Thickness-dependent charge transport across CdO/La0.3Ca0.7MnO3 n-n junction interfaces

Abstract

Understanding the charge transport across functional oxide interfaces is vital for designing thin film devices for applications in spintronics, sensors, uncooled bolometers, p–n and n–n junctions, capacitors, diodes, field–effect and memory devices, and neuromorphic systems. In this work, n–n junction–based CdO/La0.3Ca0.7MnO3 (CdO/LCMO) heterostructures with varying LCMO layer thicknesses were fabricated on Al2O3 substrates using a sol–gel assisted chemical solution deposition (CSD) technique. Temperature–dependent resistivity measurements were performed to investigate the charge transport behaviour across the junctions. All heterostructures exhibit insulating transport with two distinct electronic transitions: the charge–ordered transition (TCO) and the antiferromagnetic transition (TN) at lower temperatures. Mott–type variable range hopping (VRH) was identified as the dominant transport mechanism, enabling estimation of key parameters such as the density of states near the Fermi level N(Ef), average hopping distance, and hopping energy. The temperature coefficient of resistance (TCR) was also evaluated, with high values near room temperature indicating strong potential for uncooled bolometer and thermal sensor applications. The observed sharp resistivity change due to the charge–ordering transition is directly responsible for enhanced TCR. The study further clarifies the influence of LCMO layer thickness on transport properties and TCR behaviour, establishing thickness as an effective tuning parameter. Additionally, these heterostructures serve as model systems for exploring charge transport at n–n junctions involving a narrow–bandgap semiconductor (CdO) and a charge–ordered complex oxide (LCMO), providing a versatile platform for phase–engineered oxide electronics.