Investigação do efeito de fotocondutividade em poços quânticos de SnTe/PbEuTe

Abstract

In this work, we study the photoconductivity effect in p-type IV-VI semiconductors SnTe/P b0,9Eu0,1T e. The samples were grown using molecular beam epitaxy, resulting in high quality 30 nm-wide structures. Photoconductivity measurements are made for temperatures below 200 K, with radiation varying from infrared (IR, 940 nm) to ultraviolet (UV, 398 nm) wavelengths. A positive photoresponse is observed for temperatures greater than 10 K, with persistent photoconductivity when the light is turned off. Analysis of the photoconductivity decay curves showed that defect states are present in the energy band structure of SnTe, and that different defects are activated, as functions of the radiation energy. For temperatures below 10 K, a transition from positive to negative photoconductivity is observed when the sample is illuminated by UV light. To explain the negative effect, Hall measurements were made in order to obtain the carrier concentration and mobility under light and dark conditions, comparing the variation of these parameters using UV radiation. With this information, the negative photoconductivity effect is explained with a classical transport model that predicts the transition for temperatures below 4 K. Magnetoresistance measurements showed that there is no contribution of the topological surface states for the electrical transport under illumination. In a second sample, photoconductivity measurements were conducted for lights ranging from IR, through visible to UV, in order to verify the dependence of negative photoconductivity on radiation energy. It was observed that the negative effect indeed manifests only for radiations with energies greater than 2 eV, starting with yellow. This leads to the conclusion that the negative photoconductivity is originated from the energy bands above 2 eV.