Effect of AlN interlayer thickness on leakage currents in Schottky contacts to Al0.25Ga0.75N/AlN/GaN heterostructures

The leakage current mechanism in Schottky contacts (SCs) to A_l0.25Ga_0.75N/GaN heterostructures incorporated by thin high-temperature (HT) AlN interlayer has been investigated using current-voltage measurements, atomic force microscopy, and deep level transient spectroscopy. The HT AlN interlayer thickness has a significant effect on the leakage current in SCs. The leakage current density is reduced to 1.1×10^-4 A/cm² rapidly when the growth time of AlN interlayer increases from 0 to 10 s, and then changes to increase with increasing the growth time. Correspondingly, the heterostructure with 10 s AlN interlayer has the least number of surface pinholes. HT AlN thickness also influences significantly the density of the electron traps with the activation energy of 0.762 eV in Al_0.25Ga_0.75N barrier. It is suggested that HT AlN interlayer adjusts microstructures and defect states density in Al_1-xGa_xN barrier, and leakage via these defect states makes the primary contribution to the leakage in SCs to Al_1-xGa_xN/GaN heterostructures.