THEORETICAL-ANALYSIS OF THE BREAKDOWN VOLTAGE IN PSEUDOMORPHIC HFETS

In this paper a two-dimensional (2-D) model based on a solution to the moments of the Boltzmann transport equation is used to study breakdow n in pseudomorphic Heterojunction Field Effect Transistors (HFET's), T he effects of the energy conservation equation and the space charge ef fects of generated carriers are studied in the model. The model is the n used to study breakdown in GaAs channel and In0.53Ga0.47As channel H FET's. The model shows that impact ionization breakdown in these struc tures is dominated by generation in two regions: 1) the high field reg ion near the corner of the gate, and 2) the channel near the top heter ojunction, Next, the effect of a thin pseudomorphic layer, which has a high threshold energy for impact ionization, is studied, This layer i s shown to significantly improve the breakdown voltage of the HFET if used properly. Finally the effects of doping on breakdown voltage of t hese HFET's are studied, This study shows that increased doping can im prove the maximum estimated output power of these devices.