UV‐Induced Multilevel Current Amplification Memory Effect in Zinc Oxide Rods Resistive Switching Devices

Abstract

Zinc oxide (ZnO) devices represent an alternative in the semiconductor technology for their application in resistive switching memory devices and ultraviolet (UV) photodetectors due to their chemical and electrical properties. The multilevel current amplification of ZnO rods RRAM devices induced by UV light illumination is reported here for the first time. The resistive switching mechanism underlying in this type of devices is attributed to the formation of conductive filaments composed of oxygen vacancies. The analysis of the photodecay processes carried out on the devices fabricated with different electrodes shows that the type of interface (Ag/ZnO and Au/ZnO) affects the surface barrier height, which influences the photodecay rate. It is shown that by applying UV light, higher relaxation constants (slower photodecay rates) are obtained and lead to multilevel current amplification behavior.

Recent Developments and Perspectives for Memristive Devices Based on Metal Oxide Nanowires

“…Enhanced photoconductivity properties compared to bulk materials or thin films can be observed in nanostructures, since a larger harvesting activity of photons and surface state densities are correlated with the high surface to volume ratio of these structures. An increase of resistive switching performances in terms of endurance has been reported also in ZnO NR arrays contacted by Ag and FTO electrodes by Russo et al [294] Instead, an opposite trend was reported by Bera et al [292] that observed a suppression of resistive switching characteristics as a consequence of UV illumination in ZnO NRs/Nb-doped SrTiO 3 heterojunctions. In this case, authors pointed out that the illumination conditions (with a xenon light source, spectrum in the range 200-2500 nm) can strongly modify the I-V characteristic inducing resistive switching.…”

Piezophototronic Effect Modulated Multilevel Current Amplification from Highly Transparent and Flexible Device Based on Zinc Oxide Thin Film

“…The fundamental processes behind the observed experimental results are related to strain‐induced polarization charges, which in turn can effectively modulate the oxygen absorption/desorption process, resulting in tunable optoelectronic performance . In fact, multilevel photo current amplification with UV illumination in ZnO‐based device has been demonstrated due to oxygen absorption/desorption process by Russo et al For better understanding, the band diagram of the device under the thermal equilibrium condition is presented in Figure d …”

“…As strain changes from the compressive to the tensile, it is found that the current decreases, as also occurs with illuminating intensities. This indicates that the current across the device can be modulated over a wide range by applying strain as well as UV intensity, offering multilevel operation . A comprehensive map of photocurrent values was obtained by tuning of the UV intensities and the mechanical strain, as shown in Figure c.…”

“…Figure a shows the current–voltage ( I – V ) characteristics of the external strain‐free ZnO/AgNWs/PET device under dark and with UV illumination (λ = 365 nm, 4 mW cm –2 ). The current increased with I – V cycles under UV illumination (marked by the red arrow), due to an increase in photogenerated electron–hole ( e – h ) pairs . On the other hand, the current decreased gradually in the dark condition (marked by the green arrow), indicating the recombination process.…”

“…Under UV illumination, photoinduced hole–electron pairs are generated. Out of which the holes react with chemisorbed oxygen on surface, as per h + + O 2 − (ad) = O 2 (g) reaction and electron remains with in the ZnO . As a result, free electron concentration within the ZnO increases.…”