| Avalanche Photodiodes (APDs) based on III-V compound semiconductors are a key component of current and future high-performance optical communications systems. Recent experimental data has shown that simple homojunction APDs with very thin multiplication regions have performance capabilities that equal or even surpass those of more complex structures. In order to evaluate potential designs, a detailed understanding of impact ionization and other physical processes that determine APD performance is needed. The Monte Carlo method is an ideal tool for the exploration of such a complex system. However, proper evaluation of the gain, noise, and response characteristics of APDs, particularly those with very thin multiplication regions, requires concurrent simulation of hole electron transport with the most realistic possible models--a property lacking in previous efforts. In addition, the sheer diversity of APD designs demands a Monte Carlo simulator with tremendous versatility.; Consequently, we have developed an entirely new Monte Carlo simulation software library based on object-oriented programming principles. This simulation tool, MOMENTS, is written in C++ and has a modular design that provides unprecedented levels of flexibility, extensibility, maintainability, and performance in Monte Carlo simulation not only for APDs but also for a broad range of other applications. We present a detailed description of the design methodology of this library, its features, and its usage. We have also used the MOMENTS library to construct an APD simulator that exploits the most realistic available models for the study of GaAs homojunction APDs with very thin multiplication regions. Results from this simulator are presented. These results serve not only to demonstrate the promising characteristics of this new class of devices, but also to illuminate the serious deficiencies in widely employed impact ionization models. |
