Enhancement of photosensitivity in chemically deposited CdSe thin films by air annealing

Abstract

Improvement in photosensitivity, (σphoto−σdark)/σdark, of chemically deposited CdSe thin films on annealing in air is discussed. The as-prepared films of ∼0.5 μm 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: ∼10 (200 °C), ∼102 (300 °C), ∼103 (400 °C), and ∼107 (450 °C). Air annealing at temperatures beyond 450 °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 ∼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.