High speed optical modulation in Ge quantum wells using quantum confined stark effect

We focus on the optimization of SiGe material deposition, the minimization of the parasitic capacitance of the probe pads for high speed, low voltage and high contrast ratio operation. The device fabrication is based on processes for standard Si electronics and is suitable for mass-production. We present observations of quantum confinement and quantum-confined Stark effect (QCSE) electroabsorption in Ge quantum wells (QWs) with SiGe barriers grown on Si substrates. Though Ge is an indirect gap semiconductor, the resulting effects are at least as clear and strong as seen in typical III-V QWstructures at similar wavelengths. We also demonstrated a modulator, with eye diagrams of up to 3.5 GHz, a small driving voltage of 2.5 V and a modulation bandwidth at about 10 GHz. Finally, carrier dynamics under ultra-fast laser excitation and high-speed photocurrent response are investigated.