Mechanism of current flow in a Au–Ti–Al–Ti–n$^+$-GaN ohmic contact in the temperature range of 4.2–300 K

The temperature dependence of the contact resistivity $\rho_c(T)$ of Au–Ti–Al–Ti–n$^+$-GaN ohmic contacts is studied experimentally and substantiated theoretically in the temperature range $T$ = 4.2–300 K. It is shown that the saturation portion of $\rho_c(T)$ is observed in the low-temperature measurement region (4.2–50 K). As the temperature increases, $\rho_c$ decreases by the exponential law. The experimental and calculated dependences $\rho_c(T)$ are in agreement. The obtained results make it possible to conclude the field nature of the current transfer for the saturation region of $\rho_c(T)$ and the thermal-field one, for the exponential region.