A large project (START) on "Simulation of Advanced Semiconductor Devices" funded by the Austrian Federal Ministry for Science and Research (BMWF) through the Austrian Science Fund (FWF) enters into its fifth year.
The project includes several research topics, such as modeling of novel semiconductors (strained Si/SiGe, various III-Vs, as well as the Group IV-VI material systems). The device applications include advanced high-frequency high-power Heterojunction Bipolar Transistors (HBTs) and High Electron Mobility Transistors (HEMTs), as well as quantum wires and high-efficiency solar cells.
Physics-based analytical models for the lattice, thermal, band structure, and transport properties of various semiconductor materials, as well as models for important high-field and high-doping effects taking place in the devices, are derived and implemented in the device simulator Minimos-NT. The models are calibrated against experimental data from our scientific partners. Novel device structures are investigated, designed, and optimized.
For example, a recent work confirms that multiple avalanching Gunn domains are responsible for the superfast switching observed in GaAs bipolar transistors. Results from two-dimensional hydrodynamic simulations help to understand the generation, transient behavior, and absorption of these domains. The switching includes fairly complex processes: a variation in the number of domains during the transient, a variation in domain amplitude and width, and a variation in the ionization rates within the domains and in the density and energy of the electron-hole plasma between them. The work is very challenging, since the computation of a single transient requires a few weeks, or even months, on the fastest machines currently available, even after major code optimizations.