Developments in germanium-on-silicon epitaxy by reduced pressure chemical vapor deposition

High quality epitaxial layers of germanium have been deposited directly on a range of silicon substrates using reduced pressure chemical vapor deposition (RP-CVD). Relaxed Ge layers were realized on (001), (110) and (111) orientations with surface roughness below 2 nm in each case, and below 1 nm for (001). Stacking faults were virtually eliminated, while the threading dislocation density was minimized; for (001) this was 1 × 10⁷ cm^-2, whereas for (111) it was highest at 2 × 10⁸ cm^-2. With such Ge layers many applications are made possible. Examples given include heterostructures with extremely high hole mobility, both at low- and room temperature, and single photon avalanche diodes.