Strong compensation effects related to the empty channel in p-type transparent conductive material Cu₃TaS₄: a first-principles study

Wide band gap chalcogenide semiconductors have attracted much attention as p-type transparent conductive materials mainly because of their high hole mobility and ease of p-type doping. Cu₃TaS₄ has recently emerged as a promising candidate for a p-type transparent conductive material owing to its wide band gap, light hole effective mass and high optical transparency. Nevertheless, understanding the p-type conducting mechanism of Cu₃TaS₄ remains elusive. In this study, the electronic structure, optical properties, defect properties and p-type conductivity of Cu₃TaS₄ are systematically investigated based on first-principles calculations. The results show that Cu₃TaS₄ is an indirect band gap semiconductor with an electronic band gap of 2.97 eV and exhibits high transparency in the visible light region. Furthermore, the lowest defect formation energy of copper vacancies under Cu poor conditions confirms the intrinsic p-type conductivity of Cu₃TaS₄. However, the intrinsic p-type conductivity of Cu₃TaS₄ is restricted by the strong compensation effect of the n-type defect, interstitial Cu(Cu_i). Even with extrinsic p-type doping, the p-type conductivity remains unimproved due to the compensation effect. The ease of formation of Cu_i is related to the empty "channel" along the (100) direction within the Cu₃TaS₄ crystal. As a result, the existence of the empty "channel" and the strong compensation effect of Cu_i lead to difficulties in achieving high hole concentration and excellent p-type conductivity for Cu₃TaS₄.