Defect-assisted tunneling via Ni/$n$–GaN Schottky barriers

Schottky barriers on GaN is considered on the basis of an analysis of the features of the current-voltage characteristics of Ni/$n$–GaN diodes. It is found that the forward I–V characteristics on a semilogarithmic scale have the form of curves with steps at biases corresponding to the Gaussian bands of localized states of defects in the GaN band gap. It is shown that the experimental current-voltage characteristics are in agreement with a simple physical model that takes into account the thinning of the Schottky barrier due to the space charge of ionized deep centers, which stimulates the concentration of the electric field near the Schottky contact and tunneling of electrons by hopping between local centers through the near-contact layer. At forward biases, this causes an exponential increase in the tunneling current of electrons thermally activated to an energy corresponding to the peak of the Gaussian band. The recharging of the states of the Gaussian band is accompanied by a decrease in the probability of tunneling and the appearance of a current plateau on the forward lg I(Vj) curves. An increase in the space charge of deep centers under reverse bias leads to tunneling leakage and limits the breakdown voltage.