205 research outputs found
Electrical isolation of n-type and p-type InP layers by proton bombardment
The evolution of the sheet resistance(Rs) of n-type and p-type conductive InP layers during proton irradiation and the stability of the formed isolation during postirradiation annealing were investigated. It was found that the threshold dose (Dth) to convert the conductive layer to a highly resistive one is different for n- and p-type samples with similar initial free carrier concentrations. From our results, one infers that the antisite defects and/or related defect complexes formed by the replacement collisions are the carrier trapping centers, where InP is responsible for electron trapping and PIn for the hole trapping. A time dependence of the Rs was observed after each irradiation step to doses of ≅Dth and higher. This time variation is related to metastable processes involving free carriers. The thermal stability of the isolation of n-type samples is limited to temperatures lower than 200 °C, irrespectively of the irradiated dose. For p-type samples the thermal stability of electrical isolation is extended to 450–500 °C.This work was partly supported by Conselho Nacional
de Pesquisas (CNPq, Brazil) under Contract No. 200541/
99-4
Engineering the side facets of vertical [100] oriented InP nanowires for novel radial heterostructures
In addition to being grown on industry-standard orientation, vertical [100] oriented nanowires present novel families of facets and related cross-sectional shapes. These nanowires are engineered to achieve a number of facet combinations and cross-sectional shapes, by varying their growth parameters within ranges that facilitate vertical growth. In situ post-growth annealing technique is used to realise other combinations that are unattainable solely using growth parameters. Two examples of possible novel radial heterostructures grown on these vertical [100] oriented nanowire facets are presented, demonstrating their potential in future applications
Dynamics and control of gold-encapped gallium arsenide nanowires imaged by 4D electron microscopy
Eutectic related reaction is a special chemical/physical reaction involving
multiple phases, solid and liquid. Visualization of phase reaction of composite
nanomaterials with high spatial and temporal resolution provides a key
understanding of alloy growth with important industrial applications. However,
it has been a rather challenging task. Here we report the direct imaging and
control of the phase reaction dynamics of a single, as-grown free-standing
gallium arsenide nanowire encapped with a gold nanoparticle, free from
environmental confinement or disturbance, using four-dimensional electron
microscopy. The non-destructive preparation of as-grown free-standing nanowires
without supporting films allows us to study their anisotropic properties in
their native environment with better statistical character. A laser heating
pulse initiates the eutectic related reaction at a temperature much lower than
the melting points of the composite materials, followed by a precisely
time-delayed electron pulse to visualize the irreversible transient states of
nucleation, growth and solidification of the complex. Combined with theoretical
modeling, useful thermodynamic parameters of the newly formed alloy phases and
their crystal structures could be determined. This technique of dynamical
control and 4D imaging of phase reaction processes on the nanometer-ultrafast
time scale open new venues for engineering various reactions in a wide variety
of other systems
An efficient modeling workflow for high-performance nanowire single-photon avalanche detector
Single-photon detector (SPD), an essential building block of the quantum
communication system, plays a fundamental role in developing next-generation
quantum technologies. In this work, we propose an efficient modeling workflow
of nanowire SPDs utilizing avalanche breakdown at reverse-biased conditions.
The proposed workflow is explored to maximize computational efficiency and
balance time-consuming drift-diffusion simulation with fast script-based
post-processing. Without excessive computational effort, we could predict a
suite of key device performance metrics, including breakdown voltage,
dark/light avalanche built-up time, photon detection efficiency, dark count
rate, and the deterministic part of timing jitter due to device structures.
Implementing the proposed workflow onto a single InP nanowire and comparing it
to the extensively studied planar devices and superconducting nanowire SPDs, we
showed the great potential of nanowire avalanche SPD to outperform their planar
counterparts and obtain as superior performance as superconducting nanowires,
i.e., achieve a high photon detection efficiency of 70% with a dark count rate
less than 20 Hz at non-cryogenic temperature. The proposed workflow is not
limited to single-nanowire or nanowire-based device modeling and can be readily
extended to more complicated two-/three dimensional structures
Characterization of deep level traps responsible for isolation of proton implanted GaAs
Deep level transient spectroscopy was employed to determine the electrical properties of defects induced in metalorganic chemical-vapor deposition grown n-type and p-type GaAs during proton bombardment. Thermal stability of these defects was investigated and correlation with defects responsible for isolation of GaAs by ion bombardment was discussed. The annealing temperature region (220–250 °C) is similar to proton isolated GaAs below the threshold dose for complete isolation. At least four of the five traps observed in n-type GaAs are not simple interstitial-vacancy pairs. For p-type GaAs we have observed an unknown level with apparent energy of ~0.64 eV
Evolution of InAs branches in InAs/GaAs nanowire heterostructures
Branched nanowireheterostructures of InAs∕GaAs were observed during Au-assisted growth of InAs on GaAsnanowires. The evolution of these branches has been determined through detailed electron microscopy characterization with the following sequence: (1) in the initial stage of InAsgrowth, the Au droplet is observed to slide down the side of the GaAsnanowire, (2) the downward movement of Aunanoparticle later terminates when the nanoparticle encounters InAsgrowing radially on the GaAsnanowire sidewalls, and (3) with further supply of In and As vapor reactants, the Aunanoparticles assist the formation of InAs branches with a well-defined orientation relationship with GaAs∕InAs core/shell stems. We anticipate that these observations advance the understanding of the kink formation in axial nanowireheterostructures.The Australian Research Council is acknowledged for
the financial support of this project. One of the authors
M.P. acknowledges the support of an International Postgraduate
Research Scholarship
Ultrafast trapping times in ion implanted InP
As⁺ and P⁺implantation was performed on semi-insulating (SI) and p-type InP samples for the purpose of creating a material suitable for ultrafast optoelectronic applications. SI InP samples were implanted with a dose of 1×10¹⁶ cm⁻² and p-type InP was implanted with doses between 1×10¹² and 1×10¹⁶ cm⁻². Subsequently, rapid thermal annealing at temperatures between 400 and 700 °C was performed for 30 sec. Hall-effect measurements, double-crystal x-ray diffraction, and time-resolved femtosecond differential reflectivity showed that, for the highest-annealing temperatures, the implanted SI InP samples exhibited high mobility, low resistivity, short response times, and minimal structural damage. Similar measurements on implantedp-type InP showed that the fast response time, high mobility, and good structural recovery could be retained while increasing the resistivity
A study of quantum well solar cell structures with bound-to-continuum transitions for reduced carrier recombination
A bound-to-continuum quantum well solar cell structure is proposed, and the band structure and absorption spectra are analyzed by the use of an eight band k⋅p model. The structure is based on quantum wells that only support bound states for the valence band. The absence of bound conduction band states has a number of potential advantages, including a reduction of electron trapping and, therefore, a reduction of quantum well induced photocarrier recombination due to reduced spatial overlap of the electron and hole wavefunctions.Thanks are due to the Australian Research Council for
the financial support of this research
Strain relaxation and phonon confinement in self-assembled InAsSb/InP (001) quantum dashes: Effect of deposition thickness and composition
This paper presents a study on the strain relaxation and phonon confinement effect in InAsSb/InP
quantum dashes QDashes. The phonon mode with a frequency between that of InAs-like
longitudinal optical mode and that of InP transverse optical mode is determined to be originated
from InAsSb QDashes. Despite the small height of the QDashes, their phonon frequency is found
to be mainly determined by the strain relaxation in the dashes. With increasing InAsSb deposition
thickness and Sb composition in InAsSb dashes, the phonon mode shows an upward shift of its
frequency due to the increased compressive strain.Financial support from Australian Research Council
DP0774366 is gratefully acknowledged
- …