A photodetector is an optoelectronic device that detects and converts optical signals into electrical signals. Photodiodes, phototransistors, and photoconductors are examples of these devices.
Although there are many different types of photodetectors with different mechanisms and structures, the representative behaviour can be summarised as a limited number: the output current of a photodiode changes from a rectified to a fully-on state after illumination, whereas the output current of a photoconductor or a phototransistor change from a fully-off to a fully-on state.
From the standpoint of signal change behaviour, a new device that changes the output current from fully-off to rectified state should exist, and it may play an important role in future optoelectronic systems such as optical logic, high-precision imaging, and information processing. For example, rectification controlled by light can avoid the crosstalk issue of photodetector arrays without the use of selectors, allowing the array’s integration to be improved further.
Dong-Ming Sun Group of the Institute of Metal Research, Chinese Academy of Sciences recently proposed a new device called a photon-controlled diode in a paper published in National Science Review, which can change the output current from a fully-off state to a rectified state after illumination, resulting in an anti-crosstalk photomemory array without the use of selectors.
The photon-controlled diode, which is essentially a n/n MoS2 junction inserted between two graphene/MoS2 Schottky junctions at the cathode and anode, was created using a lateral n/n MoS2 junction as a channel, graphene as contact electrodes, and hexagonal boron nitride (h-BN) as a photogating layer material.
The Schottky junctions, which are controlled by light, suppress or permit the rectification behaviour of the n/n junction, allowing the output current of the photon-controlled diode to change from fully off to rectified. The light-to-dark rectification ratio can reach over 106. Its responsivity as a photodetector exceeds 105 A/W, but by increasing the thickness of the photogating layer, the device transforms into a multifunctional photomemory with the highest nonvolatile responsivity of 4.8107 A/W and the longest retention time of 6.5 106 s reported so far.
Using photon-controlled diodes as pixel units, a 33 photomemory array is created with no selectors, demonstrating no crosstalk as well as wavelength and power density selectivity functions. This research paves the way for future high-integration, low-power, and intelligent optoelectronic systems.