The two-dimensional device simulator PRISM (PRogram for Investigating Semiconductor Models) [1], which is a general purpose device simulator, has been adapted to simulate III-V heterojunction FET's [2]. PRISM can now simulate silicon devices (as MOSFET's, bipolar transistors, SO1 structures, etc.,), GaAs MESFET's, Schottky diodes and AIGaAsl GaAs HEMT's.
The program makes use of the finite element method to solve the Poisson equation and the finite boxes method to solve the continuity equations for electrons and holes. There is also an ongoing effort to implement the heat transport equation [3]. The finite element method has rarely been used in HEMT-simulations. The main advantages of this method are the flexibility in defining sloped device contours and the possibilic to refine the mesh only locally, so that the number of nodes only increases moderately, as opposed to the situation with finite difference simulators. This advantage is very usefull for HEMT's were the thin AlGaAs/GaAs heterojunction region ( 40 nm) has to be simulated accurately compared to the bulk region.
Simulations of AlGaAslGaAs HEMT's have been performed, and comparisons with measurements on HEMT's [4] processed in IMEC have been made. The simulated I-V characteristics and the transconductance curves agree very well. Also sheet concentrations and band diagrams can be extracted from the simulation results.