Modeling and Characterization of Vertical GaN Schottky Diodes with AlGaN Cap Layers

A new gallium nitride (GaN) Schottky device structure suitable for power electronic applications is discussed. A GaN Schottky diode with an ultrathin AlGaN cap layer was fabricated using an Ni/Au metal stack as the Schottky electrode. C-V measurements at various temperatures were used to calculate a barrier height of 0.65 V with a free electron concentration of 5 × 10¹⁵ cm^-3 both of which appear temperature independent. A forward conduction model based on a thermionic emission-diffusion process with tunneling through the AlGaN barrier was developed and compared favorably to experimental data. A reverse conduction model utilizing thermionic field emission (TFE) with a triangular energy barrier is presented and then improved upon with a scaling factor that modifies the barrier thickness. This TFE model compares more favorably with the experimental data than the standard thermionic emission model typically used in Schottky diodes. Both the forward conduction and reverse conduction characteristics were assessed at room temperature and elevated temperature. The model can be used to predict how the physical parameters of the device affect its I-V characteristics.