The electrical characteristics of GaN p–n junctions grown on freestanding GaN substrates by metal–organic chemical vapor deposition were investigated. The current–voltage (I–V) characteristics of the GaN p–n diode showed relatively low values and, little temperature dependence of the reverse leakage current. The breakdown voltage of the GaN p–n diode was 900 V and the leakage current at 600 V was 1 µA/cm2 or less. The inverse of squared capacitance–voltage (1/C2–V) data showed a linear relationship, indicating an abrupt junction at the p–n interface. Little temperature dependence of the C–V curve was also observed. Plasma etching before the growth of the p-GaN layer induced a large leakage current and a lower breakdown voltage, probably due to the disorder of atomic bonds and the nitrogen depletion at the plasma-etched surface. The insertion of a regrown n-GaN layer between the p-GaN and the plasma-treated n-GaN surface was effective in suppressing the leakage current and recovering the breakdown voltage.
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