Direct-gap exciton and optical absorption in the Ge/SiGe quantum well system

The ground-level direct-gap excitons and quantum-confined Stark effect (QCSE) electroabsorption in the Ge/SiGe quantum well structures are studied using the tunneling resonance modeling and the variational method. The exciton radius, transition energy, binding energy, and optical oscillator strength are calculated for various quantum well thicknesses (5–35 nm) and vertical electric fields (0–105 V/cm) simultaneously. The relative direct-gap-to-indirect-gap absorption ratios are compared. A quantum well implementation scheme with relatively broad thickness range of ∼5–15 nm can provide moderate excitonic absorption and contrast ratio for long wavelength operation. This investigation will improve the QCSE electroabsorption efficiency in the Ge quantum well system.