Study of CdTe/CdS-thin films by isotope dilution, neutron activation analysis, inductively coupled plasma mass spectrometry and secondary ion mass spectrometry

Thin polycrystalline CdTe films can be used as materials for solar cells. The CdTe surface is etched with H₃PO₄/HNO₃ solution to remove soluble Cd compounds and to leave insoluble Te compounds on the surface and thus creating a layer between CdTe and the electrode material. Different analytical methods have been used for studying the effect of the etching procedure relating to the electrode deposition on the CdTe surface. The penetration of phosphorus from the etchant without an intentional CdTe doping may be beneficial for the thin film structure. Phosphorus has been determined by isotope dilution, and cadmium and tellurium by instrumental neutron activation analysis and inductively coupled plasma mass spectrometry in the dissolved samples. All the samples have also been analysed by secondary ion mass spectrometry. It was shown that P penetrates the film. The first 40 nm contains P in a P/Cd atomic ratio of about 0.5. In the next layers the ratio is about 0.1. The etchant leaves a thin Te-enriched layer on the surface of the film. This was detected from the SIMS profile, but not from the diluted nitric acid dissolved fractions because of the low Te solubility.