Photogating in Low Dimensional Photodetectors

Abstract

Low dimensional materials including quantum dots, nanowires, 2D materials, and so forth have attracted increasing research interests for electronic and optoelectronic devices in recent years. Photogating, which is usually observed in photodetectors based on low dimensional materials and their hybrid structures, is demonstrated to play an important role. Photogating is considered as a way of conductance modulation through photoinduced gate voltage instead of simply and totally attributing it to trap states. This review first focuses on the gain of photogating and reveals the distinction from conventional photoconductive effect. The trap‐ and hybrid‐induced photogating including their origins, formations, and characteristics are subsequently discussed. Then, the recent progress on trap‐ and hybrid‐induced photogating in low dimensional photodetectors is elaborated. Though a high gain bandwidth product as high as 109 Hz is reported in several cases, a trade‐off between gain and bandwidth has to be made for this type of photogating. The general photogating is put forward according to another three reported studies very recently. General photogating may enable simultaneous high gain and high bandwidth, paving the way to explore novel high‐performance photodetectors.

WSe2 Photovoltaic Device Based on Intramolecular p–n Junction

“…The transfer characteristics of the device with V ds = 1 V in dark and under 520 nm illumination are demonstrated in Figure c. The dark current decreases with the increase of a negative back‐gate voltage since the channel is depleted and the Dirac point occurs at V gs = −31 V. Interestingly, unlike common phototransistors in which the photocurrent decreases simultaneously with the dark current, the photocurrent of our device increases while dark current roughly decreases with V gs ←18 V. The p–n junction may play a key role in this phenomenon, so we measure the short‐circuit current of our device with V gs ranging from −40 to 40 V. The dark current in this condition is on the scale of 10 −13 A, mainly depending on the measuring limit of source meter, such a low dark current may facilitate the weak signal detecting . With the WSe 2 channel gradually p‐doped by the increasing negative back‐gate voltage, the Pd–WSe 2 Schottky junction decays and a strong intramolecular p–n junction occurs.…”

UV Photodetectors Based on BiOCl Nanosheet Arrays: The Effects of Morphologies and Electrode Configurations

“…Accordingly, the combination of long lifetime and short transit time of charge carriers might result in photoconductive gain . However, due to low yield of photoinduced electron–hole pairs as well as the severe trapping and recombination of charge carriers in the as‐prepared BiOCl nanosheet with plenty of surface defects, the charge carriers can hardly pass the electrode gap for multiply times within their lifetimes, leading to the low photoconductive gain . The photocurrent of PD based on a single BiOCl nanosheet is quite small and hard to be detected except with very exquisite equipment.…”

Emerging Applications of Elemental 2D Materials

“…Figure c shows that in general the responsivity of 2D‐material‐based photodetectors is as high (0.1–1 A W −1 ) or even higher (up to 10 7 A W −1 ) than traditional materials. However, the average response times are much slower (ms rather than ns timescales) due to a number of factors such as photogating, device architecture as well as trapped charges at interfaces and defects . Future improvements in device performance should result in lower response times (higher bandwidths) and higher responsivities.…”