On the relation between low-temperature epitaxial growth conditions and the surface morphology of epitaxial Si and Si1−xGex layers, grown in an ultrahigh vacuum, very low pressure chemical vapour deposition reactor

In this paper we describe the intimate relation between the surface morphology of epitaxial Si and Si1-xGex layers and the pressure during growth. All the experiments were done at a temperature of 625-degrees-C and the pressure was varied between 10(-4) and 2 x 10(-1) Torr. The layers were grown in an ultrahigh vacuum very low pressure chemical vapour deposition reactor (UHV-VLPCVD) with a gas mixture of SiH4 and GeH4 without the addition of H-2. Based on the pressure and the growth-initiating conditions, we distinguish two different growth modes, based on a different surface morphology and growth rate. The first mode (mode I) is characterized by a high growth rate and good surface morphology, whereas in mode II the growth rate is significantly lower and the surface morphology substantially rougher. We present also a qualitative explanation for these observations in terms of hydrogen coverage and impingement rate of precursor molecules on the growing crystal surface.