Reproducing GaN HEMT Kink Effect by Simulating Field-Enhanced Barrier Defect Ionization

Abstract

The kink effect, long observed in GaN high electron mobility transistors (HEMTs), is investigated with the Fermi kinetics transport hot electron simulation method. Fermi kinetics assigns piecewise Fermi-Dirac electron distributions to the conduction band valleys determined by the GaN electronic band structure and computes their behavior according to the thermodynamics of ideal Fermi gases. Charge fluxes are determined from moments of the Boltzmann equation, including nonparabolic electron densities of states and group velocities, as well as phonon and ionized impurity scattering. The model has been further generalized to include field-enhanced tunneling ionization of deep traps. Comparing simulations with measured data suggests that the kink effect could be caused by field-enhanced ionization of deep AlGaN barrier traps beneath the gate and close to the GaN/AlGaN interface. Further simulations indicate hot electrons may play key roles in both the trap emission and capture processes.