Sheet density of electrons in spacer layer of AlGaN/GaN MODFET: calculating and analysing

The finite barrier height at an AlGaN/GaN heterointerface causes the nonvanishing probability of penetration of electrons into it. Therefore a nonzero carrier concentration appears also in the spacer layer of an AlGaN/GaN MODFET. The existence of that charge has not been yet quantitatively considered, but its influence is observed on high gate polarisation in AlGaAs/GaAs heterostructures. Theoretical investigation of surface concentration in this layer n/sub t/ for various gate voltages has shown an increasing characteristic if the gate voltage is increased. The comparison between surface concentration in the spacer layer and in the channel suggests that the former cannot be considered negligible, especially for higher values of gate voltage, when it becomes comparable with the latter. The possible consequences of this effect on device operation undoubtedly deserves to be examined (at least as the influence of parasitic capacitances, if the considerably degraded mobility of these electrons compared to the mobility of channel carriers is accepted beforehand).