The heteroepitaxy of Ge on Si: A comparison of chemical vapor and vacuum deposited layers

Epitaxial growth of Ge on Si has been investigated by two techniques: vacuum deposition and chemical vapor deposition (CVD). Vacuum-deposited Ge layers (physical vapor deposition, PVD) on heated Si substrates (≤ 500 °C) have smooth surface morphologies with a surface crystalline quality which improves with Ge layer thickness. Layers prepared by the CVD technique at 500–600 °C are comparable with the PVD prepared layers. Main defects in both PVD and CVD layers are dislocations initiating at the Ge/Si interface. Chemical vapor-deposited Ge layers grown at a substrate temperature of 700–800 °C exhibit poor crystalline quality and often are polycrystalline. Chemical vapor-deposited layers grown at a substrate temperature of 900 °C, again are good quality epitaxial layers. In this case, in addition to dislocations, stacking faults are present. All the studied layers are highly conductive and p-type. The conduction and valence band discontinuities determined from electrical measurements are 0.05±0.04 eV and 0.39±0.04 eV, respectively