Study of the leakage current mechanism in Schottky contacts to Al0.25Ga0.75N/GaN heterostructures with AlN interlayers

The leakage current mechanism in Schottky contacts (SCs) to Al 0.25 Ga 0.75 N/GaN heterostructures incorporated by a thin high-temperature (HT) AlN interlayer has been investigated using current–voltage measurements, atomic force microscopy and deep level transient spectroscopy. It is found that the HT AlN interlayer thickness has a significant effect on the leakage current in SCs. The leakage current density decreases to 1.1 × 10 −4 A cm −2 when the growth time of the AlN interlayer increases from 0 to 10 s, and then changes to increase with increasing growth time. Correspondingly, the heterostructure with the AlN growth time of 10 s has the least number of surface pinholes. The thickness of the HT AlN also influences the density of electron traps with the activation energy of 0.762 eV in an Al 0.25 Ga 0.75 N barrier. It is suggested that the HT AlN interlayer adjusts the microstructure and the defect state density in the Al 1− x Ga x N barrier, and the leakage via these defect states makes the main contribution to the leakage current in SCs to Al 1− x Ga x N/GaN heterostructures.