Alban Gassenq

GeSn/Ge heterostructure short-wave infrared photodetectors on silicon

A surface-illuminated photoconductive detector based on Ge0.91Sn0.09 quantum wells with Ge barriers grown on a silicon substrate is demonstrated. Photodetection up to 2.2µm is achieved with a responsivity of 0.1 A/W for 5V bias. The spectral absorption characteristics are analyzed as a function of the GeSn/Ge heterostructure parameters. This work demonstrates that GeSn/Ge heterostructures can be used to developed SOI waveguide integrated photodetectors for short-wave infrared applications.

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.

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.

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.

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.

Heterogeneous Integration of GaInAsSb p-i-n Photodiodes on a Silicon-on-Insulator Waveguide Circuit

We report the integration of GalnAsSb p-i-n photo diodes on a silicon-on-insulator waveguide circuit. The device operates with low dark current (1.13 μA at -0.1 V) at room temperature. A high responsivity of 0.44 A/W is measured at 2.29 μm. This yields 1.63 × 10⁹ cmHz^1/2/W of Johnson-noise-limited-detectivity.

Air-stable short-wave infrared PbS colloidal quantum dot photoconductors passivated with Al2O3 atomic layer deposition

A PbS colloidal quantum dot photoconductor with Al2O3 atomic layer deposition (ALD) passivation for air-stable operation is presented. Two different types of inorganic ligands for the quantum dots, S2− and OH−, are investigated. PbS/S2− photoconductors with a cut-off wavelength up to 2.4 μm are obtained, and a responsivity up to 50 A/W at 1550 nm is reported. The corresponding specific detectivity is ∼3.4 × 108 Jones at 230 K. The 3-dB bandwidth of the PbS/S2− and PbS/OH− photodetectors is 40 Hz and 11 Hz, respectively.

Structural and optical properties of 200 mm germanium-on-insulator (GeOI) substrates for silicon photonics applications

Integrated laser sources compatible with microelectronics represent currently one of the main challenges for silicon photonics. Using the Smart CutTM technology, we have fabricated for the first time 200 mm optical Germanium-On-Insulator (GeOI) substrates which consist of a thick layer of germanium (typically greater than 500 nm) on top of a thick buried oxide layer (around 1 µm). From this, we fabricated suspended microbridges with efficient Bragg mirror cavities. The high crystalline quality of the Ge layer should help to avoid mechanical failure when fabricating suspended membranes with amounts of tensile strain high enough to transform Ge into a direct bandgap material. Optical GeOI process feasibility has successfully been demonstrated, opening the way to waferscale fabrication of new light emitting devices based on highly-tensely strained (thanks to suspended membranes) and/or doped germanium.

Lattice strain and tilt mapping in stressed Ge microstructures using X-ray Laue micro-diffraction and rainbow filtering

Micro-Laue diffraction and simultaneous rainbow-filtered micro-diffraction were used to measure accurately the full strain tensor and the lattice orientation distribution at the sub-micron scale in highly strained, suspended Ge micro-devices. A numerical approach to obtain the full strain tensor from the deviatoric strain measurement alone is also demonstrated and used for faster full strain mapping. We performed the measurements in a series of micro-devices under either uniaxial or biaxial stress and found an excellent agreement with numerical simulations. This shows the superior potential of Laue micro-diffraction for the investigation of highly strained micro-devices.

Fabrication and Characterization of GaSb-Based Monolithic Resonant-Cavity Light-Emitting Diodes Emitting Around 2.3 μm and Including a Tunnel Junction

In this paper, the process of fabrication of GaSb-based electrically injected resonant-cavity LEDs near 2.3 mum is detailed. The electrical and optical properties of these diodes operating in continuous wave at room temperature are also presented. The different tested monolithic structures have similar designs with two doped AlAsSb/GaSb Bragg mirrors and an active region with eight GaInAsSb quantum wells. Performances of devices containing or not an n++-InAsSb/p++-GaSb tunnel junction (TJ) can be compared. The large improvements of electrical resistance as well as output power, observed when a TJ is included, demonstrate all the advantages to use such a technology for the realization of electrically injected vertical cavity structures emitting in the mid-IR on GaSb substrate.