J.C. Harmand

Analysis of vapor-liquid-solid mechanism in Au-assisted GaAs nanowire growth

GaAs nanowires were grown by molecular-beam epitaxy on (111)B oriented surfaces, after the deposition of Au nanoparticles. Different growth durations and different growth terminations were tested. After the growth of the nanowires, the structure and the composition of the metallic particles were analyzed by transmission electron microscopy and energy dispersive x-ray spectroscopy. We identified three different metallic compounds: the hexagonal β′Au7Ga2 structure, the orthorhombic AuGa structure, and an almost pure Au face centered cubic structure. We explain how these different solid phases are related to the growth history of the samples. It is concluded that during the wire growth, the metallic particles are liquid, in agreement with the generally accepted vapor-liquid-solid mechanism. In addition, the analysis of the wire morphology indicates that Ga adatoms migrate along the wire sidewalls with a mean length of about 3μm.

GaInAs/GaAs quantum-well growth assisted by Sb surfactant: Toward 1.3 μm emission

The growth of highly strained GaInAs quantum wells on GaAs is investigated in the presence of Sb. Sb appears as an adequate isoelectronic surfactant: the lateral relaxation of strain is shown to be significantly delayed in comparison with a Sb-free growth. This effect is used to extend the emission wavelength of GaInAs quantum wells. We obtained a 9-nm-thick Ga0.59In0.41As0.986Sb0.008 quantum wells with smooth interfaces, emitting at 1.27 μm at room temperature.

Investigations on GaInNAsSb quinary alloy for 1.5 μm laser emission on GaAs

GaInNAsSb quantum wells grown by molecular-beam epitaxy on GaAs substrates were investigated. Intricate incorporation mechanisms of the constituents in this quinary alloy were seen. In highly strained indium-rich alloys, antimony incorporation is strongly reduced, and a beneficial surfactant effect is observed. Due to this effect, high structural quality is preserved even for an uncompensated 2.67% strained multiquantum-well structure. Narrow luminescence linewidth (35 meV) could be achieved near 1.55 μm wavelength with these quantum wells. Laser emission is demonstrated at 1.50 μm with threshold current density of 3.5 kA/cm2.

Quantum-well saturable absorber at 1.55μm on GaAs substrate with a fast recombination rate

We propose and realize a structure designed for fast saturable absorber devices grown on GaAs substrate. The active region consists of a 1.55μm absorbing GaInNAsSb quantum well (QW) surrounded by two narrow QWs of GaAsN with a N concentration up to 13%. Photoexcited carriers in the GaInNAsSb QW are expected to recombine by tunneling into the wide distribution of subband gap states created in the GaAsN QW. An absorption study shows that edge energy and excitonic peak intensity of the GaInNAsSb QW are not affected by the proximity of the GaAsN QWs. Pump-probe measurements provide information on the carrier relaxation dynamics which is dependent on spacer thickness, as expected for a tunneling process. We show that this process can be enhanced by increasing the N content in the GaAsN layers. Using this design, we have realized a monolithic GaAs-based saturable absorber microcavity with a 1∕e recovery time of 12ps.

Floor free 10-Gb/s transmission with directly modulated GaInNAs-GaAs 1.35-/spl mu/m laser for metropolitan applications

Among the new semiconductor materials for telecom devices, the GaInNAs-GaAs structure presents interesting properties for low-cost applications, like high differential gain and high T/sub 0/. Another key aspect of the performance is the behavior of the GaInNAs-GaAs based lasers under high bit rate direct modulation. Here, we demonstrate the dynamic capabilities of GaInNAs-GaAs three-quantum-well ridge structure through 2.5-Gb/s directly modulated laser emission and transmission on standard fiber, in the temperature range 25/spl deg/C-85/spl deg/C. Besides transmission is demonstrated up to 10 Gb/s at 25/spl deg/C on the same fiber, without penalty and bit-error-rate floor.

In situ passivation of GaAsP nanowires

We report on the structural and optical properties of GaAsP nanowires (NWs) grown by molecular-beam epitaxy. By adjusting the alloy composition in the NWs, the transition energy was tuned to the optimal value required for tandem III-V/silicon solar cells. We discovered that an unintentional shell was also formed during the GaAsP NW growth. The NW surface was passivated by an in situ deposition of a radial Ga(As)P shell. Different shell compositions and thicknesses were investigated. We demonstrate that the optimal passivation conditions for GaAsP NWs (with a gap of 1.78 eV) are obtained with a 5 nm thick GaP shell. This passivation enhances the luminescence intensity of the NWs by 2 orders of magnitude and yields a longer luminescence decay. The luminescence dynamics changes from single exponential decay with a 4 ps characteristic time in non-passivated NWs to a bi-exponential decay with characteristic times of 85 and 540 ps in NWs with GaP shell passivation.

1.55-µm tunable doped-fiber vertical-cavity surface emitting laser

Tunable vertical cavity surface emitting lasers (VCSELs), available as either MEMS-VCSELs [1] or fiber-VCSELs [2–3], are attractive sources for applications in areas including spectroscopy, sensing and communications, but are typically limited to output powers of ∼1mW. Here, we report initial results on a Master Oscillator Power Amplifier (MOPA)-like embodiment of fiber-VCSEL as a means of addressing this power scaling issue. This preserves the attractive attributes of the fiber-VECSEL including (i) continuously-tunable single-longitudinal mode operation with high side mode suppression, (ii) inherent fiber coupling making them suitable for remote interrogation, (iii) easy optical pumping and (iv) separate optimization of the gain structure and output coupling, whilst facilitating amplification at wavelengths for which rare-earth-doped fibers are well-established.

Semiconductor nanowires in InP and related material systems: MBE growth and properties

In this work, we report on the Au-assisted MBE of various InP and related material NWs on InP(111)B substrates. The influence of growth conditions on the InAsP insertion geometry and composition in InP nanowire is evidenced. Ex-situ thermal annealing produces significant changes to the PL spectra of these heterostructures. It is shown that InP/InAsP/InP heterostructures are well suited for fabrication of emitters in the telecommunication wavelength range 1.3-1.55 mum.

Femtosecond pulse generation at 1530nm using a GaInNAsSb SESAM

We describe the operation of a femtosecond Cr4+:YAG laser that has been mode locked using a novel GaInNAsSb SESAM. 230 fs pulses were generated at an average output power of 280 mW.

Micro-Raman study of GaAs nanowires

In GaAs nanowires, the effective Raman tensor is dominated by dielectric anisotropy leading to similar angular variations of allowed TO and forbidden LO phonon scattering from both zinc blende and wurtzite crystalline symmetry. Resonant Raman scattering studies give evidence of a novel excitonic transition in wurtzite wires at 90 meV above to the lowest exciton in zinc blende ones in agreement with recent theoretical predictions.