DEPENDENCE OF ELECTRONIC-PROPERTIES OF HYDROGENATED AMORPHOUS-GE ON DEPOSITION CONDITION

Hydrogenated amorphous Ge(a-Ge:H) thin films are prepared by the capacitive-coupled plasma chemical vapor deposition method using GeH4 as a reactive gas. The deposition temperature and radio frequency (rf) power density are changed from 100-degrees-C to 260-degrees-C and from 0.2 W/cm2 to 2 W/cm2, respectively. The dependence of the optical and electronic properties including the infrared absorption, photo- and dark conductivities on both the deposition temperature and rf power density are examined. For a substrate temperature of 175-degrees-C, the photo- and dark conductivities exhibit maxima and the bimolecular recombination process in the photoconduction becomes dominant compared to the monomolecular recombination process. It is also found that the value of the energy gap is proportional to the hydrogen content in the region below 2 at.%. When the rf power density is increased from 0.2 to 2.0 W/cm2 under the constant substrate temperature of 160-degrees-C, the films are improved although the hydrogen content is unchanged.