Highly conductive B-doped hydrogenated amorphous Si (a-Si:H) as well as amorphous SiC alloys (a-SiC:H) have been prepared from (SiH4)/(B2H6/SiH4) and (SiH4/CH4)/(B2H6/SiH4) plasmas, respectively by a novel surface-temperature-modulation method. Films produced by this technique exhibit a higher conductivity as compared to the conventionally prepared films, i.e., 7.0xl0-3Scm-1 for p-type a-Si:H with an optical gap of 1.7eV and 5.5xl0-5Scm-1 for p-type a-SiC:H of optical gap 1.9ev.