4.4 Carrier Mobility

Mobility models which account for the specific physics in a given semiconductor material are crucial for device modeling. While for Silicon there exist well established models [337], the III-V material system still poses certain challenges (e.g. negative differential mobility) and nevertheless, is not so well studied (especially concerning InN). Also certain device specific effects such as high electric fields and very strong gradients of electric fields have to be considered for the simulation of HEMTs.

Several groups have proposed various models and model parameter sets for the simulation of GaN-based devices. Farahmand et al. [253] provide a low-field model which accounts for temperature and ionized impurity concentrations as well as a high-field model based on Monte Carlo simulation results. Another low-field model, valid in a large temperature and concentration range is proposed by Mnatsakanov et al. [338]. A highly parameterized field-dependent model based on an extensive data pool was developed by Schwierz [175]. Turin et al. [339] propose another high-field model which delivers excellent agreement with the results from MC simulations. All those models are suited only for the drift-diffusion transport model. However, the latter is not able to deliver accurate results for sub-micron devices [340], therefore a hydrodynamic transport model is necessary, too.