Evaluation of thin films intermixing by photoacoustic spectroscopy

•Photoacoustic spectroscopy is sensitive to changes in interfaces between thin films.•The spectral band position is related to the alloy composition at the interface.•CdTe and CdS interdiffusion was associated with the thicknesses of the thin films. In this paper, we show the usefulness of photoacoustic spectroscopy (PAS) to monitor the intermixing at the thin films heterojunction. CdTe/CdS bilayers with different thicknesses were used to analyze the effect of S-Te interdiffusion on the PAS spectra. Unlike the spectrum measured by the optical transmittance technique, the photoacoustic spectrum shows an optical absorption band, in addition to the absorption edge corresponding to the CdTe layer. The position of the band changes from 2.31 to 1.93 eV depending on the CdTe layer thickness in the structure. The band shifts were associated with the composition of the ternary CdS1-xTex alloy at the interface. Our interpretation of the results was supported by the PAS-Phase-Resolved and the X-Ray photoelectron spectroscopy techniques.