OPTICAL PROPERTIES OF THE SEMICONDUCTORS SYSTEM Cu2(1-X)Ag2XGeSe3

Abstract

In this work we have investigated the optical absorption properties in the alloy Cu2 (1-x)Ag2xGeSe3. The absorption coefficient measurements were made in the temperature range 10 to 300 K for concentration x = 0 and at room temperature for concentrations x = 0.25, 0.5, 0.75, 1. The Elliot-Toyozawa model was employed to perform the analysis of the optical absorption spectral for all concentrations. The linear dependency near the fundamental edge confirms that all the compounds for the different concentrations have a semiconductor character and presents a direct energy gap in the near infrared at pressure and room temperature. The energy gap of the compound Cu2GeSe3 increases as the temperature diminishes. This behavior depends mainly on three effects that are generated at low temperatures: thermal expansion, electron-phonon interaction and factor Debye-Waller. The optical energy gap variation with temperature for Cu2GaSe3 was fitted to a semi-empirical model that takes into account two of the first named effects and whose behavior is similar to that observed in semiconductors of the families Cu-III-VI2 and Cu2-IV-VI3. On the other hand, a study of the optical energy gap variation with concentration has not been reported yet. The system Cu2(1-x)Ag2xGeSe3 shows a concavity upwards in the variation of the optical energy gap with concentration and is described by an equation EG(x)= a + bx + cx2