Ultraviolet emitting (Y 1− xGd x) 2O 3− δ thin films deposited by radio frequency magnetron sputtering: Combinatorial modeling, synthesis, and rapid characterization

Abstract

Gadolinium-doped, yttrium oxide thin films have been deposited on silicon (001) substrates by radio-frequency (RF) magnetron reactive sputtering that exhibit cathodoluminescence (CL) at ultraviolet frequencies. The maximum CL brightness occurred at λ∼314–315 nm characteristic of the 6P 3 / 2 → 8S ( λ = 314 nm) transition observed in Gd-doped, yttrium oxide powders. The radiative recombination takes place at the rare earth activator Gd 3+ site embedded in the Y 2O 3− δ host; the optical transition resides within the band gap of the Y 2O 3− δ host and the transition observed is characteristic of atomic gadolinium. A combinatorial approach to sputtering was used to deposit a film of variable composition from 1 to 23 at.% Gd in Y 2O 3− δ in order to rapidly discern the composition node of optimal CL brightness. A simulation was created for the purpose of predicting the film combinatorial composition for binary and ternary alloys prior to sputtering experiments in order to facilitate our combinatorial thin film synthesis technique. The model prediction varied from the real experimental composition profile by only 2.2 at.% Gd ± 1.6 at.% proving the predictor as a useful aide to complement combinatorial thin film experiments. A film of composition Y 1.56Gd 0.44O 3.25 (8.3 at.% Gd) yielded the maximum CL brightness. CL brightness increased continuously up to the 8.3 at.% Gd composition due to the increased number of activators present in the host. Beyond this composition the brightness drastically decreased. The oxygen composition in the combinatorial film was strongly dependent on the Gd composition; films were sub-stoichiometric δ > 0 below ∼6 at.% Gd and was over-stoichiometric δ < 0 beyond this composition.