LOW-TEMPERATURE EPITAXIAL-GROWTH OF IN-SITU B-DOPED SI1-XGEX FILMS

We report in-situ boron doping of Si1-xGex films epitaxially grown on Si(100) by low-pressure chemical vapour deposition (LPCVD) process. Th e experiments are performed in an ultraclean hot-wall system using ult ra-pure SiH4-GeH4-H-2-B2H6 gas mixtures. The incorporation rate of B w as proportional to the B2H6 partial pressure and was larger for Ge-ric h films. It was proposed that the increase in B incorporation rate wit h increasing Ge fraction was caused by the larger surface adsorption r ate of B-hydride on Ge atoms than on Si atoms. Since the incorporation rate of B increased with exposure time of B2H6 during Si1-xGex deposi tion at early stage, it was suggested that B doping was limited by the B-hydride adsorption rate. Hall measurements showed that carrier conc entration was equal to B concentration in the range 3x10(17)-2x10(20) cm-3, regardless of the Ge fraction, and Hall mobility passed through a minimum value for Si0.75Ge0.25 films regardless of the film thicknes s.