# Recent Advances in Photodetectors Based on Two-Dimensional Material/Si Heterojunctions
###### Abstract  
Two-dimensional (2D) materials have gained significant attention owing to their exceptional electronic and optoelectronic properties, including high carrier mobility, strong light-matter interaction, layer-dependent band structure and band gap. The passivated surface of 2D materials enables the fabrication of van der Waals (vdW) heterojunctions by integrating them with various other materials, such as nanowires, nanosheets and bulk materials. Heterojunction photodetectors, specifically those composed of 2D materials and silicon (Si), have attracted considerable interest due to the well-established processing techniques associated with Si and the excellent performance of the related devices. The hybrid dimension vdW heterojunction composed of 2D materials and Si has the advantages of excellent performance, low fabrication cost, and easy integration with silicon-based devices. It has unique advantages in the field of heterojunction photodetectors. This review provides an overview of the recent advancements in photodetectors based on 2D material/Si heterojunctions. First, we present the background and motivation of the review. Next, we discuss the key performance metrics for evaluating photodetector performance. Then, we review the recent progress made in the field of 2D material/Si heterojunction photodetectors. Finally, we summarize the findings and offer future prospects. two-dimensional material; heterojunctions; photodetectors +
Footnote †: journal: Applied Sciences  
**Citation:** [PERSON]; [PERSON]; [PERSON]. Si-based photodetectors, such as Si p-n photodiodes, Si p-i-n photodiodes and Si avalanche photodiodes, are of great importance. The band gap of Si is about 1.1 eV, which sets the long wavelength limit (around 1100 nm) for Si-based photodetectors, thus restricting their ability to detect infrared (IR) light [42]. Moreover, Si-based photodetectors exhibit poor performance in the ultraviolet (UV) wavelength range due to strong surface recombination [43]. In addition, the fabrication process for Si p-n and p-i-n photodiodes is complex and costly [44]. While other types of photodetectors, such as InGaAs, HgCdTe and quantum well-based photodetectors, are available, their fabrication methods are also intricate and expensive. Therefore, there is a need to explore novel photodetector designs that offer high responsivity, fast response speed, broad spectral response and cost-effectiveness. Low-dimensional materials have important applications in photodetectors due to their excellent photoelectric properties, such as III-V nanowire-based photodetectors with good detection performance [45]. However, one-dimensional materials are difficult to grow on a large scale, and it is difficult to achieve the large-scale integration of devices. Quantum dot photodetectors often need to be fabricated based on III-V multilayer film technology, which is expensive and difficult to integrate with Si-based circuits [46]. Therefore, compared to bulk materials and other low-dimensional materials, 2D materials stand out in photodetectors because of their unique physical and optical properties. Considering the facile integration of 2D materials with 3D materials through vdW forces and the well-established Si processing techniques, 2D material/Si heterojunction-based photodetectors have received considerable attention in recent years. An example of this is the fabrication of graphene/Si Schottky photodiodes, where graphene was transferred onto the surface of Si [47]. The photodiodes have exhibited a photodetection performance comparable to commercial Si photodiodes. Exploring the broadband light absorption of thick graphene films, the thick graphene/Si photodiode was able to detect incident light with a wavelength of 4 \(\upmu\)m [48]. By replacing the 2D material with a Weyl semimetal, the detection range of the 2D material/Si photodiode was extended to an ultrabroad band range of up to 10.6 \(\upmu\)m [49]. Two-dimensional material/Si heterojunction photodetectors offer several advantages over single-component photodetectors.