THERMAL AND HYDROGEN PLASMA ANNEALING OF AMORPHOUS HYDROGENATED CARBON

We have studied the changes in the optical properties of amorphous hydrogenated carbon due to variety of annealing processes. Whether the sample is annealed at 225-degrees-C for one hour in vacuum, in hydrogen gas, or in a hydrogen plasma, the photoluminescence intensity decreases, the bandgap decreases, and the intensity of the Urbach tails increases. All of these annealing processes increase the density of defect states, most likely by driving hydrogen out of the film. This is in marked contrast to the observation by one group of previous workers that the luminescence intensity increases by an order of magnitude due to a vacuum anneal.