THz spectroscopy has been applied to investigate the photo-induced and intrinsic conductivity in SnO2 nanowires using the Drude-Smith model. The refractive index of the nanowires was found to decrease from 2.4 to 2.1 with increasing THz frequency and the dc mobility of the non-excited nanowires was determined to be 72 ± 10 cm2/Vs. Measurements reveal that scattering times are carrier density dependent, while a strong suppression of long transport is evident. Intensity-dependent measurements provided an estimate of the Auger coefficient found to be γ = (7.2 ± 2.0) × 10−31 cm6/s.

We present a theoretical study of an n-type InAs nanowire with built-in InAs/InP heterojunctions in the effective-mass approximation via self-consistent Poisson–Schrödinger calculations in cylindrical coordinates. Rapid convergence and efficiency are achieved by (i) a suitable transformation of the radial part of the Hamiltonian matrix thereby maintaining symmetry (ii) using quantum mechanical perturbation theory to derive an expression for the change in electron density with electrostatic potential. We calculate the energy levels in a 150 Å long InAs quantum dot surrounded by 50 Å long InP barriers within an InAs quantum wire of radius 200 Å, having a doping level of 3×1016 cm−3 and conduction-band discontinuities of ΔECB=0.6 eV. In equilibrium, the lowest quantum dot state is at 15 meV above the Fermi level and we find that upon variation of the applied collector–emitter voltage VCE, resonance occurs at VCE=88 mV. This is in good agreement with an experimental study of resonant tunneling in a nominally undoped InAs/InP nanowire of similar dimensions grown in the [111] direction, where resonance was detected at VCE=80 mV, and a small shift (<5 mV) in its position occurred upon inverting the voltage polarity. We rule out barrier asymmetry, bandbending due to impurities or defects, and contact effects as being the origin of the resonant-voltage shift, and attribute it to the strain-induced charges at the InP/InAs interfaces. Both InAs and InP segments are shown to be under in-plane compression giving a piezoelectric field of 0.155 meV/Å in the InAs quantum dot while resonant tunneling, as calculated, occurs at 84 mV for VCE<0 and at 87 mV for VCE>0. This is in contrast to two-dimensional pseudomorphic heteroepitaxy, where the InP is under in-plane tensile strain yielding a very strong resonance-voltage shift (≫5 mV). The small magnitude of the measured shift indicates that in nanowires any strain at the heterointerfaces relaxes within a few atomic layers.

Indium tin oxide nanowires were grown by the reaction of In and Sn with O2 at 800 °C via the vapor-liquid-solid mechanism on 1 nm Au/Si(001). We obtain Sn doped In2O3 nanowires having a cubic bixbyite crystal structure by using In:Sn source weight ratios > 1:9 while below this we observe the emergence of tetragonal rutile SnO2 and suppression of In2O3 permitting compositional and structural tuning from SnO2 to In2O3 which is accompanied by a blue shift of the photoluminescence spectrum and increase in carrier lifetime attributed to a higher crystal quality and Fermi level position.

Ultrafast hole carrier relaxation dynamics in CuO nanowires have been investigated using transient absorption spectroscopy. Following femtosecond pulse excitation in a non-collinear pump-probe configuration, a combination of non-degenerate transmission and reflection measurements reveal initial ultrafast state filling dynamics independent of the probing photon energy. This behavior is attributed to the occupation of states by photo-generated carriers in the intrinsic hole region of the p-type CuO nanowires located near the top of the valence band. Intensity measurements indicate an upper fluence threshold of 40 μJ/cm2 where carrier relaxation is mainly governed by the hole dynamics. The fast relaxation of the photo-generated carriers was determined to follow a double exponential decay with time constants of 0.4 ps and 2.1 ps. Furthermore, time-correlated single photon counting measurements provide evidence of three exponential relaxation channels on the nanosecond timescale.