Nondestructive High-Power-High-Temperature Raman Spectroscopy for Probing Microscopic Structural Variations in CZTSe Alloys

Even though absorber layers fabricated by different methods may yield comparable efficiencies and appear to be similar under conventional probes, such as low power Raman, PL, XRD, they could in fact be quite different in their microscopic structures. We have developed a novel nondestructive spectroscopy approach, high-power-high-temperature (HPHT) Raman spectroscopy, which is capable of revealing the microscopic structural variations of complex alloys like CZTSe over a large area. CZTSe films prepared by sputtering and co-evaporation methods were examined and compared in both lateral and depth directions. In general, high power (HP) illumination brought qualitatively different changes to the CZTSe samples, not only in the CZTSe Raman peaks but also in the secondary phases, which suggests that there is some subtle microscopic differences between the two types of samples. In addition, 2D Raman mapping revealed a larger spatial extension of the local heating effect caused by HP illumination in the sputtered film, which also indicates that two nominally similar films might have different thermal conductivities. High temperature (HT) measurement, which offers uniform heating as opposed to local heating with high power, further enhances the capability of the approach.