Rectifying behavior and photovoltage effect in La1.3Sr1.7Mn2O7/SrTiO3-Nb heterostructure

Abstract

Perovskite oxide heterostructure possesses attractive magnetic, optical and electric properties, such as superconducting interface between two insulators, two-dimensional electron gas, positive giant magnetoresistance, photoelectric response characteristic, magnetocaloric effect, and coexistent different magnetic structures. Especially for the photoelectric response behaviors of A1-xAxMnO3 (A=La, Pr etc.; A = Sr, Ca etc.) perovskite manganese oxide heterostructure, one has made a systematic study on the photoelectric conversion efficiency, the photovoltaic response speed, and the in-plane lateral photovoltage. Besides A1-xAxMnO3 structure, manganese oxides can also exhibit the double layered perovskite structure A2-2xA1+2xMn2O7. Double layered perovskite structure can be regarded as the layers of perovskite and rock salt which are alternately stacked. This double layered perovskite manganese oxide (such as La2-2xSr1+2xMn2O7) is a natural structure of the tunnel structure: ferromagnetic metal layer-insulating layer-ferromagnetic metal layer. Double layered perovskite manganese oxide has not only the characteristics of giant magnetoresistance, but also the novel physical properties, such as persistent photoconductivity, etc. However, there are few reports on the physical properties of the double layered perovskite manganite oxides, heterostructures, especially the photovoltaic properties. In this work, the La1.3Sr1.7Mn2O7 (LSMO) film is deposited on an n-type SrTiO3-Nb (NSTO) single crystal substrate by a pulsed laser deposition method. Additionally, we study the transporting properties of LSMO/NSTO heterostructure and its photovoltaic effect. The heterostructure exhibits benign rectifying and palpable photovoltaic effect. Under the 532 nm laser irradiation, the photovoltage first increases and then decreases with temperature rising. The maximal photovoltage reaches 400 mV at 150 K which is consistent with the metal-insulator transition temperature of LSMO film. It is indicated that the photovoltaic effect of the heterostructure is regulated by the inner transporting characteristics of LSMO film. The dynamical process of the heterostructure, photovoltaic response, is analyzed. Meanwhile, by analyzing the relationship between the photovoltage and time, it is found that the rising edge fits to the first order exponential function, which is related to the migration of carriers. While the falling edge of second-order exponential function indicates that the compound of carriers has two different physical processes: 1 corresponds to the neutralization process of the carriers aggregated on both junction sides through the external circuit, and 2 corresponds to the annihilation process of non-equilibrium carriers. The carrier lifetime of our p-n junction is longer, on the order of ms, than those of other manganese oxides p-n junctions. Remarkably, the time constants of both the rising edge and falling edge first increase and then decrease as temperature increases, and the maximum values occur at the metal-insulator transition temperature of LSMO film.