Presence of a (1x1) oxygen overlayer on bare ZnO(0001) surfaces and at Schottky interfaces

TL;DR

This study reveals a stable (1x1) oxygen overlayer on bare and metal-coated ZnO(0001) surfaces, challenging previous theoretical predictions and providing insights into surface and interface structures relevant for device fabrication.

Contribution

It provides experimental evidence of an oxygen overlayer on ZnO(0001) surfaces and interfaces, contradicting prior theoretical instability predictions.

Findings

Presence of a (1x1) oxygen overlayer on bare ZnO(0001) surfaces.

Oxygen overlayer observed at metal-ZnO interfaces.

No significant atomic relaxations under typical processing conditions.

Abstract

The atomic surface and interface structure of bare and metal-coated ZnO(0001) Zn-polar wafers were investigated via surface x-ray diffraction. All bare samples showed the presence of a (1x1) overlayer of oxygen atoms located at the on-top position above the terminating Zn atom, a structure predicted to be unstable by several density functional theory calculations. The same oxygen overlayer is clearly seen at the interface of ZnO with both elemental and oxidized metal contact layers. No significant atomic relaxations are observed at surfaces and interfaces processed under typical device fabrication conditions.