I. Introduction
Diamond power devices are considered to be important components in the next-generation low-loss power electronics. The diamond semiconductor possesses a wideband gap of 5.5 eV, leading to an extremely high electric-field strength of 10 MV/cm, which is superior to other materials such as GaN and 4H-SiC [1], [2]. Power devices are required to be operated with very high reliability in automobiles, trains, infrastructures, and so on. Since they must sustain high voltages in the kilo-volt range, inclusion of defects in the crystal lattices, which causes leakage current, must be suppressed. However, such defects are frequently observed in the devices and deteriorate their performance. Therefore, the correlation of defects and leakage current can be important information to improve the material growth and device fabrication technologies [3]–[6].