Photoconductors using vertical arrays of InAs/InAs1-xSbx nanowires with varying Sb composition x have been fabricated and characterized. The spectrally resolved photocurrents are strongly diameter dependent with peaks, which are red-shifted with diameter, appearing for thicker wires. Results from numerical simulations are in good agreement with the experimental data and reveal that the peaks are due resonant modes that enhance the coupling of light into the wires. Through proper selection of wire diameter, the absorptance can be increased by more than one order of magnitude at a specific wavelength compared to a thin planar film with the same amount of material. A maximum 20% cut-off wavelength of 5.7 µm is obtained at 5K for a wire diameter of 717 nm at a Sb content of x = 0.62, but simulations predict that detection at longer wavelengths can be

Polytype nanodots are arguably the simplest nanodots than can be made, but their technological control was, up to now, challenging. We have developed a technique to produce nanowires containing exactly one polytype nanodot in GaAs with thickness control. These nanodots have been investigated by photoluminescence, which has been cross-correlated with transmission electron microscopy. We find that short (4-20 nm) zincblende GaAs segments/dots in wurtzite GaAs confine electrons and that the inverse system confines holes. By varying the thickness of the nanodots we find strong quantum confinement effects which allows us to extract the effective mass of the carriers. The holes at the top of the valence band have an effective mass of approximately 0.45 m0 in wurtzite GaAs. The thinnest wurtzite nanodot corresponds to a twin plane in zincblende GaAs and gives efficient photoluminescence. It binds an exciton with a binding energy of roughly 50 meV, including central cell corrections.

We have investigated a large set of individual wurtzite/zinc-blende GaAs heterojunction nanowires using transmission electron microscopy (TEM), photoluminescence (PL), and cathodoluminescence (CL). In several cases we have combined PL and TEM on the same wire. We find a fairly deep emission that shows a strong blueshift with increasing excitation power density. By using a variety of experiments we show that this emission is due to recombination across a heterojunction with a type II band alignment. The data give a valence band offset of about 100 meV, in excellent agreement with theoretical predictions. Spatially resolved CL data on heterojunction nanowires and PL data on pure wurtzite nanowires show that the band gap of wurtzite GaAs is very close to the band gap of zinc-blende GaAs.

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Vainorius, N. (2016). Radial nanowire lightemitting diodes in the (AlxGa1-x)yIn1-yP material system. Abstract from 18th International Conference on Crystal Growth and Epitaxy, Nagoya, Japan.

Ternary nanowires (NWs) often exhibit varying material composition along the NW growth axis because of different diffusion properties of the precursor molecules. This constitutes a problem for optoelectronic devices for which a homogeneous material composition is most often of importance. Especially, ternary GaInP NWs grown under a constant Ga-In precursor ratio typically show inhomogeneous material composition along the length of the NW due to the complexity of low temperature precursor pyrolysis and relative rates of growth species from gas phase diffusion and surface diffusion that contribute to synthesis of particle-assisted growth. Here, we present the results of a method to overcome this challenge by in situ tuning of the trimethylindium molar fraction during growth of ternary Zn-doped GaInP NWs. The NW material compositions were determined by use of x-ray diffraction, scanning transmission electron microscopy and energy dispersive x-ray spectroscopy and the optical properties by photoluminescence spectroscopy.

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It is of contemporary interest to fabricate nanowires having quantum confinement and one-dimensional subband formation. This is due to a host of applications, for example, in optical devices, and in quantum optics. We have here fabricated and optically investigated narrow, down to 10 nm diameter, wurtzite GaAs nanowires which show strong quantum confinement and the formation of one-dimensional subbands. The fabrication was bottom up and in one step using the vapor-liquid-solid growth mechanism. Combining photoluminescence excitation spectroscopy with transmission electron microscopy on the same individual nanowires, we were able to extract the effective masses of the electrons in the two lowest conduction bands as well as the effective masses of the holes in the two highest valence bands. Our results, combined with earlier demonstrations of thin crystal phase nanodots in GaAs, set the stage for the fabrication of crystal phase quantum dots having full three-dimensional confinement.