CdSe thin films : chemical deposition using N,N-dimethylselenourea and ion exchange reactions to modify electrical conductivity

Deposition of CdSe thin films from chemical baths containing cadmium citrate or cadmium tartrate complex ions and using N,N-dimethylselenourea as the source of selenide is presented. Good quality thin films of thickness in the 0.1--0.5 [mu]m range were deposited at 24 or 50 C. The as-prepared films are of poor crystallinity. On annealing in air at 450 C for 1 h, well-defined diffraction peaks matching with the hexagonal phase of CdSe are observed. These films have electrical conductivities ([sigma][sub dark]) [approximately]10[sup [minus]8] [Omega][sup [minus]1] cm[sup [minus]1] and are only weakly photosensitive. However, the photosensitivity improves to [approximately]10[sup 6] on annealing in air at 450 C. Ion-exchange reactions of the films in dilute HgCl[sub 2] solutions lead to [sigma][sub dark] [approximately]1[Omega][sup [minus]1] cm[sup [minus]1] (n-type) with low photosensitivities. Annealing of these films at temperature > 200 C leads to a reduction in [sigma][sub dark] while it enhances the photosensitivity. Immersion of the CdSe films in dilute CuCl[sub 2] solution makes the films p-type, [sigma][sub dark] [approximately] 0.1 [Omega][sup [minus]1] cm[sup [minus]1]. Annealing of these films at temperature > 200 C causes degradation of the films. XPS depth profiles of the films are presented to illustrate the ion-exchange reactions.