Abstract

Development of thinner and lighter photodetectors is in demand as sensing and imaging elements that are loaded on wearable electronics. Photodetectors driven by carrier intra-band transitions such as silicon and gallium arsenide have been on a market for a long time. However, these photodetectors are not suitable for ultra-thin photodetectors since reducing their active layers also reduces light absorption acquired by the active layers. Therefore, we proposed an alternative photodetector that satisfies both thinness and high responsivity [1]. The photodetector is driven by photo-thermoelectric conversion and detects incident light through light absorption and thermoelectric conversion of a thin film with nanohole (NH) arrays. When light illuminate the one end of the NH film, plasmons are excited on the NH structures and generate local heating, resulting in a temperature difference between the ends of the thin film. As a result, the temperature difference between the ends of the thin film is converted into an electric voltage by Seebeck effect, leading to an indication of light incidence. The NH on the thin film photodetector functions as an optical coupler that absorbs incident light and a thin-film thermoelectric element that converts a thermal gradient into an electric voltage. It means that the NH periodicity has a key role not only in light absorption but also in thermoelectric property since the NH periodicity may inhibit the phonon transportation, resulting in a reduction of thermal conductivity of the film and an improvement in the thermoelectric property. To clarify the effect of the NH periodicity on the thermoelectric properties of the bismuth telluride (BiTe) compound thin film photodetector, we prepared photodetectors with different NH periodicities and investigated the relationship among the NH periodicity, extinction, and responsivity.

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