R. Bardoux

Kyoto University, Kioto, Kyōto, Japan

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Publications (12)27.28 Total impact

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    ABSTRACT: We observed crossed transitions and anti-Stokes emissions in single quantum-dot-like objects embedded in the active layer of InGaN/GaN quantum disks by two-photon absorption techniques. We proposed a phenomenological model based on the interplay between Auger effect and crossed transitions to explain the origin of anti-Stokes emissions and the preferential excitation of 0D objects at the expense of their surroundings. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (RRL) - Rapid Research Letters 05/2013; 7(5):344-347. · 2.39 Impact Factor
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    ABSTRACT: Selective area growth technique is very promising for the realization of optoelectronic nano-devices based on InGaN/GaN quantum disks, as it allows precise positioning of the nano-objects on the substrate. However, this fabrication method induces a pronounced pyramidal shape of the nano-columnar heterostructures. To understand how the optical properties of these heterostructures are affected by this shape, we investigated the linear polarization of the luminescence from 0-dimensional localization centers included in their active layer. Our experimental results and our simulation show that a complex strain distribution exist in the active layer and also that quantum dot-like objects can be used to probe the local strain distribution through nano-scale heterostructures.
    Optical Materials Express 01/2013; 3(1). · 2.92 Impact Factor
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    ABSTRACT: As an advantage, random lasers may be elaborated from a large variety of materials and do not require any cavity oscillators that usually necessitate complicated and expensive fabrication techniques. Since the feedback process of those non-conventional laser systems is provided by light interference in a disordered medium, spectral and temporal uncertainties are usually considered as an intrinsic part of their optical proprieties. We investigated random laser action under two photon absorption experiments through an auto-organized InGaN/GaN quantum-disks ensemble. Thanks to our experimental approach, we evidence random lasing based on a gain medium constituted by point-sized structures. In such context, a stabilised and individual emission mode is observed as for conventional semiconductor lasers. By controlling the emission energy of these nanostructures, a tuneable and stable random laser may be built. Moreover, our findings suggest that disordered medium should play an important role in the conception of low cost quantum dot and up conversion laser systems.
    Optics Express 05/2011; 19(10):9262-8. · 3.55 Impact Factor
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    Physical Review B (Condensed Matter and Materials Physics). 04/2009; 79:155307--6.
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    ABSTRACT: We report microphotoluminescence spectroscopy performed on individual and ensemble InGaN/GaN quantum disks (Q-disks). The typical spectrum of a single Q-disk exhibited the contribution of localization centers (LCs) formed in the InGaN active layer of the Q-disks, characterized by sharp lines appearing on the low energy side of the spectra. In addition, a broader emission peak identified as the luminescence of the quasi-two-dimensional (2D) InGaN active layer surrounding the LCs appears systematically at higher energy. Time-resolved photoluminescence experiment performed on single Q-disks exhibited the excitonic transfer, from the 2D InGaN active layer to LCs, at the submicroscopic scale. Excitation power dependence studies and linear polarization analysis allowed us to identify a biexciton complex confined in a LC in a single Q-disk with a surprising positive binding energy of 13 meV. The absence of screening effect by increasing the excitation power density and the fast excitonic radiative lifetime of a few hundred picoseconds that we measured on several individual Q-disks indicate that the absence of internal electric field in the structure can explain the observed positive biexciton binding energy.
    Physical review. B, Condensed matter 01/2009; · 3.77 Impact Factor
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    ABSTRACT: We report micro-photoluminescence studies of single GaN/AlN quantum dots grown along the (0001) crystal axis by molecular beam epitaxy on Si(111) substrates. The emission lines exhibit a linear polarization along the growth plane, but with varying magnitudes of the polarization degree and with principal polarization axes that do not necessarily correspond to crystallographic directions. Moreover, we could not observe any splitting of polarized emission lines, at least within the spectral resolution of our setup (1 meV). We propose a model based on the joint effects of electron-hole exchange interaction and in-plane anisotropy of strain and/or quantum dot shape, in order to explain the quantitative differences between our observations and those previously reported on, e.g. CdTe- or InAs-based quantum dots.
    Physical Review B 06/2008; 77(23):235315. · 3.66 Impact Factor
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    ABSTRACT: We present single dot spectroscopy of hexagonal GaN/AlN self-assembled quantum dots (QDs) grown by MBE along the (0001) axis. The GaN quantum dots are grown on an AlN epilayer on Si (111) substrate, with dot densities between 108 and 1011 cm-2. We study the micro-photoluminescence spectra of a few quantum dots. In the energy range corresponding to the smaller dots we observe several groups of peaks, each group corresponding to the emission of a unique quantum dot. These groups are identified through their time-correlated spectral diffusion. The measured linewidth of the transition is 2 meV (resolution limited).
    AIP Conference Proceedings 05/2007; 893:941.
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    ABSTRACT: We study wurtzite GaN/AlN quantum dots (QDs) by time-resolved photoluminescence. The properties of nitride based nano-objects are significantly affected by strong built-in electric fields existing in this crystalline phase. These fields induce a spatial separation of electrons and holes in the quantum dot, a Stark shift of the transition energy, and they slow their radiative recombination down to tens of microseconds of decay time for the largest quantum dots. Such long decay times are responsible for the screening of internal fields by using moderate excitation intensities, thus modifying drastically both the energy and the rate of photon emission. Consequently it is difficult to perform spectroscopic studies of these QDs in the regime where a single electron-hole (e-h) pair is present at the most in each dot. Using a pulsed laser excitation, we study the time-resolved dynamics of carrier recombinations, waiting for complete recombination of all electron-hole pairs in the dots. We clearly exhibit the conditions where no screening of the internal electric field occurs. We especially obtain the transition energy and the mono-exponential decay, i.e the radiative recombination time, of the last e-h pair present in the dot, for a wide range of QD sizes. These results are analyzed within an envelope function model for the electron and hole confinement. The effective electric field, averaged over the strain distribution in the dots, is determined to be of 9.0 ± 0.5 MV/cm.
    physica status solidi (c) 01/2007; 4(1):183.
  • Materials Science Forum - MATER SCI FORUM. 01/2007;
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    ABSTRACT: We report microphotoluminescence studies of single GaN∕AlN quantum dots grown by molecular beam epitaxy on Si(111) substrates. Small groups of emission lines characterize each single dot, with linewidths mostly limited by our experimental setup to 1 or 2 meV. By using time-dependent microphotoluminescence, we observe both the continuous and discontinuous spectral diffusion of these lines, assigned to the trapping of charges at defects in the vicinity of the dots. We show that this trapping takes place on a large variety of time scales, which depend on the photogeneration. It induces energy shifts that also cover some range, yielding both some unresolved broadening and discrete positions of the emission line. We propose that this results from different local configurations, mainly in terms of the distance between the defects and the dots.
    Physical Review B 11/2006; 74(19):195319. · 3.66 Impact Factor
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    ABSTRACT: Wurtzite GaN/AlN quantum dots �QDs� are studied by time-resolved photoluminescence. Careful measurements allow us to reach the regime of a single electron-hole pair per dot, evidenced by a monoexponential decay of the luminescence and a stop of the time-dependent shift of the emission energy. The transition energy and the radiative lifetime of the QD ground state are measured in the absence of any electric field screening effect, for a wide range of QD heights. These results are analyzed within an envelope function model for the electron and hole confinement. The effective electric field, averaged over the strain distribution in the dots, is determined to be of 9.0±0.5 MV/cm.
    Physical Review B 03/2006; 73(11):113304. · 3.66 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Wurtzite GaN/AlN quantum dots (QDs) are studied by time-resolved photoluminescence. Careful measurements allow us to reach the regime of a single electron-hole pair per dot, evidenced by a monoexponential decay of the luminescence and a stop of the time-dependent shift of the emission energy. The transition energy and the radiative lifetime of the QD ground state are measured in the absence of any electric field screening effect, for a wide range of QD heights. These results are analyzed within an envelope function model for the electron and hole confinement. The effective electric field, averaged over the strain distribution in the dots, is determined to be of 9.0±0.5MV/cm .
    Physical Review B 03/2006; 73:113304--4. · 3.66 Impact Factor