Samson Edmond

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.

Quantum-confined Stark effect measurements in Ge/SiGe quantum-well structures.

We investigate the room-temperature quantum-confined Stark effect in Ge/SiGe multiple quantum wells (MQWs) grown by low-energy plasma-enhanced chemical vapor deposition. The active region is embedded in a p-i-n diode, and absorption spectra at different reverse bias voltages are obtained from optical transmission, photocurrent, and differential transmission measurements. The measurements provide accurate values of the fraction of light absorbed per well of the Ge/SiGe MQWs. Both Stark shift and reduction of exciton absorption peak are observed. Differential transmission indicates that there is no thermal contribution to these effects.

Room temperature direct gap electroluminescence from Ge/Si0.15Ge0.85 multiple quantum well waveguide

We report room temperature direct gap electroluminescence (EL) from a Ge/Si0.15Ge0.85 multiple quantum well (MQW) waveguide. The excitonic direct gap transition and the dependence of the EL intensity on the injection currents and temperature are clearly observed. EL from the Ge/SiGe MQWs is shown to have a transverse-electric polarization. These results demonstrate the strong potential of the Ge/Si0.15Ge0.85 MQWs in terms of the realization of a monolithically integrated light source on the Si platform.

Ge/SiGe multiple quantum well photodiode with 30 GHz bandwidth

We demonstrate high speed Ge/SiGe multiple quantum wells photodiodes using a surface-illuminated vertical p-i-n structure. The device, with a mesa diameter of 12 μm, exhibits a low dark current of 231 nA at −1 V bias. An optical bandwidth of 10 and 26 GHz is measured at −1 and −4 V reverse bias, respectively, and reaches over 30 GHz at a reverse bias of −7 V. These results prove the suitability of Ge/SiGe multiple quantum well structures for high performance optoelectronic devices required for optical interconnection applications.

Polarization dependence of quantum-confined Stark effect in Ge/SiGe quantum well planar waveguides

We report room-temperature quantum-confined Stark effect in Ge/SiGe multiple quantum wells (MQWs) with light propagating parallel to the plane of the Ge/SiGe MQWs for applications in integrated photonics. Planar waveguides embedded in a p-i-n diode are fabricated in order to investigate the absorption spectra at different reverse bias voltages from optical transmission measurements for both TE and TM polarizations. Polarization dependence of the absorption spectra of the Ge/SiGe MQWs is clearly observed. The planar waveguides exhibit a high extinction ratio and low insertion loss over a wide spectral range for TE polarization.

Quantum-confined Stark effect at 1.3 μm in Ge/Si 0.35 Ge 0.65 quantum-well structure

Room-temperature quantum-confined Stark effect in a Ge/SiGe quantum-well structure is reported at the wavelength of 1.3 μm. The operating wavelength is tuned by the use of strain engineering. Low-energy plasma-enhanced chemical vapor deposition is used to grow 20 periods of strain-compensated quantum wells (8 nm Ge well and 12 nm Si(0.35)Ge(0.65) barrier) on Si(0.21)Ge(0.79) virtual substrate. The fraction of light absorbed per well allows for a strong modulation around 1.3 μm. The half-width at half-maximum of the excitonic peak of only 12 meV allows for a discussion on physical mechanisms limiting the performances of such devices.

10-Gb/s Ge/SiGe Multiple Quantum-Well Waveguide Photodetector

The authors report on high speed operation of a Ge/SiGe multiple quantum-well waveguide photodetector. At -3 V, 10 Gb/s operation is demonstrated at wavelengths of 1405 and 1420 nm with a responsivity as high as 0.8 A/W. The device, 3 μm wide and 80 μm long, exhibits a dark current of 474 nA at a reverse bias of -1 V. These results pave the way for the use of Ge/SiGe multiple quantum-well structures as efficient active waveguide devices in silicon compatible integrated circuits.

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.

Strong quantum-confined Stark effect from light hole related direct-gap transitions in Ge quantum wells

A strong quantum-confined Stark effect (QCSE) from light hole related transitions at the Γ point (LH1-cΓ1) in Ge/Si0.15 Ge 0.85 multiple quantum wells is demonstrated from both photocurrent and optical transmission measurements. Our experimental results show a large and sharp optical absorption peak due to LH1-cΓ1 transitions, and its associated strong absorption change based on the QCSE. By exploiting LH1-cΓ1 transitions, optical modulators with improved compactness and competitive extinction ratio and optical loss can be envisioned for low energy chip-scale optical interconnect applications.