| Popis: |
The authors prepared a-Ge:H films with different thicknesses and measured their spectral photoconductivity, which was found to increase with both film thickness and light wavelength. As an explanation, reduced photoconductivity under the illuminated surface is assumed. The eta mu tau -product of a film is given by its photoconductivity measured between ohmic contacts and represents a property of the photoelectrons. A two-layer model ascribes different eta mu tau -products to a front layer of the film and to the rest of it, called the bulk layer. By fitting the two-layer model to the present experiments the authors find a front-layer thickness of 55 nm, a surface eta mu tau -product of 1*10/sup -8/ cm/sup 2//V, and a bulk-layer eta mu tau -product of 5*10/sup -7/ cm/sup 2//V. The effective eta mu tau -product, determined under the assumption of a homogeneous film, approaches the bulk value when both film thickness and light wavelength reach a value of 1 mu m. No light degradation of the a-Ge:H films is found. > |
