Complex oxide growth using simultaneous in situ RHEED and x-ray reflectivity: When is one layer complete?

TL;DR

This study demonstrates how simultaneous in situ RHEED and x-ray reflectivity can be used to accurately determine layer completion during oxide growth, revealing phase control of RHEED oscillations and a phase-independent method for layer completion detection.

Contribution

It introduces a method to control RHEED oscillation phase and a phase-independent approach to identify layer completion during oxide growth.

Findings

RHEED and x-ray reflectivity oscillate during layer growth.

Substrate annealing conditions influence RHEED phase.

Exponential relaxation times indicate layer completion regardless of RHEED phase.

Abstract

During layer-by-layer homoepitaxial growth, both the Reflection High-Energy Electron Diffraction (RHEED) intensity and the x-ray reflection intensity will oscillate, and each complete oscillation indicates the addition of one monolayer of material. However, it is well documented, but not well understood, that the phase of the RHEED oscillations is not constant and thus the maxima in the RHEED intensity oscillations do not necessarily occur at the completion of a layer. We demonstrate this using simultaneous in situ x-ray reflectivity and RHEED during layer-by-layer growth of SrTiO$_3$. We show that we can control the RHEED oscillation phase by changing the pre-growth substrate annealing conditions, changing the RHEED oscillation phase by nearly 180$^\circ$. In addition, during growth via pulsed laser deposition, the exponential relaxation times between each laser pulse can be used to determine when a layer is complete, independent of the phase of the RHEED oscillation.