Multiplier Effects of Photodetectors—Source of Gain

A photodetector is a type of optoelectronic device with excellent photoelectric conversion abilities, which has especially important applications in many fields such as optical communication, image sensing, aerospace/environmental detection, and military safety. Among these applications, the multiplier effect of optoelectronic devices has been widely explored because photodetectors can convert a very weak optical signal into electrical signal output and offer amazing electron multiplication abilities. To date, hundreds of multiplier effects of photodetectors have been reported. However, there are few reviews on the multiplier effects of such devices. Here, a review of the multiplier effects of photodetectors covering detection spectra from ultraviolet to infrared is presented, including photodetectors based on inorganic materials, organic materials, and organic/inorganic materials. First, we provide brief insights into the detection mechanisms of multiplier effects of photodetectors and introduce the merits that represent key factors for a reasonable comparison of different photodetectors. Then, the multiplier effect on different types of material photodetectors is reviewed. Notably, we summarize the optimization directions of the performance of the multiplier photodetectors, including improving the external quantum efficiency, reducing the dark current, and increasing the response speed and spectral regulation. Finally, an outlook is delivered, the challenges and future directions are discussed, and general advice for designing and realizing novel high-performance photodetectors with multiplier effects is given to provide a guideline for the future development of this fast-developing field. The bottlenecks of existing multiplier technology are also analyzed, which has strong reference significance for the future development of this field.