On polaron stability in Ag-doped ZnO films

• Published in: Applied physics. A, Materials science & processing Materials science & processing, 2024-03, Vol.130 (3), Article 207
• Main Authors: Sarkisian, A. R., Aghamalyan, N. R., Nersisyan, M. N., Petrosyan, S. I., Poghosyan, A. R., Ghambaryan, I. A., Badalyan, G. R., Hovsepyan, R. K., Kafadaryan, Y. A.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Condensed Matter Physics; Decay rate; Machines; Manufacturing; Nanotechnology; Optical and Electronic Materials; Oxide coatings; Physics; Physics and Astronomy; Polarons; Processes; Red shift; Shape functions; Silver; Surfaces and Interfaces; Thin Films; Ultrafines; Zinc oxide; Zinc oxides
• ISSN: 0947-8396; 1432-0630
• DOI: 10.1007/s00339-024-07324-x

The MIR reflectivity spectra ranging from 4000 to 900 cm −1 of the polarons in zinc oxide films doped with 0.24 at.% silver (AgZnO) as a function of temperature (190–360 K) in weakly concentrated gaseous methane environment were obtained. The decay rate, energy and intensity of polaron states at 1248 and 1484 cm –1 are analyzed using the Lorentzian line-shape function. The lines show the redshift (~ 3%) with an increase in temperature. The width and intensity of the line at 1248 cm –1 decrease by 23% and 38%, respectively, with an increase in temperature to 360 K. The one-phonon line at 1484 cm –1 broadens by ~ 50%, and the intensity decreases by 54% upon reaching a temperature of 330 K, and at T ≥ 350 K, the line 1484 cm –1 decays into many ultrafine weakly localized states due to the formation of a hydrocarbon adsorbate, which acts as a charge trapping center on the AgZnO surface. The calculated polaron scattering time τ  = 2.2 fs decreases to 1.8 fs as the temperature rises from 250 to 360 K. The frequency dependences of the optical conductivity determined by Kramers–Kronig relations show a localization-delocalization crossover near 1900 cm –1 . At frequencies below 1900 cm –1 , the carriers are localized, and dc-conductivity satisfies the criterion of the Mott-VRH model with the hopping energy of 0.43 T 3/4  meV.