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Growth and characterisation of group-III nitride-based nanowires for devices

Abstract

One of the main goals of this thesis was to get more insight into the mechanisms driving the growth of nitride nanowires by plasma-assisted molecular beam epitaxy (PA-MBE). The influence of the group-III and group-V flux as well as the substrate temperature T{sub sub} has been studied leading to the conclusion that the III-V ratio determines the growth mode. Ga desorption limits the temperature range to grow GaN nanowires and dissociation of InN is the limiting factor for InN nanowire growth. A reduction of the surface diffusivity on polar surfaces under N-rich conditions explains the anisotropic growth. Growth kinetics of the nanowires show that there are two important contributions to the growth. The first is growth by direct impingement and its contribution is independent of the nanowire diameter. The second contribution comes from atoms, which absorb on the substrate or wire sidewalls and diffuse along the sidewalls to the top of the wire, which acts as an effective sink for the adatoms due to a reduced surface mobility on the polar top of the wires. This diffusion channel, which is enhanced at higher T{sub sub}, becomes more significant for smaller wire diameters, because its contribution scales like 1/d. Experiments with  More>>
Authors:
Publication Date:
Aug 30, 2007
Product Type:
Thesis/Dissertation
Report Number:
ETDE-DE-1796
Resource Relation:
Other Information: TH: Diss. (Dr.rer.nat.)
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; GALLIUM NITRIDES; PLASMA; MOLECULAR BEAM EPITAXY; SUBSTRATES; DESORPTION; SURFACES; KINETICS; ATOMS; MOBILITY; DIFFUSION; INTERFACES; SILICON; STRAINS; STACKING FAULTS; SPECTRA; FERMI LEVEL; TRANSMISSION ELECTRON MICROSCOPY; LATTICE PARAMETERS; QUANTUM WIRES; CRYSTAL GROWTH; INDIUM NITRIDES; ANISOTROPY; ADSORPTION; HETEROJUNCTIONS; WIDTH; THIN FILMS; AMORPHOUS STATE; SILICON NITRIDES; HEXAGONAL LATTICES; BAND THEORY; ENERGY GAP; OPTICAL PROPERTIES; ELECTRONIC STRUCTURE; CARRIER DENSITY
OSTI ID:
21058844
Research Organizations:
Rheinisch-Westfaelische Technische Hochschule Aachen (Germany). Fakultaet fuer Mathematik, Informatik und Naturwissenschaften
Country of Origin:
Germany
Language:
English
Other Identifying Numbers:
TRN: DE08G7590
Availability:
Commercial reproduction prohibited; OSTI as DE21058844
Submitting Site:
DE
Size:
185 pages
Announcement Date:
Jul 24, 2008

Citation Formats

Meijers, R J. Growth and characterisation of group-III nitride-based nanowires for devices. Germany: N. p., 2007. Web.
Meijers, R J. Growth and characterisation of group-III nitride-based nanowires for devices. Germany.
Meijers, R J. 2007. "Growth and characterisation of group-III nitride-based nanowires for devices." Germany.
@misc{etde_21058844,
title = {Growth and characterisation of group-III nitride-based nanowires for devices}
author = {Meijers, R J}
abstractNote = {One of the main goals of this thesis was to get more insight into the mechanisms driving the growth of nitride nanowires by plasma-assisted molecular beam epitaxy (PA-MBE). The influence of the group-III and group-V flux as well as the substrate temperature T{sub sub} has been studied leading to the conclusion that the III-V ratio determines the growth mode. Ga desorption limits the temperature range to grow GaN nanowires and dissociation of InN is the limiting factor for InN nanowire growth. A reduction of the surface diffusivity on polar surfaces under N-rich conditions explains the anisotropic growth. Growth kinetics of the nanowires show that there are two important contributions to the growth. The first is growth by direct impingement and its contribution is independent of the nanowire diameter. The second contribution comes from atoms, which absorb on the substrate or wire sidewalls and diffuse along the sidewalls to the top of the wire, which acts as an effective sink for the adatoms due to a reduced surface mobility on the polar top of the wires. This diffusion channel, which is enhanced at higher T{sub sub}, becomes more significant for smaller wire diameters, because its contribution scales like 1/d. Experiments with an interruption of the growth and sharp interfaces in TEM images of heterostructures show that the suggestion in literature of a droplet-mediated PA-MBE nitride growth has to be discarded. Despite a thin amorphous silicon nitride wetting layer on the substrate surface, both GaN and InN nanowires grow in the wurtzite structure and epitaxially in a one-to-one relation to the Si(111) substrate surface. There is no evidence for cubic phases. TEM images and optical studies display a high crystalline and optical quality of GaN and InN nanowires. The substrate induces some strain in the bottom part of the nanowires, especially in InN due to the lower T{sub sub} than for GaN, which is released without the formation of dislocations. Only some stacking faults sometimes form at the base of the wires. Optical spectra also exhibit a band gap consistent with strain-free GaN in the upper part of the wires. For InN a band gap value of 0.7-0.8 eV has been determined at low temperatures. The doping concentration and the position of the Fermi-level in InN depend very much on the crystalline quality. In general the luminescence of GaN and InN improves with increased T{sub sub}. For GaN the defect-related peaks decrease and in InN the carrier concentration is reduced. Optical spectra confirm the effective incorporation of the dopant species in the nanowires despite a large nanowire surface and unfavourable growth conditions for doping, which are required for nitride nanowire growth. (orig.)}
place = {Germany}
year = {2007}
month = {Aug}
}