Propriedades de transporte elétrico e fotoconducão em filmes epitaxiais de PbTe:CaF2

Abstract

In this work, an investigation was conducted into the photoconductivity effect in epitaxial films of PbTe and PbTe doped with CaF2 at different doping temperatures: 610 °C, 700 °C, and 1250 °C. Measurements of electrical resistivity, photoconductivity, and the Hall effect were carried out over a temperature range from 300 K to 1.9 K, both with and without light incidence on the sample surfaces, revealing a strong impact of doping on the electrical and photoconductive properties of the films. The results demonstrated that doping with CaF2 significantly alters the photoconductivity behavior, with a marked increase in its amplitude at low temperatures, showing values approximately 100 times higher than those obtained at room temperature. Additionally, it was observed that the persistent photoconductivity effect is suppressed in samples doped at 610 °C and 700 °C, in contrast to the results for samples doped at 1250 °C and PbTe, where this effect is observed throughout the entire analyzed temperature range. From the exponential fitting of the photoconductivity curves, energy barriers associated with persistence were determined. The PbTe film exhibited the deepest energy barrier, followed by the sample doped at 610 °C, which also revealed an additional shallow energy barrier at low temperatures, possibly related to the suppression of the persistent photoconductivity effect. In contrast, for the sample doped at 700 °C, this correlation could not be established, as only a very shallow energy barrier was identified. Hall effect measurements confirmed that the increase in photoconductivity in the PbTe and PbTe doped with CaF2 at 1250 °C samples is due to an increase in carrier concentration when samples are illuminated, whereas for the PbTe samples doped at 610 °C and 700 °C, it is attributed to an increase in carrier mobility. Finally, a simple classical Drude model for photoconductivity amplitude was employed to describe the observed effects.