GB1407098A - Electroluminescent device - Google Patents

Abstract

1407098 Electroluminescence INSTITUT POLUPROVODNIKOV AKADEMII NAUK UKRAINSKOI SSR 8 Dec 1972 56858/72 Heading C4S An electroluminescent device comprises EL layer 4 between an opaque reflective electrode 2 and a partially transparent reflective electrode 6 forming a Faby-Perot cavity, protective layer 3 of a refractive index close to or equal to that of the EL layer, and the coeff. of diffusion of layer 3 into EL layer 4 and that of electrode 2 into the protective layer and the protective layer thickness being selected so that no diffusion of electrode 2 and substantially no diffusion of the protective layer into the EL layer occurs at the thermal annealing temperatures. The phosphor may be Mn doped vacuum evaporated ZnS, Et doped ZnS or Mn doped ZnSe, the opaque electrode of Al, the partially transparent electrode of Au, and the protective layer of undoped crystallized ZnS film. Substrate 1 may be glass or quartz, electrode 2 vacuum evaporated, cathode sprayed or chemically deposited and of high reflection index (R # 65%) and of Au, Ag or Mn, layer 3 of insulating oxides e.g. Ta 2 O 5 or SiO and crystallized to reduce diffusion. Layer 3 is preferably based on the phosphor but undoped, refractive indices being equal. The optical thickness of layer 3 with layer 4 satisfies the interference relationship for maximum emission at a given wavelength and viewing angle with the metaldielectric junction phase-jump allowance. 20 to 25 nm. thick insulator layer 5 inhibits shortcircuit effects. Fields may be 10<SP>5</SP> to 10<SP>6</SP> v./cm. and emission colour variable as layer 4 thickness. Examples disclose specific thicknesses and material combinations. In fabrication, an evaporated Au layer and undoped ZnS may be annealed in vacuo at 550‹ to 660‹ C. resulting in crystallization, the EL layer then two step sprayed by evaporation on a cold substrate, Mn being introduced by vacuum evaporation as a pure metal (1 to 5% conc.) and a further undoped layer sprayed, the device being annealed at 650‹ to 700‹ C. for crystallization and activator diffusion.