Abstract
Monolithically integrated, active photonic devices on Si are key components in Si-based large-scale electronic-photonic integration for future generations of high-performance, low-power computation and communication systems. Ge has become an interesting candidate for active photonic devices in Si photonics due to its pseudo-direct gap behavior and compatibility with Si complementary metal oxide semiconductor (CMOS) processing. In this paper, we present a review of the recent progress in Ge-on-Si active photonics materials and devices for photon detection, modulation, and generation. We first discuss the band engineering of Ge using tensile strain, n-type doping, Sn alloying, and separate confinement of Γ vs. L electrons in quantum well (QW) structures to transform the material towards a direct band gap semiconductor for enhancing optoelectronic properties. We then give a brief overview of epitaxial Ge-on-Si materials growth, followed by a summary of recent investigations towards low-temperature, direct growth of high crystallinity Ge and GeSn alloys on dielectric layers for 3D photonic integration. Finally, we review the most recent studies on waveguide-integrated Ge-on-Si photodetectors (PDs), electroabsorption modulators (EAMs), and laser diodes (LDs), and suggest possible future research directions for large-scale monolithic electronic-photonic integrated circuits on a Si platform.
Highlights
In our information age, information and communication technology (ICT) already consumes ~5% of electricity worldwide in 2012 [1]
Based on photoreflectance and ellipsometry measurements of GeSn alloy thin films deposited on Si by chemical vapor deposition (CVD), it has been suggested that the Sn composition needed for indirect to direct gap transition should not exceed 11 at % for relaxed GeSn [44]
We review the latest progress in monolithic Ge-on-Si active photonic materials and devices, including band engineering, materials growth, device structures, and the current status of Ge PDs, electroabsorption modulators (EAMs) and laser diodes (LDs)
Summary
Information and communication technology (ICT) already consumes ~5% of electricity worldwide in 2012 [1]. A significant challenge for high-volume, large-scale EPICs on Si is active photonic devices for light generation, modulation and detection. These devices are conventionally based on direct band gap III-V semiconductors to benefit from the efficient direct gap transitions. Utilizing the efficient direct gap transition of Ge and band engineering techniques to further reduce the energy difference between the direct and indirect band gaps, high-performance Ge-on-Si PDs, electroabsorption modulators (EAMs) and prototype laser diodes (LDs) have been demonstrated in recent years. We review recent progress in band engineering, materials growth and the design/performance of integrated Ge active photonic devices on Si. We propose some possible directions for future investigations. The results demonstrate that Ge-on-Si is an ideal solution for monolithic, large-scale electronic-photonic integration
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