Refractive index of ZnO ultrathin films alternated with Al₂O₃ in multilayer heterostructures

Abstract

The design of optoelectronic devices made with ZnO superlattices requires the knowledge of the refractive index, which currently can be done only for films thicker than 30 nm. In this work, we present an effective medium approach to determine the refractive index of ZnO layers as thin as 2 nm. The approach was implemented by determining the refractive index of ZnO layers ranging from 2 nm to 20 nm using spectroscopic ellipsometry measurements in multilayers. For a precise control of morphology and thickness, the superlattices were fabricated with atomic layer deposition (ALD) with alternating layers of 2 nm thick Al2O3 and ZnO, labeled as N ZnO-Al2O3, where N = 10, 20, 30, 50, 75 and 100. The total thickness of all superlattices was kept at 100 nm. The approach was validated by applying it to similar superlattices reported in the literature and fitting the transmittance spectra of the superlattices.

Revisiting Optical Material Platforms for Efficient Linear and Nonlinear Dielectric Metasurfaces in the Ultraviolet, Visible, and Infrared

“…Its stoichiometry has been adjusted by varying the deposition duty cycles of atomic layer deposition (ALD), which can deposit atomically thin layers via self-limiting chemical reactions. Changing the number of aluminum oxide (AlO) and ZnO layers causes the optical properties to vary, and hence, n and k in the UV region decrease as the Al dopant concentration increases − (Figure c).…”

Recent progress in organic-based radiative cooling materials: fabrication methods and thermal management properties

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