Thermionic Field Emission in a Si-Doped AlN SBD with a Graded n+-AlGaN Top Contact Layer

Aluminum nitride (AlN) Schottky barrier diodes (SBDs) with a graded n⁺-AlGaN top contact layer, which enables low contact resistance without sacrificing AlN crystal quality, are demonstrated. From the capacitance-voltage (C-V) measurements, the net donor concentration of $8.3\times 10^{17}\ \text{cm}^{-3}$ and barrier height of 3.48 eV were obtained. The devices showed a clear rectifying current-voltage (I-V) characteristics with extremely low ideality factor of 1.10. We speculated that tunneling transport appears in the forward I-V characteristics due to the high electric field, and the calculation based on the thermionic field emission (TFE) model showed good agreement with the experimental data. The barrier height of 3.38 eV, which is consistent with the value from the C-V measurements, was obtained. The temperature dependence of I-V characteristics was also measured and discussed.