Spatially-resolved luminescence and crystal structure of single core-shell nanowires measured in the as-grown geometry
Ali AlHassan, Jonas Lähnemann, Steven Leake, Hanno Küpers, Michael Niehle, Danial Bahrami, Florian Bertram, Ryan B. Lewis, Arman Davtyan, Tobias Schülli, Lutz G… 展开作者
Ali AlHassan, Jonas Lähnemann, Steven Leake, Hanno Küpers, Michael Niehle, Danial Bahrami, Florian Bertram, Ryan B. Lewis, Arman Davtyan, Tobias Schülli, Lutz Geelhaar, Ullrich Pietsch
备注：
This is an author-created, un-copyedited version of an article published in Nanotechnology. IOP Publishing Ltd. is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1361-6528/ab7590
We report on the direct correlation between the structural and optical properties of single, as-grown core-multi-shell GaAs/In$_{0.15}$Ga$_{0.85}$As/GaAs/AlAs/GaAs nanowires. Fabricated by molecular beam epitaxy on a pre-patterned Si(111) substrate, on a row of well separated nucleation sites, it was possible to access individual nanowires in the as-grown geometry. The polytype distribution along the growth axis of the nanowires was revealed by synchrotron-based nanoprobe X-ray diffraction techniques monitoring the axial 111 Bragg reflection. For the same nanowires, the spatially-resolved emission properties were obtained by cathodoluminescence hyperspectral linescans in a scanning electron microscope. Correlating both measurements, we reveal a blueshift of the shell quantum well emission energy combined with an increased emission intensity for segments exhibiting a mixed structure of alternating wurtzite and zincblende stacking compared with the pure crystal polytypes. The presence of this mixed structure was independently confirmed by cross-sectional transmission electron microscopy.
CdSe quantum dots (QDs) with different organic linker molecules are attached to ZnO nanowires (NWs) to study the luminescence dynamics and the electron tunneling from the QDs to the nanowires in time-resolved photoluminescence (PL) and photoconductivity measurements. The PL transients of the QD luminescence indicate two different recombination channels: the direct recombination inside the QD core and the recombination via QD surface defect states. After linking the QDs to the ZnO NW surface, photo-induced electron tunneling from an excited state of the QD into the conduction band of the nanowi…
(In,Ga)N insertions embedded in self-assembled GaN nanowires are of current interest for applications in solid state light emitters. Such structures exhibit a notoriously broad emission band. We use cathodoluminescence spectral imaging in a scanning electron microscope and micro-photoluminescence spectroscopy on single nanowires to learn more about the mechanisms underlying this emission. We observe a shift of the emission energy along the stack of six insertions within single nanowires that may be explained by compositional pulling. Our results also corroborate reports that the localization o…
Core-shell nanowire heterostructures form the basis for many innovative devices. When compound nanowire shells are grown by directional deposition techniques, the azimuthal position of the sources for the different constituents in the growth reactor, substrate rotation, and nanowire self-shadowing inevitably lead to sequential deposition. Here, we uncover for In$_{0.15}$Ga$_{0.85}$As/GaAs shell quantum wells grown by molecular beam epitaxy a drastic impact of this sequentiality on the luminescence efficiency. The photoluminescence intensity of shell quantum wells grown with a flux sequence cor…
In this work, a numerical approach to investigate the room temperature luminescence emission from core/shell nanowire is presented where GaN quantum discs (QDiscs), periodically distributed in AlxGa1-xN nanowire, is considered as core and AlxGa1-xN as shell. Thin disk shaped (Ring shaped) n-doped region has been placed at the GaN/ AlxGa1-xN (AlxGa1-xN /air) interface in AlxGa1-xN region in axial (radial) directions. To obtain energy levels and related wavefunctions, self-consistent procedure has been employed to solve Schrodinger-Poisson equations with considering the spontaneous and piezoelec…
The optical properties of a stack of GaN/AlN quantum discs (QDiscs) in a GaN nanowire have been studied by spatially resolved cathodoluminescence (CL) at the nanoscale (nanoCL) using a Scanning Transmission Electron Microscope (STEM) operating in spectrum imaging mode. For the electron beam excitation in the QDisc region, the luminescence signal is highly localized with spatial extension as low as 5 nm due to the high band gap difference between GaN and AlN. This allows for the discrimination between the emission of neighbouring QDiscs and for evidencing the presence of lateral inclusions, abo…
Electron irradiation of GaN nanowires in a scanning electron microscope strongly reduces their luminous efficiency as shown by cathodoluminescence imaging and spectroscopy. We demonstrate that this luminescence quenching originates from a combination of charge trapping at already existing surface states and the formation of new surface states induced by the adsorption of C on the nanowire sidewalls. The interplay of these effects leads to a complex temporal evolution of the quenching, which strongly depends on the incident electron dose per area. Time-resolved photoluminescence measurements on…
GaAs nanowires (NWs) grown by molecular-beam epitaxy may contain segments of both the zincblende (ZB) and wurtzite (WZ) phases. Depending on the growth conditions, we find that optical emission of such NWs occurs either predominantly above or below the band gap energy of ZB GaAs [E(g,ZB)]. This result is consistent with the assumption that the band gap energy of wurtzite GaAs [E(g,WZ)] is larger than E(g,ZB) and that GaAs NWs with alternating ZB and WZ segments along the wire axis establish a type II band alignment, where electrons captured within the ZB segments recombine with holes of the ne…
The strong light-matter interaction in transition Metal dichalcogenides (TMDs) monolayers (MLs) is governed by robust excitons. Important progress has been made to control the dielectric environment surrounding the MLs, especially through hexagonal boron nitride (hBN) encapsulation, which drastically reduces the inhomogeneous contribution to the exciton linewidth. Most studies use exfoliated hBN from high quality flakes grown under high pressure. In this work, we show that hBN grown by molecular beam epitaxy (MBE) over a large surface area substrate has a similarly positive impact on the optic…
We investigate the 3.45-eV luminescence band of spontaneously formed GaN nanowires on Si(111) by photoluminescence and cathodoluminescence spectroscopy. This band is found to be particularly prominent for samples synthesized at comparatively low temperatures. At the same time, these samples exhibit a peculiar morphology, namely, isolated long nanowires are interspersed within a dense matrix of short ones. Cathodoluminescence intensity maps reveal the 3.45-eV band to originate primarily from the long nanowires. Transmission electron microscopy shows that these long nanowires are either Ga polar…
Using an approximate time-dependent density functional theory method, we calculate the absorption and luminescence spectra for hydrogen passivated silicon nanoscale structures with large aspect ratio. The effect of electron confinement in axial and radial directions is systematically investigated. Excited state relaxation leads to significant Stokes shifts for short nanorods with lengths less than 2 nm, but has little effect on the luminescence intensity. The formation of self-trapped excitons is likewise observed for short nanostructures only; longer wires exhibit fully delocalized excitons w…
We develop an InAs nanowire gate-all-around field-effect transistor using a transparent conductive zinc oxide (ZnO) gate electrode, which is in-situ atomic layer deposited after growth of gate insulator of Al2O3. We perform magneto-transport measurements and find a crossover from weak localization to weak antilocalization effect with increasing gate voltage, which demonstrates that the Rashba spin-orbit coupling is tuned by the gate electrode. The efficiency of the gate tuning of the spin-orbit interaction is higher than those obtained for two-dimensional electron gas, and as high as that for …
N-type doping of GaAs nanowires has proven to be difficult because the amphoteric character of silicon impurities is enhanced by the nanowire growth mechanism and growth conditions. The controllable growth of n-type GaAs nanowires with carrier density as high as 1020 electron/cm3 by self-assisted molecular beam epitaxy using Te donors is demonstrated here. Carrier density and electron mobility of highly doped nanowires are extracted through a combination of transport measurement and Kelvin probe force microscopy analysis in single-wire field-effect devices. Low-temperature photoluminescence is…
Several of the key issues of planar (Al,Ga)N-based deep-ultraviolet light emitting diodes could potentially be overcome by utilizing nanowire heterostructures, exhibiting high structural perfection and improved light extraction. Here, we study the spontaneous emission of GaN/(Al,Ga)N nanowire ensembles grown on Si(111) by plasma-assisted molecular beam epitaxy. The nanowires contain single GaN quantum disks embedded in long (Al,Ga)N nanowire segments essential for efficient light extraction. These quantum disks are found to exhibit intense emission at unexpectedly high energies, namely, signif…
We report on experimental determination of the strain and bandgap of InAsP in epitaxially grown InAsP-InP core-shell nanowires. The core-shell nanowires are grown via metal-organic vapor phase epitaxy. The as-grown nanowires are characterized by transmission electron microscopy, X-ray diffraction, micro-photoluminescence ($μ$PL) spectroscopy and micro-Raman ($μ$-Raman) spectroscopy measurements. We observe that the core-shell nanowires are of wurtzite (WZ) crystal phase and are coherently strained, with the core and the shell having the same number of atomic planes in each nanowire. We determi…
New insights into controlling nanowire merging phenomena are demonstrated in growth of thin ZnO nanowires using monodispersed Au colloidal nanoparticles as catalyst. Both nanowire diameter and density were found to be strongly dependent on the density of Au nanoparticles. Structural analysis and spectral cathodoluminescence imaging of the c-plane nanowire cross-sections reveal that thin isolated nanowires growing from the Au nanoparticles begin to merge and coalesce with neighbouring nanowires to form larger nanowires when their separation reaches a threshold distance. Green luminescence, whic…
We report nonlinear behavior in the motion of driven nanowire cantilevers. The nonlinearity can be described by the Duffing equation and is used to demonstrate mechanical mixing of two distinct excitation frequencies. Furthermore, we demonstrate that the nonlinearity can be used to amplify a signal at a frequency close to the mechanical resonance of the nanowire oscillator. Up to 26 dB of amplitude gain are demonstrated in this way.
We report on realization and transport spectroscopy study of single quantum dots (QDs) made from InSb nanowires grown by molecular beam epitaxy (MBE). The nanowires employed are 50-80 nm in diameter and the QDs are defined in the nanowires between the source and drain contacts on a Si/SiO$_2$ substrate. We show that highly tunable QD devices can be realized with the MBE-grown InSb nanowires and the gate-to-dot capacitance extracted in the many-electron regimes is scaled linearly with the longitudinal dot size, demonstrating that the devices are of single InSb nanowire QDs even with a longitudi…
The influence of a distributed Bragg reflector composed of ZnTe, MgTe, and MgSe superlattices on photoluminescence of self assembled CdTe quantum dots (QD) emitting in the yellow spectral range is investigated. In the case of QDs grown on a distributed Bragg reflector the photoluminescence intensity is enhanced by more than one order of magnitude, whereas the single QD lines are broadened as compared to the case of QDs grown on a ZnTe buffer. Structural and chemical analysis reveal an unintentional formation of a thin ZnSe layer induced by the growth interruption needed for the deposition of t…
Semiconductor nanowires have emerged as versatile components in superconducting hybrid devices for Majorana physics and quantum computing. The transport properties of nanowires can be tuned either by field-effect or doping. We investigated a series of InAs nanowires which conductivity has been modified by n-type doping using tellurium. In addition to electron microscopy studies, the wires were also examined with atomic probe tomography to obtain information about the local incorporation of Te atoms. It was found that the Te atoms mainly accumulate in the core of the nanowire and at the corners…
Superconductor-semiconductor nanowire hybrid structures are useful in fabricating devices for quantum information processing. While selective area growth (SAG) offers the flexibility to grow semiconductor nanowires in arbitrary geometries, in-situ evaporation of superconductors ensures pristine superconductor-semiconductor interfaces, resulting in strong induced superconductivity in the semiconducting nanowire. In this work, we evaporated islands of superconductor tin on InAs SAG nanowires, by using in-situ shadowing with high aspect-ratio pre-fabricated SiOx dielectric walls. Our technique al…
We report in-situ synthesis of crystalline indium islands on InAs nanowires grown by molecular beam epitaxy. Structural analysis by transmission electron microscopy showed that In crystals grew in a tetragonal body-centred crystal structure within two families of orientations relative to wurtzite InAs. The crystalline islands had lengths < 500 nm and low-energy surfaces, suggesting that growth was driven mainly by surface energy minimization. Electrical transport through In/InAs devices exhibited Cooper pair charging, evidencing charge parity preservation and a pristine In/InAs interface, with…
We have investigated micro-photoluminescence ($μ$-PL) and excitation ($μ$-PLE) spectra of a single GaAs/AlGaAs quantum dot grown on a GaAs (411)A surface. We observed sharp resonant lines in both $μ$-PL and $μ$-PLE spectra, corresponding to the discrete energy levels of the dot. When the sample was excited at one of the resonant lines, resonant luminescence lines appear not only in Stokes side but also in anti-Stokes side. We discuss the possible origins of the anomalus anti-Stokes luminescence.
We report on growth of InP-InAs core-shell nanowires and demonstration of the formation of single quantum structures, which show Coulomb blockade effect, over entire lengths of the nanowires. The core-shell nanowires are grown by a selective area growth technique via metal-organic vapor phase epitaxy. The as-grown core-shell nanowires are found to be of wurtzite crystals. The InP cores have a hexagonal cross section, while the InAs shell are grown preferentially on specific {1$\bar{1}$00} facets, leading to the formation of the core-shell nanowires with an overall triangular cross section. The…
Realizing single photon sources emitting in the telecom band on silicon substrates is essential to reach complementary-metal-oxide-semiconductor (CMOS) compatible devices that secure communications over long distances. In this work, we propose the monolithic growth of needlelike tapered InAs/InP quantum dot-nanowires (QD-NWs) on silicon substrates with a small taper angle and a nanowire diameter tailored to support a single mode waveguide. Such a NW geometry is obtained by a controlled balance over axial and radial growths during the gold-catalyzed growth of the NWs by molecular beam epitaxy. …
In this work we present how the optical properties of ZnSe nanowires are modified by the presence of Ag nanoparticles on the sidewalls of the ZnSe nanowires. In particular we show that the low-temperature luminescence of the ZnSe nanowires changes its shape, enhancing the phonon-replicas of impurity related recombination and affecting rise and decay times of the transient absorption bleaching at room temperatures, with an increase of the former and a decrease of the latter. In contrast, the deposition of Au NPs on the ZnSe nanowires does not change the optical properties of the sample. We sugg…
We analyze the emission of single GaN nanowires with (In,Ga)N insertions using both micro-photoluminescence and cathodoluminescence spectroscopy. The emission spectra are dominated by a green luminescence band that is strongly blueshifted with increasing excitation density. In conjunction with finite-element simulations of the structure to obtain the piezoelectric polarization, these results demonstrate that our (In,Ga)N/GaN nanowire heterostructures are subject to the quantum-confined Stark effect. Additional sharp peaks in the spectra, which do not shift with excitation density, are attribut…
Straight, axial InAs nanowire with multiple segments of GaInAs were grown. High resolution X-ray energy-dispersive spectroscopy (EDS) mapping reveal the distribution of group III atoms at the axial interfaces and at the sidewalls. Significant Ga enrichment, accompanied by a structural change is observed at the GaInAs/InAs interfaces and a higher Ga concentration for the early grown GaInAs segments. The elemental map and EDS line profile infer Ga enrichment at the facet junctions between the sidewalls. The relative chemical potentials of ternary alloys and the thermodynamic driving force for li…
High quality heteroepitaxial two-dimensional (2D) InSb layers are very difficult to realize owing to the large lattice mismatch with other widespread semiconductor substrates. A way around this problem is to grow free-standing 2D InSb nanostructures on nanowire (NW) stems, thanks to the capability of NWs to efficiently relax elastic strain along the sidewalls when lattice-mismatched semiconductor systems are integrated. In this work, we optimize the morphology of free-standing 2D InSb nanoflags (NFs). In particular, robust NW stems, optimized growth parameters, and the use of reflection high-e…
We present the room temperature (RT) near-infrared (NIR) photoluminescence (PL) properties of Si/Ge nanowire (NW) grown silicon wafers which were treated by vapor of HF:HNO3 chemical mixture. This treatment activates or enhances the PL intensity at NIR region ranging from 1000 nm to 1800 nm. The PL consists of a silicon band-edge emission and a broad composite band which was centered at around 1400-1600 nm. The treatment modifies the wafer surface particularly at defect sites particularly pits around NWs and NW surfaces by etching and oxidation of Si and Ge. This process can induce spatial con…
Theoretically core-multishell nanowires under a cross-section of hexagonal geometry should exhibit peculiar confinement effects. Using a hard X-ray nanobeam, here we show experimental evidence for carrier localization phenomena at the hexagon corners by combining synchrotron excited optical luminescence with simultaneous X-ray fluorescence spectroscopy. Applied to single coaxial n-GaN/InGaN multiquantum-well/p-GaN nanowires, our experiment narrows the gap between optical microscopy and high-resolution X-ray imaging, and calls for further studies on the underlying mechanisms of optoelectronic n…
Quench, Glow, or Stay Silent: Distance-Controlled Up-Conversion Emission near Metallic Nanowires
Nicolaus Copernicus University in Toruń（托伦哥白尼大学）；Université Bourgogne Europe, CNRS, Laboratoire Interdisciplinaire Carnot de Bourgogne ICB UMR 6303（勃艮第欧洲大学、法国国家科学研究中心、勃艮第跨学科卡诺实验室）；Institute of Physical Chemistry Polish Academy of Sciences（波兰科学院物理化学研究所）；Wroclaw University of Science and Technology（弗罗茨瓦夫科技大学）
Photoluminescence from bulk HfS$_2$ grown by the chemical vapor transport method is reported. A series of emission lines is apparent at low temperature in the energy range of 1.4 - 1.5 eV. Two groups of the observed excitonic transitions followed by their replicas involving acoustic and optical phonons are distinguished using classical intensity correlation analysis. The emission is attributed to the recombination of excitons bound to iodine (I$_2$) molecules intercalated between layers of HfS$_2$. The I$_2$ molecules are introduced to the crystal during the growth as halogen transport agents …
It was predicted by Wigner in 1934 that the electron gas will undergo a transition to a crystallized state when its density is very low. Whereas significant progress has been made towards the detection of electronic Wigner states, their clear and direct experimental verification still remains a challenge. Here we address signatures of Wigner molecule formation in the transport properties of InSb nanowire quantum dot systems, where a few electrons may form localized states depending on the size of the dot (i.e. the electron density). By a configuration interaction approach combined with an appr…
We investigate monocrystalline InAs nanowires (NWs) which are grown by molecular beam epitaxy (MBE) and induced by focused ion beam (FIB) implanted Au spots. With this unique combination of methods an increase of the aspect ratio, i.e. the length to width ratio, of the grown NWs up to 300 was achieved. To control the morphology and crystalline structure of the NWs, the growth parameters like temperature, flux ratios and implantation fluence are varied and optimized. Furthermore, the influence of the used molecular arsenic species, in particular the As$_2$ to As$_4$ ratio, is investigated and a…
Silicon nanowires grown along the <100>-direction with a bulk Si core are studied with density functional calculations. Two surface reconstructions prevail after exploration of a large fraction of the phase space of nanowire reconstructions. Despite their energetical equivalence, one of the reconstructions is found to be strongly metallic while the other one is semi-metallic. This electronic-structure behavior is dictated by the particular surface states of each reconstruction. These results imply that doping is not required in order to obtain good conducting Si nanowires.
We report on photocurrent and photoconductance processes in a freely suspended p-doped single GaAs nanowire. The nanowires are grown by molecular beam epitaxy (MBE), and they are electrically contacted by a focused ion beam (FIB) deposition technique. The observed photocurrent is generated at the Schottky contacts between the nanowire and metal source-drain electrodes, while the observed photoconductance signal can be explained by a photogating effect induced by optically generated charge carriers located at the surface of the nanowire. Both optoelectronic effects are sensitive to the polariza…
We present an original approach to fabricate single GaAs/AlGaAs core-shell nanowire with robust and reproducible transport properties. The core-shell structure is buried in an insulating GaAs overlayer and connected as grown in a two probe set-up using the highly doped growth substrate and a top diffused contact. The measured conductance shows a non-ohmic behavior with temperature and voltage-bias dependences following power laws, as expected for a quasi-1D system.
We present a novel two-step approach for the selective area growth (SAG) of GaAs nanowires (NWs) by molecular beam epitaxy which has enabled a detailed exploration of the NW diameter evolution. In the first step, the growth parameters are optimized for the nucleation of vertically-oriented NWs. In the second step, the growth parameters are chosen to optimize the NW shape, allowing NWs with a thin diameter (45 nm) and an untapered morphology to be realized. This result is in contrast to the commonly observed thick, inversely tapered shape of SAG NWs. We quantify the flux dependence of radial va…
Nanoprobe X-ray diffraction (nXRD) using focused synchrotron radiation is a powerful technique to study the structural properties of individual semiconductor nanowires. However, when performing the experiment under ambient conditions, the required high X-ray dose and prolonged exposure times can lead to radiation damage. To unveil the origin of radiation damage, we compare nXRD experiments carried out on individual semiconductor nanowires in their as grown geometry both under ambient conditions and under He atmosphere at the microfocus station of the P08 beamline at the 3rd generation source P…
GaN nanowire ensembles with axial InGaN multi-quantum wells (MQWs) were grown by molecular beam epitaxy. In a series of samples, we varied the In content in the MQWs from almost zero to about 20%. Within the nanowire ensemble, the MQWs fluctuate strongly in composition and size. Statistical information about the composition was obtained from x-ray diffraction and Raman spectroscopy. Photoluminescence at room temperature was obtained in the range from 2.2 eV to 2.5 eV depending on In content. Contrary to planar MQWs, the intensity increases with increasing In content. We compare the observed em…
We present electronic transport measurements of GaAs nanowires grown by catalyst-free metal-organic chemical vapor deposition. Despite the nanowires being doped with a relatively high concentration of substitutional impurities, we find them inordinately resistive. By measuring sufficiently high aspect-ratio nanowires individually in situ, we decouple the role of the contacts and show that this semi-insulating electrical behavior is the result of trap-mediated carrier transport. We observe Poole-Frenkel transport that crosses over to phonon-assisted tunneling at higher fields, with a tunneling …
We suggest a new method of quantum information processing based on the precise placing of P-31 isotope atoms in a quasi-one-dimensional Si-28 nanowire using isotope engineering and neutron-transmutation doping of the grown structures. In our structure, interqubit entanglement is based on the indirect interaction of P-31 nuclear spins with electrons localized in a nanowire. This allows one to control the coupling between distant qubits and between qubits separated by non-qubit neighboring nodes. The suggested method enables one to fabricate structures using present-day nanolithography. Numerica…
Induced superconductivity in selective-area grown SnTe devices
MESA+ Institute, University of Twente（特温特大学 MESA+ 研究所）；Department of Applied Physics, Eindhoven University of Technology（埃因霍温理工大学应用物理系）；II. Physikalisches Institut, Universität zu Köln（科隆大学第二物理研究所）；Eurofins Materials Science Eindhoven（欧洲分析检测材料科学埃因霍温）；IBM Research Europe Zürich（IBM 苏黎世欧洲研究中心）
The strain configuration induced by the lattice mismatch in a core-shell nanowire is calculated analytically, taking into account the crystal anisotropy and the difference in stiffness constants of the two materials. The method is applied to nanowires with the wurtzite structure or the zinc-blende structure with the hexagonal / trigonal axis along the nanowire, and the results are compared to available numerical calculations and experimental data. It is also applied to multishell nanowires, and to core-shell nanowires grown along the $<001>$ axis of cubic semiconductors.
We characterize in-situ grown parallel nanowires bridged by a superconducting island. The magnetic-field and temperature dependence of Coulomb blockade peaks measured across different pairs of nanowire ends are consistent with a sub-gap state extended over the hybrid parallel-nanowire island. Being gate-tunable, accessible by multiple terminals and free of quasiparticle poisoning, these nanowires show promise for the implementation of several proposals that rely on parallel nanowire platforms.
In this PhD thesis, quantum devices based on molecular-beam epitaxy grown InAs semiconductor with an in-situ grown epitaxial Al film were investigated. Novel device geometries were realized that allow for the study of bound states that emerge at low temperatures in semiconducting nanowires due to the presence of spin-orbit coupling, Zeeman effect, and superconducting proximity effect. Experiments utilizing either gate-defined nanowires in two-dimensional heterostructures or vapor-liquid-solid grown nanowires with a full-shell of Al are presented. Devices and experimental methods were developed…
Self-assembled nanowire (NW) crystals can be grown into nearly defect-free nanomechanical resonators with exceptional properties, including small motional mass, high resonant frequency, and low dissipation. Furthermore, by virtue of slight asymmetries in geometry, a NW's flexural modes are split into doublets oscillating along orthogonal axes. These characteristics make bottom-up grown NWs extremely sensitive vectorial force sensors. Here, taking advantage of its adaptability as a scanning probe, we use a single NW to image a sample surface. By monitoring the frequency shift and direction of o…
The optical properties of quantum dots embedded in a catalytically grown semiconductor nanowire are studied theoretically. In comparison to dots in a bulk environment, the excitonic absorption is strongly modified by the one-dimensional character of the nanowire phonon spectrum. In addition to pronounced satellite peaks due to phonon-assisted absorption, we find a finite width of the zero-phonon line already in the lowest-order calculation.
GaAs nanowires are grown by molecular beam epitaxy using a self-catalyzed, Ga-assisted growth technique. Position control is achieved by nano-patterning a SiO2 layer with arrays of holes with a hole diameter of 85 nm and a hole pitch varying between 200 nm and 2 \mum. Gallium droplets form preferentially at the etched holes acting as catalyst for the nanowire growth. The nanowires have hexagonal cross-sections with {110} side facets and crystallize predominantly in zincblende. The interdistance dependence of the nanowire growth rate indicates a change of the III/V ratio towards As-rich conditi…
