High-quality ge films on Si substrates using Sb surfactant-mediated graded SiGe buffers

High-quality Ge films were grown on Si substrates by solid-source molecular beam epitaxy using SiGe graded layer and Sb surfactant-mediation technique. Transmission electron microscopy measurements show that samples grown using this method have a lower threading dislocation density than those grown by other typical methods, such as grading at high temperature (700 degreesC) only, grading at intermediate temperature (510 degreesC) only, and the use of low temperature Si buffer. A relaxed Ge film on a 4-mum-thick graded buffer was grown and shown to have a threading dislocation density of 5.4x10(5) cm(-2) and surface roughness of 35 A. Ge p-i-n diodes were fabricated and tested. Under a reverse bias of 1 V, the p-i-n Ge mesa photodiodes exhibit a very low dark current density of 0.15 mA/cm(2). (C) 2001 American Institute of Physics.