ORCID Profile
0000-0002-4773-8147
Current Organisation
Ecole Polytechnique
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: AIP Publishing
Date: 21-05-2014
DOI: 10.1063/1.4874875
Abstract: High aspect ratio, rod-like and single crystal phase GaAs nanowires (NWs) were grown by gold catalyst-assisted hydride vapor phase epitaxy (HVPE). High resolution transmission electron microscopy and micro-Raman spectroscopy revealed polytypism-free zinc blende (ZB) NWs over lengths of several tens of micrometers for a mean diameter of 50 nm. Micro-photoluminescence studies of in idual NWs showed linewidths smaller than those reported elsewhere which is consistent with the crystalline quality of the NWs. HVPE makes use of chloride growth precursors GaCl of which high decomposition frequency after adsorption onto the liquid droplet catalysts, favors a direct and rapid introduction of the Ga atoms from the vapor phase into the droplets. High influxes of Ga and As species then yield high axial growth rate of more than 100 μm/h. The diffusion of the Ga atoms in the liquid droplet towards the interface between the liquid and the solid nanowire was investigated by using density functional theory calculations. The diffusion coefficient of Ga atoms was estimated to be 3 × 10−9 m2/s. The fast diffusion of Ga in the droplet favors nucleation at the liquid-solid line interface at the center of the NW. This is further evidence, provided by an alternative epitaxial method with respect to metal-organic vapor phase epitaxy and molecular beam epitaxy, of the current assumption which states that this type of nucleation should always lead to the formation of the ZB cubic phase.
Publisher: AIP Publishing
Date: 20-02-2017
DOI: 10.1063/1.4977003
Abstract: Carrier and spin recombination are investigated in p-type GaAs of acceptor concentration NA = 1.5 × 1017 cm−3 using time-resolved photoluminescence spectroscopy at 15 K. At low photocarrier concentration, acceptors are mostly neutral and photoelectrons can either recombine with holes bound to acceptors (e-A0 line) or form excitons which are mostly trapped on neutral acceptors forming the (A0X) complex. It is found that the spin relaxation is faster for free electrons that recombine through the e-A0 transition due to exchange scattering with either trapped or free holes, whereas spin flip processes are less likely to occur once the electron forms with a free hole an exciton bound to a neutral acceptor. An increase in the photocarrier concentration induces a cross-over to a regime where the bimolecular band-to-band (b-b) emission becomes more favorable due to screening of the electron-hole Coulomb interaction and ionization of excitonic complexes and free excitons. Then, the formation of excitons is no longer possible, the carrier recombination lifetime increases and the spin lifetime is found to decrease dramatically with a concentration due to fast spin relaxation with free photoholes. In this high density regime, both the electrons that recombine through the e-A0 transition and through the b-b transition have the same spin relaxation time.
Publisher: AIP Publishing
Date: 15-06-2012
DOI: 10.1063/1.4730396
Abstract: Images of the steady-state luminescence of passivated GaAs self-standing films under excitation by a tightly focussed laser are analyzed as a function of light excitation power. While unipolar diffusion of photoelectrons is dominant at very low light excitation power, an increased power results in a decrease of the diffusion constant near the center of the image due to the onset of ambipolar diffusion. The results are in agreement with a numerical solution of the diffusion equations and with a physical analysis of the luminescence intensity at the centre of the image, which permits the determination of the ambipolar diffusion constant as a function of electron concentration.
Publisher: AIP Publishing
Date: 28-03-2017
DOI: 10.1063/1.4979097
Abstract: Using a microfabricated p-type GaAs Hall bar, it is shown that the combined application of co-planar electric and magnetic fields enables the observation of spatial oscillations of the photoluminescence circular polarization due to the precession of drifting spin-polarized photoelectrons. Observation of these oscillations as a function of electric field gives a direct measurement of the minority carrier drift mobility and reveals that the spin coherence length can be tuned up to more than 10μm with electric fields below 1 kV/cm.
Publisher: AIP Publishing
Date: 05-09-2017
DOI: 10.1063/1.4985831
Abstract: We investigate the diffusion of charge and spin at 15 K in p-type GaAs, combining transient-grating and energy-resolved microluminescence measurements to cover a broad range of photoelectron density. At very low optical power, in a unipolar nondegenerate regime, charge and spin diffuse at the same rate, implying that the spin-drag effects are negligible. Upon increasing the photoelectron concentration up to about 1016 cm–3, the charge diffusion constant decreases because of ambipolar electrostatic interactions with the slower-diffusing holes while the spin diffusion constant is reduced only weakly by the ambipolar interaction. A further increase in the excitation power causes increases in both the charge and spin diffusion constants as a consequence of the Pauli principle since the photoelectron gas becomes degenerate.
Publisher: American Physical Society (APS)
Date: 16-05-2022
Publisher: American Physical Society (APS)
Date: 09-12-2013
Publisher: AIP Publishing
Date: 14-07-2014
DOI: 10.1063/1.4889799
Abstract: A new approach is demonstrated for investigating charge and spin diffusion as well as surface and bulk recombination in unpassivated doped semiconductors. This approach consists in using two complementary, conceptually related, techniques, which are time-resolved photoluminescence (TRPL) and spatially resolved microluminescence (μPL) and is applied here to p+ GaAs. Analysis of the sole TRPL signal is limited by the finite risetime. On the other hand, it is shown that joint TRPL and μPL can be used to determine the diffusion constant, the bulk recombination time, and the spin relaxation time. As an illustration, the temperature variation of these quantities is investigated for p+ GaAs.
Publisher: American Physical Society (APS)
Date: 30-09-2015
Publisher: SPIE-Intl Soc Optical Eng
Date: 29-01-2016
Publisher: SPIE
Date: 28-08-2014
DOI: 10.1117/12.2060198
Publisher: AIP Publishing
Date: 02-03-2015
DOI: 10.1063/1.4914357
Abstract: The charge and spin mobilities of minority photoelectrons in p+-GaAs are determined by monitoring the effect of an electric field on the spatial profiles of the luminescence and of its polarization. By using electric fields to increase the photoelectron temperature Te without significantly changing the hole or lattice temperatures, the charge and spin mobilities are shown to be principally dependent on Te. For Te & 70 K, both the charge and spin mobilities vary as Te−1.3, while at lower temperatures this changes to an even more rapid Te−4.3 law. This finding suggests that current theoretical models based on degeneracy of majority carriers cannot fully explain the observed temperature dependence of minority carrier mobility.
Publisher: AIP Publishing
Date: 09-04-2018
DOI: 10.1063/1.5026478
Abstract: We have combined spatially resolved steady-state micro-photoluminescence with time-resolved photoluminescence to investigate the exciton diffusion in a WSe2 monolayer encapsulated with hexagonal boron nitride. At 300 K, we extract an exciton diffusion length of LX = 0.36 ± 0.02 μm and an exciton diffusion coefficient of DX = 14.5 ± 2 cm2/s. This represents a nearly 10-fold increase in the effective mobility of excitons with respect to several previously reported values on nonencapsulated s les. At cryogenic temperatures, the high optical quality of these s les has allowed us to discriminate the diffusion of the different exciton species: bright and dark neutral excitons, as well as charged excitons. The longer lifetime of dark neutral excitons yields a larger diffusion length of LXD=1.5±0.02 μm.
Publisher: AIP Publishing
Date: 19-10-2015
DOI: 10.1063/1.4933189
Abstract: The electric field-induced modifications of the spatial distribution of photoelectrons, photoholes, and electronic spins in optically pumped p+ GaAs are investigated using a polarized luminescence imaging microscopy. At low pump intensity, application of an electric field reveals the tail of charge and spin density of drifting electrons. These tails disappear when the pump intensity is increased since a slight differential drift of photoelectrons and photoholes causes the buildup of a strong internal electric field. Spatial separation of photoholes and photoelectrons is very weak so that photoholes drift in the same direction as photoelectrons, thus exhibiting a negative effective mobility. In contrast, for a zero electric field, no significant ambipolar diffusive effects are found in the same s le.
Publisher: American Physical Society (APS)
Date: 17-04-2015
Publisher: AIP Publishing
Date: 13-09-2013
DOI: 10.1063/1.4821139
Abstract: For n- and p-type semiconductors doped above the 1016 cm−3 range, simple analytical expressions for the surface recombination velocity S have been obtained as a function of excitation power P and surface state density NT. These predictions are in excellent agreement with measurements on p-type GaAs films, using a novel polarized microluminescence technique. The effect on S of surface passivation is a combination of the changes of three factors, each of which depends on NT: (i) a power-independent factor which is inversely proportional to NT and (ii) two factors which reveal the effect of photovoltage and the shift of the electron surface quasi Fermi level, respectively. In the whole range of accessible excitation powers, these two factors play a significant role so that S always depends on power. Three physical regimes are outlined. In the first regime, illustrated experimentally by the oxidized GaAs surface, S depends on P as a power law of exponent determined by NT. A decrease of S such as the one induced by sulfide passivation is caused by a marginal decrease of NT. In a second regime, as illustrated by GaInP-encapsulated GaAs, because of the reduced value of S, the photoelectron concentration in the subsurface depletion layer can no longer be neglected. Thus, S−1 depends logarithmically on P and very weakly on surface state density. In a third regime, expected at extremely small values of P, the photovoltage is comparable to the thermal energy, and S increases with P and decreases with increasing NT.
Location: Chile
No related grants have been discovered for Fabian Cadiz.