The growth of amorphous hydrogenated carbon (a-C : H) from the plasma deposition of C2H2, C2H4, or CH4 is reported. Measurements of the infrared absorption spectra, the optical gaps, and the photoluminescence spectra of these thin films are compared with each other, to those on a-C : H by previous workers, and to those on a-Si : C. The possibility of an a-C : H/a-Si : H hetero-junction solar cell is suggested.