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 breakdown in pseudomorphic Heterojunction Field Effect Transistors (HFETs). The effects of the energy conservation equation and the space charge effects of generated carriers are studied in the model. The model is then used to study breakdown in GaAs channel and In/sub 0.53/Ga/sub 0.47/As channel HFETs. The model shows that impact ionization breakdown in these structures is dominated by generation in two regions: (1) the high field region near the corner of the gate, and (2) the channel near the top heterojunction. Next, the effect of a thin pseudomorphic layer, which has a high threshold energy for impact ionization, is studied. This layer is shown to significantly improve the breakdown. voltage of the HFET if used properly. Finally the effects of doping on breakdown voltage of these HFETs are studied. This study shows that increased doping can improve the maximum estimated output power of these devices.