Growth of high quality Ge epitaxial films on Si substrate by low temperature buffer technique

High-quality and thick Ge epitaxial films are grown on Si substrates utilizing the low-temperature(LT) buffer technique by ultrahigh vacuum chemical vapor deposition(UHV-CVD) and are characterized by atomic force microscope, X-ray diffraction, and Raman spectroscopy. The results show that the LT Ge buffer is rough due to the three-dimensional islands formations, but the misfit stress is nearly fully relaxed. Fortunately, the rough LT Ge surface is effectively smoothed by subsequent growth at elevated temperature when the LT Ge buffer is thick enough and the compressive strain is largely relaxed. Finally, the210 nm Ge epitaxial film with smooth surface(root-mean-square roughness of1.2 nm), low threading dislocation density(5×105 cm-2), and sharp and symmetric X-ray diffraction peak(full width at half maximum of~460 arc sec) is achieved on LT Ge buffer with thickness of90 nm.