Reverse Schottky gate current in AlGaN-GaN high-electron-mobility-transistors

Two theoretical one-dimensional models are developed for reverse currents through Schottky gate contacts on AlGaN-GaN high-electron-mobility-transistors (HEMTs) and compared with measurement data. One model covers ideal triangular and square junction barriers and contains current contributions of thermionic emission, thermionic field emission, and tunneling of electrons from the contact metal towards the two dimensional electron gas (2-DEG) at the AlGaN-GaN interface. The second model describes the contribution of trap assisted tunneling through a Schottky barrier. Both models are compared with measurements done on AlGaN-GaN diodes at reverse voltages between threshold voltage and zero volt, which is the regime in which the current flow can be described by one-dimensional models. The trap assisted tunneling model cannot explain the data. The first model agrees with the measurements only if it is assumed that the barrier is triangular and that the current only flows through a fraction (2 x 10(-4)) of the junction area, probably through defect patches. The triangular barrier in the defects has a barrier height of 0.58 eV. This result is consistent with previously reported findings of defect patches at the AlGaN surface