Figure - available from: Journal of Physics D: Applied Physics
This content is subject to copyright. Terms and conditions apply.
(a) Schematic diagram of the experimental scattering geometry. (b) Calculated intensity polar pattern of the unpolarized scattered light as a function of the incident polarization respect to the wire axis for backscattering configurations. (c), (d) Polar plots for the TO and LO modes and for ILO/ITO > ratio intensities versus the angle of the polarization of the incident light with respect to the nanowire axis for a wire lying on silicon and on air, respectively. The lines are guides to the eyes.
Source publication
We report on the use of photonic resonances in Raman spectroscopy on single nanowires for the enhancement of forbidden modes and the study of the interaction of phonons with free-carriers. This is achieved by suspending nanowire over a trench and detecting Raman scattered light with light polarized along the radial direction. Thanks to the photonic...
Similar publications
In this report, we describe a low-cost fabrication process for highly sensitive SERS substrate by using thermal evaporation technique. The SERS substrate structure consists of silver nanoparticles deposited on monolayer, bilayer and few layer graphene. The fabricated SERS substrates are investigated by field emission scanning electron microscope (F...
A new strategy named integrated plasmon-enhanced Raman scattering (iPERS) spectroscopy that features a configuration of evanescent field excitation and inverted collection is presented, which well unites the local field enhancement and far field emission, couples localized and propagating surface plasmons, integrates the SERS substrates and Raman s...
To increase the information per pixel in stimulated Raman scattering (SRS) microscopy as well as to correct from artifacts, it is valuable to acquire images at two different Raman shifts. We present a three-color SRS approach acquiring two perfectly registered SRS images where both pump beams are modulated at distinct frequencies while demodulating...
In recent 20 years, fibre laser system has been developed rapidly and widely used for its high quality, high efficiency, high robustness, and compactness. However, there are still many factors (such as non-linear effect, thermal effect, and mode instability) that limit the further increase of power of fibre laser system. Stimulated Raman scattering...
We present a facile and cost-effective manner to fabricate a highly sensitive and stable surface enhanced Raman scattering (SERS) substrate. First, a silicon nanowire array (SiNWA) is tailored by metal-assisted chemical etching (MaCE) method as a scaffold of the desired SERS substrate. Next, with an oblique angle deposition (OAD) method, optimized...
Citations
... For example, planar native defects in the form of stacking faults with the direction of growth in the c axis, which are often found in layered materials due to very low formation energy, could activate forbidden modes [25,[42][43][44]. Additionally, the breakdown of selection rules can be activated by the photonic nature of the light-nanowire interaction, which can modify the light polarization inside the nanowire [45][46][47][48]. ...
Earth-abundant and low-cost semiconductors, such as zinc phosphide (Zn3P2), are promising candidates for the next generation photovoltaic applications. However, synthesis on commercially available substrates, which favors the formation of defects, and controllable doping are challenging drawbacks that restrain device performance. Better assessment of relevant properties such as structure, crystal quality and defects will allow faster advancement of Zn3P2, and in this sense Raman spectroscopy can play an invaluable role. In order to provide a complete Raman spectrum reference of Zn3P2, this work presents a comprehensive analysis of vibrational properties of tetragonally-structured Zn3P2 (space group P42/nmc) nanowires, from both experimental and theoretical perspectives. Low-temperature high-resolution Raman polarization measurements have been performed on single-crystalline nanowires. Different polarization configurations have allowed selective enhancement of A1g, B1g and Eg Raman modes, while B2g modes were identified from complementary unpolarized Raman measurements. Simultaneous deconvolution of all Raman spectra with Lorentzian curves has allowed identification of 33 peaks which have been assigned to 34 (8A1g + 9B1g + 3B2g + 14Eg) out of the 39 theoretically predicted eigenmodes. The experimental results are in good agreement with the vibrational frequencies that have been computed by first-principles calculations based on density functional theory. Three separate regions were observed in the phonon dispersion diagram: (i) low frequency region (< 210 cm-1) which is dominated by Zn-related vibrations, (ii) intermediate region (210-225 cm-1) which represents a true phonon gap with no observed vibrations, and (iii) high frequency region (> 225 cm-1) which is attributed to primarily P-related vibrations. The analysis of vibrational patterns has shown that non-degenerate modes involve mostly atomic motion along the long crystal axis (c-axis), while degenerate modes correspond primarily to in-plane vibrations, perpendicular to the long c-axis. These results provide a detailed reference for identification of the tetragonal Zn3P2 phase, and can be used for building Raman based methodologies for effective defect screening of bulk materials and films, which might contain structural inhomogeneities.
... In doped polar semiconductors, such as GaAs, the LO mode can couple to collective oscillations of free carriers producing a coupled-phonon-plasmon mode (CPPM) [28]. The line shape analysis of the CPPM can be used to estimate the free carriers concentrations and holes mobility for p-type GaAs epilayers [28,29] and NWs [18,27,30,31]. The Raman scattering intensity of the CPPM can be described by [32]: ...
Effective and controllable doping is instrumental for enabling the use of III-V semiconductor nanowires in practical electronics and optoelectronics applications. To this end, dopants are incorporated during self-catalyzed growth via vapour-liquid-solid mechanism through the catalyst droplet or by vapour-solid mechanism of the sidewall growth. The interplay of these mechanisms together with the competition between axial elongation and radial growth of nanowires can result in dopant concentration gradients along the nanowire axis. Here, we report an investigation of Be-doped p-type GaAs nanowires grown by the self-catalyzed method on lithography-free Si/SiOx templates. The influence of dopant incorporation on the structural properties of the nanowires is analysed by scanning and transmission electron microscopy. By combining spatially resolved Raman spectroscopy and transport characterization, we are able to estimate the carrier concentration, mobility and resistivity on single nanowire level. We show that Be dopants are incorporated predominantly by vapour-solid mechanism for low Be flux, while the relative contribution of vapour-liquid-solid incorporation is increased for higher Be flux, resulting in axial dopant gradients that depend on the nominal doping level.
... For example, surface phonon modes have been reported [23] in NWs due to their large surface-tovolume ratio. Despite the fact that GaAs NWs have been investigated intensively by Raman spectroscopy [23][24][25], there are hardly any reports on detailed Raman scattering measurements on Mn doped GaAs NWs. In this work, the influence of Mn ion-implantation at elevated temperatures on GaAs:Zn NWs has been studied in detail. ...
Recent progress in the realization of magnetic GaAs nanowires (NWs) doped with Mn has attracted a lot of attention due to their potential application in spintronics. In this work, we present a detailed Raman investigation of the structural properties of Zn doped GaAs (GaAs:Zn) and Mn-implanted GaAs:Zn (Ga0.96Mn0.04As:Zn) NWs. A significant broadening and redshift of the optical TO and LO phonon modes are observed for these NWs compared to as-grown undoped wires, which is attributed to strain induced by the Zn/Mn doping and to the presence of implantation-related defects. Moreover, the LO phonon modes are strongly damped, which is interpreted in terms of a strong LO phonon-plasmon coupling, induced by the free hole concentration. Moreover, we report on two new interesting Raman phonon modes (191 and 252 cm-1) observed in Mn ion-implanted NWs, which we attribute to Eg (TO) and A1g (LO) vibrational modes in a sheet layer of crystalline arsenic present on the surface of the NWs. This conclusion is supported by fitting the observed Raman shifts for the SO phonon modes to a theoretical dispersion function for a GaAs NW capped with a dielectric shell.
... The measurements were realized in backscattering geometry with the nanowires suspended over a trench, in order to enhance the response of the longitudinal optical phonon mode. 59 ■ ASSOCIATED CONTENT ...
III-V nanowires are candidate building blocks for next generation electronic and optoelectronic platforms. Low bandgap semiconductors such as InAs and InSb are interesting because of their high electron mobility. Fine control of the structure, morphology and composition are key to the control of their physical properties. In this work we present how to grow catalyst-free InAs1-xSbx nanowires, which are stacking fault- and twin defect-free over several hundreds of nanometers. We evaluate the impact of their crystal phase purity by probing their electrical properties in a transistor-like configuration and by measuring the phonon-plasmon interaction by Raman spectroscopy. We also highlight the importance of high quality dielectric coating for the reduction of hysteresis in the electrical characteristics of the nanowire transistors. High channel carrier mobilities and reduced hysteresis open the path for high-frequency devices fabricated using InAs1-xSbx nanowires.
Semiconductor nanowire lasers are single-element structures that can act as both gain material and cavity for optical lasing. They have typical dimensions on the order of an optical wavelength in diameter and several micrometres in length, presenting unique challenges for testing and characterisation. Optical microscopy and spectroscopy are powerful tools used to study nanowire lasers; here, we review the common techniques and analytical approaches often used and outline potential pitfalls in their application. We aim to outline best practise and experimental approaches used for characterisation of the material, cavity and lasing performance of nanowires towards applications in biology, photonics and telecommunications.
Dopant atoms can be incorporated into nanowires either via the vapor-liquid-solid mechanism through the catalyst droplet or by the vapor-solid growth on the sidewalls. Si is a typical n-type dopant for GaAs, but in nanowires it often suffers from a strongly amphoteric nature in the vapor-liquid-solid process. This issue can be avoided by using Te, which is a promising but less common alternative for n-type doping of GaAs nanowires. Here, we present a detailed investigation of Te-doped self-catalyzed GaAs nanowires. We use several complementary experimental techniques, such as atom probe tomography, off-axis electron holography, micro-Raman spectroscopy, and single-nanowire transport characterization, to assess the Te concentration, the free-electron concentration, and the built-in potential in Te-doped GaAs nanowires. By combing the experimental results with a theoretical model, we show that Te atoms are mainly incorporated by the vapor-liquid-solid process through the Ga droplet, which leads to both axial and radial dopant gradients due to Te diffusion inside the nanowires and competition between axial elongation and radial growth of nanowires. Furthermore, by comparing the free-electron concentration from Raman spectroscopy and the Te-atom concentrations from atom probe tomography, we show that the activation of Te donor atoms is 100% at a doping level of 4×1018cm−3, which is a significant result in terms of future device applications.
The ability to manipulate light-matter interaction in semiconducting nanostructures is fascinating for implementing functionalities in advanced optoelectronic devices. Here, we report the tailoring of radiative emissions in a ZnTe/ZnTe:O/ZnO core-shell single nanowire coupled with one-dimensional aluminum bowtie antenna array. The plasmonic antenna enables changes in the excitation and emission processes, leading to an obvious enhancement of near band edge emission (2.2 eV) and sub-gap excitonic emission (1.7 eV) bound to intermediate band states in ZnTe/ZnTe:O/ZnO core-shell nanowire as well as surface-enhanced Raman scattering at room temperature. The increase of emission decay rate in the nanowire/antenna system, probed by time-resolved photoluminescence spectroscopy, yields an observable enhancement of quantum efficiency induced by local surface plasmon resonance. Electromagnetic simulations agree well with the experimental observations, revealing a combined effect of enhanced electric near-field intensity and the improvement of quantum efficiency in ZnTe/ZnTe:O/ZnO nanowire/antenna system. The capability of tailoring light-matter interaction in low-efficient emitters may provide an alternative platform for designing advanced optoelectronic and sensing devices with precisely controlled response.
InAsSb nanowires are promising elements for thermoelectric devices, infrared pho- todetectors, high-speed transistors, as well as thermophotovoltaic cells. By changing the Sb alloy fraction the mid-infrared bandgap energy and thermal conductivity may be tuned for specic device applications. Using both terahertz and Raman non-contact probes, we show that Sb alloying increases the electron mobility in the nanowires by over a factor of 3 from InAs to InAs0.65Sb0.35. We also extract the temperature- dependent electron mobility via both terahertz and Raman spectroscopy and we re- port the highest electron mobilities for InAs0.65Sb0.35 nanowires to date, exceeding 16,000 cm²V⁻¹s⁻¹ at 10 K.
