LIGHT-INDUCED-CHANGES IN THE ELECTRICAL CONDUCTIVITIES AND PHOTOLUMINESCENCE IN UNDOPED AMORPHOUS-GERMANIUM AND SILICON-GERMANIUM ALLOYS OFSMALL-X

Light-induced metastable changes in both the photoconductivity and dar k conductivity are reported for undoped a-Ge:H and a-SixGe1-x:H films deposited by plasma-enhanced chemical-vapor deposition. Measurements w ere made to determine the dependence of the dark conductivity, the pho toconductivity, the photoluminescence, and the photocurrent on the lig ht intensity. For the a-Ge:H and the a-SixGe1-x:H films measured, expo sure to light increased the dark conductivity by a factor of 3 and the photoconductivity by about 30 percent at room temperature, which is c ontrary to the majority of the results observed for typical undoped a- Si:H films. The dependence of the photocurrent on the light intensity, I-ph proportional to F-gamma, demonstrated that gamma slightly increa sed in a-SixGe1-x:H, and not in a-Ge:H, after a prolonged light exposu re. A substantial decrease in the photoluminescence spectrum was also observed for a-SixGe1-x:H films and could be explained in terms of the generation of either nonradiative or deep radiative centers.