Showing papers by "Eric Tournié published in 2002"

Mechanisms affecting the photoluminescence spectra of GaInNAs after post-growth annealing

Abstract: We have investigated by photoluminescence spectroscopy and x-ray diffraction the influence of ex situ postgrowth annealing on the properties of a series of dedicated Ga(In)(N)As ternary and quaternary quantum wells (QWs) confined by various barrier layers. We show that the low growth temperature and not N per se, is largely responsible for the low radiative efficiency of Ga(In)NAs QWs. Furthermore, postgrowth annealing induces a blueshift of the photoluminescence line in the case of quaternary GaInNAs QWs only, while x-ray diffraction reveals the absence of compositional change. We conclude with the occurrence of a local reorganization of the N-bonding configuration within the GaInNAs quaternary material during annealing.

Nanoindentation study of Zn1−xBexSe heteroepitaxial layers

Abstract: We present a study of the nanoindentation behaviour of Zn1−xBexSe heteroepitaxial layers grown onto (001)-oriented GaP and GaAs substrates in the whole composition range 0≤x≤1. The alloy composition, applied peak load and orientation of the Berkovich indenter have been found to significantly affect the nanoindentation response of these films. In particular, the Young's modulus increases relatively steadily with beryllium composition (though discontinuities are observed at x0.2 and 0.7–0.9), whilst hardness reaches a maximum at x0.7–0.9. Hardness is anisotropic, as it depends upon the orientation of the side of the Berkovich pyramid relative to the [100] direction. The variation of hardness and Young's modulus are related to the percolative behaviour of Zn1−xBexSe. Our results show that the mechanical properties of ZnSe (in which the type of bonding is essentially ionic) are greatly improved by alloying with BeSe (in which the bonding is essentially covalent), though they remain well below those of usual III–V compounds such as GaAs or GaP.

Raman study of Zn1−xBexSe/GaAs systems with low Be content (x⩽0.20)

Abstract: We present an experimental and theoretical investigation of the Raman line shape of long-wavelength phonons with longitudinal optical (LO) symmetry from both sides of Zn1−xBexSe/GaAs (001) heterojunctions with special emphasis on samples with low Be content (x⩽020) First the built-in p-type LO phonon–plasmon (LO–P) coupled mode at the near-interfacial substrate is used as a sensitive probe to investigate the interfacial quality The corresponding hole gas is reinforced when the ZnBeSe layers are nominally p doped by nitrogen This provides clear evidence for effective hole transfer across the junction, and thereby indicates a minimized density of interfacial defects In the nitrogen-doped layers hole densities as high as 1017 cm−3, in accordance with capacitance–voltage measurements, are directly inferred from clear weakening of the ZnSe-like LO mode due to LO–P coupling Concerning the intrinsic properties of the alloys, we demonstrate that the asymmetric broadening of the ZnSe-like LO mode is determin

Vibrational Evidence for Percolative Behavior in ZnBeSe

Abstract: We propose a picture based on simple percolative concepts for the basic understanding of vibrational properties in the new attractive class of ternary semiconductor alloys made of materials with highly contrasted bond stiffness. In Zn 1-x Be x Se this accounts for the activation of a strong extra BeSe-like optical mode for x between the percolation thresholds of the Be-Se and Zn-Se bonds. Latter mode is attributed to Be-Se bonds within the quasi-continuous Be-rich hard-like cluster which forms above the percolation threshold.

Displaced Substitutional Phosphorus Acceptors in Zinc Selenide

Abstract: Spin-flip Raman scattering experiments reveal that shallow phosphorus acceptors in ZnSe grown epitaxially on GaAs are subject to a local crystal field of trigonal symmetry. In relaxed layers, the trigonal field dominates the macroscopic biaxial tensile strain field. The trigonal field is also observed in pseudomorphic layers, where the sign of the overall macroscopic biaxial strain is reversed. In both cases, the wavefunction of the hole bound at the acceptor appears to be sufficiently localised for the effects of the macroscopic strain field to be severely reduced. This increased localisation relative to nitrogen acceptors and the appearance of the trigonal field are in excellent agreement with the results of previous total energy pseudopotential calculations, which predict that substitutional phosphorus acceptors should be displaced from selenium sites in (111) directions.

Self-compensation of the phosphorus acceptor in ZnSe

Abstract: ZnSe epilayers doped with plasma-activated phosphorus have been investigated by means of optical and electrical measurements. It is found that P Se forms a shallow acceptor with binding energy of 85 meV which is identified in the optical emission spectra. In these samples we also observe an energy level near 90 meV from the valence band using deep level transient spectroscopy. We assign it to the P Se acceptor identified in photoluminescence. Also, deeper levels were observed with binding energies up to 450 meV. Some of them are metastable and give rise to persistent photoconductivity. We discuss their relevance taking into account that all samples investigated in the study were highly resistive.

Control of the polarity of GaN epilayers using a Mg adsorption layer

Abstract: The polarity of GaN epilayers grown by molecular beam epitaxy is controlled using Mg. This is achieved by exposing the surface to a Mg flux under growth interruption. Reflection high energy electron diffraction (RHEED) indicates the formation of Mg/sub 3/N/sub 2/. Overgrowing GaN on this surface leads to a polarity inversion either from [0001] to [000-1] or [000-1] to [0001]. The change of the polarity is followed in situ by RHEED since the surface reconstruction of GaN surface exposed to a NH/sub 3/ flux is polarity dependent: (2/spl times/2) for Ga-polarity and (1/spl times/1) for N-polarity. The polarity inversion was further confirmed by convergent beam electron diffraction. Finally, high resolution transmission electron microscopy (TEM) images show different interface morphologies between Ga/N and N/Ga polarity inversions. The control of the GaN polarity open the way for novel structures dedicated to nonlinear optics.

Light-Hole and Heavy-Hole Excitons: the Right Probe for the Physics of Low N Content GaAsN

Abstract: We have performed transmittance and piezomodulated transmittance measurements of as-grown GaAsN layers on GaAs substrates. The absorption shows energy an splitting of the ground state transition and a simultaneous increase of the splitting with the increase of the N content. This indicates the presence of a strain, which lifts the light- and heavy-hole valence band degeneracy. Surprisingly the piezomodulated transmittance shows that the heavy-hole exciton is the ground state! This implies that the GaAsN layers have a lattice parameter larger than that of GaAs and are under compression. The origin of the lattice parameter increase is the incorporation of N atoms on interstitial sites.

Correlations between growth mode and structural and optical properties of GaInNAs quantum wells grown by MBE

Abstract: The GaInNAs (GINA) quaternary alloy has been intensively studied in the last years because of its promises for developing GaAs-based long-wavelength laser application. Indeed, high performance GINA-based laser structures have been demonstrated in the range of 1.3 /spl mu/m.