YMnO₃-based photocapacitive detectors in the visible light regime

YMnO₃ is one of the few materials that exhibit ferroelectricity and antiferromagnetism. Ferroelectricity and antiferromagnetism in case of YMnO₃ can be observed up to 900 K and 80 K, respectively. The remanent polarization of YMnO₃ amounts to 2 uC/cm² and metal-YMnO₃-metal thin film structures can be switched between a high resistance state (HRS) and a low resistance state (LRS). In case of YMnO₃ thin film, the transition from HRS to LRS (set process) occurs at the voltages 10 V and higher, while the transition from LRS to HRS (reset process) is triggered at the smaller voltages. This unipolar resistive switching is nonvolatile and has a resistance ratio of 5 orders of magnitude [1]. In pure YMnO₃, absorption occurs throughout the entire visible light region, resulting in its black color [2]. This work investigates the effect of light-irradiation on the capacitance of YMnO₃-based metal-ferroelectric-insulator-semiconductor (MFIS) structures. The thickness and optical constants of all layers of the MFIS diodes have been investigated using spectral ellipsometry measurements with a VASE ellipsometer assuming the refraction index of SiN to be 1.95 [3]. The DC bias for the capacitance measurements was swept from +10 to -20 V and back under different light-irradiation at a sweep rate of 230 mV/s. It has been found that under dark conditions two nonvolatile capacitance minima exists at -11 and at -3.55 V, possibly when the YMnO₃ is in the LRS and HRS state, respectively. If we rewrite the +10 and -20 V branch in shorter period of time then, low capacitance state (LCS) is non-volatile and pseudo volatile, respectively. Under illumination the capacitance at the two minima increases in the visible spectral range, depending on the wavelength illumination, YMnO₃ thickness and capacitance state.
[1] A. Bogusz et al., IEEE Xplore (2013), DOI:10.1109/ISCDG.2013.656319
[2] A. E. Smith et al., J. Am. Chem. Soc. 131, 17084 (2009)
[3] A. Laades et al., Phys. Stat. Sol. C 9, 2124 (2012)