Effects of surface states on the "kink" (or an abnormal increase in output conductance with the drain voltage) in GaAs MESFETs are studied by two-dimensional (2-D) simulations. It is shown that the kink could arise due to a space-charge effect originated from impact ionization of holes and the following hole trapping by the surface states. The onset voltage for current rise depends on the nature of surface states, which strongly affects the potential profiles. Transient or dynamic simulation indicates that the trap-related kink phenomenon should be a rather slow process. Substrate-related kink dynamics are also analyzed.
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