E. Tournié

On the origin of carrier localization in Ga1−xInxNyAs1−y/GaAs quantum wells

We have investigated by temperature-dependent photoluminescence (PL) spectroscopy as-grown GaInNAs, InGaAs, and GaAsN quantum wells (QWs) embedded in a GaAs matrix. The evolution of the PL peak position and of the PL linewidth shows evidence of a strong carrier localization for the GaInNAs QWs only. The high delocalization temperature, in the 150 K range, indicates the presence of a high density of possibly deep-localizing potential wells. In addition, a higher density of nonradiative recombination centers appears to result in stronger carrier localization. Transmission electron microscopy reveals well defined, flat interfaces, in these comparatively high N-content (yN∼0.04–0.05) QWs. Our results thus demonstrate that the origin of localization in GaInNAs QWs is the concomitant presence of both In and N, which may result in strain and/or composition fluctuations.

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

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.

Silicon-Based Photonic Integration Beyond the Telecommunication Wavelength Range

In this paper we discuss silicon-based photonic integrated circuit technology for applications beyond the telecommunication wavelength range. Silicon-on-insulator and germanium-on-silicon passive waveguide circuits are described, as well as the integration of III-V semiconductors, IV-VI colloidal nanoparticles and GeSn alloys on these circuits for increasing the functionality. The strong nonlinearity of silicon combined with the low nonlinear absorption in the mid-infrared is exploited to generate picosecond pulse based supercontinuum sources, optical parametric oscillators and wavelength translators connecting the telecommunication wavelength range and the mid-infrared.

Novel plastic strain‐relaxation mode in highly mismatched III‐V layers induced by two‐dimensional epitaxial growth

Using cross‐section and plan‐view transmission electron microscopy we demonstrate that the initial plastic relaxation of highly mismatched layers grown along [100] is governed by the growth mode. During MBE growth of InAs on GaAs in the Stranski‐Krastanov (SK) mode, 60o ‐type dislocations are generated at the island edges and then glide to the interface to relieve the strain. The resulting interfacial microstructure consists of an inefficient arrangement of misfit dislocations. On the other hand, when InAs is forced to grow in a two‐dimensional (2D) mode, only pure edge‐type dislocations are generated and they are located exactly at the epilayer/substrate interfacial plane. These results are explained by a different dislocation nucleation mechanism imposed by the planar morphology of the highly strained film.

Annealing effects on the crystal structure of GaInNAs quantum wells with large In and N content grown by molecular beam epitaxy

The impact of rapid thermal annealing on the optical emission of GaInNAs/GaAs quantum wells (QWs) grown by molecular beam epitaxy with high In and N content is shown to be highly dependent on the crystal structure of the QWs, as determined by transmission electron microscopy. Due to the presence of higher concentrations of nonradiative recombination centers, the annealing temperature required to obtain maximum photoluminescence emission is higher for the QW with strong structural modulation of the upper interface [at the onset of three-dimensional (3D) growth], intermediate for the two-dimensional (2D) grown QW with compositional fluctuations, and lower for the homogeneous 2D grown QW. Moreover, the transition from homogeneous 2D growth, to 2D growth with compositional fluctuations, and finally 3D growth, leads to progressively deeper carrier localization states below the conduction-band edge. Increasing annealing temperatures gradually shifts the localization states closer to the conduction-band edge, pr...

Silicon-based heterogeneous photonic integrated circuits for the mid-infrared

In this paper we present our recent work on mid-infrared photonic integrated circuits for spectroscopic sensing applications. We discuss the use of silicon-based photonic integrated circuits for this purpose and detail how a variety of optical functions in the mid-infrared besides passive waveguiding and filtering can be realized, either relying on nonlinear optics or on the integration of other materials such as GaSb-based compound semiconductors, GeSn epitaxy and PbS colloidal nanoparticles.

Nanoscale analysis of the In and N spatial redistributions upon annealing of GaInNAs quantum wells

By using transmission electron microscopy on as-grown and annealed GaInNAs/GaAs heterostructures, we demonstrate that annealing induces a correlated behavior of both In and N species within the GaInNAs quantum well. While no intermixing occurs, the analysis of the strain situation reveals that the main driving force for the observed inward diffusion is not composition gradients at the interfaces, but local strain fields. This mechanism leads to the improvement of the photoluminescence (PL) properties and to the blueshift of the PL peak.

Silicon-on-insulator spectrometers with integrated GaInAsSb photodiodes for wide-band spectroscopy from 1510 to 2300 nm

We present a silicon-on-insulator (SOI) based spectrometer platform for a wide operational wavelength range. Both planar concave grating (PCG, also known as echelle grating) and arrayed waveguide grating (AWG) spectrometer designs are explored for operation in the short-wave infrared. In addition, a total of four planar concave gratings are designed to cover parts of the wavelength range from 1510 to 2300 nm. These passive wavelength demultiplexers are combined with GaInAsSb photodiodes. These photodiodes are heterogeneously integrated on SOI with benzocyclobutene (DVS-BCB) as an adhesive bonding layer. The uniformity of the photodiode characteristics and high processing yield, indicate a robust fabrication process. We demonstrate good performance of the miniature spectrometers over all operational wavelengths which paves the way to on-chip absorption spectroscopy in this wavelength range.

Continuous-wave operation above room temperature of GaSb-based laser diodes grown on Si

We have investigated specifically designed GaSb-based laser diodes epitaxially grown on a Si substrate. We demonstrate continuous-wave operation of these laser diodes emitting near 2 μm up to 35 °C with several mW/facet output powers, limited by our experimental setup. Our results open the way to direct monolithic III-V/Si integration.

GaSb-Based Laser, Monolithically Grown on Silicon Substrate, Emitting at 1.55

We have investigated the potential of GaSb-based lasers for emission at 1.55 μm and monolithic integration on silicon. We designed an active region based on strained Ga_0.8In_0.2Sb quantum-wells aiming a good carrier confinement. To validate this design, the active region was first used in edge-emitting lasers grown on GaSb substrates. Continuous-wave operation at 1.56 μm has been achieved up to 45°C. The same laser structure grown on Si substrate showed room-temperature operation in pulsed regime at 1.55 μm with a threshold current density of 5 kA/cm².