# Surface passivated and encapsulated ZnO atomic layer by high-$\kappa$ ultrathin MgO layer

## TL;DR

This study demonstrates that surface passivation and encapsulation of ZnO with ultrathin MgO layers significantly improve its optical and electronic properties, making MgO a promising high-$5$ dielectric for ZnO-based optoelectronics.

## Contribution

It provides detailed band-offset measurements and insights into heterostructure band alignment, advancing understanding of ZnO/MgO interfaces for device applications.

## Key findings

- Improved optical and electronic properties of ZnO with MgO encapsulation.
- Determined valence and conduction band offsets for heterostructures.
- MgO acts as an effective high-$5$ dielectric for ZnO devices.

## Abstract

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.