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Register a new userMagneto-photoluminescence in GaAs/AlAs core-multishell nanowires: a theoretical investigation
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The magneto-photoluminescence in modulation doped core-multishell nanowires is predicted as a function of photo-excitation intensity in non-perturbative transverse magnetic fields. We use a self-consistent field approach within the effective mass approximation to determine the photoexcited electron and hole populations, including the complex composition and anisotropic geometry of the nano-material. The evolution of the photoluminescence is analyzed as a function of i) photo-excitation power, ii) magnetic field intensity, iii) type of doping, and iv) anisotropy with respect to field orientation.
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We study the electronic states of core multi-shell semiconductor nanowires, including the effect of strong magnetic fields. We show that the multi-shell overgrowth of a free-standing nanowire, together with the prismatic symmetry of the substrate, may induce quantum confinement of carriers in a set of quasi-1D quantum channels corresponding to the nanowire edges. Localization and inter-channel tunnel coupling are controlled by the curvature at the edges and the diameter of the underlying nanowire. We also show that a magnetic field may induce either Aharonov-Bohm oscillations of the energy levels in the axial configuration, or a dimensional transition of the quantum states from quasi-1D to Landau levels for fields normal to the axis. Explicit predictions are given for nanostructures based on GaAs, InAs, and InGaN with different symmetries.
We predict inelastic light scattering spectra from electron collective excitations in a coaxial quantum well embedded in a core-multishell GaAs/AlGaAs nanowire. The complex composition, the hexagonal cross section and the remote doping of typical samples are explicitly included, and the free electron gas is obtained by a DFT approach. Inelastic light scattering cross sections due to charge and spin collective excitations belonging to quasi-1D and quasi-2D states, which coexist in such radial heterostructures, are predicted in the non-resonant approximation from a fully three-dimensional multi-subband TDDFT formalism. We show that collective excitations can be classified in azimuthal, radial and longitudinal excitations, according to the associated density fluctuations, and we suggest that their character can be exposed by specific spectral dispersion of inelastic light scattering along different planes of the heterostructure.
Strong increase in the intensity of the peaks of excited magneto-exciton (ME) states in the photoluminescence excitation (PLE) spectra recorded for the ground heavy-hole magneto-excitons (of the 1sHH type) has been found in a GaAs/AlGaAs superlattice in strong magnetic field B applied normal to the sample layers. While varying B the intensities of the PLE peaks have been measured as functions of energy separation $Delta E$ between excited ME peaks and the ground state of the system. The resonance profiles have been found to have maxima at $Delta E_{rm max}$ close to the energy of the GaAs LO-phonon. However, the value of $Delta E_{rm max}$ depends on quantum numbers of the excited ME state. The revealed very low quantum efficiency of the investigated sample allows us to ascribe the observed resonance to the enhancement of the non-radiative magneto-exciton relaxation rate arising due to LO-phonon emission. The presented theoretical model, being in a good agreement with experimental observations, provides a method to extract 1sHH magneto-exciton ``in-plane dispersion from the dependence of $Delta E_{rm max}$ on the excited ME state quantum numbers.
We study structural and chemical transformations induced by focused laser beam in GaAs nanowires with axial zinc-blende/wurtzite (ZB/WZ) heterostucture. The experiments are performed using a combination of transmission electron microscopy, energy-dispersive X-ray spectroscopy, Raman scattering, and photoluminescence spectroscopy. For the both components of heterostructure, laser irradiation under atmospheric air is found to produce a double surface layer which is composed of crystalline arsenic and of amorphous GaO$_{x}$. The latter compound is responsible for appearance of a peak at 1.76 eV in photoluminescence spectra of GaAs nanowires. Under increased laser power density, due to sample heating, evaporation of the surface crystalline arsenic and formation of $beta$-Ga$_{2}$O$_{3}$ nanocrystals proceed on surface of the zinc-blende part of nanowire. The formed nanocrystals reveal a photoluminescence band in visible range of 1.7-2.4 eV. At the same power density for wurtzite part of the nanowire, total amorphization with formation of $beta$-Ga$_{2}$O$_{3}$ nanocrystals occurs. Observed transformation of WZ-GaAs to $beta$-Ga$_{2}$O$_{3}$ nanocrystals presents an available way for creation of axial and radial heterostuctures ZB-GaAs/$beta$-Ga$_{2}$O$_{3}$ for optoelectronic and photonic applications.
The electronic structure of bulk fcc GaAs, fcc and tetragonal CrAs, and CrAs/GaAs supercells, computed within LMTO local spin-density functional theory, is used to extract the band alignment (band offset) for the [1,0,0] GaAs/CrAs interface in dependence of the spin orientation. With the lateral lattice constant fixed to the experimental bulk GaAs value, a local energy minimum is found for a tetragonal CrAs unit cell with a slightly ($approx$ 2%) reduced longitudinal ([1,0,0]) lattice constant. Due to the identified spin-dependent band alignment, half-metallicity of CrAs no longer is a key requirement for spin-filtering. Encouraged by these findings, we study the spin-dependent tunneling current in [1,0,0] GaAs/CrAs/GaAs heterostructures within the non-equilibrium Greens function approach for an effective tight-binding Hamiltonian derived from the LMTO electronic structure. Results indicate that these heterostructures are probable candidates for efficient room-temperature all-semiconductor spin-filtering devices.
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