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7. Summary and Conclusions

Due to the rapid progress of Si technology and the introduction of new device types and materials, it is a challenging task to develop and improve models for TCAD device simulation. In this development process it is essential to have access to reliable data from measurements, but as device fabrication gets more and more complex also experiments become more expensive and - as a major drawback - also more time consuming. As a consequence it is of increasing interest to obtain data by simulations based on more fundamental methods.

In this work it has been shown that Monte Carlo methods based on a full-band dispersion relation are a powerful tool in this respect. Full-band Monte Carlo is generally applicable to hot carrier problems, because an accurate representation of the band structure at higher energies is essential here. Beyond that, the simulator has been extended to handle transport in arbritrarily strained Si, Ge and SiGe alloys. This is an important feature, since modern high performance MOSFET devices rely heavily on strain engineering techniques to increase the performance. It has been exemplarily demonstrated that in Si the electron mobility is increased by a strain setup and that in Ge the higher hole mobility compared to Si can be further increased by the introduction of strain.

These effects are explained by an evaluation and theoretical interpretation of band structure data from EPM calculations. It is concluded that the electronic mobility increase or decrease, depending on the setup, stems from an energy separation of the valleys, which also lifts their degeneracy, and from a change in the effective masses in transport direction. For hole transport the latter effect is also valid, but there is also a contribution from the relative shift of the heavy hole, light hole and split-off bands.

It has been also demonstrated that the high computational costs of full-band Monte Carlo can be reduced by the implementation of performance optimizing features like rejection algorithms or irregular mesh refinement in -space. These features in combination with the availability of successively increasing computational power indicate that full-band Monte Carlo will play a stronger role in device simulation in the future.

In this work Monte Carlo techniques are also applied to simulate blocked impurity band photo detectors. These devices operate at temperatures below . The scattering models were extended to deliver valid results in this temperature range. Some simulation results of the avalanche effect in blocked impurity band devices were presented. The avalanche effect can be used to operate the devices as single photons detectors.


next up previous contents
Next: Bibliography Up: Dissertation Gerhard Karlowatz Previous: 6. BIB Devices

G. Karlowatz: Advanced Monte Carlo Simulation for Semiconductor Devices