays of nanopillars are fabricated by dry etching using self-assembly of colloidal SiO2 particles for masking. The physico-chemistry of etching and the effect of etch-mask parameters are investigated to control the shape, aspect ratios and spatial coverage of the nanopillar arrays. The optimization of etch parameters and the utilization of erosion of etch masks is evaluated to obtain desired pillar shapes from cylindrical to conical. Using this fabrication method, high quality nanopillar arrays were realized in several InP-based and GaAs-based structures, including quantum wells and multilayer heterostructures. Optical properties of these pillars are investigated using different optical spectroscopic techniques. These nanopillars, single and in arrays, show excellent photoluminescence (PL) at room temperature and the measured PL line-widths are comparable to the as-grown wafer, indicating the high quality of the fabricated nanostructures. The substrate-free InP nanopillars have carrier life times similar to reference epitaxial layers, yet an another indicator of high material quality. InGaAs layer, beneath the pillars is shown to provide several useful functions. It effectively blocks the PL from the InP substrate, serves as a sacrificial layer for generation of free pillars, and as a “detector” in cathodoluminescence (CL) measurements. Diffusion lengths independently determined by time resolved photoluminescence (TRPL) and CL measurements are consistent, and carrier feeding to low bandgap InGaAs layer is evidenced by CL data. Total reflectivity measurements show that nanopillar arrays provide broadband antireflection making them good candidates for photovoltaic applications.  A novel post etch, sulfur-oleylamine (S-OA) based chemical process is developed to etch III-V materials with monolayer precision, in an inverse epitaxial manner along with simultaneous surface passivation. The process is applied to push the limits of top-down fabrication and InP-based high optical quality nanowires with aspect ratios more than 50, and nanostructures with new topologies (nanowire meshes and in-plane wires) are demonstrated.  The optimized process technique is used to fabricate nanopillars in InP-based multilayers (InP/InGaAsP/InP and InP/InGaAs/InP). Such multilayer nanopillars are not only attractive for broad-band absorption in solar cells, but are also ideal to generate high optical quality nanodisks of these materials. Finally, the utility of a soft stamping technique to transfer free nanopillars/wires and nanodisks onto Si substrate is demonstrated. These nanostructures transferred onto Si with controlled densities, from low to high, could provide a new route for material integration on Si.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , xvi, 75 p.
Keyword [en]
III-V nanostructures, colloidal lithography, top-down fabrication, dry etching, quantum well, multilayer structures, nanowires, nanopillars, nanodisks, mono-layer etching, surface passivation, photoluminescence, carrier life time, total reflectivity, photonic crystals, nanomesh
National Category
Physical Sciences Nano Technology
Identifiers
URN: urn:nbn:se:kth:diva-117766ISBN: 978-91-7501-633-7 (print)OAI: oai:DiVA.org:kth-117766DiVA: diva2:602977
Public defence
2013-02-25, Sal/Hall C1, KTH-ICT, Electrum, Isafjordsgatan 26, Kista, 10:00 (English)
Opponent
Supervisors
Note

QC 20130205

Available from: 2013-02-05 Created: 2013-02-04 Last updated: 2013-11-11Bibliographically approved
List of papers
1. Fabrication of Submicrometer InP Pillars by Colloidal Lithography and Dry Etching
Open this publication in new window or tab >>Fabrication of Submicrometer InP Pillars by Colloidal Lithography and Dry Etching
2010 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 157, no 9, II896-II899 p.Article in journal (Refereed) Published
Abstract [en]

A simple method for the fabrication of submicrometer InP pillars with large surface area coverage has been developed based on a combination of colloidal lithography and inductively coupled plasma (ICP) etching technique using Cl-2/H-2/CH4/Ar chemistry. Pillars with different sizes could be fabricated by using colloidal SiO2 particles with different sizes dispersed on the sample serving as masks. Pillars with lateral diameters as small as 60 nm and aspect ratios as high as 10: 1 have been obtained. The effects of etch parameters such as radio-frequency power, ICP power, and etching time on pillar fabrication are investigated. By a suitable choice of etch parameters and utilizing erosion of colloidal (mask) SiO2 particle during etching, the height of the pillars as well as their shape can be modified from nearly cylindrical to conical shapes. Such a control on the shape of the structures in addition to the large surface coverage could be useful for applications in photovoltaics and for the fabrication of photonic crystals. For instance, continuous grading of the refractive index can be obtained for surfaces covered with conical pillars, which can be used as antireflecting surfaces in solar cells or for light extraction in light emitting diodes.

Keyword
LIGHT-EMITTING-DIODES, NATURAL LITHOGRAPHY, ARRAYS, GAAS, NANOPILLARS, EFFICIENCY, PARTICLES, NANOWIRE, CRYSTAL, MASK
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-30290 (URN)10.1149/1.3464764 (DOI)000280348300044 ()2-s2.0-77955816667 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20110222Available from: 2011-02-22 Created: 2011-02-22 Last updated: 2017-12-11Bibliographically approved
2. Nanostructuring of InP by colloidal lithography and ICP etching for photovoltaic applications
Open this publication in new window or tab >>Nanostructuring of InP by colloidal lithography and ICP etching for photovoltaic applications
Show others...
2011 (English)In: Conference Proceedings - International Conference on Indium Phosphide and Related Materials, 2011Conference paper, Published 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.

Series
Conference Proceedings - International Conference on Indium Phosphide and Related Materials, ISSN 1092-8669
Keyword
Close packed; Close packed structures; Colloidal lithography; Colloidal masks; Colloidal particle; Cost-effective methods; Different heights; Different sizes; Etch process; Hexagonal structures; ICP etching; InP; Lag effects; Nano-structuring; Nanopillars; Oxygen plasma treatments; Photovoltaic applications; Silica particles; Size reductions; Surface wettability; Uniform coverage; Wide area
National Category
Nano Technology Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-104535 (URN)2-s2.0-84863231917 (Scopus ID)978-3-8007-3356-9 (ISBN)
Conference
Compound Semiconductor Week (CSW/IPRM), 2011 and 23rd International Conference on Indium Phosphide and Related Materials, Berlin, 22-26 May 2011
Note

QC 20140905

Available from: 2012-11-05 Created: 2012-11-05 Last updated: 2017-03-24Bibliographically 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. Carrier dynamics in InP nanopillar arrays fabricated by low-damage etching
Open this publication in new window or tab >>Carrier dynamics in InP nanopillar arrays fabricated by low-damage etching
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2013 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, no 21, 212106- p.Article in journal (Refereed) Published
Abstract [en]

We present a comprehensive characterization of the optical quality of InP nanopillars (NPs) fabricated by a top down approach using micro-photoluminescence (mu-PL), time-resolved PL, and cathodoluminescence (CL). A lattice matched InGaAs layer provided beneath the 1 mu m tall NPs functions as a "detector" in CL for monitoring carrier diffusion in InP NP. Carrier feeding to the InGaAs layer indicated by a double exponential PL decay is confirmed through CL mapping. Carrier lifetimes of over 1 ns and the appreciably long diffusion lengths (400-700 nm) in the InP NPs indicate very low surface damage making them attractive for optoelectronic applications.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2013
Keyword
Surface Recombination Velocity, Indium-Phosphide Nanowires, Wave-Guides, Superlattices, Luminescence, Spectroscopy, Passivation
National Category
Nano Technology Physical Sciences
Identifiers
urn:nbn:se:kth:diva-117747 (URN)10.1063/1.4808447 (DOI)000320620400037 ()2-s2.0-84879115969 (Scopus ID)
Funder
Swedish Research Council, 349-2007-8664EU, FP7, Seventh Framework Programme, 248855Knut and Alice Wallenberg Foundation
Note

QC 20130806. Updated from submitted to published.

Available from: 2013-02-04 Created: 2013-02-04 Last updated: 2017-12-06Bibliographically approved
5. 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
6. Top-Down Fabrication of High Quality III–V Nanostructures by Monolayer Controlled Sculpting and Simultaneous Passivation
Open this publication in new window or tab >>Top-Down Fabrication of High Quality III–V Nanostructures by Monolayer Controlled Sculpting and Simultaneous Passivation
2013 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 23, no 13, 1620-1627 p.Article in journal (Refereed) Published
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.

Keyword
semiconductor nanostructures, monolayer etching, surface passivation, nanowires, top-down fabrication, membranes
National Category
Nano Technology Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-104528 (URN)10.1002/adfm.201202201 (DOI)000317019100003 ()2-s2.0-84875827561 (Scopus ID)
Funder
Swedish Research Council, 349-2007-8664EU, FP7, Seventh Framework Programme, 248855
Note

QC 20130507

Available from: 2012-11-05 Created: 2012-11-05 Last updated: 2017-12-07Bibliographically approved
7. Generation of substrate free III-V nanodisksfrom user-defined multilayer nanopillar arrays
Open this publication in new window or tab >>Generation of substrate free III-V nanodisksfrom user-defined multilayer nanopillar arrays
(English)Article in journal (Other academic) Submitted
Abstract [en]

High material quality InP-based multilayer nanopillar (NP) arrays are fabricated using a combination of self-assembly of silica particles for mask generation and dry etching. In particular, the NP arrays are made from user-defined epitaxial multi-layer stacks with specific materials and layer thickness. Additional degree of flexibility in the structures is obtained by changing the lateral diameters of the NP multi-layer stacks. Pre-defined NP arrays made in InGaAsP/InP and InGaAs/InP NPs are then used to generate substrate-free nanodisks of a chosen material from the stack by selective etching. A soft-stamping method is demonstrated to transfer the generated nanodisks with arbitrary densities onto Si. It is shown that the transferred nanodisks retain their smooth surface morphologies and their designed geometrical dimensions. Both InP and InGaAsP nanodisks display excellent photo-luminescence properties, with line-widths comparable to unprocessed reference epitaxial layers of similar composition. The multilayer NP arrays are potentially attractive for broad-band absorption in third-generation solar-cells. The high optical quality, substrate-free InP and InGaAsP nanodisks on Si offer a new path to explore alternative ways to integrate III-V on Si by bonding nanodisks to Si. The method also has the advantage of re-usable III-V substrates for subsequent layer growth.

National Category
Nano Technology Physical Sciences
Identifiers
urn:nbn:se:kth:diva-117750 (URN)
Funder
Swedish Research Council, 349-2007-8664EU, FP7, Seventh Framework Programme, 248855
Note

QS 2013

Available from: 2013-02-04 Created: 2013-02-04 Last updated: 2013-02-05Bibliographically approved

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