Dislocation-governed current-transport mechanism in (Ni/Au)-AlGaN/AlN/GaN heterostructures

The current-transport mechanisms in (Ni/Au)-Al0,22Ga0,78N/AlN/GaN heterostructures were studied by using temperature dependent forward-bias current-voltage (I-V) characteristics in the temperature range of 80-410 K. In order to determine the current mechanisms for (Ni/Au)-Al0,22Ga0,78N/AlN/GaN heterostructures, we fitted the experimental I-V data to the analytical expressions given for the current-transport mechanisms in a wide range of applied biases and at different temperatures. The contributions of thermionic-emission, generation-recombination, tunneling, leakage currents that are caused by inhomogeneities, and defects at the metal-semiconductor interface current mechanisms were all taken into account. The best fitting results were obtained for the tunneling current mechanism. On the other hand, we did not observe sufficient agreement between the experimental data and the other current mechanisms. The temperature dependencies of the tunneling saturation current (I-t) and tunneling parameters (E-0) were obtained from fitting results. We observed a weak temperature dependence of the saturation current and the absence of the temperature dependence of the tunneling parameters in this temperature range. The results indicate that in the temperature range of 80-410 K, the mechanism of charge transport in the (Ni/Au)-Al0.22Ga0.78N/AlN/GaN heterostructure is performed by tunneling among those dislocations intersecting the space charge region. The dislocation density (D) that was calculated from the I-V characteristics, according to a model of tunneling along the dislocation line, gives the value of 0.24x10(7) cm(-2). This value is close in magnitude to the dislocation density that was obtained from the x-ray diffraction measurements.