Research Projects

Photodetector is a very important optoelectronic device used for the detection of different regions of the electromagnetic spectrum according to the sensitivity of the detector in these regions. The sensitivity of the photodetector depends upon the energy band gap of the material used to fabricate a photodetector. NIR to MIR photodetection is technologically very desirable but the photodetectors used in this region of the electromagnetic spectrum still facing the challenge of room temperature operation. 2D materials such as graphene, transition metal chalcogenides, black phosphorous (bP) etc. have numerous favourable properties for their use in photodetection applications. These properties include layer dependent optical band gap and van der Waals stacking between the layers. Layers dependent tunability in bandgap allows to tune the sensitivity of the photodetector in different regions of the electromagnetic spectrum while van der Waals stacking allows the fabrication of van der Waals heterostructure based devices which are free from chemical bonding at the heterostructure interface. Absence of chemical bonding at the interface of heterostructures provides them near ideal operation which can improve the device functionality making the path for room temperature operations. Additionally, the 2D van der Waals materials such as transition metal chalcogenides, black phosphorous (bP) have the large optical anisotropy, which allows to detect polarization states of the incident radiation. Polarization detection is crucial aspect of photodetection, and the traditional polarization detection system require tedious and complex integration of polarization sensitive components. The use of van der Walla heterostructures enables the photodetectors to be polarization sensitive. Despite these factors, the heterostructures based photodetection devices suffer from dark current which limits the device detectivity at weak signals. This issue can be resolved by stacking a hexagonal Boron Nitride (hBN) layer at the heterostructures. Hexagonal boron nitride (hBN) is widely considered to be the most promising 2D insulator having high degree of anisotropy. This layer will induce asymmetric tunnelling between the photogenerated signals and dark signals which can be optimized by carefully controlling the hBN layer thickness. The proposed photodetection device will be three terminal devices consisting of two van der Waals heterostructures. It will have the structure as transition metal chalcogenide or bP/hBN/bi-layer or monolayer graphene/hBN/few layer graphene. Two van der Waals heterostructures will be expected to control the device in the batter way to reduce the effect of dark current of the device performance.