Flat, relaxed Ge epitaxial layers with low threading dislocation density (TDD) of 1.94 x 10(6) cm(-2) were grown on Si(001) by ultrahigh vacuum chemical vapor deposition. High temperature Ge growth at 500 degrees C on 45 nm low temperature (IT) Ge buffer layer grown at 300 degrees C ensured the growth of a flat surface with RMS roughness of I nm; however, the growth at 650 degrees C resulted in rough intermixed SiGe layer irrespective of the use of low temperature Ge buffer layer due to the roughening of IT Ge buffer layer during the temperature ramp and subsequent severe surface diffusion at high temperatures. Two-dimensional Ge layer grown at IT was very crucial in achieving low TDD Ge epitaxial film suitable for device applications. (C) 2009 Elsevier B.V. All rights reserved.