Figure 2: Cross-section of HFET model (a) triode operation with its four physical zones and the voltages at the boundaries between them. (b) Saturated operation with its 5 physical zones. Except for Z4, the dotted line indicates the electron path in the 2DEG just below the AlGaN/GaN interface. In Z4, the 2DEG is disrupted and the electrons disperse away from the interface to form a net space charge in the GaN, as discussed in the text.