A theoretical study on the dynamic process of the lateral photovoltage in perovskite oxide heterostructures

The lateral photovoltaic process on the La0.9Sr0.1MnO3 /SrNb0.01Ti0.99O3 heterostructure is revealed by solving time-dependent drift-diffusion equations in a two dimensional scenario. We find that both the conventional lateral photovoltage LPV effect and the Dember effect contribute to the LPV. Under a low irradiation, the conventional LPV process plays a main role in the lateral photovoltaic process. With the laser pulse energy large enough, the Dember process becomes dominant. Due to the competition between Dember and conventional lateral photovoltage, a laterally modulated photovoltage can be obtained theoretically on the n-type side of the heterostructure. © 2010 American Institute of Physics. doi:10.1063/1.3313943 Much attention has been paid to the photovoltaic effect on perovskite heterostructures due to its potential application on the generation of photovoltaic and photocurrent detectors. Under a nonuniform irradiation on a p-n junction, an additional photovoltage parallel to the plane of the junction can be produced, besides the transverse photovoltage. This photovoltage is recognized as lateral photovoltage LPV. 1 According to the conventional LPV theory, 1‐5 in the nonuniformly irradiated p-n junction, the photoinduced electrons and holes near the irradiation center are separated into n- and p-type sides by the built-in field respectively. Then electrons and holes diffuse out of irradiation regions in the n- and p-type sides, respectively. 5 Thus, the electric potential nearer the irradiation center is higher than that far from the center on the p-type side, while it is lower on the n-type side. However, an unusual LPV phenomenon has recently been observed in both the La0.9Sr0.1MnO3 /SrNb0.01Ti0.99O3 LSMO/SNTO and La0.7Sr0.3MnO3 /Si heterojunctions. 6 In this observation, the photoinduced electric potential near the irradiation center on the two sides of the p-n junction, are both higher than those far from the irradiation center in pand n-type regions, respectively. This phenomenon challenges the conventional LPV explanation. 6 Therefore, Dember effect 7 has been introduced in Ref. 6 to qualitatively explain the unusual lateral LPV in the heterostructures. Dember effect, which is induced by the difference of carriers’ hole and electron diffusion coefficients, has been widely studied on many semiconductor surfaces and applied on producing terahertz THz rays. 8‐10 In the Ref. 6, it has been pointed out that larger LPV produced in heterostructures than that in the bulk materials perhaps suggests some potential applications of the Dember effect in heterostructures. Thus, our theoretical understanding on the dynamic process of LPV in heterostructures should be helpful for obtaining some THz sources. Nevertheless, the evolution process from the conventional and Dember LPV effects remains unknown, an insight understanding of this phenomena or a systematic theoretical study which can describe both the conventional and the unusual LPV effects are still absent. In this work, we present a unified description for the unusual LPV process by solving the time-dependent driftdiffusion equations, which reveals the evolution process from the conventional and Dember effect with the increase in the irradiated laser pulse energy. Under a low energy laser irradiation, most of the photoinduced electrons and holes are separated by the strong built-in electric field and then diffuse away from the irradiated region in the n- and p-type sides, respectively, being identical with the conventional lateral photovoltaic process. With the increase in the laser pulse energy, due to the limitation of the built-in field, and the unseperated carriers directly diffuse along the lateral direction on both sides of the p-n junction, which causes Dember process. Due to the competition between Dember and conventional lateral photovoltage processes, a laterally modulated photovoltage is obtained theoretically on the n-type side of the heterostructure. The two-dimensional 2D time-dependent driftdiffusion equations 11 consist of Poisson equation and the car