Comprehensive study of Raman optical response of typical substrates for thin-film growth under 633 nm and 785 nm laser excitation

Abstract

Raman spectroscopy is one of the most efficient and non-destructive techniques for characterizing materials. However, it is challenging to analyze thin films using Raman spectroscopy since the substrates beneath the thin film often obscure its optical response. Here, we evaluate the suitability of fourteen commonly employed single-crystal substrates for Raman spectroscopy of thin films using 633 nm and 785 nm laser excitation systems. We determine the optimal wavenumber ranges for thin-film characterization by identifying the most prominent Raman peaks and their relative intensities for each substrate and across substrates. In addition, we compare the intensity of background signals across substrates, which is essential for establishing their applicability for Raman detection in thin films. The substrates LaAlO₃ and Al₂O₃ have the largest free spectral range for both laser systems, while Al₂O₃ has the lowest background levels, according to our findings. In contrast, the substrates SrTiO₃ and Nb:SrTiO₃ have the narrowest free spectral range, while GdScO₃, NGO and MgO have the highest background levels, making them unsuitable for optical investigations.