title: Strong quantum-confined Stark effect in germanium quantum-well structures on silicon.
abstract: Silicon is the dominant semiconductor for electronics, but there is now a growing need to integrate such components with optoelectronics for telecommunications and computer interconnections. Silicon-based optical modulators have recently been successfully demonstrated; but because the light modulation mechanisms in silicon are relatively weak, long (for example, several millimetres) devices or sophisticated high-quality-factor resonators have been necessary. Thin quantum-well structures made from III-V semiconductors such as GaAs, InP and their alloys exhibit the much stronger quantum-confined Stark effect (QCSE) mechanism, which allows modulator structures with only micrometres of optical path length. Such III-V materials are unfortunately difficult to integrate with silicon electronic devices. Germanium is routinely integrated with silicon in electronics, but previous silicon-germanium structures have also not shown strong modulation effects. Here we report the discovery of the QCSE, at room temperature, in thin germanium quantum-well structures grown on silicon. The QCSE here has strengths comparable to that in III-V materials. Its clarity and strength are particularly surprising because germanium is an indirect gap semiconductor; such semiconductors often display much weaker optical effects than direct gap materials (such as the III-V materials typically used for optoelectronics). This discovery is very promising for small, high-speed, low-power optical output devices fully compatible with silicon electronics manufacture.
authors.affiliation: Solid State and Photonics Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA. yhkuo@stanford.edu
authors.forename: Yu-Hsuan
authors.initials: YH
authors.lastname: Kuo
authors.forename: Yong Kyu
authors.initials: YK
authors.lastname: Lee
authors.forename: Yangsi
authors.initials: Y
authors.lastname: Ge
authors.forename: Shen
authors.initials: S
authors.lastname: Ren
authors.forename: Jonathan E
authors.initials: JE
authors.lastname: Roth
authors.forename: Theodore I
authors.initials: TI
authors.lastname: Kamins
authors.forename: David A B
authors.initials: DA
authors.lastname: Miller
authors.forename: James S
authors.initials: JS
authors.lastname: Harris