Competition Between Positive and Negative Terahertz Photoconductivity in Variable Thickness Hg1-xCdxTe Epitaxial Layers

In this work, we demonstrate that the terahertz photoconductivity in Hg
_1-x
Cd
_x
Te epitaxial films (x <; 0.15) is featured by superimposed positive and negative components. The dramatic drop of the positive photoresponse as the sample thickness decreases indicates that the bulk-related processes crucially contribute to the non-equilibrium transport. At the same time, the features observed in magnetic field provide us with arguments for an edge transport channel formation. We discuss the sign-alternating photoconductivity kinetics in terms of a model that takes into account both the bulk electron excitation and the surface/interface state contribution.