  Atomically transparent vertically aligned ZnO-based van der Waals material
have been developed by surface passivation and encapsulation with atomic layers
of MgO using materials by design; the physical properties investigated. The
passivation and encapsulation led to a remarkable improvement in optical and
electronic properties. The valence-band offset $\Delta E_v$ between MgO and
ZnO, ZnO and MgO/ZnO, and ZnO and MgO/ZnO/MgO heterointerfaces are determined
to be 0.37 $\pm$0.02, -0.05$\pm$0.02, and -0.11$\pm$0.02 eV, respectively; the
conduction-band offset $\Delta E_c$ is deduced to be 0.97$\pm$0.02,
0.46$\pm$0.02, and 0.59$\pm$0.02 eV indicating straddling type-I in MgO and
ZnO, and staggering type-II heterojunction band alignment in ZnO and the
various heterostructures. The band-offsets and interfacial charge transfer are
used to explain the origin of $n$-type conductivity in the superlattices.
Enhanced optical absorption due to carrier confinement in the layers
demonstrates that MgO is an excellent high-$\kappa$ dielectric gate oxide for
encapsulating ZnO-based optoelectronic devices.
