A theoretical study on the dynamic process of the lateral photovoltage in perovskite oxide heterostructures
A theoretical study on the dynamic process of the lateral photovoltage in perovskite oxide heterostructures
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DOI：
10.1063/1.3313943
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发表时间：
2010-02
影响因子：
4
通讯作者：
Leng Liao;K. Jin;C. Ge;Chun-lian Hu;Hui‐bin Lu;Guo‐zhen Yang
中科院分区：
文献类型：
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作者：
Leng Liao;K. Jin;C. Ge;Chun-lian Hu;Hui‐bin Lu;Guo‐zhen Yang
在二维情况下，通过求解随时间变化的漂移扩散方程，揭示了La0.9Sr0.1MnO3/SrNb0.01Ti0.993异质结的横向光伏过程。我们发现，传统的横向光伏LPV效应和Dember效应都对LPV有贡献。在低照度下，传统的LPV工艺在横向光伏工艺中起主要作用。当激光脉冲能量足够大时，Dember过程占主导地位。由于Dember和常规横向光伏的竞争，理论上可以在异质结的n型一侧获得横向调制的光伏。©2010美国物理研究所。DOI：10.1063/1.3313943由于其在光伏和光电流探测器方面的潜在应用，钙钛矿异质结构的光伏效应引起了人们的极大关注。在p-n结的非均匀照射下，除了横向光电压外，还可以产生一个平行于结平面的附加光电压。这种光伏被认为是横向光伏LPV。1根据传统的LPV理论，1-5在非均匀辐照的p-n结中，辐照中心附近的光生电子和空穴分别被内置场分成n型和p型边。然后，电子和空穴分别从n型和p型边的辐照区域扩散出来。因此，在p型侧，靠近照射中心的电势高于远离中心的电势，而在n型侧，电势较低。然而，最近在La0.9Sr0.1MnO3/SrNb0.01Ti0.993LSMO/SNTO和La0.7Sr0.3MnO3/Si异质结中都观察到了不寻常的LPV现象。6在本实验中，在p型和n型区域，p-n结两侧靠近辐照中心的光生电势均高于远离辐照中心的光生电势。这一现象挑战了传统的LPV解释。6因此，文献[6]引入了Dember效应7。6定性地解释了异质结中异常的横向LPV。由于载流子的空穴扩散系数和电子扩散系数的不同而产生的Dember效应，在许多半导体表面都得到了广泛的研究，并被应用于产生太赫兹THz射线。参考文献8-10指出在异质结构中产生的LPV比在块体材料中产生的LPV更大，这可能暗示了Dember效应在异质结构中的一些潜在应用。因此，我们对异质结中LPV动态过程的理论理解将有助于获得某些THz源。然而，从常规LPV效应到Dember LPV效应的演化过程仍然是未知的，对这一现象的深入理解或能够描述常规LPV效应和异常LPV效应的系统的理论研究仍然缺乏。在这项工作中，我们通过求解含时漂移扩散方程，对这一反常的LPV过程给出了统一的描述，揭示了随着辐照激光脉冲能量的增加，从传统效应和Dember效应的演化过程。在低能量激光照射下，大部分光生电子和空穴被较强的内置电场分开，然后分别在n型和p型一侧扩散离开受照区，这与传统的横向光伏工艺相同。随着激光脉冲能量的增加，由于内置场的限制，未分离的载流子直接沿p-n结两侧的横向扩散，从而产生Dember过程。由于Dember和常规横向光伏工艺的竞争，理论上在异质结的n型一侧获得了横向调制的光伏。二维含时漂移扩散方程11由泊松方程和CAR组成
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