Optoelectronic Simulation At The Device And Circuit Level

Device modeling for circuit simulation provides an essential coupling between new device development and its application toward systems integration. In the exploratory research and development environment, it is important to analyze the potential impact of new devices on systems performance by timely development of device models and circuit simulation capability. The conventional approach, which involves developing and coding new model equations into an existing circuit simulator, requires a significant amount of time not only for model development, but also for code debugging. SMILE (illinois Simulator for the Modeling of Integrated-circuit Level Elements) was created to overcome this bottleneck. iSMILE is a versatile “SPICE-like‘’ circuit simulator which allows for easy userdefinition of new circuit-level models [ 11. While a major portion of the program source code must be rewritten i n order to introduce a new device model into a conventional circuit simulator, with SMILE, implementation of a new model requires only the creation of a Fortran model input file (MIF) containing the circuit model topology and the device terminal characteristics. SMILE automatically generates source code internally to build simulation capability based on this model file. Once the new model has been added, it can be accessed at the input deck level like other standard devices such as the MOSFET and the BJT. In view of the fact that it can be used to easily implement new, user-defined models, iSMILE can be considered a superset of SPICE. The ease of new model implementation makes iSMILE ideal for simulating optoelectronic components for which new models have not yet been implemented in existing circuit simulators. In addition to models for conventional electronic devices (MOSFET, BJT, diode, etc.), we have implemented models for MSM photodetectors [2], multiple quantum-well laser diodes [3], and HEMTs 141 for use in optoelectronic circuit simulation. The MSM, laser diode and HEMT models have been successfully used in the design and simulation of several optoelectronic subsystems including both photoreceivers and transmitters. As an example, the equivalent-circuit model for the quantum-well laser diode is depicted in Figure I . This model is based on the well-known rate equations which describe the rates of change of the charge and photon density in the quantum well in terms of physical laser parameters: