# Trends in Performance Limits of the HOT Infrared Photodetectors
## 7 Conclusions  
In the last decade considerable progress in fabrication of SWIR and MWIR 2D material and CQD photodetectors has been demonstrated together with their integration into thermal imaging cameras. At current status of technology, the performance of both types of photodetectors is inferior in comparison with HgCdTe photodiodes. It seems that only PbS CQD photodetectors characterized by multicolor sensitivity and detectivity comparable to InGaAs detectors (which are currently the most common in commercial applications) have been located at the good position in IR material family at present time. Figure 20: Room-temperature spectral detectivity curves of the commercially available photodetectors [PV Si and InGaAs, PC PbS and PbSe, HgCdTe photodiodes (solid lines reference [33])]. The experimental data for different types of CQD photodetectors are marked by dot points (reference [49; 70; 78; 79; 80; 81]). Also, spectral detectivity of new emerging T2 SL IB QCIPs are included [38]. PC—Photoconductor, PV—Photodiode. Discovery of graphene in 2004 gave a new impetus on technology development and investigations of 2D layered materials where their uncommon electronic and optical properties make them promising candidates for IR photodetectors. Despite spectacular demonstration of high detectivity like this achieved for black phosphorus layered photodetectors in MWIR spectral range [46] and noble TMD photodetectors like PdSe\({}_{2}\)/MoS\({}_{2}\) heterojunction with record detectivity in LWIR range at room temperature [47], many challenges remain to be introduced to exploit the distinct advantages of these new materials. The prospect of commercialization of 2D material photodetectors depends on their large-scale integration with existing photonic and electronic platforms like CMOS technologies, high operability, spatial uniformity temporal stability, and affordability. Industry fabrication of devices is in the early stage of development and manufacturability. In general, pristine narrow gap 2D materials are characterized by weak optical absorption and short carrier lifetime. Various ingenious approaches (electron trap layers, photogating effect with the graphene fast transfer channel) enhance sensitivity, however on the other side, degrade the electronic performance including carrier mobility. In this way high 2D material photodetector sensitivity collides with slow response time what seriously limits their practical applications. In spite of sixty years development history of HgCdTe, it ultimate HOT performance limit has not been achieved. In order to achieve this goal, the doping concentration below \(5\times 10^{13}\) cm\({}^{-3}\) is required. This level of doping concentration has been recently achieved in fully-depleted HgCdTe FPAs by Teledyne Technologies. At present stage of HgCdTe technology, the semiempirical rule Rule 07 (specified in 2007), widely popular in IR community as a reference for other technologies, was found not to fulfil primary expectations. In this paper, it was shown that the potential properties of HOT HgCdTe photodiodes operating above 3 \(\upmu\)m guarantees achieving more than order of magnitude higher detectivity (above \(10^{10}\) Jones) in comparison with value predicted by Rule 07, and this detectivity is limited by background. In this context it is rather difficult to compete 2D material and CQD photodetectors with HgCdTe photodiodes. Conceptualization, A.R., P.M.; writing--Original draft preparation, A.R., P.M., M.K. and W.H. ; writing--Review and editing, A.R., P.M., M.K. and W.H. ; visualization, A.R., P.M., M.K. and W.H. ; supervision, A.R. and P.M.; project administration, A.R., P.M. and M.K. ; funding acquisition, A.R., P.M. and M.K. All authors have read and agreed to the published version of the manuscript. This research was funded by the Polish National Science Centre; grant number OPUS-UMO-018/31/B/ST7/01541, HARMONIA-UMO-2018/30/M/ST7/00174, OPUS-UMO-2017/27/B/ST7/01507 and UMO-2019/33/B/ST7/00614. Not applicable.