Unveiling the red electroluminescence in LSMO-SRO thin film heterostructures

Abstract

Herein, intense red electroluminescence (674 nm) in a La0.7Sr0.3MnO3(LSMO)-SrRuO3(SRO) thin films heterostructure obtained by RF-magnetron sputtering is reported for the first time. This novel phenomenon may open a new door in the field of optoelectronics and new generation devices based on multiferroic heterostructure. The structural properties were analyzed using grazing incidence x-ray diffraction demonstrating a rhombohedral structure for LSMO with (024) preferential orientation and an orthorhombic structure for SRO films with (121) preferential orientation. Raman and x-ray photoelectron spectroscopy (XPS) results demonstrated a mix of phases present in LSMO thin films. The thickness analysis was performed using scanning electron microscopy (SEM) in cross section and the thickness was found to be 123 nm and 49 nm for LSMO and SRO, respectively. XPS analysis for LSMO revealed that point defects associate to Mn cations and oxygen vacancies modify the total electrical conductivity and due to Mott transitions, suggest a p-type semiconductor behavior. For the SRO film, the XPS analysis demonstrated a change in the stoichiometry of the film surface, which provides a large amount of oxygen vacancies indicating a metal oxide transition with effects that involve multiple degrees of freedom (charge, spin, and lattice). The electrical behavior observed in the heterostructure corresponds to a metal-semiconductor junction showing a Schottky conduction mechanism in positive bias and a space charge limited conduction mechanism in negative bias. The red electroluminescence effect is discussed considering both a radiative recombination process occurred at the interface due to the presence of Mn2+ ions and an energy transfer mechanism assisted by the migration of the high amount of oxygen vacancies present in the interface.