High-pressure H-2 cleaning is proposed for precleaning wafers used in low-temperature silicon epitaxial growth to remove such contaminants as oxygen and carbon at the interface between the epitaxial layer and the substrate in ultrahigh-vacuum/chemical vapor deposition. Increasing the H-2 partial pressure up to 1300 Pa during H-2 cleaning at 850 degrees C was found to produce a smooth surface with the contaminants perfectly removed. To investigate the effects of roughness and contaminants in the wafer surface on the crystallinity of the epitaxial layer, p-n diodes were fabricated in the epitaxial layer and their characteristics were measured. Annealing at an H-2 partial. pressure of 120 Pa produced roughness and contaminants in the wafer surface causing a leakage current. Annealing at 1300 Pa produced smooth clean surfaces and no leakage current was observed. These results suggest that the electronic properties of epitaxial layers are influenced by contaminants and roughness in the wafer surface. High pressure H-2 cleaning reduces roughness and removes contaminants in the surface, resulting in good electronic properties in the epitaxial layer.