Atomic layer deposition of aluminum doped zinc-oxide thin films for zero-index optics

Ultra-thin and ultra-smooth transparent conducting oxide materials with epsilon-near-zero (ENZ) (real part of material permittivity crosses zero) properties are important for zero-index optical applications, for instance, perfect absorption and advanced quantum/nonlinear ENZ applications. In this paper, we demonstrate the use of atomic layer deposition (ALD) technique to fabricate high quality aluminium doped zinc oxide (AZO) nanofilms with precisely controlled thicknesses and desired optical properties in the near-infrared spectral region.

The ultra-thin (< 100 nm) and ultra-smooth (RMS roughness ~ 1.5 nm) AZO films are synthesized by ALD using diethylzinc (DEZ), trimethylaluminum (TMA), and water precursors on two different substrates (silicon and fused silica). Spectroscopic ellipsometry is used to characterize the optical and electrical properties of the deposited AZO films. We show that the ENZ frequency and the growth rate of AZO are strongly dependent on the substrate, and they can be precisely tuned by deposition parameters such as dopant ratio and deposition temperature. These ALD grown AZO nano-layers with tunable ENZ frequencies enable the development of ultra-compact and tunable metamaterial devices.