2D layered nanomaterials for semiconductor channel have recently been attracting great attentions from researchers in many possibilities of future applications such as high speed electronics, flexible electronics, and immunity of short channel effects in scale-down transistors. Among many 2D materials molybdenum disulfide (MoS2) is known as a pacesetting material, since it has displayed excellent carrier mobility, a high on/off current ratio, and a good subthreshold swing in a field-effect transistor (FET) form as a 2D n-type channel. In contrast to MoS2, MoTe2 is p-type 2D nanoflake and it has an appropriate bandgap for both visible and infrared light photodetection.
Here, we have fabricated 2D WSe2/MoS2 and MoTe2/MoS2 multilayers van der Waals heterojunction PN diode and its application for visible-near infrared broadband multi-detection. The MoTe2/MoS2 PN diode shows excellent performance with an ideality factor of 1.7 and high rectification (ON/OFF) ratio of over 104. This PN diode exhibits spectral photo-responses from ultraviolet (405 nm) to near infrared (1310 nm) with obvious photovoltaic behaviors. In addition to the static behavior, photocurrent switching behaviors are clearly observed under periodic illuminations at up to 100 KHz. WSe2/MoS2 PN diode demonstrate excellent static and dynamic device performances at a low voltage of 3 V, with an ON/OFF current ratio higher than 106, ideality factors of 1.5, dynamic rectification at a high frequency of 1 kHz, high photoresponsivity of 180 mA W–1. The two types of devices show a linear response within optical power density range from 10-5 Wcm-2 to 1 Wcm-2.
The properties of photoelectrochemical (PEC) cells have mainly been investigated with a focus on PEC hydrogen production. Because anodic current begins to flow when PEC cell is under illumination, and that this current varies as a function of light intensity, PEC cells can be used as a photodetector. Different from other image sensors, PEC cells can detect the light immersed in solutions due to their PEC properties. To verify the feasibility of using silicon-based PEC cell as an image sensor, we demonstrated a single pixel imaging system based on compressive sensing. Compressive sensing is an algorithm designed to recover signals from a small number of measurements, assuming that the signal of interest can be represented in a sparse way. In this study, we have demonstrated multispectral imaging using a siliconbased PEC cell with compressive sensing. The images were obtained in three primary colors (red, green, and blue). Due to the high photoresponse, stability and unique characteristic that silicon-based PEC cell can be used underwater, the silicon-based PEC cell is expected to be utilized in the future as a photodetector for various applications. We believe this study would be a great example of advanced developments in an optoelectronic system based on PEC cells.