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We use polarized photocurrent spectroscopy in a nanowire device to investigate the band structure of hexagonal Wurtzite InAs. Signatures of optical transitions between four valence bands and two conduction bands are observed which are consistent with the symmetries expected from group theory. The ground state transition energy identified from photocurrent spectra is seen to be consistent with photoluminescence emitted from a cluster of nanowires from the same growth substrate. From the energies of the observed bands we determine the spin orbit and crystal field energies in Wurtzite InAs. This information is essential to the development of crystal phase engineering of this important III-V semiconductor., Comment: 25 pages, 5 figures

There is tremendous interest in measuring the strong electron–phonon interactions seen in topological Weyl semimetals. The semimetal NbIrTe4 has been proposed to be a Type-II Weyl semimetal with 8 pairs of opposite Chirality Weyl nodes which are very close to the Fermi energy. We show using polarized angular-resolved micro-Raman scattering at two excitation energies that we can extract the phonon mode dependence of the Raman tensor elements from the shape of the scattering efficiency versus angle. This van der Waals semimetal with broken inversion symmetry and 24 atoms per unit cell has 69 possible phonon modes of which we measure 19 modes with frequencies and symmetries consistent with Density Functional Theory calculations. We show that these tensor elements vary substantially in a small energy range which reflects a strong variation of the electron–phonon coupling for these modes.

Recently, Fickenscher et al. [1] have shown that, in a core-multi-shell structure where a GaAs quantum well is embedded into an AlGaAs shell wrapped around a [111] oriented GaAs nanowire, the electron and hole ground states are strongly confined to the corners of the hexagonally symmetric quantum well. Thus this confinement defines quantum wires which run along the length of the nanowires along its corners. Here we review single nanowire photoluminescence measurements which show the significant confinement energy of the excitons. For well widths larger than 5 nm, optical transitions between electron and hole excited states can be seen in excitation spectra, while for widths less than 5 nm only the ground state optical transitions are observed. For well widths smaller than 5 nm, high resolution spatially resolved photoluminescence measurements show directly the appearance of localized states. Single nanowire spectra from the 4 nm QWT sample display ultranarrow emission lines on the high energy side of the luminescence band. Spatially-resolved PL images show that these quantum dots are localized randomly along the length of the wire.

We use Raman scattering to study the spatially-resolved strain and stress in a complex zinc blende GaAs/GaP heterostructured nanowire which contains both axial and radial interfaces. The nanowires are grown by metal-organic chemical vapor deposition in the [111] direction with Au nano particles as catalysts, High spatial resolution Raman scans along the nanowires show the GaAs/GaP interface is clearly identifiable. We interpret the phonon energy shifts in each material as one approaches the interface.

Nanolasers hold promise for applications including integrated photonics, on-chip optical interconnects and optical sensing. Key to the realization of current cavity designs is the use of nanomaterials combining high gain with high radiative efficiency. Until now, efforts to enhance the performance of semiconductor nanomaterials have focused on reducing the rate of non-radiative recombination through improvements to material quality and complex passivation schemes. Here we employ controlled impurity doping to increase the rate of radiative recombination. This unique approach enables us to improve the radiative efficiency of unpassivated GaAs nanowires by a factor of several hundred times while also increasing differential gain and reducing the transparency carrier density. In this way, we demonstrate lasing from a nanomaterial that combines high radiative efficiency with a picosecond carrier lifetime ready for high speed applications., Until now, efforts to enhance the performance of nanolasers have focused on reducing the rate of non-radiative recombination. Here, Burgess et al. employ controlled impurity doping to increase the rate of radiative recombination.

We study the photocurrent from photoexcited charged carriers excited with lasers of energy both above and below the energy gap in CdS nanostructures. We observe non-linear photocurrents in CdS nanosheet devices in the metal-semiconductor-metal configuration with Schottky contacts for sub-band gap excitations. Analysis of two-photon absorption dominated photocurrents reveals a nonlinear coefficient of β = 2 cm/GW for these nanosheet devices, which is comparable to those of bulk CdS. We demonstrate the use of the photocurrent polarization measurements to determine the orientation of atoms in the nanosheet.

We demonstrate the newly developed technique Photomodulated Rayleigh Scattering spectroscopy in order to probe the electronic band structure of single semiconductor nanowires. We show that both the electronic transition energies and nanowire diameter can be measured simultaneously and with high accuracy in a single non-destructive measurement. We demonstrate our results for zincblende GaAs as well as wurtzite InP nanowires where we probed the band gaps and transition energies at both room and low temperatures. This technique should advance the study of optical properties of single nanowires as well as other types of nanostructures.

Temporally and spatially resolved photoluminescence has been used to study patterned structures prepared by focused ion beam (FIB) implantation of multiple quantum wells (MQWs) followed by rapid thermal annealing (RTA). Exciton lifetimes at different positions across the interface between implanted and unimplanted regions suggest that the interface between these two regions is of good quality. Anisotropic exciton diffusion is also observed, suggesting that these structures provide lateral confinement for excitons.