S. Sauvage

Enhancement of second-harmonic generation in a one-dimensional semiconductor photonic band gap

We demonstrate significant enhancement of second-order nonlinear interactions in a one-dimensional semiconductor Bragg mirror operating as a photonic band gap structure. The enhancement comes from a simultaneous availability of a high density of states, thanks to high field localization, and the improvement of effective coherent length near the photonic band edge.

Long-wavelength (≈15.5 μm) unipolar semiconductor laser in GaAs quantum wells

A unipolar semiconductor laser emitting in the mid-infrared spectral region is demonstrated. The laser scheme relies on a simple three-level system in GaAs/AlGaAs asymmetric coupled quantum wells. Population inversion between excited states is achieved by optical pumping of electrons from the ground state with a CO2 laser. Long-wavelength (≈15.5 μm) laser emission is demonstrated. The laser is operated in the pulsed regime up to a temperature of 110 K and with an output peak power ≈0.4 W at 77 K. Unipolar quantum well semiconductor lasers based on this principle are capable of covering the long wavelength mid-infrared spectral region above 12 μm.

Recent advances in germanium emission [Invited]

The optical properties of germanium can be tailored by combining strain engineering and n-type doping. In this paper, we review the recent progress that has been reported in the study of germanium light emitters for silicon photonics. We discuss the different approaches that were implemented for strain engineering and the issues associated with n-type doping. We show that compact germanium emitters can be obtained by processing germanium into tensile-strained microdisks.

Midinfrared photoconductivity of Ge/Si self-assembled quantum dots

We have investigated the midinfrared photoconductivity of Ge/Si self-assembled quantum dots. The self-assembled quantum dots were grown by ultra-high-vacuum chemical vapor deposition on Si(001). The photoresponse of the p-type device exhibits resonances in the midinfrared around 10 μm wavelength. The resonance of the photocurrent shifts to lower energy as the applied bias increases. The photocurrent is weakly dependent on the incoming polarization of the infrared light. The photocurrent is analyzed in terms of bound-to-bound and bound-to-continuum transitions in the valence band. The photocurrent peaks are correlated to the photoluminescence of the device.

Control of tensile strain in germanium waveguides through silicon nitride layers

Germanium ridge waveguides can be tensilely strained using silicon nitride thin films as stressors. We show that the strain transfer in germanium depends on the width of the waveguides. Carrier population in the zone center Γ valley can also be significantly increased when the ridges are oriented along the 〈100〉 direction. We demonstrate an uniaxial strain transfer up to 1% observed on the room temperature direct band gap photoluminescence of germanium. The results are supported by 30 band k·p modeling of the electronic structure and the finite element modeling of the strain field.

High quality tensile-strained n-doped germanium thin films grown on InGaAs buffer layers by metal-organic chemical vapor deposition

We show that high quality tensile-strained n-doped germanium films can be obtained on InGaAs buffer layers using metal-organic chemical vapor deposition with isobutyl germane as germanium precursor. A tensile strain up to 0.5% is achieved, simultaneously measured by x-ray diffraction and Raman spectroscopy. The effect of tensile strain on band gap energy is directly observed by room temperature direct band gap photoluminescence.

Saturation of intraband absorption and electron relaxation time in n-doped InAs/GaAs self-assembled quantum dots

We have observed the saturation of intraband absorption in InAs/GaAs self-assembled quantum dots. The investigated n-doped self-assembled quantum dots exhibit an intraband absorption within the conduction band, which is peaked at an 8 μm wavelength. The saturation of the intraband absorption is achieved with an infrared pump delivered by a pulsed free-electron laser. The saturation of the transition is observed for an intensity around ≈0.6 MW cm−2. The electron relaxation time under intraband excitation is measured by time-resolved pump–probe experiments. An electron relaxation time T1≈3 ps is reported.

Intersubband stimulated emission in GaAs/AlGaAs quantum wells: Pump-probe experiments using a two-color free-electron laser

Intersubband stimulated emission under optical pumping has been observed in the conduction band of GaAs–AlGaAs quantum wells. The asymmetric coupled quantum wells which exhibit three conduction bound levels are designed to exhibit population inversion under optical pumping. An optical excitation at λ=9.2 μm is used to bleach the absorption between the ground and second excited subband. The population inversion between excited subbands is pumped and probed on a picosecond time scale by a tunable two-color free-electron laser. The stimulated amplification is studied at low temperature in infrared waveguides as a function of the waveguide length and of the probe wavelength. A stimulated gain ≈80 cm−1 is measured at 12.5 μm in agreement with calculations.

Near-infrared gallium nitride two-dimensional photonic crystal platform on silicon

We demonstrate a two-dimensional free-standing gallium nitride photonic crystal platform operating around 1550 nm and fabricated on a silicon substrate. Width-modulated waveguide cavities are integrated and exhibit loaded quality factors up to 34 000 at 1575 nm. We show the resonance tunability by varying the ratio of air hole radius to periodicity, and cavity hole displacement. We deduce a ∼7.9 dB/cm linear absorption loss for the suspended nitride structure from the power dependence of the cavity in-plane transmission.

Ge/Si self-assembled quantum dots grown on Si(001) in an industrial high-pressure chemical vapor deposition reactor

We report on the structural and optical properties of Ge/Si self-assembled quantum dots epitaxially grown on Si(001). The Ge islands are grown in an industrial 200 mm single-wafer chemical vapor deposition reactor. The surface density of the Ge islands is as much as 2×1010 cm−2. The islands exhibit a maximum photoluminescence at 1.55 μm wavelength. The photoluminescence energy is correlated to the three-dimensional quantum confinement energy and to the size and geometry of the clusters, as observed by cross-section transmission electron microscopy.