Properties of a-C : H light-blocking layer used for optical isolation of a-Si : C : H photosensor in reflective liquid crystal spatial light modulators

Novel employment of the absorbing a-C:H layer for optical isolation of an a -Si:C:H photosensor in the reflective liquid crystal optically addressed sp atial light modulators is discussed, The dependences of electrical resistiv ity rho, Tauc gap E-T and an absorption coefficient alpha at 633 nm on the deposition rate of the a-C:H films in the interval from 1 to 10 Angstrom s( -1) were compared and correlations between these properties were ascertaine d to match the a-C:H layer with the a-Si:C:H layer electrically. Current-vo ltage characteristics of ITO/a-C:H and ITO/a-Si:C:H/a-C:H thin-film structu res were measured using a mercury droplet contact. Our investigations showe d that the absorbing a-C:H layer with alpha similar to 4 x 10(4) cm(-1) at lambda = 633 nm(-1), rho in the range from 10(10) to 10(11) Omega cm, and E -T in the range from 1.25 up to 1.5 eV can ensure effective optical isolati on and be a well matched couple with the a-Si:C:H photoconductor. The photo current and dark current I-V characteristics of such ITO/a-Si:C:Wa-C:H thin -film structures were symmetrical. The ratio between photocurrents and dark currents of such structures was governed by the photosensitivity of the a- Si:C:H layer and depended on the electrical resistance of the a-C:H layer.