Alternating Current Photoconductivity of Vacuum-Deposited Films of CdSe, CdS, and CdTe, Excited with Intensity-Modulated Light

Abstract

An experimental investigation of the use of sinusoidally intensity-modulated light (IML) to investigate vacuum-deposited CdSe, CdS, and CdTe films has been carried out. A definite plateau has been observed in the amplitude–frequency response for the first time reflecting the direct observation of a discrete trapping level by this technique. The trap energy is 0.09 eV with a trapping cross section of 10−17 cm2 and a trap density of 1016 cm−3 for the level observed in specially prepared films of CdSe. These results were confirmed by thermally stimulated current studies on the same samples. The effects of temperature, light intensity, and certain fabrication parameters on the amplitude–frequency response of the films are presented.Applying the theory for extrinsic IML, studies of CdS films show that excitation occurs from localized levels to the conduction band. CdTe films also show trapping due to localized levels, but a complete analysis of this material was not possible because its response time is too fast.