Eu~(2+)-DOPED ALE SrS AND CaS RED TFEL PHOSPHORS

摘要

Recent progress in the layered diffusion doping of SrS films grown by atomic layer epitaxy (ALE) to produce bright blue and green phosphors has motivated the development of a red phosphor using the same processing technique. A suitable red phosphor would make full-color active matrix electroluminescence (AMEL) using a patterned pixel approach possible. ALE SrS and CaS films are doped with Eu to evaluate their use as red alternating-current thin-film electoluminescent (ACTFEL) phosphors. A red SrS phosphor is especially attractive as a means to realize a single-host, full-color system when used with blue and green SrS:Cu ACTFEL phosphors. SrS and CaS films are grown by ALE and doped with Eu to produce phosphor layers in ACTFEL devices. Eu dopant incorporation is accomplished via diffusion from a dopant source layer using rapid thermal annealing. The ALE/layered diffusion doping approach promises improved manufacturability since it is accomplished at lower processing temperatures than when phosphor layers are deposited by sputtering or evaporation. The ACTFEL devices under study are fabricated as follows. An un-doped SrS or CaS film is deposited onto a glass substrate coated with layers of indium tin oxide and aluminum-titanium oxide, which serve as the bottom transparent contact and the bottom insulator, respectively, of the ACTFEL device. The MS (M=Ca, Sr) layer is ALE deposited using H_2S and M(thd)_2 precursors, where thd stands for 2,2,6,6-tetramethyl-3,5-heptanedionate. Next, thin layers of the appropriate dopant species, in this case EuCl_3, are thermally evaporated onto the MS film. Rapid thermal annealing in an Ar atmosphere is then performed in order to diffuse the dopants into the MS film. The anneal temperatures used are 700℃ for SrS and 810℃ for CaS. A top insulating layer of silicon oxynitride is deposited by plasma-enhanced chemical vapor deposition, and aluminum dots are thermally evaporated as the top contact.