ELECTRONIC AND OPTICAL-PROPERTIES OF GE-SI SUPERLATTICES

Germanium and silicon elemental semiconductors are indirect bandgap, cubic materials that are used in the manufacture of the great majority of semiconductor electronic Epitaxial techniques, largely borrowed and adapted from group III-V compound semiconductor technology, have been applied successfully to produce heterostructures and superlattices from Ge and Si. Theory shows that some of these structures behave like direct bandgap materials, while other structures can be used for optical second harmonic generation. On the other hand, it has been well understood for many years that neither silicon, nor germanium, nor any germanium-silicon alloy could ever show such behaviour. Recent progress in germanium-silicon heterostructures is reviewed in the context of developing a new materials system for photonic devices based entirely on silicon and germanium and suitable for optical waveguides, modulators, sources, and detectors.