Mohamed-Said Rouifed

23 GHz Ge/SiGe multiple quantum well electro-absorption modulator

We report on high speed operation of a Ge/SiGe multiple quantum well (MQW) electro-absorption modulator in a waveguide configuration. 23 GHz bandwidth is experimentally demonstrated from a 3 µm wide and 90 µm long Ge/SiGe MQW waveguide. The modulator exhibits a high extinction ratio of more than 10 dB over a wide spectral range. Moreover with a swing voltage of 1 V between 3 and 4 V, an extinction ratio as high as 9 dB can be obtained with a corresponding estimated energy consumption of 108 fJ per bit. This demonstrates the potentiality of Ge/SiGe MQWs as a building block of silicon compatible photonic integrated circuits for short distance energy efficient optical interconnections.

Recent progress in GeSi electro-absorption modulators

Abstract Electro-absorption from GeSi heterostructures is receiving growing attention as a high performance optical modulator for short distance optical interconnects. Ge incorporation with Si allows strong modulation mechanism using the Franz–Keldysh effect and the quantum-confined Stark effect from bulk and quantum well structures at telecommunication wavelengths. In this review, we discuss the current state of knowledge and the on-going challenges concerning the development of high performance GeSi electro-absorption modulators. We also provide feasible future prospects concerning this research topic.

Advances Toward Ge/SiGe Quantum-Well Waveguide Modulators at 1.3μm

The paper reports on the developments of Ge/SiGe quantum well (QW) waveguide modulators operating at 1.3 μm. Two modulator configurations have been studied: The first one is based on QW structures grown on a 13-μm SiGe buffer on bulk silicon. Light was directly coupled and propagated in Ge/Si_0.35Ge_0.65 QWs. Using a 3-μm-wide and 50-μm-long modulator, an extinction ratio (ER) up to 6 dB was obtained at 1.3 μm. In the second configuration, the aim is to integrate Ge/SiGe QW on standard silicon-on-insulator (SOI) waveguides. A reduction of buffer thickness is then required to allow the light coupling from Si waveguide to Ge/SiGe QW. To this purpose, first we demonstrated QCSE with a thin (360-nm-thick) Si_0.08Ge_0.92 buffer on silicon using the well-known Ge/Si_0.15Ge_0.85 QWs (operated at a wavelength of 1.4 μm). Based on these promising experimental results, we theoretically investigated properties of a Ge/Si_0.65Ge_0.35 QW modulator integrated on SOI waveguides. 7.7 dB ER were predicted with 4 dB optical insertion loss and an estimated energy consumption of 59 fJ/bit for a modulator length as short as 69 μm.

Towards low energy consumption integrated photonic circuits based on Ge/SiGe quantum wells

Abstract Despite being an indirect bandgap material, germanium (Ge) recently appeared as a material of choice for low power consumption optical link on silicon. Thanks to a low energy difference between direct and indirect energy bandgap, optical transitions around the direct gap can be used to achieve strong electroabsorption or photodetection in a material already used in microelectronics circuits. However, many challenges have to be addressed such as the growth of germanium-rich structures on silicon or the modeling of these structures around both direct and indirect bandgaps. This paper will explore recent achievements in Ge/SiGe quantum wells structures. Quantum confined Stark effect has been studied for different quantum well designs and light polarization. Both absorption and phase variations have been characterized and will be reported. Carrier recombination processes is also an intense research topic, in order to evaluate the competition between direct and indirect band gap emission as a function of temperature. Main results and conclusion will be introduced. Finally, high performance photonic devices (modulator and photodetector) that have already been demonstrated will be presented. At the end the challenges faced by Ge/SiGe QW as a new photonic platform will be presented.

Electroabsorption based on quantum-confined Stark effect from Ge/SiGe multiple quantum wells

High speed Ge multiple quantum well (MQWs) electro-absorption (EA) modulator is reported. Device development procedures from the epitaxial growth of high quality Ge MQWs by LEPECVD technique, fabrication, and characterization of optoelectronic device are described.

Ge quantum-well waveguide modulator at 1.3μm

We report on the developments of Ge/SiGe quantum well (QW) waveguide modulators operating at 1.3 μm. First we studied QW structures grown on a 13-μm SiGe buffer on bulk silicon. Light was directly coupled and propagated in the active region. Using a 3-μm wide and 50-μm long modulator, an extinction ratio larger than 4 dB was obtained for a drive voltage lower than 5 V in a 15 nm wavelength range. Then simulations were performed to evaluate the performances of an integrated modulator on silicon on insulator (SOI) platform. An eigenmode expension method was used to model the vertical optical coupling between SOI waveguide and Ge/SiGe devices. It is shown that a reduction of the thickness of the buffer leads to a significant improvement in the performances (extinction ratio, insertion loss) and footprint of the waveguide-integrated devices.

Ge/SiGe quantum well optical modulator

We report different experimental results showing the large potential of Ge/SiGe quantum well structures as a promising solution forlow power consumption and large bandwidth optical modulators in silicon photonics technology. First, high speed operation of such a Ge/SiGe multiple quantum well (MQW) electro-absorption modulator is reported, with 23 GHz bandwidth demonstrated from a 3 μm wide and 90 μm long Ge/SiGe MQW waveguide. Then the flexibility to shift the absorption band edge from 1.42 to 1.3 μm is illustrated by strain engineering of the Ge wells. Finally electrorefraction by Quantum Confined Stark Effect (QCSE) is demonstrated, opening the route towards phase modulators based on Ge/SiGe MQWs.

Phase-shift in waveguide integrated Ge quantum wells

We report on the electro-refractive effect in Ge/SiGe multiple quantum wells grown by low energy plasma enhanced chemical vapor deposition (LEPECVD). The electro-refractive effect was experimentally characterized by the shift of Fabry-Perot fringes in the transmission spectra of a 64 μm long slab waveguide. A refractive index variation up to 1.3 × 10-3 was measured with an applied electric field of 88 kV/cm at 1475 nm, 50 meV below the excitonic resonance, with a VπLπ figure of merit of 0.46 V×cm. The device performances are promising for the realization of Mach Zehnder modulators in the Ge-Si material platform.

Ge/SiGe Quantum Well Optical Modulators

Ge/SiGe quantum wells structures appear as a promising solution for compact low power consumption optical modulators. The presentation will give an overview of recent results including high speed absorption and phase modulation. Article not available.

Room temperature direct-gap electroluminescence in Ge/SiGe quantum well waveguides

Room temperature direct gap electroluminescence (EL) from a Ge/Si0.15Ge0.85 MQW waveguide was experimentally studied. The dependence of the EL intensity on the injection current and temperature was measured. The direct gap EL from Ge/SiGe MQWs was shown to be transverse-electric (TE) polarized, confirming that the EL originates from recombination with a HH state.