The uniformity and quality of epitaxial, ultrathin germanium-on-insulator (GOI) layers are studied as a function of Ge regrowth under different surfactant conditions. It is shown that using antimony as a surfactant during the solid phase epitaxial regrowth of the germanium layers provides a higher crystal quality and much flatter surfaces than samples grown without antimony. However, the diffusion of even a small percentage of a monolayer of antimony into the GOI layer may cause a thin n(+) &DPRIME; delta-doped&DPRIME; layer to remain on the surface of the wafer, making device fabrication difficult. It is shown that using a surface layer of silicon as a surfactant that is not-expected to interact electronically with the Ge (unlike Sb), acceptable surface smoothness may be achieved. Physical mechanisms behind this are discussed. © 2005 American Vacuum Society.