Jean Baptiste Rodriguez

We present a terahertz intensity modulator optically controlled at 1550 nm and integrated within a standard hollow-core rectangular waveguide operating in the 0.75-1.1 THz frequency range (WR1.0 standard). The relevant figures of merit for the component are presented; including insertion losses below 5 dB, average modulation depth of 70%, and a modulation bandwidth of 15 MHz. An analytical model relating the photogenerated carrier lifetime to the modulator bandwidth is presented.

The quantum spin Hall effect (QSHE), a hallmark of topological insulators, enables dissipationless, spin-polarized edge transport and has been predicted in various two-dimensional materials. However, challenges such as limited scalability, low-temperature operation, and the lack of robust electronic transport have hindered practical implementations. Here, we demonstrate the QSHE in an InAs/GaInSb/InAs trilayer quantum well structure operating at elevated temperatures. This platform meets key criteria for device integration, including scalability, reproducibility, and tunability via electric field. When the Fermi level is positioned within the energy gap, we observe quantized resistance values independent of device length and in both local and nonlocal measurement configurations, confirming the QSHE. Helical edge transport remains stable up to T = 60 kelvin, with further potential for higher-temperature operation. Our findings establish the InAs/GaInSb system as a promising candidate for integration into next-generation devices harnessing topological functionalities, advancing the development of topological electronics.

We successfully fabricated interband cascade lasers (ICLs) emitting at 4.7 µm on GaSb, GaAs, and Si substrates, demonstrating threshold current densities between 212 and 288 A/cm ² in pulsed operation at room temperature. While ICLs on mismatched substrates exhibited higher series resistance, they showed lower thermal resistance, suggesting that reducing series resistance could improve device performance. All lasers operated in continuous-wave mode up to 30°C, and aging tests on ICLs grown on Si over 500 hours showed no performance degradation. These results confirm the tolerance of ICLs to dislocations, even at longer wavelengths.

We study the molecular beam epitaxy of GaSb layers on Ge-based templates grown on Si substrates by low-energy plasma-enhanced chemical vapor deposition. First, we study the growth mechanism to obtain a GaSb surface free of emerging antiphase boundaries on Ge substrates, and then we transfer this mechanism to Ge-based templates. Our investigations reveal that this mechanism is hindered by the crosshatch pattern formed during the Ge-based template growth. We demonstrate that using low-miscut (1°) Si substrates or chemical-mechanical polishing mitigates the effects of the crosshatch pattern, enabling the growth of GaSb layers free of emerging antiphase boundaries. These results represent a further step towards the monolithic integration of III-V on mid-infrared photonic platforms.

The monolithic integration of III-Sb materials on Si substrates enables the development of novel functionalities and promising device applications. However, due to the large lattice mismatch to Si, direct heteroepitaxy of III-Sb results in a very large and disadvantageous dislocation density. Here, we report on the effect of strained AlSb interlayers in GaSb as dislocation filters for the epitaxy on Si(001) substrates. The epitaxial stress introduced by the lattice mismatched AlSb layer leads to threading dislocation bending at the interfaces as a strain relieving mechanism, thereby facilitating the reaction and annihilation of dislocations during their lateral glide process. Using comprehensive electron channeling contrast imaging and scanning transmission electron microscopy, we measure the dislocation density at the surface and after filter and cap layers of different thicknesses and analyze the effect of plastic strain relaxation on dislocation reduction. The reduction mechanism is discussed in the context of misfit dislocation networks forming at the respective compressively and tensile strained interfaces. With the new findings, an effective double filter layer structure with adopted layer thicknesses could be realized, which has resulted in a very low threading dislocation density of 1.7×107cm−2.

A single mode distributed feedback (DFB) interband cascade laser (ICL) grown on a (001) Si substrate has been developed. The designed DFB ICL with a grating on top of the ridge emits at a wavelength near 3.4 μm, suited for methane gas sensing, and operates in continuous wave up to 35 °C, with a maximum output power of 4 mW/facet at 15 °C and a side mode suppression ratio of 20 dB in the whole operating range. Methane detection has been demonstrated by integrating the DFB ICL on Si with a quartz-enhanced photoacoustic spectroscopy setup, a step forward in the development of integrated photonic gas sensors on silicon platforms.

The monolithic integration of III‐V semiconductors on Si emerges as a promising approach for realizing photonic integrated circuits. However, the performance and reliability of epitaxially grown devices on Si are hampered by the threading dislocation density (TDD) generated during the growth. In this study, the efficiency of a structure, combining III‐Sb‐based insertion layers and thermal annealing is evaluated, on the reduction of the emerging TDD in GaSb buffer layers grown on Si(001) substrates by molecular beam epitaxy. the impact of the thickness, composition, and number of the insertion layers is extensively explored. Then a detailed study of the annealing cycles with different conditions is conducted. A record TDD in the low 10⁷ cm⁻² for a 2.25 µm GaSb buffer grown on Si(001) is ultimately demonstrated.

We propose a strategy to monolithically integrate active III-V lasers and passive dielectric devices, where the passive waveguides are fabricated after the MBE growth of the III-V semiconductors on a planar Si substrate. This avoids any airgap at the active/passive interface, replaced by a thin dielectric interface layer which improves the light coupling efficiency. We demonstrate GaSb DLs butt-coupled to SiN waveguides with ∼23% transmission after 2 mm SiN, corresponding to ∼35% transmission at the active/passive interface. We propose several routes to further increase the transmission factor. This strategy eliminates the need for trenches or pockets, which have been shown to cause poor quality material near the dielectric stack facet and to affect the laser lifetime. This strategy thus paves the way for an optimized route to monolithically integrate active and passive photonic devices with a high light coupling efficiency.

Interband cascade lasers typically have significantly lower threshold current and power consumption than quantum cascade lasers. They can also have advantages regarding costs and compactness with the photonic integration onto silicon substrates by epitaxial growth. This research introduces a novel examination of the relative intensity noise and the modulation dynamics of a silicon-based Fabry–Perot interband cascade laser emitting at 3.5 μm. The investigation delves into crucial parameters, such as relaxation oscillation frequency, differential gain, gain compression, and K-factor. The resonance patterns identified in relative intensity noise curves can provide essential insights for the thorough characterization of high-defect mid-infrared semiconductor structures intended for high-speed applications. Moreover, this study demonstrates the feasibility of reaching 10 Gbit/s free-space transmission using a silicon-based interband cascade laser in conjunction with an interband cascade infrared photodetector.