Electrical and photogalvanic properties of Fe:LiNbO3 thin films fabricated by ion slicing

With the constantly growing global energy demand and the connected deterioration of the physical environment, great efforts are being devoted to develop renewable and carbon-free energy sources. The ability of photovoltaic to harvest electric energy from light makes it one of the promising technologies to help solving the energy problem. Classical photovoltaic technology, which is based on p-n junctions, could be improved by the transition to ferroelectric materials that exhibit a bulk photovoltaic effect. These materials could provide access to higher power conversion efficiencies, thanks to their higher achievable open-circuit voltages, while the lack of a p-n junction would make them simpler and cheaper to fabricate. It has been recently proposed that a way to increase the conversion efficiency of ferroelectric photovoltaic could be through the use of nano-sized crystals. Focusing our attention on iron doped lithium niobate as a prototypical material, the proposed experiment involves the fabrication of Fe:LN heterostructures based on a commercial Fe:LN Smart-Cut(TM) thin film, with junctions on metal or semiconductor electrodes. The ultimate goal is to investigate how the current photogeneration behaves at the nano-scale; for this reason, it is mandatory to understand the physics behind the charge transport processes, the role of the interfaces and the impact of the ferroelectric switching on the final device. The study of the electrical and photogalvanic properties is achieved by analysing current-voltage characteristic curves measured with a source meter both in dark and lit conditions. The analysis of dark I-V curves shows that Richardson-Schottky and Poole-Frenkel models are the most appropriate ones to describe the charge transport in our samples, as expected from considering their band diagrams. Then, the particular current peaks observed in the case of PEDOT:PSS electrodes are attributed to the polarization switching of the crystalline film. Their characterization provides an estimation of the main related quantities, such as the spontaneous polarization and the coercive and residual fields, which are compared successfully with results from other works reported in literature. Finally, the measured photogalvanic currents are studied in relation to the illumination irradiance, producing results in line with those present in literature.