We studied the roles of lightly doped carbon in a series of n-GaN Schottky diode epitaxial structures on freestanding GaN substrates, and evaluated the effects of the doping on diode performances. A large variation of compensation ratio was observed for carbon doping at (1-2) ' 10 16 cm %3 . A model was proposed to explain this phenomenon, in which a vulnerable balance between donor-type C Ga and deep acceptor C N strongly affected the free-carrier generation. Application of Norde plots and reverse biased leakage current in current-voltage measurements suggested provisional optimization for a free-carrier concentration of 8 ' 10 15 cm %3 to achieve a tradeoff between breakdown voltage and onresistance of the n-GaN diodes.

We report electrical characteristics of 12 Ni Schottky contacts formed on an m-plane surface, which is a cleaved side surface of a c-plane free-standing n-GaN wafer. We observed a variety of distributions of surface steps with heights up to 5 nm in the contact area. The Schottky barrier heights obtained from current–voltage, capacitance–voltage, and photoresponce results distribute in a small range of 0.67–0.79 eV. The n-value is as good as 1.01 to 1.04. Independent of the step height, the barrier height and n-value variations are nearly absent. One possible reason for this is that the step facets consist of an m-plane. We found that the cleaving method can be utilized to form Schottky contacts on m-plane n-GaN surfaces in order to reveal the basic characteristics.

The effects of the inductively coupled plasma (ICP) etching damage on the electrical characteristics of low-Mg-doped p-GaN Schottky contacts were evaluated by high-temperature isothermal capacitance transient spectroscopy. A large single peak for an acceptor-type surface state was dominantly detected for as-grown samples. The energy level and state density were obtained to be 1.18 eV above the valence band, which is close to a Ga vacancy (VGa), and 1.5×1013 cm-2, respectively. It was speculated that a small portion of Ga atoms were missing from the surface, and a high VGa density was observed in a few surface layers. The peak intensity decreased by 60% upon annealing at 800 °C, and further decrease was found by ICP etching. This decrease is consistent with the suppression of the memory effect in current–voltage characteristics. Upon annealing and ICP etching, since the VGa structure might be disordered, the peak intensity decreased.

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