ENHANCEMENT OF PHOTOSENSITIVITY IN CHEMICALLY DEPOSITED CDSE THIN-FILMS BY AIR ANNEALING

Improvement in photosensitivity, (sigma(photo) - sigma(dark))/sigma(dark), of chemically deposited CdSe thin films on annealing in air is discussed. The as-prepared films of approximately 0.5 mum thickness show photosensitivities of < 10 under 600 W m-2 illumination. Upon annealing the films in air for 1 h each at various temperatures their photosensitivity increases depending on the temperature of annealing: approximately 10 (200-degrees-C), approximately 10(2) (300-degrees-C), approximately 10(3) (400-degrees-C), and approximately 10(7) (450-degrees-C). Air annealing at temperatures beyond 450-degrees-C was found to cause degradation in the photosensitivity. The high photosensitivity is also accompanied by growth in photocurrent while maintaining a fast decay of approximately 6 decades in < 1 s after shutting off the illumination. Such a short decay time is unusual with chemically deposited photoconductive thin films. The results are explained on the basis of improvement in crystallinity and increase in chemisorption of oxygen upon annealing the films in air. X-ray-diffraction data and x-ray photoelectron spectroscopy depth profiling of the annealed films are presented in support of this explanation.