  High-quality dielectric-semiconductor interfaces are critical for reliable
high-performance transistors. We report the in-situ metalorganic chemical vapor
deposition (MOCVD) of Al$_2$O$_3$ on $\beta$-Ga$_2$O$_3$ as a potentially
better alternative to the most commonly used atomic layer deposition (ALD). The
growth of Al$_2$O$_3$ is performed in the same reactor as Ga$_2$O$_3$ using
trimethylaluminum and O$_2$ as precursors without breaking the vacuum at a
growth temperature of 600 $^0$C. The fast and slow near interface traps at the
Al$_2$O$_3$/ $\beta$-Ga$_2$O$_3$ interface are identified and quantified using
stressed capacitance-voltage (CV) measurements on metal oxide semiconductor
capacitor (MOSCAP) structures. The density of shallow and deep level initially
filled traps (D$_{it}$) are measured using ultra-violet (UV) assisted CV
technique. The average D$_{it}$ for the MOSCAP is determined to be 7.8 $\times$
10$^{11}$ cm$^{-2}$eV$^{-1}$. The conduction band offset of the Al$_2$O$_3$/
Ga$_2$O$_3$ interface is also determined from CV measurements and found out to
be 1.7 eV which is in close agreement with the existing literature reports of
ALD Al$_2$O$_3$/ Ga$_2$O$_3$ interface. The current-voltage characteristics are
also analyzed and the average breakdown field is extracted to be approximately
5.8 MV/cm. This in-situ Al$_2$O$_3$ dielectric on $\beta$-Ga$_2$O$_3$ with
improved dielectric properties can enable Ga$_2$O$_3$-based high performance
devices.
