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We report a theoretical model for characterization of a double heterojunction (DH) photovoltaic detector for application in the midinfrared (MIR) wavelength region. The physics-based closed-form model developed here has been applied to study the characteristics of an n ϩ -InAsSbP-n 0 -InAsSb-p ϩ -InAsSbP DH detector grown by liquidphase epitaxy (LPE) for possible application in the 2-to 5-m wavelength region. The results obtained from the experimental measurements have been compared and contrasted with those predicted on the basis of the theoretical model. The model can be used to explain the various physical mechanisms that shape the characteristics of the device under room-temperature operation. It can also be used to optimize the performance of the photodetector to suit specific requirements. The study reveals that compositional grading in the active and the cladding regions of a DH grown by LPE is responsible for the reduction of the responsivity and detectivity of the device in the shorter wavelength region.

Cave and karst systems represent some of the least studied extreme environments on the planet. Caves are in most cases characterized by extreme nutrient deficiency and utter darkness (Dong et al., 2020), characteristics quite inhospitable to life. However, understanding the karst critical zone (Chen et al., 2018) is of fundamental importance to vast numbers of the global population who rely on karst aquifers for fresh drinking water supplies (Stevanovic, 2019). Possibly the least well-established connections within karst and cave science revolve around the role of microbial communities within karst, their sources, abundance, community structure and their ability to adapt and even thrive in cave environments (Engel, 2010). It is possible that microbial communities play a central role in the karst aquifer system; their utilisation and consumption of key nutrients (C, N, S, and P) may help to balance the anthropogenic increase in nutrient loads to many karst environments. With microbes holding such a