Optical phonons in pentanary compound (AgxCu1-x)2ZnSnS4 semiconductor: A raman study

The present study reports the phonon modes in the pentanary compound semiconductor (AgxCu1-x)(2)ZnSnS4 (ACZTS) (0 <= x <= 1) as identified using Raman Spectroscopy. When traversing from Cu2ZnSnS4 (x = 0) to Ag2ZnSnS4 (x= 1), the Raman shifts corresponding to B(T0), B(LO) and E(TO) modes that occur at 254, 285 and 307 cm(-1), respectively, decreased to 223, 269 and 295 cm(-1). Such a gradual change in the Raman shift corresponding to Cu2ZnSnS4 (CZTS) upon Ag-alloying is a characteristic of one-mode behavior. On the other hand, there was no change in the Raman shifts corresponding to the modes A1, E(LO), B-2(TO) and B-2(LO), that remained at 332, 348, 360 and 371 cm(-1) , respectively; this observation along with the fact that Raman shift for the A-mode started appearing both at 336 and 345 cm(-1) with Ag-alloying, suggest that the Raman scattering in the ACZTS compounds most likely demonstrate the two-mode behavior. Further, with increased Ag-alloying the ratios I-2(85)/I-302 and I-336/(I-364 + I-371) derived from the Raman spectra, increased from 1.44 and 1.96, to 2.49 and 2.43, respectively, which indicates that the extent of disorder decreased in CZTS with Ag-alloying; this was further supported by the dramatic changes observed in the hole-type carrier density which is strongly affected by the disorder. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The study investigated phonon modes in the pentanary compound semiconductor ACZTS using Raman Spectroscopy, finding changes in Raman shifts during Ag-alloying indicating potential two-mode behavior in the compounds. The ratios derived from Raman spectra also showed decreased disorder in CZTS with increased Ag-alloying, supported by changes in carrier density.