On the charge transport models in high intrinsic defect doped transparent and conducting p-type Cu–Cr–O delafossite thin films

Abstract

Abstract In contemporary optoelectronic devices, the transparent conductive oxides commonly demonstrate n-type conduction characteristics, with indium-doped tin oxide emerging as a prominent example. However, in applications involving fully invisible electronics that necessitate p-type conductive oxides, there exists a demand for a quintessential material possessing properties akin to its n-type counterpart. CuCrO2, a delafossite semiconductor based on copper, presently represents a notable compromise between optical and electrical attributes within the realm of p-type semiconductors. Despite numerous studies focusing on this material, the charge carrier transport regime within the material remains unclear. The commonly reported hole transport mechanism in CuCrO2 is the small polaron model. However, this work evidences several contradictions when this transport mechanism is assumed. Using the same methodology as previous studies, we investigated the holes’ transport mechanism by the means of the measurement of electrical conductivity and the Seebeck coefficient at varying temperatures. Different charge transport models in high intrinsic defect doped CuCrO2 thin films are explored: small polarons, grain boundaries scattering in degenerate semiconductors, and variable range hopping with nearest neighbor hopping. The small polaron model does not provide conclusive results within the temperature range analyzed. Interestingly, no specific hole transport mechanism can be undoubtedly selected. The limitations of the models highlight the influence of peculiar defects within CuCrO2 thin films on the hole transport mechanism, particularly the adoption of well-ordered copper vacancies columns.