Effects of thermal annealing and long-term ageing on electronic defects in CdSe thin films

Abstract

Defect distributions in CdSe thin films, ‘as deposited’, following thermal annealing, and after 10 years ’ storage under room conditions are investigated. Steady-state photoconductivity measurements at low temperatures suggest a decrease in the density of ‘slow ’ recombination centres following annealing or storage. Transient photocurrent and thermally stimulated current spectroscopies reveal a peak in the density of states at 0.65 eV below the conduction band edge in the as-deposited film. This broadens and shifts towards the conduction band edge on annealing. Stored films exhibit an almost flat defect distribution, which may result from a combination of both types of defect. Raman scattering measurements suggest that both storage and annealing result in increased structural order