Study On Photoelectric Properties Of Perovskite-type Rare Earth Nickel RNiO₃ Films

The various physical properties of perovskite materials make it a research hotspot in condensed matter physics.Among them,perovskite-type rare earth nickelate RNiO₃?R is a rare earth element,R? La?attracts people's attention due to its unique electronic structure and easily controlled photoelectric properties.RNiO₃ is a relatively widebandgap p-type semiconductor,which is helpful for the development and design of new types solar blind photodetectors.It has broad application prospects in space exploration and environment monitoring.In this paper,a series of perovskite nickelate thin films were prepared using pulsed laser deposition technology.The photoelectric properties of RNiO₃?R=Sm,Gd,Pr,Nd?films were systematically studied.The physical mechanism of the RNiO₃ properties influenced by various factors such as oxygen vacancy concentration,temperature and electron orbit are analyzed in detail.First,high-quality SmNiO₃ and GdNiO₃ epitaxial thin films were prepared on the ntype semiconductor Nb: SrTiO₃ substrate by pulse laser deposition equipment and high oxygen pressure annealing.The ultraviolet photoelectric properties of SmNiO₃/Nb: SrTiO₃ and GdNiO₃/Nb: SrTiO₃ p-n junctions were studied.The presence of a built-in electric field in the p-n junction helps the vertical separation of photogenerated carriers,SmNiO₃/Nb: SrTiO₃ obtained an open circuit voltage of 0.62 V and a position sensitivity of 22.2 m V/mm under 266 nm UV laser illumination;GdNiO₃/Nb: SrTiO₃ obtains an open circuit voltage of 0.60 V and a position sensitivity of 52.2 m V/mm.The experimental results show that the built-in electric field at the interface of the heterojunction can spontaneously and effectively separate photogenerated carriers,and the performance of the detector can be effectively improved by controlling the band structure of the heterojunction.Secondly,the PrNiO₃/Nb: SrTiO₃ heterojunctions were prepared,the influence of ambient temperature on their photoelectric properties were studied and the effect of the interface of the heterojunction on the photoelectric response was explored.The photoelectric conversion rate of the heterojunction was improved by controlling the thickness of the film and the concentration of oxygen vacancies,and an open circuit voltage of 0.63 V and a position sensitivity of 28 m V/mm were obtained.The thickness of film plays an important role in the size of the built-in field and the recombination efficiency of photogenerated carriers.The change of oxygen vacancy concentration will improve the optical band gap and semiconductor performance of the film.By studying the influence of temperature on the heterojunction resistivity,carrier mobility and time response characteristics,it was confirmed that the lateral photovoltaic ultrafast response characteristics of the heterojunction originated from the ultrahigh interface carrier concentration and mobility.Finally,we prepared a series of high-quality NdNiO₃ epitaxial films under different growth conditions,and combined with first-principles calculations to confirm the internal mechanism of the influence of oxygen vacancy concentration on the photoelectric properties of NdNiO₃.The NdNiO₃ film prepared in the lower oxygen pressure contains a large amount of oxygen vacancies.It has high resistance and low electrocatalytic oxygen evolution capacity.As the growth oxygen partial pressure increases,the resistance of the film becomes smaller and the catalytic ability is enhanced.XPS and other test results show that the increase in in oxygen pressure will change Ni ion from high spin Ni²⁺ to Ni³⁺ with eg orbit occupancy close to 1.The NdNiO₃ film prepared under high oxygen pressure has a low oxygen vacancy concentration and exhibits metallic properties at room temperature.This is because a decrease in the oxygen vacancy concentration will enhance the hybrid strength of the Ni 3d and O 2p orbital of the NdNiO₃ film.First-principles calculations also show that oxygen vacancies can significantly improve the band structure and electronic structure of the film.By studying the effect of oxygen vacancy concentration on the film metal-insulator phase transition,electrocatalytic oxygen evolution reaction and magnetic properties,it is clear that the oxygen vacancy concentration in the film can effectively improve the band structure and electronic structure of the material and affect its electrical transmission characteristics.