鐵酸鉍作為現在熱門的鐵電材料，因有著相對高的居禮溫度和尼爾溫度，其在室溫下具有多鐵性的特性。此外，相較於其他鐵電材料，鐵酸鉍有著較低的能隙，使其在可見光以及紫外光波段能夠有良好的吸收特性。
本研究中，採用了兩種不同的金屬電極圖形，為直線型電極以及彎曲型電極，每種電極皆包含5種不同數量之指叉電極。設計之目的在於探討每種圖形在不同入射光偏振的模式下，產生的光電流以及磁滯曲線。作為主動介電層材料的鐵酸鉍，透過射頻磁控濺鍍系統沉積於矽基板上，而氧化銦錫用於2個電極圖形之材料。
首先對BFO薄膜進行XRD、XPS以及吸收量測。XRD圖表明BFO薄膜在室溫之下屬於R3c空間群且沒有觀察到第二相或雜質。在XPS圖表明BFO薄膜中存在大量比例的氧空缺。
在量測包含三大部分。首先，研究中在不同圖形下量測了一系列的磁滯曲線，並證明了鉍鐵氧體薄膜中的空間電荷分佈不均。這些不對稱電荷會產生額外的電場而抵消自發極化的極性，進而導致在測量的磁滯曲線中觀察到去極化。
其次，測量了元件的光電流和暗電流，結果表明僅檢測到光電流的輕微增加，這是由於受到 BFO 膜中大量氧空位導致暗電流過大的不利影響。而這些氧空位充當電子電洞對複合中心，會直接導致光電流的減少。
在第三部分中，使用線性偏振光和圓形偏振光作為光檢測的入射光源。如測量結果所示，在圓形偏振光的照射下，無論其旋性方向為何，與線性偏振光相比，具有彎曲指叉電極能夠檢測到更高的光電流。特別是具有八對彎曲指叉電極的元件，能夠使電流增強高達近 60%。
除了磁滯曲線和光暗電流量測，也對元件進行響應度量測。在與具有彎曲型電極的元件相比，具有直線型電極的元件能夠達到2.15A/W的響應度。

Bismuth ferrite, one of the popular ferroelectric materials, has multiferroic properties at room temperature due to its relatively high Curie temperature and Néel temperature. In addition, compared with other ferroelectric materials, bismuth ferrite has a lower bandgap, which enables it to have good absorption properties in the visible and ultraviolet light regions.
In this study, two different metal electrode patterns are adopted, namely, the straight and curved electrodes, each of which contains 5 different numbers of interdigitated electrodes. The design purpose is to investigate the photocurrent and hysteresis loop as a result of exposing each pattern to different incident light polarizations. Bismuth ferrite, as an active dielectric material for light absorption, is deposited on a silicon substrate by RF magnetron sputtering, while indium tin oxide is used as the material for the two electrode patterns.
In the material analysis part, XRD, XPS and absorption measurements are performed on the BFO films. The XRD patterns show that BFO film belongs to the R3c space group at room temperature, and the second phases or impurities are not observed. The XPS images show that the BFO films contain a large proportion of oxygen vacancies.
The measurements consist of three parts. First, a series of hysteresis curves of the component under study is measured with distinct patterns, evincing the bismuth ferrite film with inhomogeneous distribution of space charges. These asymmetrical charges are expected to generate an additional electric field to counteract the polarity of the spontaneous polarization, leading to depolarization as observed from the measured hysteresis loops.
Second, both the photocurrent and dark current of the devices are measured, which further reveals that a slight increase in photocurrent has only been detected which is adversely affected by a large dark current brought forth by a large number of oxygen vacancies in the BFO film. These oxygen vacancies act as electron-hole pair recombination centers that are directly responsible for the curtailment of the photocurrent.
In the third part, both linearly and circularly polarized light beams are used as incident light for photodetection. As measurements have shown, with the illumination of the circularly polarized light, regardless of its handedness, the sample with the curved interdigitated electrode would yield the detection of a higher photocurrent as compared to linearly polarized light. Specifically, the device with eight pairs of curved interdigitated electrodes could render a current enhancement up to nearly 60%.
In addition to the hysteresis curve and photocurrent/dark current measurements, the responsivities of the devices are also characterized. As compared to the photodetectors with curved electrodes, the ones with straight interdigitated electrodes could achieve a responsivity of 2.15 A/W.

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