Sensitive Photodetectors Based on MoS2/TiO2 and Their Applications

The interaction between light and matter represents a vital scientific issue, leading to numerous technological advancements, including photodetectors, photodiodes, solar cells, photoresistors, and photoelectric memristors. These scientific problems and technical applications are mainly based on the semiconductors, so a deeper understanding of the photoelectric effects in semiconductors is needed to drive progress in the field.
The photoelectric effects in semiconductors are mainly reflected in the changes of photovoltage and photoconductance, which correspond well to the lateral photovoltaic effect (LPE) and the bipolar-resistance effect (BRE), respectively. We investigate the lateral photovoltaics and spatial resistance on p-Si surfaces under 520 nm laser stimulation. Because of the surface states of p-Si, the lateral photovoltage sensitivity can reach 286 mV/mm, and the spatial resistance change ratio can reach 1059%. Then, we modulate these two effects by growing three different morphologies of MoS2 on the Si surface. Due to the photosensitive properties of MoS2 nano-particles, the lateral photovoltage sensitivity can be enhanced up to 368 mV/mm, and the spatial resistance change ratio can reach 2202%. This modulation strategy can realize both photovoltage-based detection and photoconductivity-based detection, which provides a reliable reference for the study of photoelectric devices.
In addition to MoS2, we find that covering the surface of p-Si with TiO2 films also greatly enhances the optical response of the device. Using the photosensitive properties of TiO2 and the effects of oxygen vacancy in anatase TiO2, we successfully obtain the giant laser induced resistance effect in Ag/TiOx/p-Si structure, and its electrical conductivity is enhanced by about 4000 times with the response time of less than 24 μs (the response time of most TiO2 thin film devices is in the order of milliseconds to seconds), which greatly improves the performance of TiO2-based photodetectors.
Based on the above excellent optical response performance of MoS2/TiO2, we fabricate ITO/MoS(2-x)Ox/Ti/p-Si structure device. This device exhibits photoelectric-cooperative regulating multi-level resistance characteristics, which has great application potential in the field of multivalued logic (MVL) technology. We use the type-Ⅲ heterojunction formed by MoS(2-x)Ox and Ti to achieve negative differential resistance (NDR) effect, and we analyze its potential in ternary logic processing. Then, utilizing the photosensitive characteristics of the structures, laser is introduced to regulate the effect, so that the device additionally presents quaternary/binary logic under low/high bias. Finally, we achieve the processing of binary/ternary/quaternary logic on a single device through different control methods. This work provides new ideas and directions for the development of MVL technology.
In summary, we have conducted a detailed study on the optoelectronic characteristics of TiO2 and MoS2, respectively. These two materials have been combined to create a multi-level resistive switching device that can be applied to MVL processing under different control methods. We believe that these works have deepened our understanding of optoelectronic effects in semiconductors and broadened the application fields of novel optoelectronic detectors.