<p>Photodetectors are devices that convert light's photon energy to an electrical signal. They are essential for many scientific executions, such as fiber optic systems for communication, controlling processes, environmental monitoring, safety and security, and defense-related purposes. Photodetectors play a key role in optoelectronic systems with integrated circuits. In the last few years, highly efficient photodetectors (PDs) have been extensively researched to enable fast speeds, large-bandwidth, and low-noise communication devices. In our review, we present the classification of photodetectors including materials, characteristics, and classes. This work also focuses on the figure of merits, measurement of frequency characteristics, and noise in photodetectors. The efficiency enhancement and the performance of each material are summarized. The equivalent circuit model and commercial software packages for modeling photodetectors are highlighted. We present our perspectives on the development of photodetectors and comment on recent directions. Challenges, new trends, and future work are discussed.</p>