Advances in Gallium-Based Metal Monochalcogenide Photodetectors: From Fundamental Physics to Heterojunction Engineering

Two-dimensional (2D) metal monochalcogenides (MMCs) have emerged as a pivotal class of semiconductors, offering unique optoelectronic properties that bridge the gaps left by graphene and transition metal dichalcogenides. This review provides a comprehensive analysis of gallium-based MMCs, specifically GaS and GaSe, detailing their evolution from fundamental material physics to advanced device applications. We begin by elucidating the core sensing mechanisms-photoconductive, photogating, and photovoltaic effects-that govern light-matter interactions in 2D systems, followed by a rigorous definition of the figures-of-merit essential for evaluating photodetector performance. The article systematically surveys contemporary synthesis strategies, contrasting top-down exfoliation methods with bottom-up growth techniques such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and pulsed laser deposition (PLD). A significant focus is placed on heterojunction engineering, highlighting how the integration of Ga-based MMCs into van der Waals heterostructures and 2D/3D interfaces can enhance carrier mobility, prolong photocarrier lifetimes, and enable self-powered operation. By synthesizing the current state of research, this work underscores the transformative potential of gallium-based MMCs in the development of next-generation, high-sensitivity multispectral photodetectors.