# Trends in Performance Limits of the HOT Infrared Photodetectors
## 5 2D Material Infrared Photodetectors
### Detectivity: HgCdTe Photodiode Versus 2D Material Photodetectors  
Figure 10 presents detectivity, D\({}^{*}\) curves gathered from literature for HOT MWIR and LWIR photodetectors both for commercially available devices (PV Si and InGaAs, PC PbS and PbSe, HgCdTe photodiodes) and IB QCIP T2 SLs, as well as for 2D material photodetectors. All experimental data gathered in Figure. 10 indicates on sub-BLIP photodetectors performance. As is shown, the literature data for 2D material photodetectors in LWIR above 3 um is limited to several device structures. The Gr/FGF detector utmost detectivity in MWIR is comparable to HgCdTe. However, especially high detectivity (higher than for HgCdTe photodiodes) is demonstrated for black phosphorus arsenic (bPAs) detectors [46]. Their sensitivity enters the second atmospheric transmission window. Here it must be stressed, that the serious drawback of black phosphorus is surface instability in ambient conditions what can considerably limit its prospective applications [55; 65]. More promising is stable TMD photodetectors like PdSe\({}_{2}\)/MoS\({}_{2}\) heterojunction with record detectivity in LWIR range at room temperature. However, their practical application lies in perfect material synthesis and processing being still under development.  
Figure 12 compares the experimental detectivity, D\({}^{*}\) published in literature for different types of single element 2D material photodetectors operating at room temperature with theoretically predicted curves for P-i-N HOT HgCdTe detectors. As is presented, the detectivity values for selected 2D material photodetectors are close to data presented for commercial detectors (PV Si and Ge, PV InGaAs, PC PbS and PbSe, PV HgCdTe), and in the case of black phosphorus and TMD detectors are even higher. The enhanced sensitivity of 2D material photodetectors is introduced by bandgap engineering and photogating effect, what degrades the electronic material properties. In consequence, the layered-material photodetectors are characterized by limited linear dynamic range of operation and slow response time.  
To summarize the discussion in this section about 2D material IR HOT photodetectors we can conclude that:  
* in general, the 2D material IR detectors performance is lower in comparison to the commercially available detectors, especially HgCdTe and new emerging III-V compounds including T2 SLs,
* responsivity improvement by using combination of 2D materials with bulks (hybrid photodetectors) owing to the photogating effect causes the limited linear dynamic range due to the charge relaxation time, which lead to decrease in sensitivity with incident optical power,
* responsivity of hybrid and chemically functionalized 2D material photodetectors is comparable with detectors existing on the global market; however, a significant decrease in operating speed (bandwidth) is observed; in general, their response time (millisecond range and longer) is three orders of magnitude longer compared to commercially available photodetectors (microsecond range and shorter) [12],
* the commercialization potential will not just depend on the detector performance, but on the distinct advantages in the ability for fabrication of large scale high quality 2D materials at a low cost,
* experimental data presented by the Teledyne Technologies group [66] support theoretical prediction of background limited P-i-N HgCdTe photodiodes and gives further encouragement for their operation in near room-temperature conditions.