An X-Ray Photoelectron Spectroscopy Study of Elements' Chemical States in SrGa₂S₄:Ce Blue Electroluminescent Thin Films

Abstract

SrGa2S4:Ce blue electroluminescent thin films with a (440) single orientation have been prepared by a multisource deposition method using a molecular beam epitaxy (MBE) apparatus. The elements' chemical states and the doped oxygen effects on them have been analyzed by X-ray photoelectron spectroscopy (XPS). A small variation in the elements' chemical state with depth indicates that the growth of the thin film is stable. Sr ions exhibit no chemical shift due to a Sr–O bond, but Ga ions exhibit a chemical shift due to a Ga–S bond and a larger shift due to a Ga–O bond, indicating that the oxygen ion does not substitute for a S site in which the S ion bonds with the Sr ion. No Ce4+ ions have been detected and no oxidation of Ce3+ ions occurs even if some of the S ligands of Ce3+ are replaced by doped oxygen ions. The trivalent state of Ce is stable in the SrGa2S4 crystal.

Core level photoelectron spectroscopy of LiGaS2 and Ga–S bonding in complex sulfides

“…is a real source of a shoulder at the lower binding energy side of S 2p line reported earlier for SrGa 2 S 4[30]. The S 2s core level presented inFig.…”

Blue emitting Sr2Ga2S5:Ce phosphor thin films grown by multisource deposition

“…12 For SrGa 2 S 4 , we reported that the Ga-S bonds were covalent, while the Sr-S bonds were ionic by the measurement of x-ray photoelectron spectroscopy. 13 Since the distance of Ga-S in Sr 2 Ga 2 S 5 is shorter than SrGa 2 S 4 , electron clouds of S ions spread strongly toward Ga ions. The Ga-S bond is thus more covalent than SrGa 2 S 4 .…”

Atomic Composition and Structural Properties of Blue Emitting BaAl2S4:Eu Electroluminescent Thin Films

“…This is due to the selective sputtering of sulfur by etching with a high ion beam energy, as previously reported for a SrGa 2 S 4 :Ce system. 15) These phases observed in XPS analyses are examined using other methods as reported in the latter sections of this paper. It was found that an additional layer with extremely high oxygen content is formed between the top ZnS layer and the BaAl 2 S 4 :Eu layer (Fig.…”