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In this letter, slow and fast trap states in metal-oxide-semiconductor (MOS) capacitors fabricated on recessed AlGaN/GaN heterostructures were studied by frequency dependent conductance measurements. In particular, the comparison of devices before and after annealing in forming gas allowed to ascribe the fast states (with characteristic response time in the range of 5-50 mu s) to SiO2/GaN "interface traps," and the slow states (50-100 mu s) to "border traps" located few nanometers inside the SiO2 layer. These results can be important to predict and optimize the threshold voltage stability of hybrid MOS-based transistors on GaN.

This letter reports on the temperature behavior of the structural and electrical properties of Ti/Al/Ni/Au contacts to AlGaN/GaN heterostructures. While Ohmic contacts formed at 750 °C showed a decreasing temperature behavior of the specific contact resistance RC, which was explained by a thermionic field emission mechanism, an increasing trend is observed in the contacts formed at 850 °C. In this case, RC exhibits a "metal-like" behavior, i.e., describable by a T^1.8 dependence. The microstructural analysis of the interfacial region allowed to explain the results with the formation of metallic intrusions contacting directly the two dimensional electron gas.

In this letter, the physical effects of the local surface thin thermal oxidation on the current transport in AlGaN/GaN heterostructures are reported. Current-voltage measurements performed on appropriate test patterns demonstrated that a selective oxidation process at 900 degrees C enables the suppression of the current flow through the two-dimensional electron gas. The electrical insulation was achieved even though structural analysis showed that the formed oxide did not reach the depth of the AlGaN/GaN heterointerface. The combination of capacitance-voltage measurements with depth-resolved scanning capacitance microscopy enabled to correlate the electrical results to the doping and the compositional stability of the material during oxidation. (c) 2008 American Institute of Physics.

In this letter, a correlation between the nanoscale localized electrical properties of the Pt/GaN Schottky barrier and the temperature behavior of macroscopic Schottky diodes is demonstrated. Although a significant improvement of the ideality factor of the diodes is achieved after annealing at 400 degrees C, local current-voltage measurements, performed with a biased tip of a conductive atomic force microscope, revealed the inhomogeneous nature of the barrier. Its nanoscale degree of homogeneity was quantitatively described by means of Tung's model [Phys. Rev. B 45, 13509 (1992)], allowing the authors to explain the temperature dependence of the electrical characteristics of the macroscopic diodes.