Assembling air-sensitive 2D Van Der Waals heterostructures for photodetectors

Abstract

This project explored the fabrication and characterization of air-sensitive 2D Van Der Waals heterostructures for use in photodetector applications. The 2D materials that were utilized were Hexagonal Boron Nitride (hBn) which was used for encapsulation purposes due to its insulative nature, Molybdenum Disulfide (MoS2) and Black Phosphorus (BP) due to its superior monolayer properties and characteristics. A heterostructure stack was then formed using suitable target flake of appropriate thickness and size then a lateral heterojunction was formed between the stack and electrodes after being placed onto an electrode pattern. Due to the air-sensitive nature of BP, only the stacking of hBn and MoS2 was conducted in ambient conditions. The bulk of the stacking and dry transfer process was conducted inside the inert environment of the Glovebox system, so as to avoid degradation of BP when exposed to ambient conditions. Subsequently, characterization techniques such as Atomic Force Microscopy (AFM) and Raman Spectroscopy were utilized to determine the effectiveness and optoelectronic properties of the heterostructure stack for photodetectors. AFM was utilized to determine the thickness of the layers and surface topography of the surface sample. Raman Instruments were used to identify the Raman peaks, optoelectronic properties, photocurrent mapping and IV-characteristic curves of the heterostructure stack. All graph plots were plotted using MATLAB version 2024a. There was enhanced stability due to the hBn encapsulation, type-II band alignment at the MoS2/BP interface which enabled efficient charge separation, self-powered operation as there was photo response at 0V and tuneable gain under bias. This project demonstrated the potential for low-noise, broadband photodetector applications using not only this hBn-MoS2-BP heterostructure but for other heterostructures as well and contributed to advancing the research and understanding of air-sensitive 2D Van Der Waals heterostructures for optoelectronic applications.