In the past few decades, there have been tremendous advances in optoelectronic integrated circuits (OEICs), primarily because of their widespread use in optical communication systems. Among OEICs, some of the key drivers have been high performance, low cost, and small size of photoreceivers. And in photoreceivers and optical receivers, the photodetector and preamplifiers are critical components. The photodetector's function is to convert light (photons) or radiant energy into charge carriers, electrons and holes, which can then be processed, stored, or transmitted again . Further, a monolithically integrated photoreceiver has several advantages–low parasitics, compact size, and low cost. To date, various designs and structures of photodetectors, transistors, and integrated circuits have been used to produce high-performance integrated photoreceivers. In the design of integrated photoreceivers, various devices and circuit parameters are involved. To obtain the best possible photoreceiver performance, the parameters of both the photodetector and the preamplifier should be optimized. Therefore, we concentrate on describing some important photodetector structures and optical receivers. An example of a typical optical detection system is shown in Fig. 5.1 [1–4]. In an optical communication system, the photodetector can be configured either as a direct or incoherent detector, or as a coherent detector.