Poole−Frenkel Effect and Phonon-Assisted Tunneling in GaAs Nanowires (original) (raw)

Mobility and carrier density in p-type GaAs nanowires measured by transmission Raman spectroscopy

Nanoscale, 2012

The unambiguous measurement of carrier concentration and mobility in semiconductor nanowires remains a challenging task. This is a consequence of their one-dimensional nature and the incompatibility with Hall or van der Pauw measurements. We propose a method that allows the direct determination of mobility and carrier concentration in nanowires in a contact-less manner. We demonstrate how forward Raman scattering enables the measurement of phonon-plasmon interactions. By applying this method to p-type GaAs nanowires, we were able to directly obtain values of the carrier concentration between 3.0 Â 10 17 and 7.4 Â 10 18 cm À3 and a mobility of 31 cm 2 (V s) À1 at room temperature. This study opens the path towards the study of plasmon-phonon interactions in semiconductor nanowires.

Anomalous ambipolar transport in depleted GaAs nanowires

Physical review, 2022

We have used a polarized microluminescence technique to investigate photocarrier charge and spin transport in n-type depleted GaAs nanowires (≈ 10 17 cm −3 doping level). At 6K, a longdistance tail appears in the luminescence spatial profile, indicative of charge and spin transport, only limited by the length of the NW. This tail is independent on excitation power and temperature. Using a self-consistent calculation based on the drift-diffusion and Poisson equations as well as on photocarrier statistics (Van Roosbroeck model), it is found that this tail is due to photocarrier drift in an internal electric field nearly two orders of magnitude larger than electric fields predicted by the usual ambipolar model. This large electric field appears because of two effects. Firstly, for transport in the spatial fluctuations of the conduction band minimum and valence band maximum, the electron mobility is activated by the internal electric field. This implies, in a counter intuitive way, that the spatial fluctuations favor long distance transport. Secondly, the range of carrier transport is further increased because of the finite NW length, an effect which plays a key role in one-dimensional systems.

Tailoring the carrier mobility of semiconductor nanowires by remote dielectrics

Journal of Applied Physics, 2007

The dielectric environment of thin semiconductor nanowires can affect the charge transport properties inside the wire. In this work, it is shown that Coulomb impurity scattering in thin nanowires can be damped strongly by coating the wire with a high-dielectric. This leads to an increase in the mobility of free charges inside the wire and can be used as a post-growth technique to improve the conductivity of thin nanowires.

Contactless monitoring of the diameter-dependent conductivity of GaAs nanowires

Nano Research, 2010

Contactless monitoring with photoelectron microspectroscopy of the surface potential along individual nanostructures, created by the X-ray nanoprobe, opens exciting possibilities to examine quantitatively size-and surface-chemistry-effects on the electrical transport of semiconductor nanowires (NWs). Implementing this novel approach-which combines surface chemical microanalysis with conductivity measurements-we explored the dependence of the electrical properties of undoped GaAs NWs on the NW width, temperature and surface chemistry. By following the evolution of the Ga 3d and As 3d core level spectra, we measured the positiondependent surface potential along the GaAs NWs as a function of NW diameter, decreasing from 120 to ~20 nm, and correlated the observed decrease of the conductivity with the monotonic reduction in the NW diameter from 120 to ~20 nm. Exposure of the GaAs NWs to oxygen ambient leads to a decrease in their conductivity by up to a factor of 10, attributed to the significant decrease in the carrier density associated with the formation of an oxide shell.

Towards low-dimensional hole systems in Be-doped GaAs nanowires

Nanotechnology, 2017

GaAs was central to the development of quantum devices but is rarely used for nanowire-based quantum devices with InAs, InSb and SiGe instead taking the leading role. p-type GaAs nanowires offer a path to studying stronglyconfined 0D and 1D hole systems with strong spin-orbit effects, motivating our development of nanowire transistors featuring Be-doped p-type GaAs nanowires, AuBe alloy contacts and patterned local gate electrodes towards making nanowirebased quantum hole devices. We report on nanowire transistors with traditional substrate back-gates and EBL-defined metal/oxide top-gates produced using GaAs nanowires with three different Be-doping densities and various AuBe contact processing recipes. We show that contact annealing only brings small improvements for the moderately-doped devices under conditions of lower anneal temperature and short anneal time. We only obtain good transistor performance for moderate doping, with conduction freezing out at low temperature for lowlydoped nanowires and inability to reach a clear off-state under gating for the highlydoped nanowires. Our best devices give on-state conductivity 95 nS, off-state conductivity 2 pS, on-off ratio ∼ 10 4 , and sub-threshold slope 50 mV/dec at T = 4 K. Lastly, we made a device featuring a moderately-doped nanowire with annealed contacts and multiple top-gates. Top-gate sweeps show a plateau in the sub-threshold region that is reproducible in separate cool-downs and indicative of possible conductance quantization highlighting the potential for future quantum device studies in this material system.

High electron mobility in strained GaAs nanowires

Nature Communications, 2021

Transistor concepts based on semiconductor nanowires promise high performance, lower energy consumption and better integrability in various platforms in nanoscale dimensions. Concerning the intrinsic transport properties of electrons in nanowires, relatively high mobility values that approach those in bulk crystals have been obtained only in core/shell heterostructures, where electrons are spatially confined inside the core. Here, it is demonstrated that the strain in lattice-mismatched core/shell nanowires can affect the effective mass of electrons in a way that boosts their mobility to distinct levels. Specifically, electrons inside the hydrostatically tensile-strained gallium arsenide core of nanowires with a thick indium aluminium arsenide shell exhibit mobility values 30–50 % higher than in equivalent unstrained nanowires or bulk crystals, as measured at room temperature. With such an enhancement of electron mobility, strained gallium arsenide nanowires emerge as a unique means...

Transport characterization in nanowires using an electrical nanoprobe

Semiconductor Science and Technology, 2010

Electrical transport in semiconductor nanowires is commonly measured in a field effect transistor configuration, with lithographically defined source, drain and in some cases, top gate electrodes. This approach is labor intensive, requires high-end fabrication equipment, exposes the nanowires to extensive processing chemistry and places practical limitations on minimum nanowire length. Here we describe an alternative, simple method for characterizing electrical transport in nanowires directly on the growth substrate, without any need for post growth processing. Our technique is based on contacting nanowires using a nano-manipulator probe retrofitted inside of a scanning electron microscope. Using this approach, we characterize electrical transport in GaN nanowires grown by catalyst-free selective epitaxy, as well as InAs and Ge nanowires grown by a Au-catalyzed vapor solid liquid technique. We find that in situations where contacts are not limiting carrier injection (GaN and InAs nanowires), electrical transport transitions from Ohmic conduction at low bias to space-charge-limited conduction at higher bias. Using this transition and a theory of space-charge-limited transport which accounts for the high aspect ratio nanowires, we extract the mobility and the free carrier concentration. For Ge nanowires, we find that the Au catalyst forms a Schottky contact resulting in rectifying current-voltage characteristics, which are strongly dependent on the nanowire diameter. This dependence arises due to an increase in depletion width at decreased nanowire diameter and carrier recombination at the nanowire surface.

The Native Material Limit of Electron and Hole Mobilities in Semiconductor Nanowires

ACS Nano, 2016

Piezoelectric surface acoustic waves are employed to induce radio frequency spatiotemporal dynamics of photogenerated electrons and holes in the GaAs core of individual GaAs/AlGaAs core/shell semiconductor nanowires. Comparison of the timedependent interband optical recombination to numerical simulations allow to determine the charge carrier transport mobilities of electrons, μ e = 500 −250 +500 cm 2 /(V s), holes, μ h = 50 −30 +50 cm 2 /(V s) and their ratio μ e :μ h = (20 ± 5):1. Our method probes carrier transport at low carrier density. Thus, the obtained values represent the native material limit of these nanowires, determined by their structural properties. We show that for near-pristine nanowires, individual twin defects do not significantly affect electrical transport, in strong contrast to polytypic nanowires. In the acoustoelectrically modulated emission, we observe unambiguous signatures of (i) hole localization within long wurtzite-rich segments and (ii) electrons in zinc blende regions being reflected at the interface to a wurtziterich region. The experimentally observed periodic emission bursts are faithfully reproduced by advanced numerical simulations which include static band edge discontinuities between a single wurtzite segment in an otherwise pure zinc blende nanowire. Otherwise using the same input parameters as for near-pristine zinc blende nanowires, we can deduce from our simulations a minimum conduction band offset of ΔE C ≈ 20 meV at the interface between the zinc blende part and the wurtzite-rich region. These results furthermore confirm that a single wurtzite segment with sufficiently large band offsets efficiently traps holes and blocks electron transport.