  Vertical (-201) and (010) beta-Ga2O3 Schottky barrier diodes (SBDs) were
fabricated on single-crystal substrates grown by edge-defined film-fed growth
(EFG) method. High resolution X-ray diffraction (HRXRD) and atomic force
microscopy (AFM) confirmed good crystal quality and surface morphology of the
substrates. The electrical properties of both devices, including
current-voltage (I-V) and capacitance-voltage (C-V) characteristics, were
comprehensively measured and compared. The (-201) and (010) SBDs exhibited
on-resistances (Ron) of 0.56 and 0.77 m{\Omega}cm2, turn-on voltages (Von) of
1.0 and 1.3 V, Schottky barrier heights (SBH) of 1.05 and 1.20 eV, electron
mobilities of 125 and 65 cm2/(Vs), respectively, with a high on-current of ~1.3
kA/cm2 and on/off ratio of ~109. The (010) SBD had a larger Von and SBH than
(-201) SBD due to anisotropic surface properties (i.e., surface Fermi level
pinning and band bending), as supported by X-ray photoelectron spectroscopy
(XPS) measurements. Temperature-dependent I-V also revealed the inhomogeneous
nature of the SBH in both devices, where (-201) SBD showed a more uniform SBH
distribution. The homogeneous SBH was also extracted: 1.33 eV for (-201) SBD
and 1.53 eV for (010) SBD. The reverse leakage current of the devices was well
described by the two-step trap-assisted tunneling model and the one-dimensional
variable range hopping conduction (1D-VRH) model. The (-201) SBD showed larger
leakage current due to its lower SBH and smaller activation energy. These
results indicate the crystalline anisotropy of beta-Ga2O3 can affect the
electrical properties of vertical SBDs and should be taken into consideration
when designing beta-Ga2O3 electronics.
