We fabricated Schottky barrier diodes (SBDs) on the entire surface of a ð010Þ β-Ga 2 O 3 single crystal, and investigated the leakage current in both forward and reverse directions. Subsequently, we investigated the distribution of dislocation and void etch pits on the entire surface. The dislocation etch pit density on the surface ranged from <1 ' 10 3 to 6 ' 10 4 , and its average was 1.1 ' 10 4 cm %2 . The void etch pit density on the surface ranged from <5 ' 10 2 to 7 ' 10 3 , and its average was 6 ' 10 3 cm %2 . From a comparison between the SBD leakage current and the dislocation and void etch pit densities, we found that dislocations are closely related to the SBD reverse leakage current, and that not all voids produce the leakage current.

The electrical properties of Schottky barrier diodes (SBDs) on a (001) β-Ga2O3 substrate were characterized and correlated with wet etching-revealed crystal defects below the corresponding Schottky contacts. The etching process revealed etched grooves and etched pits, indicating the presence of line-shaped voids and small defects near the surface, respectively. The electrical properties (i.e., leakage currents, ideality factor, and barrier height) exhibited almost no correlation with the density of the line-shaped voids. This very weak correlation was reasonable considering the parallel positional relation between the line-shaped voids extending along the [010] direction and the (001) basal plane in which the voids are rarely exposed on the initial surface in contact with the Schottky metals. The distribution of small defects and SBDs with unusually large leakage currents showed similar patterns on the substrate, suggesting that these defects were responsible for the onset of fatal leak paths. These results will encourage studies on crystal defect management of (001) β-Ga2O3 substrates for the fabrication of devices with enhanced performance using these substrates.

A pixel array of vertical Schottky-barrier diodes (SBDs) was fabricated and measured on the surface of a β-Ga2O3 single crystal. Subsequently, etch pits and patterns were observed on the same surface. Three types of etch pits were discovered: (1) a line-shaped etch pattern originating from a void and extending toward the [010] direction, (2) an arrow-shaped etch pit whose arrow’s head faces toward the [102] direction and, (3) a gourd-shaped etch pit whose point head faces toward the [102] direction. Their average densities were estimated to be 5 × 102, 7 × 104, and 9 × 104 cm−2, respectively. We confirmed no clear relationship between the leakage current in SBDs and these crystalline defects. Such results are obtained because threading dislocations run mainly in the [010] growth direction and do not go through the sample plate.

Sputter-deposited indium–tin oxide (ITO) electrodes became ohmic contacts for unintentionally doped β-Ga2O3(010) substrates with a carrier concentration of 2 × 1017 cm−3 after rapid thermal annealing in a wide range of annealing temperatures of 900–1150 °C. The formation of an ohmic contact is attributed to interdiffusion between ITO and β-Ga2O3, as evidenced by the results of transmission electron microscopy and energy-dispersive X-ray spectroscopy. The interdiffusion decreases the band gap and increases the donor concentration of β-Ga2O3 at the interface, and forms an intermediate semiconductor layer desirable for carrier transport. The ITO ohmic contact is particularly useful for future β-Ga2O3 devices operated at high temperatures.

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