Interband cascade lasers grown simultaneously on GaSb, GaAs and Si substrates.

We report on Sb-based interband cascade lasers simultaneously grown on GaSb, GaAs and Si substrates. 8 µm x 2 mm devices exhibited similar threshold currents around 40 mA at 20°C and achieved continuous-wave (CW) operation up to 65°C on GaSb, GaAs and Si substrates despite a dislocation density of ∼ 4.108 cm-2 for both mismatched substrates. In the CW regime the output power of the devices emitting at 3.3 µm exceeded 30 mW/facet at 20°C. ICLs on GaAs and Si were subsequently aged at 50°C with an injection current of 200 mA, i.e. five times the laser-threshold current. No degradation was observed after 500 h of CW operation, demonstrating the high performance of ICLs and their tolerance to dislocations.

Near-Field Thermophotovoltaic Conversion with High Electrical Power Density and Cell Efficiency above 14.

A huge amount of thermal energy is available close to material surfaces in radiative and nonradiative states, which can be useful for matter characterization or energy harvesting. Even though a full class of novel nanoengineered devices has been predicted over the last two decades for exploiting near-field thermal photons, efficient near-field thermophotovoltaic conversion could not be achieved experimentally until now. Here, we realize a proof of principle by using a micrometer-sized indium antimonide photovoltaic cell cooled at 77 K and approached at nanometer distances from a hot (∼730 K) graphite microsphere emitter. We demonstrate a near-field power conversion efficiency of the cell above 14% and unprecedented electrical power density outputs (0.75 W cm-2), which are orders of magnitude larger than all previous attempts. These results highlight that near-field thermophotovoltaic converters are now competing with other thermal-to-electrical conversion devices and also pave the way for efficient photoelectric detection of near-field thermal photons.

GaSb-based laser diodes grown on MOCVD GaAs-on-Si templates.

We report GaSb-based laser diodes (LDs) grown on on-axis (001) Si substrates and emitting at 2.3 µm. Two series of LDs were studied and compared. For the first series, a GaAs-based buffer layer was first grown by metal organic chemical vapor deposition (MOCVD) before growing the laser heterostructure by molecular-beam epitaxy (MBE). For the second series, a MOCVD GaSb buffer layer was added between the MOCVD GaAs buffer layer and the MBE laser heterostructure. Both series of LDs exhibited threshold currents in the 50-100 mA range and several mW output power at room temperature. They demonstrated continuous wave operation (CW) up to 70°C (set-up limited) without thermal rollover. Broad area LDs exhibited record threshold-current densities in the 250-350 A.cm-2 range for the second series of LDs, in spite of cracks that appeared during device processing. These results show that the design and fabrication steps of the buffer-layer stacks are critical issues in the epitaxial integration of GaSb-based optoelectronic devices on Si substrates and offer room for much performance improvement.

Etched-cavity GaSb laser diodes on a MOVPE GaSb-on-Si template.

We report on 2.3-µm etched-cavity GaSb-based laser diodes (LDs) epitaxially integrated on on-axis (001)Si and benchmarked against their cleaved facet counterparts. The LDs were grown in two steps. First, a GaSb-on-Si template was grown by metal-organic vapor phase epitaxy (MOVPE) before the growth of the LD heterostructure by molecular-beam epitaxy. Different etched-facet geometries operate in continuous wave well above room temperature, and their performance are similar to those of cleaved-cavity LDs. These results show that etching mirrors is a viable route to form laser cavities in the GaSb technology and that MOVPE GaSb-on-Si templates are a suitable platform for optoelectronic devices overgrowth.

Micron-sized liquid nitrogen-cooled indium antimonide photovoltaic cell for near-field thermophotovoltaics.

Simulations of near-field thermophotovoltaic devices predict promising performance, but experimental observations remain challenging. Having the lowest bandgap among III-V semiconductors, indium antimonide (InSb) is an attractive choice for the photovoltaic cell, provided it is cooled to a low temperature, typically around 77 K. Here, by taking into account fabrication and operating constraints, radiation transfer and low-injection charge transport simulations are made to find the optimum architecture for the photovoltaic cell. Appropriate optical and electrical properties of indium antimonide are used. In particular, impact of the Moss-Burstein effects on the interband absorption coefficient of n-type degenerate layers, and of parasitic sub-bandgap absorption by the free carriers and phonons are accounted for. Micron-sized cells are required to minimize the huge issue of the lateral series resistance losses. The proposed methodology is presumably relevant for making realistic designs of near-field thermophotovoltaic devices based on low-bandgap III-V semiconductors.

Fano-like resonances sustained by Si doped InAsSb plasmonic resonators integrated in GaSb matrix.

By using metal-free plasmonics, we report on the excitation of Fano-like resonances in the mid-infrared where the Fano asymmetric parameter, q, varies when the dielectric environment of the plasmonic resonator changes. We use silicon doped InAsSb alloy deposited by molecular beam epitaxy on GaSb substrate to realize the plasmonic resonators exclusively based on semiconductors. We first demonstrate the possibility to realize high quality samples of embedded InAsSb plasmonic resonators into GaSb host using regrowth technique. The high crystalline quality of the deposited structure is confirmed by scanning transmission electron microscopy (STEM) observation. Second, we report Fano-like resonances associated to localized surface plasmons in both cases: uncovered and covered plasmonic resonators, demonstrating a strong line shape modification. The optical properties of the embedded structures correspond to those modeled by finite-difference time-domain (FDTD) method and by a model based on Fano-like line shape. Our results show that all-semiconductor plasmonics gives the opportunity to build new plasmonic structures with embedded resonators of highly doped semiconductor in a matrix of un-doped semiconductor for mid-IR applications.

Brewster "mode" in highly doped semiconductor layers: an all-optical technique to monitor doping concentration.

We investigate highly-doped InAsSb layers lattice matched onto GaSb substrates by angular-dependent reflectance. A resonant dip is evidenced near the plasma frequency of thin layers. Based on Fresnel coefficient in the case of transverse electromagnetic wave, we interpret this resonance as due to the excitation of a leaky electromagnetic mode, the Brewster "mode", propagating in the metallic layer deposited on a dielectric material. Potential interest of this mode for in situ monitoring during device fabrication is also discussed.

Unlocking the monolithic integration scenario: optical coupling between GaSb diode lasers epitaxially grown on patterned Si substrates and passive SiN waveguides.

Silicon (Si) photonics has recently emerged as a key enabling technology in many application fields thanks to the mature Si process technology, the large silicon wafer size, and promising Si optical properties. The monolithic integration by direct epitaxy of III-V lasers and Si photonic devices on the same Si substrate has been considered for decades as the main obstacle to the realization of dense photonics chips. Despite considerable progress in the last decade, only discrete III-V lasers grown on bare Si wafers have been reported, whatever the wavelength and laser technology. Here we demonstrate the first semiconductor laser grown on a patterned Si photonics platform with light coupled into a waveguide. A mid-IR GaSb-based diode laser was directly grown on a pre-patterned Si photonics wafer equipped with SiN waveguides clad by SiO2. Growth and device fabrication challenges, arising from the template architecture, were overcome to demonstrate more than 10 mW outpower of emitted light in continuous wave operation at room temperature. In addition, around 10% of the light was coupled into the SiN waveguides, in good agreement with theoretical calculations for this butt-coupling configuration. This work lift an important building block and it paves the way for future low-cost, large-scale, fully integrated photonic chips.

Single-mode monolithic GaSb Vertical-Cavity Surface-Emitting Laser.

We report on the fabrication and performances of an electrically-pumped GaSb monolithic VCSEL, i.e. ,a VCSEL with two epitaxial Bragg mirrors. Selective lateral etching of a tunnel junction is used to provide current and optical confinement. Laser devices with a 6 µm tunnel-junction effective diameter operate at 2.3 µm in CW up to 70 °C, with a threshold current as low as 1.9 mA at 30 °C. The laser emission is single mode with a SMSR near 25 dB and mode-hop-free electro-thermal tunability around 14 nm. This is the first demonstration of a single-mode electrically-pumped monolithic GaSb-based VCSEL.

Study of evanescently-coupled and grating-assisted GaInAsSb photodiodes integrated on a silicon photonic chip.

In this paper we present GaInAsSb photodiodes heterogeneously integrated on SOI by BCB adhesive bonding for operation in the short-wave infrared wavelength region. Photodiodes using evanescent coupling between the silicon waveguide and the III-V structure are presented, showing a room temperature responsivity of 1.4A/W at 2.3 µm. Photodiode structures using a diffraction grating to couple from the silicon waveguide layer to the integrated photodiode are reported, showing a responsivity of 0.4A/W at 2.2 µm.

Mid-infrared III-V semiconductor lasers epitaxially grown on Si substrates.

There is currently much activity toward the integration of mid-infrared semiconductor lasers on Si substrates for developing a variety of smart, compact, sensors based on Si-photonics integrated circuits. We review this rapidly-evolving research field, focusing on the epitaxial integration of antimonide lasers, the only technology covering the whole mid-to-far-infrared spectral range. We explain how a dedicated molecular-beam epitaxy strategy allows for achieving high-performance GaSb-based diode lasers, InAs/AlSb quantum cascade lasers, and InAs/GaInSb interband cascade lasers by direct growth on on-axis (001)Si substrates, whereas GaAs-on-Si or GaSb-on-Si layers grown by metal-organic vapor phase epitaxy in large capability epitaxy tools are suitable templates for antimonide laser overgrowth. We also show that etching the facets of antimonide lasers grown on Si is a viable approach in view of photonic integrated circuits. Remarkably, this review shows that while diode lasers are sensitive to residual crystal defects, the quantum cascade and interband cascade lasers grown on Si exhibit performances comparable to those of similar devices grown on their native substrates, due to their particular band structures and radiative recombination channels. Long device lifetimes have been extrapolated for interband cascade lasers. Finally, routes to be further explored are also presented.

Quantum cascade lasers grown on silicon.

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.

Note: a high transmission Faraday optical isolator in the 9.2 µm range.

We have fabricated and characterized an n-doped InSb Faraday isolator in the mid-IR range (9.2 µm). A high isolation ratio (31(2) dB) and low insertion loss (1.9(3) dB) are obtained. Temperature dependance is analyzed. Further possible improvements are discussed, including the realization of a two-stage isolator. A similar design can be used to cover a wide wavelength range (λ ~ 7.5-30 µm).