[Show abstract][Hide abstract] ABSTRACT: Germanium has become a promising material for creating CMOS-compatible optoelectronic devices, such as modulators and detectors employing the Franz-Keldysh effect (FKE) or the quantum-confined Stark effect (QCSE), which meet strict energy and density requirements for future interconnects. To improve Ge-based modulator design, it is important to understand the contributions to the insertion loss (IL). With indirect absorption being the primary component of IL, we have experimentally determined the strength of this loss and compared it with theoretical models. For the first time, we have used the more sensitive photocurrent measurements for determining the effective absorption coefficient in our Ge/SiGe quantum well material employing QCSE. This measurement technique enables measurement of the absorption coefficient over four orders of magnitude. We find good agreement between our thin Ge quantum wells and the bulk material parameters and theoretical models. Similar to bulk Ge, we find that the 27.7 meV LA phonon is dominant in these quantum confined structures and that the electroabsorption profile can be predicted using the model presented by Frova, Phys. Rev., 145 (1966).
[Show abstract][Hide abstract] ABSTRACT: We present a simple electroabsorption model for germanium quantum wells to facilitate optical modulator design. We show this model is valid for a range of well sizes with an increased exciton-enhanced absorption for thinner wells.
Numerical Simulation of Optoelectronic Devices (NUSOD), 2010 10th International Conference on; 10/2010
[Show abstract][Hide abstract] ABSTRACT: The scattering time of electrons from the direct Γ to the indirect L valley in the conduction band of germanium/silicon-germanium quantum wells is measured to be ~250 fs. Carrier field screening is also observed and modeled.
[Show abstract][Hide abstract] ABSTRACT: We discuss the physics and device structures of optical modulators using germanium quantum wells grown on silicon substrates. These exploit the recently discovered strong electroabsorption mechanism in such wells, and promise high performance optical modulators on silicon.
[Show abstract][Hide abstract] ABSTRACT: Germanium (Ge) and silicon-germanium (Si-Ge) have the potential to integrate optics with Si IC technology. The quantum-confined Stark effect, a strong electroabsorption mechanism often observed in III-V quantum wells (QWs), has been demonstrated in Si-Ge/Ge QWs, allowing optoelectronic modulators in such group IV materials. Here, based on photocurrent electroabsorption experiments on different samples and fitting of the resulting allowed and nominally forbidden transitions, we propose more accurate values for key parameters such as effective masses and band offsets that are required for device design. Tunneling resonance modeling including conduction band nonparabolicity was used to fit the results with good consistency between the experiments and the fitted transitions.
IEEE Journal of Selected Topics in Quantum Electronics 08/2008; 14(4-14):1082 - 1089. DOI:10.1109/JSTQE.2008.918935 · 2.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An electroabsorption modulator using a side-entry architecture achieved a contrast ratio exceeding 3 dB over a 3.5 nm range in the C-band, using a voltage swing of 1 V and operating at 100degC. Modulation was due to the quantum-confined Stark effect from ten Ge/SiGe quantum wells epitaxially grown on silicon-on-insulator (SOI) wafers. The device exploits an asymmetric Fabry-Perot resonator formed between the totally internally reflecting air-SiGe interface and a frustrated total internal reflection from the buried oxide layer of the SOI substrate.
[Show abstract][Hide abstract] ABSTRACT: The quantum-confined Stark effect demonstrated in Si-Ge/Ge quantum wells promises integration of optics with silicon ICs. Using photocurrent, tunneling resonance and nonparabolicity, we propose more accurate values of key parameters for device design.
Lasers and Electro-Optics, 2008 and 2008 Conference on Quantum Electronics and Laser Science. CLEO/QELS 2008. Conference on; 01/2008
[Show abstract][Hide abstract] ABSTRACT: We demonstrate an optical link on silicon employing Ge/SiGe quantum well waveguide modulators and photodetectors. Modulators show >3 dB contrast ratio for <6 V drive for a 22 nm wavelength range. Photodetectors show external responsivity up to 0.26 A/W and high-speed detection at 2.5 Gb/s.
Lasers and Electro-Optics Society, 2007. LEOS 2007. The 20th Annual Meeting of the IEEE; 11/2007
[Show abstract][Hide abstract] ABSTRACT: The recent discovery of the quantum confined Stark effect in Ge/SiGe quantum wells with absorption coefficient modulation comparable to III-V materials will permit compact, low-power photonics components densely integrated with silicon electronics.
Group IV Photonics, 2007 4th IEEE International Conference on; 10/2007
[Show abstract][Hide abstract] ABSTRACT: A low-voltage 90 nm CMOS optical interconnect transceiver operating at 1550 nm is presented. This is the first system demonstrated using the recent quasi-waveguide angled facet electroabsorption modulator (QWAFEM), featuring simple electronic and optical packaging.
Optical Fiber Communication and the National Fiber Optic Engineers Conference, 2007. OFC/NFOEC 2007. Conference on; 04/2007
[Show abstract][Hide abstract] ABSTRACT: We present observations of quantum confinement and quantum-confined Stark effect (QCSE) electroabsorption in Ge quantum wells with SiGe barriers grown on Si substrates, in good agreement with theoretical calculations. Though Ge is an indirect gap semiconductor, the resulting effects are at least as clear and strong as seen in typical III-V quantum well structures at similar wavelengths. We also demonstrate that the effect can be seen over the C-band around 1.55-mum wavelength in structures heated to 90degC, similar to the operating temperature of silicon electronic chips. The physics of the effects are discussed, including the effects of strain, electron and hole confinement, and exciton binding, and the reasons why the effects should be observable at all in such an indirect gap material. This effect is very promising for practical high-speed, low-power optical modulators fabricated compatible with mainstream silicon electronic integrated circuits
IEEE Journal of Selected Topics in Quantum Electronics 12/2006; 11(6-12):1503 - 1513. DOI:10.1109/JSTQE.2006.883146 · 2.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a surface-normal modulator architecture for optical interconnects that offers misalignment tolerance as well as high contrast ratio over a wide wavelength range for a small drive voltage. A contrast ratio greater than 3 dB was achieved for only 0.8-V drive across a 16-nm wavelength range from 1498 to 1514 nm. The misalignment tolerance between this device, and the input optical beam was measured to be 30 μm.
IEEE Journal of Selected Topics in Quantum Electronics 04/2005; 11(2-11):338 - 342. DOI:10.1109/JSTQE.2005.845613 · 2.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a quasi-waveguide angled facet electroabsorption modulator with a contrast ratio greater than 3 dB between 1496 nm and 1506 nm for 1 V drive as well as a misalignment tolerance of 30 μm.
Lasers and Electro-Optics Society, 2004. LEOS 2004. The 17th Annual Meeting of the IEEE; 12/2004
[Show abstract][Hide abstract] ABSTRACT: We introduce an electroabsorption modulator architecture that combines desirable properties of conventional waveguide designs (e.g. low-voltage operation and optical bandwidth) and surface-normal designs (e.g. misalignment tolerance). Results for an InP/InGaAsP implementation are presented.
Lasers and Electro-Optics, 2004. (CLEO). Conference on; 06/2004