  A predicted type-II staggered band alignment with an approximately $1.4 eV$
valence band offset at the $ZnGeN_2/GaN$ heterointerface has inspired novel
band-engineered $III-N/ZnGeN_2$ heterostructure-based device designs for
applications in high performance optoelectronics. We report on the
determination of the valence band offset between metalorganic chemical vapor
deposition grown $(ZnGe)_{1-x}Ga_{2x}N_2$, for $x = 0$ and $0.06$, and $GaN$
using X-ray photoemission spectroscopy. The valence band of $ZnGeN_2$ was found
to lie $1.45-1.65 eV$ above that of $GaN$. This result agrees well with the
value predicted by first-principles density functional theory calculations
using the local density approximation for the potential profile and
quasiparticle self-consistent GW calculations of the band edge states relative
to the potential. For $(ZnGe)_{0.94}Ga_{0.12}N_2$ the value was determined to
be $1.29 eV$, $~10-20\%$ lower than that of $ZnGeN_2$. The experimental
determination of the large band offset between $ZnGeN_2$ and $GaN$ provides
promising alternative solutions to address challenges faced with pure
III-nitride-based structures and devices.
