Mathieu Leroux
Centre national de la recherche scientifique
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Featured researches published by Mathieu Leroux.
Applied Physics Letters | 2001
E. Feltin; B. Beaumont; M. Laügt; P. de Mierry; P. Vennéguès; H. Lahrèche; Mathieu Leroux; P. Gibart
The strain in GaN epitaxial layers grown on silicon (111) substrates by metalorganic vapor phase epitaxy has been investigated. The insertion of AlN/GaN superlattices was found to decrease the stress sufficiently for avoiding crack formation in an overgrown thick (2.5 μm) GaN layer. X-ray diffraction and photoluminescence measurements are used to determine the effect of these AlN/GaN superlattices on the strain in the subsequent GaN layers. A reduction of threading dislocation density is also observed by transmission electron microscopy and atomic force microscopy when such superlattices are used. Strong band edge photoluminescence of GaN on Si(111) was observed with a full width at half maximum of the bound exciton line as low as 6 meV at 10 K. The 500 arcsec linewidth on the (002) x-ray rocking curve also attests the high crystalline quality of GaN on Si (111), when using these AlN/GaN superlattices.
Journal of Applied Physics | 2007
T. Gühne; Zahia Bougrioua; P. Vennéguès; Mathieu Leroux; M. Albrecht
Low temperature spatially resolved cathodoluminescence was carried out on GaN films grown by the epitaxial-lateral-overgrowth (ELO) technique with the nonpolar (11-20) and the semipolar (11-22) orientations on R- and M-sapphires, respectively. Defect related optical transitions were identified and their localization was correlated to different regions of ELO. The sample microstructure was further investigated by plan-view and cross-section transmission electron microscopies. It is shown that the defect related emissions are mainly localized in the seed of the samples, but different defects occur as well in the wings, especially in the case of nonpolar GaN. The structural defect densities are lowest in the overgrown wings of semipolar GaN. In particular, the [0001] wing region of semipolar ELO-GaN is almost defect-free with a cathodoluminescence spectrum dominated by the GaN band-edge emission at 3.476eV.
Applied Physics Letters | 2000
P. Vennéguès; M. Benaissa; B. Beaumont; E. Feltin; P. de Mierry; S. Dalmasso; Mathieu Leroux; P. Gibart
A transmission electron microscopy study of structural defects induced by the introduction of Mg during the growth of metalorganic vapor phase epitaxy GaN is presented. These defects are assumed to be pyramidal inversion domains with an hexagonal base and {1123} inclined facets. The tip of the pyramids is always pointing toward the [0001] direction, i.e., in a Ga-terminated film, toward the substrate and in a N-terminated film, toward the surface. A chemical quantitative analysis shows that these pyramidal defects are Mg rich. They are present in all the studied films, independent of the doping level.
Journal of Applied Physics | 2000
H. P. D. Schenk; Mathieu Leroux; P. de Mierry
Wurtzite InxGa1−xN (0.01≲x≲0.14) films have been grown by metalorganic vapor phase epitaxy on sapphire substrates. Integrated photoluminescence intensity and line shapes have been studied as functions of temperature and alloy composition x. We compare the “effective” InGaN band gap energy assessed by photothermal deflection spectroscopy with a “mean” band gap energy calculated from room temperature photoluminescence spectra utilizing the van Roosbroeck–Shockley relation and assuming a Gaussian energy dependence of the subband gap absorption coefficient. The Stokes’ shift between band gap energy and 300 K photoluminescence peak is explained by this model.Wurtzite InxGa1−xN (0.01≲x≲0.14) films have been grown by metalorganic vapor phase epitaxy on sapphire substrates. Integrated photoluminescence intensity and line shapes have been studied as functions of temperature and alloy composition x. We compare the “effective” InGaN band gap energy assessed by photothermal deflection spectroscopy with a “mean” band gap energy calculated from room temperature photoluminescence spectra utilizing the van Roosbroeck–Shockley relation and assuming a Gaussian energy dependence of the subband gap absorption coefficient. The Stokes’ shift between band gap energy and 300 K photoluminescence peak is explained by this model.
Journal of Applied Physics | 2000
H. Lahrèche; Mathieu Leroux; M. Laügt; M. Vaille; B. Beaumont; P. Gibart
The growth of GaN on 6H–SiC is three dimensional (3D) and results in the formation of large islands presenting hexagonal truncated shape with {1–101} lateral facets and a top {0001} facet. In this work, we present a three steps growth process that enables us to grow high quality mirrorlike GaN layers without using AlN buffer layers. During a first step, a thin 3D GaN layer is deposited at high temperature. This layer is smoothed under ammonia flow for several minutes when the growth is interrupted. The subsequent growth of GaN is two dimensional. 600 nm thick GaN films were grown. They were analyzed by high resolution x-ray diffraction, reflectivity, and photoluminescence. All the layers are under strong tensile biaxial strain. The correlation between residual tensile strain in GaN layers and their optical properties is reported for biaxial deformations exx ranging up to 0.37%.
Applied Physics Letters | 2011
Thierry Guillet; M. Mexis; Jacques Levrat; G. Rossbach; Christelle Brimont; Thierry Bretagnon; B. Gil; R. Butté; N. Grandjean; L. Orosz; F. Réveret; J. Leymarie; J. Zúñiga-Pérez; Mathieu Leroux; F. Semond; S. Bouchoule
We demonstrate polariton lasing in a bulk ZnO planar microcavity under non-resonant optical pumping at a small negative detuning (δ ∼ −1/6 the 130 meV vacuum Rabi splitting) and a temperature of 120 K. The strong coupling regime is maintained at lasing threshold since the coherent nonlinear emission from the lower polariton branch occurs at zero in-plane wavevector well below the uncoupled cavity mode. The contribution of multiple localized polariton modes above threshold and the non-thermal polariton statistics show that the system is in a far-from-equilibrium regime, likely related to the moderate photon lifetime and in-plane photonic disorder in the cavity.
Physica Status Solidi (a) | 2002
S. Dalmasso; B. Damilano; Cyril Pernot; A. Dussaigne; D. Byrne; N. Grandjean; Mathieu Leroux; J. Massies
Multicolor, multi-quantum well light emitting diodes have been fabricated by molecular beam epitaxy by inserting quantum wells of various widths in the active region. The In content of the wells is 15%-20% and the color is governed by carrier confinement and the Stark effect. Combining a proper number of blue and yellow quantum wells allows to obtain monolithic white LEDs. The electroluminescence spectra of the diodes have been studied. At low injection, the luminescence intensity varies quadratically with the injection current, showing that the electroluminescence originates from the depleted region of the diode, and that non-radiative recombination paths exist. However, for higher injection currents, the luminescence efficiency of the wells situated near the n-side of the junction starts to vary linearly with the current, and this is accompanied by the appearance of GaN electroluminescence. We show that this is due to the entering of these wells into the neutral region of the diode, explaining the injection dependence of the color of these multicolor LEDs.
Applied Physics Letters | 1999
H. P. D. Schenk; P. de Mierry; M. Laügt; F. Omnès; Mathieu Leroux; B. Beaumont; P. Gibart
We have studied the indium incorporation into InGaN ternary alloys during low-pressure metalorganic vapor-phase epitaxy as a function of the trimethylindium flow and the growth temperature in the 800–860 °C range. Partially relaxed InxGa1−xN bulk films with indium compositions 0.02≲x≲0.14 have been grown. In relation to the band-gap energy at room temperature, determined by photothermal deflection spectroscopy, we find a downward band-gap bowing of 2.65±0.15 eV. The required change of the trimethylindium flow as a function of the growth temperature, necessary to obtain isocomposition InGaN films, can be described by an Arrhenius law. We find an indium desorption energy of 0.8±0.3 eV.
Japanese Journal of Applied Physics | 1999
N. Grandjean; Mathieu Leroux; J. Massies; M. Mesrine; M. Laügt
Ammonia has been used to grow GaN layers by molecular beam epitaxy on c-plane sapphire substrates. The ratio of nitrogen to Ga active species, i.e., the actual V/III ratio, has been varied from 1 to 4. It is found that increasing the V/III ratio improves the material properties both in terms of optoelectronic and structural quality. This is demonstrated by photoluminescence (PL) experiments, Hall measurements, secondary ion mass spectroscopy (SIMS), and atomic force microscopy. The origin of the residual n-type doping of undoped GaN layers is also discussed on the basis of SLR IS and PL results.
Optics Letters | 2011
Meletios Mexis; Sylvain Sergent; Thierry Guillet; Christelle Brimont; Thierry Bretagnon; Bernard Gil; F. Semond; Mathieu Leroux; Delphine Néel; Sylvain David; X. Checoury; Philippe Boucaud
We compare the quality factor values of the whispering gallery modes of microdisks (μ-disks) incorporating GaN quantum dots (QDs) grown on AlN and AlGaN barriers by performing room temperature photoluminescence (PL) spectroscopy. The PL measurements show a large number of high Q factor resonant modes on the whole spectrum, which allows us to identify the different radial mode families and to compare them with simulations. We report a considerable improvement of the Q factor, which reflects the etching quality and the relatively low cavity loss by inserting QDs into the cavity. GaN/AlN QDs-based μ-disks show very high Q values (Q>7000) whereas the Q factor is only up to 2000 in μ-disks embedding QDs grown on the AlGaN barrier layer. We attribute this difference to the lower absorption below bandgap for AlN barrier layers at the energies of our experimental investigation.