High quality Ge epitaxial layers on Si by ultrahigh vacuum chemical vapor deposition

Flat, relaxed Ge epitaxial layers with low threading dislocation density (TDD) of 1.94 × 106 cm− 2 were grown on Si(001) by ultrahigh vacuum chemical vapor deposition. High temperature Ge growth at 500 °C on 45 nm low temperature (LT) Ge buffer layer grown at 300 °C ensured the growth of a flat surface with RMS roughness of 1 nm; however, the growth at 650 °C resulted in rough intermixed SiGe layer irrespective of the use of low temperature Ge buffer layer due to the roughening of LT Ge buffer layer during the temperature ramp and subsequent severe surface diffusion at high temperatures. Two-dimensional Ge layer grown at LT was very crucial in achieving low TDD Ge epitaxial film suitable for device applications.