Plasmonic Photodetector Incorporating SrTiO3 Interfacial Layer

Hot carrier injection over Schottky barrier between metal and semiconductor is one of the promising ways to effectively use Ohmic losses of plasmonic structure.　Regarding plasmon induced photo-detection, much effort was... [ view full abstract ]

Hot carrier injection over Schottky barrier between metal and semiconductor is one of the promising ways to effectively use Ohmic losses of plasmonic structure.　Regarding plasmon induced photo-detection, much effort was putted in exploring high absorption structure with enough thin metal. Besides simple metal/semiconductor structure, inserting a functional interfacial layer expands research fields and applications.

In this study, we propose and demonstrate stable and bias-dependent photocurrents upon resonant plasmonic excitation with ultrathin SrTiO₃ interfaces [Adv. Funct. Mater. 2018, 1705829]. The structure is gold gratings on p-type silicon substrate; lattice matched epitaxially grown SrTiO₃ layer is inserted between them. After the cyclic voltage scanning, the device shows p-type Schottky-like rectified response. Opto-electric properties of the device, after soft-electric breakdown, are evaluated using custom built microscope system with super continuum white laser. We verified wavelength and polarization dependent photocurrent, whose resonance wavelength and polarization agree well with numerical calculations. Because the SrTiO₃ layer is epitaxially grown with perfect lattice matching, our device has shown stable electric response under reverse bias as high as 100 V, allowing tunability of the Schottky photodetector. Although we examined the photocurrent response on different SrTiO₃ thicknesses (5, 10, and 40 nm), the device with 10 and 40 nm of SrTiO₃ shows no detectable photo-induced currents. Because it is known that thicker StTiO₃ become more conductive; leaky path in thicker SrTiO₃ hinder the photo-induced current over the barrier. There should be the optimal thickness of the interfacial layer for plasmonic photo-detection scheme. 

These observations remarkably expand contemporary knowledge on the hot carrier behaviors surpassing the interfaces, and are beyond conventional considerations for designing a functional Schottky photodetectors. We believe that the investigation paves the way toward plasmon-induced photodetection for practical applications.

[Attached Figures; (Fig .1) Schematic of the device. (Fig. 2) current–voltage plots before and after soft-electric breakdown. (Fig. 3) Measured r photo-induced current of the device. ]