  This paper reports on the modulation of Schottky barrier heights (SBH) on
three different orientations of $\beta$-Ga$_2$O$_3$ by insertion of an
ultra-thin SiO$_2$ dielectric interlayer at the metal-semiconductor junction,
which can potentially lower the Fermi-level pinning (FLP) effect due to
metal-induced gap states (MIGS). Pt and Ni metal-semiconductor (MS) and
metal-interlayer-semiconductor (MIS) Schottky barrier diodes were fabricated on
bulk n-type doped $\beta$-Ga$_2$O$_3$ single crystal substrates along the
(010), (-201) and (100) orientations and were characterized by room temperature
current-voltage (I-V) and capacitance-voltage (C-V) measurements. Pt MIS diodes
exhibited 0.53 eV and 0.37 eV increment in SBH along the (010) and (-201)
orientations respectively as compared to their respective MS counterparts. The
highest SBH of 1.81 eV was achieved on the (010)-oriented MIS SBD using Pt
metal. The MIS SBDs on (100)-oriented substrates exhibited a dramatic increment
($>$1.5$\times$) in SBH as well as reduction in reverse leakage current. The
use of thin dielectric interlayers can be an efficient experimental method to
modulate SBH of metal/Ga$_2$O$_3$ junctions.
