Subsurface Imaging of Coupled Carrier Transport in GaAs/AlGaAs Core–Shell Nanowires (original) (raw)

Quasi one-dimensional transport in single GaAs/AlGaAs core-shell nanowires

Applied Physics Letters, 2011

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.

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.

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.

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...

Fabrication of Semiconductor Nanowires for Electronic Transport Measurements

Chimia, 2006

Wereportonepitaxialgrowthofinasnanowiresandthestepsnecessarytocreatedevicesforelectronic transportexperiments.Growthconditionswerefoundbytheuseofmetalorganicvaporphaseepitaxy(MoVPE)resultinginnanowireswithdesignablelengthanddiameter.Electricalpropertiesindicatediffusiveelectrontransport withanelasticmeanfreepathofaroundhundrednanometers.Coherentquantummechanicaleffectsandsingle electrontunnelingcanbeobservedatlowtemperaturesinquantumdotscreatedalongthenanowire.Wedemonstratetherealizationofhighlytunablequantumdotswithmetallictop-gates.Beyondthat,alternativetechniques tointroducepotentialbarriersbasedonlocalconstrictionsareinvestigated.

Angle-dependent magnetotransport in GaAs/InAs core/shell nanowires

Scientific Reports, 2016

We study the impact of the direction of magnetic flux on the electron motion in GaAs/InAs core/shell nanowires. At small tilt angles, when the magnetic field is aligned nearly parallel to the nanowire axis, we observe Aharonov–Bohm type h/e flux periodic magnetoconductance oscillations. These are attributed to transport via angular momentum states, formed by electron waves within the InAs shell. With increasing tilt of the nanowire in the magnetic field, the flux periodic magnetoconductance oscillations disappear. Universal conductance fluctuations are observed for all tilt angles, however with increasing amplitudes for large tilt angles. We record this evolution of the electron propagation from a circling motion around the core to a diffusive transport through scattering loops and give explanations for the observed different transport regimes separated by the magnetic field orientation.

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.

Dynamics of Optically-Generated Carriers in Si (100) and Si (111) Substrate-Grown GaAs/AlGaAs Core-Shell Nanowires

Nanoscale research letters, 2015

GaAs/Al0.1Ga0.9As core-shell nanowires (CSNWs), with average lateral size of 125 nm, were grown on gold nanoparticle-activated Si (100) and Si (111) substrates via molecular beam epitaxy. Room temperature-photoluminescence (RT-PL) from the samples showed bulk-like GaAs and Al0.1Ga0.9As bandgap emission peaks at 1.43 and 1.56 eV, respectively. Higher PL emission intensity of the sample on Si (111) compared to that on Si (100) is attributed to uniform Al0.1Ga0.9As shell passivation of surface states on Si (111)-grown CSNWs. Carrier dynamics in two different temporal regimes were studied. In the sub-nanosecond time scale (300-500 ps), time-resolved radiative recombination efficiency of carriers was examined. In the 0-4 ps range, surface field-driven ballistic transport of carriers was probed in terms of the radiated terahertz (THz) waves. Time-resolved PL measurements at 300 K revealed that the carrier recombination lifetime of the GaAs core on Si (100)-grown CSNWs is 333 ps while that...