Quantum-Confined Stark Effect in Ge/SiGe Quantum Wells on Si for Optical Modulators

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