TOWARDS A FAST PROCESS CONTROL FOR Cu(In,Ga)(Se,S)2 ABSORBERS. THE SURFACE CHALCOGEN RATIO ASSESSED BY RAMAN SPECTROSCOPY

摘要

The sulfur content in the surface of Cu(In,Ga)(Se,S)2 thin film absorber layers determines the band gap at the interface of the device. It is a crucial quantity for the open circuit voltage. Therefore, a minute control of the S/Se ratio by a fast and reliable technique appears desirable. Absorber layers of Cu(In,Ga)(Se,S)2 have been prepared by the rapid thermal processing (RTP) of stacked elemental layers. They have been analyzed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectroscopy (SIMS). Raman peaks corresponding to the A1-modes of CuInSe2, CuInS2 and CuIn(S,Se)2 are detected. A comparison of the S/Se ratio from Raman intensities of the A1-modes with the integrated S/Se ratio of XPS signal intensities reveal a direct correlation. This finding allows the establishment of Raman spectroscopy as a non-destructive in- line process control for the monitoring of the surface chalcogen ratio.