Publications de Denis Martin | EPFL Graph Search

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We report broad bandwidth blue superluminescent light-emitting diodes (SLEDs) based on a short-cavity active region. The dependencies of amplified spontaneous emission (ASE) output power and gain bandwidth on cavity length were investigated in devices whos ...

We present a combined low-temperature time-resolved cathodoluminescence and photoluminescence study of exciton recombination mechanisms in a 3.8 nm thick a-plane (Al,Ga)N/GaN quantum well (QW). We observe the luminescence from QW excitons and from excitons ...

In this study, we present the optical properties of nonpolar GaN/(Al,Ga)N single quantum wells (QWs) grown on either a- or m-plane GaN templates for Al contents set below 15%. In order to reduce the density of extended defects, the templates have been proc ...

GaAs/AlxGa1-xAs multiple-quantum-well structures with identical well thicknesses (almost-equal-to 119 angstrom) but with different Al contents x in the barrier (x almost-equal-to 0. 1, 0.2, 0.45, and 1) were grown by molecular-beam epitaxy. We report the characterization of the structures by a combination of different techniques. The x-ray-diffraction technique allows us to estimate the Al content x and to measure the period of the structure with good accuracy. Using the photographs given by high-resolution

We present a detailed study of the luminescence at 3.42 eV usually observed in a-plane epitaxial lateral overgrowth (ELO) GaN grown by hydride vapor phase epitaxy on r-plane sapphire. This band is related to radiative recombination of excitons in a commonl ...

We report thermally stable latched operation of a nonlinear Fabry-Perot device without heat sinking other than through the 0.5-mm GaAs substrate. The device has a 2-μm GaAs spacer and integrated dielectric mirrors with reflectivities of 91% and 99%. Operated in reflection at a wavelength of 886 nm, thresholds as low as 1 mW, and contrast ratios of 10:1 have been observed. Measurements of the threshold dependence on the size of the excited spot give evidence for carrier diffusion and light-diffraction effect

Time-resolved cathodoluminescence at 27 K has been performed on a-plane GaN grown by epitaxial lateral overgrowth. We detail the relaxation and recombination mechanisms of excitons [free or bound to neutral donors, or bound to I1-type basal stacking faults ...

We report on a practical method for developing InGaN-based edge emitting laser diodes of cavity length down to 45 mu m. Samples consisting of one uncoated cleaved facet and one etched facet coated with a high-reflectivity (HR) dielectric distributed Bragg ...

The incorporation of In in the growth of crescent-shaped In0.12Ga0.88As quantum wires embedded in (AlAs)(4)(GaAs)(8) superlattice barriers is studied in atomic detail using cross-sectional scanning tunneling microscopy. It is found that the In distribution in both the surface and the first subsurface layer can be atomically resolved in the empty- and filled-state images, respectively. Strong In segregation is seen at the InGaAs/GaAs interfaces, but neither an expected enhancement of the In concentration at

The temperature and excitation intensity dependencies of the photoluminescence (PL) spectra of GaAs/Al0.3Ga0.7As superlattices (SL's) having randomly distributed well widths are studied. Our results indicate that the electronic properties of disordered SL's are similar to those of other disordered semiconductors: at low energies the electronic states are essentially localized, while at higher energies they are extended. Further, the PL spectra feature a disorder-induced fine structure, and they shift to the

Differences and analogies between disorder-induced localization and electric-field-induced localization are discussed. Calculations using a tight binding model and transfer matrix method for disordered superlattices are reported. Our results indicate the existence of residual structures in the energy spectrum of the disordered superlattices, which are absent in the Stark localization case. The residual structure in the Anderson localization case can be interpreted as arising from the presence of the neighbo

The optical nonlinearity of a GaAs/AlAs periodic layered structure was experimentally investigated for the first time. The shift of the reflectivity peak with increasing intensity was observed. A reflectivity contrast of about 10:1 was obtained by varying the incident intensity. Hysteresis loops due to the response delay of both the electronic and the thermal nonlinearity were observed. All-optical logic operations were also demonstrated. A further improvement of the structure may lead to a new type of opti

We used optical pumping by the Vanderbilt free-electron laser and the technique of internal photoemission to measure with high accuracy the conduction-band discontinuity of semiconductor heterojunction interfaces. The experiment is the first application to our knowledge of a free-electron laser to interface research.

Quantum wire heterostructures, such as V- and T-shaped wires, are very promising candidates for low-threshold lasing. A crucial issue is the excitonic vs. free-carrier nature of the radiative recombination. Here, we report on magnetophotoluminescence studies of GaAs and InGaAs V-shaped wires that allow to discriminate different regimes of radiative recombination.

Fabrication and characterization of a current-injected InGaAs-GaAs quantum-wire gain-coupled distributed feedback (DFB) laser operating at 77 K at a wavelength of 923 nm are presented, Threshold current densities in broad area lasers were measured to be as low as 160 A/cm(2), The side-mode suppression ratio at twice threshold is 35 dB. A 4-mu m rib waveguide device has a threshold of 14 mA, The patterning process for the second-order DFB grating fabricated with deep UV holography and wet-chemical etching is

We report on a bulk GaAlAs mirror which is used as a saturable absorber for subpicosecond pulse generation around 835 nm. The mirror consists of a 200 nm layer of bulk GaAlAs (with approximately 5% Al content) which is grown on a linear Bragg mirror and is used as a laser end mirror. The incorporation of the bulk GaAlAs mirror into a synchronously pumped styryl-9 dye laser leads to a significant mode locking improvement and pulse shortening. Optimum operation of the laser is obtained for wavelengths near th

Transmission spectra of ordered and disordered GaAs/Al0.3Ga0.7As superlattices (SL) were measured at 2 K. The experimental results are compared with numerical simulations obtained by means of a transfer matrix method. The numerical results indicate that a multiple-quantum-well model accounts for the main features of random SL, and that a disorder-induced fine structure is present. The agreement between the measured spectra and the numerical calculations supports the predicted features.

Raman spectroscopy has been used to measure phonons in GaAs v-groove quantum wire structures containing (001) and (111) GaAs/AlAs superlattice barrier regions. Resonance enhancement permits the identification of modes in different regions of the structure, and the measured phonon frequencies provide structural information which shows clear evidence of GaAs migration during growth from (001) surfaces into the grooves. Confined and interface phonons with large in-(111) plane wavevectors are observed. (C) 1996

The full experimental evidence of fine structure in disordered superlattices is reported. The experimental results agree with the numerical predictions, thus indicating that this effect is related to residual coupling between adjacent identical wells in the case of Anderson localization. This feature indicates an intrinsic difference between disorder-induced and electric-field induced localization, where no spectral fine structure can be observed in the strong localization limit. Copyright (C) 1996 Elsevier

Ultrafast pump-probe measurements evidence the dynamical Stark splitting in the exciton absorption spectrum of a single semiconductor quantum well. The intensity of the Stark sidebands in the spectrum is comparable to the linear absorption and their separation scales as the pump field amplitude. In the time domain the Rabi oscillations are observed. The semiconductor Bloch equations solved in the Hartree-Fock approximation demonstrate that the coherent exciton-light coupling dominates over the many-body dep

Denis Martin

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Broadened Bandwidth Amplified Spontaneous Emission from Blue GaN-Based Short-Cavity Superluminescent Light-Emitting Diodes

Exciton recombination dynamics in a-plane (Al,Ga)N/GaN quantum wells probed by picosecond photo and cathodoluminescence

One-dimensional exciton luminescence induced by extended defects in nonpolar GaN/(Al,Ga)N quantum wells

Influence of Al Content in the Barrier on the Optical-Properties of Gaas/Alxga1-Xas(X=0.1-1) Multiple-Quantum-Well Structures

Exciton localization on basal stacking faults in a-plane epitaxial lateral overgrown GaN grown by hydride vapor phase epitaxy

Thermally Stable Operation of a Bistable Fabry-Perot Etalon with a Bulk Gaas Spacer

Low-temperature time-resolved cathodoluminescence study of exciton dynamics involving basal stacking faults in a-plane GaN

Short cavity InGaN-based laser diodes with cavity length below 300 mu m

Indium Distribution in Ingaas Quantum Wires Observed with the Scanning Tunneling Microscope

Temperature and excitation intensity dependencies of the photoluminescence spectra of GaAs/(AlGa)As disordered superlattices

Anderson and Stark localization in GaAs/(AlGa)As disordered superlattices

All-Optical Reflectivity Tuning and Logic Gating in a GaAs/AlAs Periodic Layered Structure

Interface Measurements of Heterojunction Band Lineups with the Vanderbilt Free-Electron Laser

Magnetic-field effects in the luminescence of V-shaped quantum wires

Distributed feedback gain-coupled lasers based on InGaAs quantum-wire arrays

Bulk GaAlAs Mirror as a Saturable Absorber for Subpicosecond Pulse Generation around 835 Nm

Absorption spectra of GaAs/Al-x Ga1-xAs random superlattices at 2 K

Resonant Raman scattering from phonons in GaAs/(GaAs)(m)(AlAs)(n) quantum wire structures

Anderson and Stark localization in superlattices: Residual coupling and fine structure

Direct observation of the excitonic ac Stark splitting in a quantum well