Photoelectric effect of hybrid ultraviolet-sensitized phototransistors from an n-type organic semiconductor and an all-inorganic perovskite quantum dot photosensitizer

High photoresponsivity MoS2phototransistor through enhanced hole trapping HfO2gate dielectric

Phototransistor using 2D semiconductor as the channel material has shown promising potential for high sensitivity photo detection. The high photoresponsivity is often attributed to the photogating effect, where photo excited holes are trapped at the gate dielectric interface that provides additional gate electric field to enhance channel charge carrier density. Gate dielectric material and its deposition processing conditions can have great effect on the interface states. Here, we use HfO2gate dielectric with proper thermal annealing to demonstrate a high photoresponsivity MoS2phototransistor. When HfO2is annealed in H2atmosphere, the photoresponsivity is enhanced by an order of magnitude as compared with that of a phototransistor using HfO2without annealing or annealed in Ar atmosphere. The enhancement is attributed to the hole trapping states introduced at HfO2interface through H2annealing process, which greatly enhances photogating effect. The phototransistor exhibits a very large photoresponsivity of 1.1 × 107A W-1and photogain of 3.3 × 107under low light illumination intensity. This study provides a processing technique to fabricate highly sensitive phototransistor for low optical power detection.

Tetrachromatic vision-inspired neuromorphic sensors with ultraweak ultraviolet detection

Sensing and recognizing invisible ultraviolet (UV) light is vital for exploiting advanced artificial visual perception system. However, due to the uncertainty of the natural environment, the UV signal is very hard to be detected and perceived. Here, inspired by the tetrachromatic visual system, we report a controllable UV-ultrasensitive neuromorphic vision sensor (NeuVS) that uses organic phototransistors (OPTs) as the working unit to integrate sensing, memory and processing functions. Benefiting from asymmetric molecular structure and unique UV absorption of the active layer, the as fabricated UV-ultrasensitive NeuVS can detect 370 nm UV-light with the illumination intensity as low as 31 nW cm^-2, exhibiting one of the best optical figures of merit in UV-sensitive neuromorphic vision sensors. Furthermore, the NeuVS array exbibits good image sensing and memorization capability due to its ultrasensitive optical detection and large density of charge trapping states. In addition, the wavelength-selective response and multi-level optical memory properties are utilized to construct an artificial neural network for extract and identify the invisible UV information. The NeuVS array can perform static and dynamic image recognition from the original color image by filtering red, green and blue noise, and significantly improve the recognition accuracy from 46 to 90%.

Photogating Effect-Driven Photodetectors and Their Emerging Applications

Rather than generating a photocurrent through photo-excited carriers by the photoelectric effect, the photogating effect enables us to detect sub-bandgap rays. The photogating effect is caused by trapped photo-induced charges that modulate the potential energy of the semiconductor/dielectric interface, where these trapped charges contribute an additional electrical gating-field, resulting in a shift in the threshold voltage. This approach clearly separates the drain current in dark versus bright exposures. In this review, we discuss the photogating effect-driven photodetectors with respect to emerging optoelectrical materials, device structures, and mechanisms. Representative examples that reported the photogating effect-based sub-bandgap photodetection are revisited. Furthermore, emerging applications using these photogating effects are highlighted. The potential and challenging aspects of next-generation photodetector devices are presented with an emphasis on the photogating effect.

Fully Photoswitchable Phototransistor Memory Comprising Perovskite Quantum Dot-Based Hybrid Nanocomposites as a Photoresponsive Floating Gate

Tremendous research efforts have been dedicated into the field of photoresponsive nonvolatile memory devices owing to their advantages of fast transmitting speed, low latency, and power-saving property that are suitable for replacing current electrical-driven electronics. However, the reported memory devices still rely on the assistance of gate bias to program them, and a real fully photoswitchable transistor memory is still rare. Herein, we report a phototransistor memory device comprising polymer/perovskite quantum dot (QD) hybrid nanocomposites as a photoresponsive floating gate. The perovskite QDs offer an effective discreteness with an excellent photoresponse that are suitable for photogate application. In addition, a series of ultraviolet (UV)-sensitive insulating polymer hosts were designed to investigate the effect of UV light on the memory behavior. We found that a fully photoswitchable memory device was fulfilled by using the independent and sequential photoexcitation between a UV-sensitive polymer host and a visible light-sensitive QD photogates, which produced decent photoresponse, memory switchability, and highly stable memory retention with a memory ratio of 10⁴ over 10⁴ s. This study not only unraveled the mystery in the fully photoswitchable functionality of nonvolatile memory but also enlightened their potential in the next-generation electronics for light-fidelity application.