Analysis of electrical properties in Ni/GaN schottky contacts on nonpolar/semipolar GaN free-standing substrates.

• GaN SBDs on a -plane, m -plane, and s5 -plane GaN bulk substrates are investigated. • The barrier inhomogeneities of the a -, m -, and s5 -plane Ni/GaN Schottky contacts are evaluated. • XPS spectra show discrepancy in the distribution of GaO x on the GaN with different planes. This work focuses on the electrical properties of Ni/n-GaN Schottky barrier diodes (SBDs) fabricated on GaN bulk substrates with different crystal orientations. For the SBDs on a -plane, m -plane, and s5 -plane GaN, the Schottky barrier heights (SBHs) exhibited magnitudes of 0.65 eV, 0.69 eV, and 0.75 eV, respectively. The relatively small SBH of a -plane devices results in a relatively larger reverse leakage current than that of m -plane and s5 -plane. In addition, the carrier concentrations extracted by C – V characteristics are comparable for the GaN substrates with different crystal orientations. The temperature-dependent I – V characteristics indicate how the barrier inhomogeneity of the Ni/GaN Schottky contacts on the a -plane GaN is smaller than the others. Based on the XPS spectra results, the discrepancy in Schottky contact characteristics stems from the different polarization charges and/or surface oxides of the different crystal planes. The low GaOx density on a -plane GaN surface contributes to the minimum barrier inhomogeneity of the corresponding SBD devices. [ABSTRACT FROM AUTHOR]