Plasma enhanced atomic layer deposition of zinc sulfide thin films

Abstract

Zinc sulfide thin films were deposited by plasma enhanced atomic layer deposition (PE-ALD) using diethylzinc and H2S/Ar plasma. The growth characteristics were studied in situ with spectroscopic ellipsometry and ex situ with x-ray reflectometry. The growth was linear and self-limited. Furthermore, it was demonstrated that the growth per cycle was less temperature dependent for the PE-ALD process compared to the thermal process. ZnS thin film properties were investigated ex situ using x-ray photoelectron spectroscopy, x-ray diffraction, ultraviolet/visible optical spectroscopy, and atomic force microscopy. The as-deposited films were crystalline with a transmittance of >90% and a band gap of 3.49 eV. ZnS films deposited by PE-ALD were smoother than films deposited by thermal ALD. The plasma enhanced ALD process may have an advantage for ALD of ternary compounds where different temperature windows have to be matched or for applications where a smooth interface is required.