Low-temperature germanium ultra-high vacuum chemical vapor deposition for back-end photonic integration

Polycrystalline germanium (poly-Ge) grown on amorphous Si (a-Si) by ultra-high vacuum chemical vapor deposition (UHVCVD) over oxide barriers at low temperatures (Tles450degC) exhibits a larger grain size and lower defect density than the as-grown poly-Ge next to the oxide barriers. Poly-Ge as deposited at 450degC is p-type, but the introduction of PH₃ during Ge deposition gives n-type poly-Ge with n = 2.1times10¹⁸ cm^-3. The possible defect reduction and range of doping make poly-Ge a strong candidate for application to CMOS-compatible back-end photonic devices.