7 Conclusion
 
A framework is given necessary for physical device simulation of GaAs based High Electron Mobility Transistors. The principles of a HEMT are explained including the limits given by the pseudomorphic AlGaAs/InGaAs/GaAs material system. Effects such as crystal strain and quantization of electrons in the channel are taken into account. The most important models such as drift diffusion transport and hydrodynamic transport and their physical parameters are presented. It appears to be very important to include tunneling through potential barriers in the simulation. The segment split method of the simulator MINIMOS­NT makes it possible to account for such effects.

A setup was developed which is capable of simulating all investigated devices which are based on the same principal epitaxial layers with a single consistent set of model parameters. To obtain a realistic description of the device characteristics also process uncertainties are explicitly allowed in the simulation. To fit the simulation results of all devices to measured data only parameters such as location and concentration of active doping, gate­to­channel separation and interface charge density had to be adjusted.

The investigated devices practically cover the complete range of technically relevant geometries. The obtained transconductances and current gain cut-off frequencies range from 460 mS/mm to over 800 mS/mm and 23 GHz to 110 GHz, respectively. Simulation of a large variety of devices with only one consistent set of parameters is the basis for predictive device simulation not only to optimize device performance but also to reduce technological effort by optimization of performance, yield and cost.

Further developments on the simulator should improve the HD model for InGaAs and AlGaAs. At present the thermionic field emission model is only capable of reproducing certain characteristics. Improved physical modeling will significantly increase the predictive capabilities of the simulator. Furthermore the rigorous inclusion of impact ionization in the presented simulation setup is very desirable.
 

   
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