Avalanche photodetectors based on two-dimensional layered materials

The past decade has witnessed a dramatic increase in interest in emerging photodetectors built from two-dimensional (2D) layered materials. A major driver of this trend is the growing demands for lightweight, uncooled, and even flexible photodetection technology. However, 2D layered materials always suffer from low light absorption coefficients due to their atomically thin nature. Impact ionization, which can achieve carrier multiplication, is a promising strategy to design 2D photodetectors with high detection efficiency. In this review, typical types of photodetection mechanisms in 2D photodetectors are first summarized. We then discuss the avalanche mechanism induced by impact ionization and avalanche photodetectors based on conventional silicon and III-V compound semiconductors. Finally, a host of emerging avalanche photodetectors based on 2D materials and their van der Waals heterostructures, and their potential applications in the field of photon-counting technologies are detailed. By reviewing the recent progress and discussing challenges faced by 2D avalanche photodetectors, this review aims to provide perspectives on future research directions of 2D material-based ultrasensitive photodetectors such as single-photon detectors.