5.1 Conclusion

Considerable effort was spent on MINIMOS-NT to get it ready for simulation of devices with high complexity in respect to materials, geometries, etc. Many of the existing physical models (bandgap, mobility, thermal conductivity, energy relaxation times, specific heat, etc.) were refined, some of them were replaced by promising new ones, and many new models were added as well. Critical issues concerning simulation of heterostructures were analyzed, such as interface modeling at heterojunctions and insulator surfaces, band structure and bandgap narrowing, the modeling of self-heating and high-field effects. Being an ancestor of the well-known MOS device simulator MINIMOS, its experience with silicon devices was inherited. Thereby, MINIMOS-NT became a generic device simulator accounting for a variety of micro-materials, including group IV semiconductors, III-V compound semiconductors and their alloys, and non-ideal dielectrics.

Several applications of industrial interest employ devices operating in a wide temperature range. Therefore, our models have been designed to meet this challenge in addition to the conventional Silicon applications. MINIMOS-NT has been successfully used for simulation of heterostructure devices, such as HEMTs and HBTs. Physics-based DC-simulations, mixed-mode device/circuit simulations, small-signal RF-parameter simulations, and device reliability investigations of high practical value were performed.

In the thesis, simulation results for several different types of GaAs-based and Si-based HBTs demonstrating the extended capabilities of MINIMOS-NT are shown, most of them in comparison with experimental data. Special emphasis is put on the simulation of high-power AlGaAs/GaAs and InGaP/GaAs HBTs. Two-dimensional DC-simulations of four different types of one-finger devices in very good agreement with measured data in a wide temperature range are demonstrated. Self-heating effects are accounted for the output device characteristics. The work is extended with transient simulation of small-signal parameters to connect DC- and RF-operation. A comparison between simulated and measured S-parameters is presented. Device reliability investigations which confirm the usefulness of device simulation for practical applications are also offered. In particular, the influence of the InGaP ledge on the device performance of InGaP/GaAs-HBTs is analyzed. Examples of SiGe HBTs and polysilicon emitter BJT conclude the work presented in the thesis.