G. Boissier

Laser Diodes for Gas Sensing Emitting at 3.06

Type-I quantum-well laser diodes with an active region constituted of GaInAsSb-AlGaInAsSb are reported. Broad-area lasers have demonstrated a threshold current density of 255 A/cm2 at room temperature. Distributed-feedback lasers have been operated in the continuous-wave regime at 20°C with a wavelength of 3.06 μm, a threshold current of 54 mA, and an output power of 6 mW.

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We report on the growth, fabrication, experimental study and application in an absorption gas setup of distributed feed-back antimonide diode lasers with buried grating. First, half laser structures were grown by molecular beam epitaxy on GaSb substrates and stopped at the top of the waveguide. A second order Bragg grating was then defined by interferometric lithography on the top of the structure and dry etched by Reactive Ion Etching. The grating was, afterwards, buried thanks to an epitaxial regrowth of the top cladding layer. Finally, the wafer was processed using standard photolithography and wet etched into 10 µm-wide laser ridges. A single frequency laser emission around 2.3 µm was recorded, a maximum output power of 25 mW and a total continuous tuning range reaching 4.2 nm at fixed temperature. A device has been used to detect methane gas and shows strong potential for gas spectroscopy. This process was also replicated for a target of 3 µm laser emission. These devices showed an output power of 2.5 mW and a SMSR of at least 23 dB, with a 2.5 nm continuous tuning range at fixed temperature.

m at Room Temperature

Optical transitions in Ga0.35In0.65As0.32Sb0.68/Al0.25Ga0.50In0.25As0.24Sb0.76 quantum wells grown by molecular beam epitaxy on GaSb substrates have been detected by photoreflectance. Based on comparison with energy level calculations, the chemical conduction band offset ratio has been determined to be 78%. This translates into 65% in the real structure (i.e., after strain inclusion) which is an evidence of the expected band offset ratio modification in a quinary barrier system in favor of enhanced confinement in the valence band, when compared to similar quantum wells but with quaternary barriers. This has allowed us to explain the main photoluminescence thermal quenching mechanisms and connect the carrier activation energies with delocalization of excitons at low temperatures and the escape of holes via the confined states ladder at room temperature.

Distributed feedback GaSb based laser diodes with buried grating: a new field of single-frequency sources from 2 to 3 µm for gas sensing applications.

We report GaInAsSb/GaSb multiple quantum well lasers with type-II band alignment operating at room temperature. Basic properties of GaInAsSb/GaSb system in presence of strains are presented. Room temperature lasing has been achieved at wavelengths up to 2.65 micrometer. For the first time, stimulated emission has been obtained from a type-III quantum well structure at room temperature at 1.98 micrometer and 2.32 micrometer for the structures with 6- and 12-angstrom-thick InAs quantum wells, respectively. Modification of the band structure near interfaces of the type-II quantum wells due to carrier injection is shown to be a decisive factor allowing to obtain low threshold lasing in quantum well structures with indirect radiative recombination.

Band Offsets and Photoluminescence Thermal Quenching in Mid-Infrared Emitting GaInAsSb Quantum Wells with Quinary AlGaInAsSb Barriers

We study a Quantum Hot Electron Transistor, an original transistor made of InAs/AlSb heterostructures with high speed intrinsic transport. It is a unipolar vertical transport device, based on the concept of hot electron transistor. Devices using different heterostructure designs have been grown, processed and characterized. Both resonant and parasitic transport of electrons is studied by mean of the static output characteristics of the transistors. We demonstrated that a key parameter is the design and thickness of the collector barrier. For 15nm-thin barriers, we obtained static current gain of 5 associated to a base transit time of 140 fs.

Mid-infrared GaSb-InAs-based multiple quantum well lasers

Modulation spectroscopy, in a form of photoreflectance (PR), has been used to study the electronic structure properties of Ga0.55In0.45AsxSb1−x/Al0.30Ga0.70AsySb1−y quantum wells (QWs) designed for the 3 μm emission range at room temperature. A number of spectral features related to QW transitions have been revealed. With the support of energy level calculations they could be identified unambiguously for the unstrained (chemical) conduction band offset of 85%, almost independent of a small As/Sb content change in both the well and the barrier. This has been recalculated into the band discontinuities of the realistic (strained) structure, which have been found to be in a good agreement with the values obtained based on the first principles method.

Experimental study of transport in InAs Quantum Hot Electron Transistor

An innovative hot electron transistor based on InAs/AlSb heterostructures is proposed and studied. First fabricated devices demonstrated static current gain of 5 at room temperature. The potential of this device for high frequency operation is also discussed.

Optical transitions and band gap discontinuities of GaInAsSb/AlGaAsSb quantum wells emitting in the 3 μm range determined by modulation spectroscopy

There has been investigated the effect of post-growth-annealing-induced interdiffusion process, and hence interface intermixing, on the electronic structure of Ga0.35In0.65As0.32Sb0.68/Al0.25Ga0.50In0.25As0.24Sb0.76 single quantum well designed to emit light in the range of about 3 µm. The band structure and optical transitions have been calculated based on the single band effective mass model and Ficks interdiffusion law. The calculation results are consistent with the experimentally observed transitions obtained by employing modulation spectroscopy. Our studies indicate that the intermixing processes in this kind of quantum wells are predominantly induced by the interdiffusion of group III atoms. The derived effective diffusion coefficient has been estimated to be of the order of 10-21 m2 s-1 for 480 °C annealing temperature.

Conception and fabrication of InAs-based hot electron transistor

We have made quantum wells laser diodes by Molecular Beam Epitaxy with emission wavelengths from 2.3 &mgr;m to 3.1 &mgr;m. With growing wavelength, threshold current densities increase almost exponentially. We obtained threshold values as low as 65 A/cm2 at 2.3 &mgr;m and 156 A/cm2 at 2.62 &mgr;m. At the same time, the valence-band offset decrease from 132 meV (at 2.3 &mgr;m) to 78 meV (at 2.6 &mgr;m). A threshold current density study shows that Auger effect is not the only responsible for the augmentation of Jth. The reduction of internal efficiency ηi has a greater impact on the increase of Jth. The diminution of the holes confinement is incriminated for the degradation of ηi with growing wavelength. Therefore, to improve Jth at higher wavelengths another kind of barrier has to be utilized (for example, thanks to the use of the quinary material AlGaInAsSb).

Effect of Annealing-Induced Interdiffusion on the Electronic Structure of Mid Infrared Emitting GaInAsSb/AlGaInAsSb Quantum Wells

Technological platforms offering efficient integration of III-V semiconductor lasers with silicon electronics are eagerly awaited by industry. The availability of optoelectronic circuits combining III-V light sources with Si-based photonic and electronic components in a single chip will enable, in particular, the development of ultra-compact spectroscopic systems for mass scale applications. The first circuits of such type were fabricated using heterogeneous integration of semiconductor lasers by bonding the III-V chips onto silicon substrates. Direct epitaxial growth of interband III-V laser diodes on silicon substrates has also been reported, whereas intersubband emitters grown on Si have not yet been demonstrated. We report the first quantum cascade lasers (QCLs) directly grown on a silicon substrate. These InAs/AlSb QCLs grown on Si exhibit high performances, comparable with those of the devices fabricated on their native InAs substrate. The lasers emit near 11 µm, the longest emission wavelength of any laser integrated on Si. Given the wavelength range reachable with InAs/AlSb QCLs, these results open the way to the development of a wide variety of integrated sensors.