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Space-charge-limited current is often observed in semiconductor nanowires due to carrier depletion and reduced electrostatic screening. We present a numerical study on geometric scaling of the space-charge-limited current in nanowires, in comparison with the thin film and bulk geometries, using an n+-n-n+-model. The model highlights the effects of the surroundings for thin films and nanowires and shows that the dielectric properties of the semiconductor have a negligible effect on the space-charge-limited transport for small dimensions. The distribution of equilibrium and injected charge concentration vary as the semiconductor dimensionality is reduced. For low doping, the ohmic current is controlled by charge diffusion from degenerate contacts rather than by the nanowire impurity concentration. The results of numerical calculations agree with a simple capacitance formalism which assumes a uniform charge distribution along the nanowire, and experimental measurements for InAs nanowires confirm these results. The numerical model also predicts that an asymmetric nanowire contact geometry can enhance or limit charge injection. [ABSTRACT FROM AUTHOR]

Minority carrier diffusion lengths in both p-type and n-type GaAs nanowires were studied using electron beam induced current by means of a nanoprobe technique without lithographic processing. The diffusion lengths were determined for Au/GaAs rectifying junctions as well as axial p-n junctions. By incorporating a thin lattice-matched InGaP passivating shell, a 2-fold enhancement in the minority carrier diffusion lengths and one order of magnitude reduction in the surface recombination velocity were achieved. [ABSTRACT FROM AUTHOR]

Several shallow donor bound exciton photoluminescence (PL) transitions are reported in ZnO nanowires doped with carbon. The emission energies are in the range of 3360.8-3361.9 meV, close to previously reported emission lines due to excitons bound to donor point defects, such as Ga, Al, In, and H. The addition of small amounts of hydrogen during growth results in a strong enhancement of the PL of these carbon related emission lines, yet PL and annealing measurements indicate no appreciable bulk hydrogen. The observation of two electron satellites for these emission lines enables the determination of the donor binding energies. The dependence of exciton localization energy on donor binding energy departs somewhat from the usual linear relationship observed for group III donors, indicating a qualitatively different central cell potential, as one would expect for a complex. Emission lines due to excitons bound to ionized donors associated with these defects are also observed. The dependence of the PL emission intensities on temperature and growth conditions demonstrates that the lines are due to distinct complexes and not merely excited states of each other. [ABSTRACT FROM AUTHOR]

We report on the surface passivation of Au-assisted Te-doped GaAs nanowires (NWs) grown by metalorganic vapor phase epitaxy. The electrical properties of individual free standing NWs were assessed using a tungsten nano-probe inside a scanning electron microscope. The diameter independent apparent resistivity of both strained and relaxed passivated NWs suggests the unpinning of the Fermi level and reduction of sidewalls surface states density. Similar currentvoltage properties were observed for partially axially relaxed GaAs/GaP NWs. This indicates a negligible contribution of misfit dislocations in the charge transport properties of the NWs. Low temperature micro-photoluminescence (μ-PL) measurements were also carried out for both uncapped and passivated GaAs NWs. The improvement of the integrated (μ-PL) intensity for GaAs/GaP NWs further confirms the effect of passivation. [ABSTRACT FROM AUTHOR]

We demonstrate the application of a simple equilibrium model based on elasticity theory to estimate the geometric limits of dislocation-free core/shell nanowires (NWs). According to these calculations, in a coherent core/shell structure, tangential strain is the dominant component in the shell region and it decreases quickly away from the heterointerface, while axial strain is the dominant component in the core and is independent of the radial position. These strain distributions energetically favour the initial relief of axial strain in agreement with the experimental appearance of only edge dislocations with line directions perpendicular to the NW growth axis at the core/shell interfaces. Such dislocations were observed for wurtzite InAs/InP and zincblende GaAs/GaP core/shell NWs with dimensions above the coherency limits predicted by the model. Good agreement of the model was also found for experimental results previously reported for GaAs/InAs and GaAs/GaSb core/shell NWs. [ABSTRACT FROM AUTHOR]

Tellurium (Te)-doping of Au-catalyzed GaAs nanowires (NWs) grown by metalorganic vapor phase epitaxy (MOVPE) via the vapor-liquid-solid (VLS) mechanism is presented. Electrical measurements were performed inside a scanning electron microscope by contacting a tungsten nanoprobe to the Au end of individual NWs grown on a heavily n-type GaAs substrate. Rectifying current-voltage (I-V) characteristics are observed due to the formation of a junction at the Au nanoparticle (NP)/NW interface. The electron concentration ne and contact barrier heights, φ0b, were determined from the analyses of these characteristics. As expected, φ0b increased (from 0.63 ± 0.03 eV to 0.71 ± 0.02 eV) with decreasing Te-precursor flow rate, corresponding to a decrease in ne from (9 ± 1) × 1017 cm-3 to (1.5 ± 0.5) × 1017 cm-3. Meanwhile, undoped NWs had space-charge-limited characteristics. There was a large influence of the residual gallium (Ga) in the NP, on barrier properties, controlled by the group V precursor flow (on or off) during the cooling of the NW sample at the end of the growth process. With the group V flow off during cooling, a decrease in φ0b from 0.79 ± 0.04 eV to 0.63 ± 0.03 eV is observed consistent with a higher Ga alloy concentration in the NP, confirmed by energy dispersive spectroscopy measurements. We also demonstrate the fabrication of core/shell, undoped/Te-doped, GaAs NWs with very high Te doping (∼1019 cm-3). [ABSTRACT FROM AUTHOR]

InAsSb/InAs type II strain balanced superlattices lattice matched to GaSb have recently been proposed as an alternative to InAs/(In)GaSb short period superlattices for mid- to long infrared photodetectors. Photoluminescence data at 4 K of OMVPE grown InAsSb (multi-) quantum wells in an InAs matrix on InAs and GaSb substrates is presented for Sb compositions between 4% and 27%. The measured transition energies are simulated with a self-consistent Poisson and Schroedinger equation solver that includes strain and band-offsets. The fitted parameters are then used to predict the type II transition energies of InAsSb/InAs strain balanced superlattice absorber stacks at 77 K for different compositions and periods. The optical matrix element was calculated and compared with InAs/(In)GaSb superlattices. The InAsSb/InAs structures can be designed with higher or equal matrix elements for longer periods. Finally, the initial optical response data of an unoptimized strain balanced InAs0.79Sb0.21/InAs detector with a 40 nm period are shown. Its cutoff wavelength is 0.15 eV (8.5 μm), in good agreement with the predicted type II transition energy of 0.17 eV. [ABSTRACT FROM AUTHOR]

We report the observation of photoluminescence (PL) transitions in ZnO epilayers grown by metalorganic vapor phase epitaxy (MOVPE) on C-sapphire substrates with linewidths as low as 0.2 meV at 4.2 K. A dominant donor bound exciton (D0X) peak at 3361.0 meV is observed in all undoped samples together with the corresponding ionized donor bound exciton (D+X) peak at 3372.9 meV. The addition of In dopant using trimethylindium results in the appearance of the I9 transition at 3357.8 meV, which has been previously attributed to In D0X transitions. By intentionally doping the epilayers with In we can calibrate the PL energy spectra, and thereby identify the dominant D0X transition in undoped material at 3361.0 meV as due to Ga donors. The In and Ga identifications are also confirmed by the observation of two electron satellites. High temperature annealing under O2 results in a strong reduction of the In and Ga transitions, and the appearance of a third line which we attribute to Al out-diffusing from the sapphire substrate. Temperature dependent PL measurements on In-doped samples above 4 K show additional lines due to well-resolved D0X (B) transitions separated by 4.6 meV for both Ga and In donors due to the crystal field splitting of the valence band. The line intensities are modeled by simple Boltzmann statistics. On the basis of comparison with accepted values of the I9 transition energy in homoepitaxial ZnO samples, we deduce a strain-induced blueshift of ∼ 1.2 meV which is consistent with residual compressive strain induced in the ZnO films due to the smaller in-plane effective lattice constant of sapphire. [ABSTRACT FROM AUTHOR]

We report the electrical properties of n-InAsSb/n-GaSb heterojunctions as a function of the GaSb doping concentration. Because of the staggered type II band alignment, strong electron accumulation occurs on the InAsSb side. For low GaSb doping, depletion occurs on the GaSb side resulting in a Schottky-like junction as previously reported. As the GaSb doping increases, the built-in voltage as well as depletion width decreases as shown using self-consistent simulations. For GaSb doping levels above 5×1017 cm-3, the junction loses its rectifying properties due to tunneling. Under zero and reverse bias voltage, the photoresponse of these diodes is solely due to the photovoltaic effect in the GaSb depletion region. For forward bias voltages >400 mV, we also observed a photoconductive response from the InAsSb layer. The proposed physical mechanism is quite different from the one suggested in a recent paper. [ABSTRACT FROM AUTHOR]

Annealing measurements performed on heavily carbon-doped InAs samples grown by organometallic vapor phase epitaxy confirm that the n-type behavior observed in this material is due to the formation of dicarbon donor defects. The structural, electrical, and optical properties of n-type carbon-doped InAs annealed at temperatures of 400 °C and higher were studied. Raman and infrared spectroscopy showed a reduction in the intensity of carbon acceptor and carbon-hydrogen lines along with an increase in the strength of the dicarbon local vibrational mode after annealing. X-ray diffraction revealed that the lattice constant of annealed samples increased toward that of the undoped samples. These changes were accompanied by increases in the electron concentration and mobility. Based on the expected energy level of dicarbon donors in GaAs, we predict that the dicarbon defects in InAs should introduce a resonant level close to or slightly above the conduction band minimum. [ABSTRACT FROM AUTHOR]

Deals with a study which analyzed gallium arsenide epilayers grown by low pressure metalorganic chemical vapor deposition using triethylgallium and tertiarybutylarsine or arsine. Experimental procedures; Growth conditions and electrical properties of gallium arsenide; Photoconductivity effect observed in gallium arsenide.

Investigates the effect of small changes in the substrate lattice constant on the photoluminescence (PL) properties of high-purity nominally undoped InP epilayers. Effect of high concentrations of substitutional dopants; Comparison of low-temperature exciton PL spectra for two high-purity epilayers during the same growth run but on different semi-insulating substrates; Assessment of substrate lattice parameter variation due to substrate dopants.

Examines the residual donor and acceptor species in a series of high purity n-type indium phosphide epilayers grown by metalorganic chemical vapor deposition using tertiarybutylphosphine and trimethylindium (TMIn). Experiment; Results.

Presents a study that investigated the source of donor impurities in high-purity gallium arsenide semiconductors using magnetophotoluminescence (MPL) spectroscopy. Analysis of the donor species; Correlation between MPL intensity and carrier concentration; Evaluation of the arsine and trimethlygallium donor impurities;

Examines magnetophotoluminescence characterization of residual donors in undoped gallium arsenide grown by metalorganic chemical vapor deposition. Details on the experiment; Results of the study; Discussion of findings.

Examines the low-temperature photoluminescence of epitaxial indium arsenide (InAs) grown by metal-organic chemical-vapor deposition (MOCVD). Description of the MOCVD growth of InAs on InAS substrates; Discussion on the InAs spectrum; Mechanisms of broadband luminescence.