Inhabiting the earth, we depend on three things for our existence: air, water and light. Compared with air and water, the visible but invisible light has made people addicted for a long time: if the light waves are like particles, they are delicate and powerful, simple and colorful. How can we unveil her charming veil, the photodetector came into being. Light itself flutters softly and is elusive, but with the help of her interaction with matter, subtle light signals can be converted into easily identifiable electrical signals and controlled. From ripple-like fluctuations to single-photon capture, whether as weak as a firefly or as strong as an X-ray burst, or as monochromatic as a laser or as broad as the solar spectrum, photodetectors have been widely used in ray detection, industrial automation control, missiles Guidance, infrared thermal imaging and infrared remote sensing, etc.

Returning to the earth beneath our feet, she itself is a real substance, composed of various elements. For thousands of years, the development of human civilization has always been accompanied by the discovery of new materials. With the advancement of scientific instruments, all kinds of amazing artificial materials emerge in an endless stream. Recently, layered two-dimensional materials have set off an upsurge in materials research. Essentially, two-dimensional materials with atomic layers (single or several layers, with a thickness of several nanometers to less than one nanometer), such as graphene, boron nitride, transition metal dichalcogenides (TMD), etc., are artificial. materials, because most of them are difficult to exist alone in nature. However, due to the controllability of the number of layers (or thickness) and the exotic physical properties, such materials have become popular in recent years. Among them, many two-dimensional materials have excellent optoelectronic properties and are widely used in photodetectors.

A new two-dimensional material: tin diselenide (SnSe2) was synthesized by chemical vapor deposition method, and its characteristics were described in detail. Different from the widely studied 2H-phase 2D materials such as MoS2, their synthesized materials exhibit 1T phase, and unlike the mostly metallic 1T-phase 2D materials, 1T-phase SnSe2 has semiconducting properties. Single crystal SnSe2 can be fabricated into atomic layer-thick SnSe2 by mechanical lift-off, and further processed into field effect transistors (FETs) and photodetectors. Tests have shown that the bilayer SnSe2 transistor has an electron mobility of about 4 cm2V-1s-1 and an on-off ratio greater than 103, and the most exciting thing is that its photodetector exhibits a room temperature response time of about 2 milliseconds. This makes SnSe2 one of the fastest photoresponse 2D materials. It is worth noting that the room temperature response time of 2 milliseconds measured experimentally has reached the lower resolution limit of the measuring instrument, and the intrinsic photo-optical response time of SnSe2 is very likely to be as low as microseconds. In addition, including SnSe2 itself, the tin selenide family itself contains three layered heterogeneous melt phases. Therefore, this system still has great potential to be tapped.

We believe that this research will open a window for optoelectronic research based on 1T two-dimensional materials, and provide new ideas for optoelectronic interactions based on atomic-layer two-dimensional materials. These materials that harness the light will write new notes for the dance of light and materials that will be intricate and graceful.
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