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2.2.2 MINIMOS-NT

The two-dimensional device simulator MINIMOS-NT [56] is an ancestor of the well-known MOS device simulator MINIMOS 6 [57]. MINIMOS-NT is a generic simulator accounting for a variety of materials, including group IV semiconductors, III-V compound semiconductors and their alloys, and non-ideal dielectrics. A stable base of material parameters for semiconductors of interest is extracted and used for device modeling issues. MINIMOS-NT is applicable to devices with high complexity in respect to materials, geometries, etc. allowing state-of-the-art simulations of MOS devices [58], HEMTs [59,60,61], SiGe HBTs [62], and III-V HBTs [63,64]. The models are verified against statistically analyzed measured data.

In MINIMOS-NT the simulation domain is partitioned into independent regions, so-called segments. This partitioning is done with respect to the material class, e.g., contacts, insulators, and semiconductors. For these segments different sets of parameters, models and algorithms can be independently defined. When the simulation domain is properly split into segments, there are no abrupt changes of the material parameters within the segments. Abrupt variations of the material parameters should only occur at the interface of two adjoining segments.

Various important physical effects, such as bandgap narrowing, surface recombination, and self heating, are taken into account. Heat generated at the heterojunctions cannot completely leave the device, especially in the case of III-V semiconductor materials. Therefore, significant self-heating occurs in the device and leads to a change of the electrical device characteristics.

Emphasis was also laid on bandgap narrowing as one of the crucial heavy-doping effects to be considered for bipolar devices [65]. A new physically-based analytical bandgap narrowing model was developed, applicable to compound semiconductors, which accounts for semiconductor material, dopant species, and lattice temperature. As the minority carrier mobility is of considerable importance for bipolar transistors, a new universal low field mobility model has been implemented in MINIMOS-NT [66]. It is based on Monte-Carlo simulation results and distinguishes between majority and minority electron mobilities.

Energy transport equations are necessary to account for non-local effects, such as velocity overshoot [67,68]. A new model for the electron energy relaxation time has been presented [69] which is based on Monte-Carlo simulation results and is applicable to all relevant semiconductors with diamond and zinc-blende structure. The energy relaxation times are expressed as functions of the carrier and lattice temperatures and, in the case of semiconductor alloys, of the material composition.

Considering the nature of the simulated devices (including abrupt SiGe/Si, InGaP/GaAs and AlGaAs/InGaP heterointerfaces) and the high electron temperatures observed at maximum bias sophisticated thermionic-field emission interface models [70] in conjunction with the hydrodynamic transport model are used. At the other (homogeneous or graded) interfaces continuous quasi-Fermi levels are assumed.


next up previous contents
Next: 2.3 Semiconductor Materials Up: 2.2 State-of-the-art Device Simulation Previous: 2.2.1 Device Simulators
Vassil Palankovski
2001-02-28