Thickness Dependence of the Physical Properties of Atomic-Layer Deposited Al2O3

TL;DR

This study explores how the physical, electronic, and optical properties of amorphous Al2O3 thin films vary with thickness, revealing size-dependent changes in refractive index and permittivity that inform device design.

Contribution

It demonstrates the impact of film thickness on the short-range order and related properties of ALD Al2O3, providing insights into size effects in amorphous oxides.

Findings

Refractive index increases with film thickness.

Permittivity increases with thickness but remains below bulk values.

Short-range order influences optical and electronic properties.

Abstract

Inspired by nature, we investigate the short-range order effect on the physical properties of amorphous materials. Amorphous Al2O3 thin films exhibit a higher proportion of their 4-coordinated Al sites close to the surface, causing variations in the average short-range order of the film. Below some thickness, the density of these films changes with size. In this work, we address the short-range order effect, through the thickness, on the electronic and optical properties of atomic layer deposited (ALD) Al2O3 thin films. Both the refractive index and the permittivity were found to vary with size. The refractive index increased with thickness, and for thick films (~50 nm) it was comparable to that of bulk amorphous Al2O3. The permittivity increased with thickness as well, but did not attain those of the bulk material. We discuss how these effects correlate with the density and short-range order. These results shed light on the size effects in thin amorphous oxides, and may guide the design of electronic and optical components and devices.