JPH03280395A - Light emitting film and thin film el element - Google Patents

Abstract

PURPOSE:To make a complex light-emitting thin film which emits the three primary colors with high brightness and high efficiency by laminating fluorescent substance films in a specified thickness range alternately with barrier layers made of a material having a larger energy gap than the mentioned thin film. CONSTITUTION:By the electron beam evaporation method, a barrier layer 2-a consisting of CaS film of 200nm in thickness is epitaxially grown on a GaAs base board 1, and thereover a fluorescent thin film 3-a consisting of Zn8.7Cd8.3S: Ag is epitaxially grown in the thickness of 1-50nm, for ex. 20nm. Further thereover barrier layers 2-b, 2-c, 2-d of the same composition as the layer 2-1 and thin films 3-b, 3-c of the same composition as the film 3-a are formed alternately. Thus, a complex light emitting substance layer 4 is completed. Thereover BaTa2O6 ceramics are sputtered to form a dielectric film 5, and finally a transparent electrode 6 consisting of ITO of 200nm in thickness is formed by the electron beam evaporation method.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a luminescent thin film that has high luminous efficiency and emits bright red, green, and blue light, and an EL element using the same.Related to related art: Computer terminals, etc. Thin film EL elements are being actively researched as flat displays used in A monochrome thin film EL display using a phosphor thin film made of manganese-doped zinc sulfide that emits yellow-orange light has already been put into practical use. Colorization is essential to support a wide range of uses as displays, and a great deal of effort is being put into the development of EL phosphors that emit light in the three primary colors of red, green, and blue. Among these, Zns is a blue-emitting phosphor:
Tm, SrS:Ce, and ZnS as a red-emitting phosphor:
Sm, CaS: Eu, and green-emitting phosphors such as ZnS: Tb and CaS: Ce are being actively researched, but the problem that the invention is trying to solve is that phosphor thin films that emit light in the three primary colors of red, green, and blue (such as There is a problem with luminance efficiency for red and green, and a problem with color purity for blue.
A color EL panel of a practical level has not been formed.1
．． ■Means for solving the problem A structure in which a phosphor thin film with a thickness of 50 m or less and more than Inm is sandwiched between barrier layers made of a material with an energy gap larger than the energy gap of the phosphor thin film, or this structure is repeated multiple times. By forming a composite light emitting body having a structure in which a phosphor thin film with a thickness of 50 m or less and 1 nm or more is sandwiched between barrier layers made of a material with an energy gap larger than the energy gap of the phosphor thin film. , electrons generated or injected by a high electric field,
Holes are trapped in the phosphor thin film and recombined efficiently through direct stirring or recombination centers.
It is thought that phosphor materials used in CRTs, fluorescent lamps, etc. can be used as phosphor thin films, and that it is possible to form phosphor thin films with high luminance and efficiency. An element structure for explaining one embodiment of an EL element is shown.

A thickness of 200 mm was deposited on a GaAs substrate l by electron beam evaporation.
A barrier layer 2-a made of a CaS thin film of 9 nm is epitaxially grown.

Using three cells containing CdS and Ag, a phosphor thin film 3-a consisting of Zrz, vcds, and ss:Ag with a thickness of 20 m was epitaxially grown, and then a CaS thin film with a thickness of 200 nm was grown on top of it. barrier layer 2
-bl 20 layer m thick Zn=, vCdi, *s:
Phosphor thin film 3-b made of Ag, 200 nm thick Ca
Barrier layer 2-c made of S thin film, Zns with a thickness of 20 m,
7Cdm, sS: Phosphor thin film 3-01 made of Ag
and a barrier layer 2 made of a CaS thin film with a thickness of 200 nm.
Composite light emitter layer 4 was completed by successively epitaxially growing -d. On top of it, BaTa2O@ceramics was RF-fed at room temperature in an argon atmosphere containing 10% oxygen.
By sputtering, a dielectric thin film 5 with a thickness of 300 nm is formed.Finally, a transparent electrode 6 made of ITO with a thickness of 200 nm is formed by electron beam evaporation to complete a thin film EL element. -L element C
yo Pulse width 30μS, 1kHz.

By applying an alternating current voltage of 180 V between the substrate 1 and the transparent electrode 6, bright green light is emitted, and by using Cu as the light emitting impurity in the phosphor thin film, bright red light is emitted. An element structure for explaining another embodiment of the thin film EL element is shown. A transparent electrode 8 made of an ITO thin film with a thickness of 200 nm is formed on a glass substrate 7 by electron beam evaporation.The upper layer 9 is a barrier layer 9 made of CaFa with a thickness of 20 m formed by electron beam evaporation.
Zn with a thickness of 10 m formed by electron beam evaporation
A composite light emitting layer 11 was completed by stacking 30 layers of S:Tm phosphor thin films 10 alternately and finally forming a barrier layer 9 made of CaF2 with a thickness of 20 m by electron beam evaporation. A thin film EL device is completed by forming a back electrode 12 made of AI with a thickness of 200 nm on top by electron beam evaporation.
In this example, bright blue light was emitted by applying an AC voltage of 30 μs, 1 kl (Z, 200 V) between the transparent electrode 8 and the back electrode 12 (above) Composite light emission using multiple layers of phosphor thin films When the phosphor thin film was one layer, it started emitting light at a low voltage, but the luminescence intensity was lower than when multiple layers were used.The thickness of the phosphor thin film was 5
If the layer is thicker than 0 nm, the electron and hole confinement effect will be insufficient and the emission intensity will decrease, and if the layer is thinner than 1 m, lattice defects will increase or the number of emission centers and recombination centers will decrease, causing the emission intensity to decrease. In addition to cadmium zinc sulfide and zinc sulfide containing luminescent impurities as shown in the examples, phosphor thin films containing calcium sulfide and strontium sulfide as main components can also be used as the phosphor thin film material. The energy gap of the material used for the barrier layer must be larger than that of the phosphor thin film. Effects of the invention in which excellent characteristics were obtained when the constants were close to each other.According to the present invention, it is possible to form a composite luminescent thin film that emits light in three primary colors with high emission brightness and efficiency. When a thin film EL element is formed using
Although it is possible to form thin-film EL devices with high luminance and efficiency, the present invention has great practical value in forming multicolor EL devices and full-color EL devices containing blue light emitting devices.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an EL element for explaining one embodiment of the present invention. FIG. 2 is a cross-sectional diagram of an EL element for explaining another embodiment of the present invention. 1 is a cross-sectional view showing the element structure of an EL element. 1...GaAs substrate 7...Glass substrate 8.
...Transparent electrode 2, 9...Barrier #3, lO・
... Phosphor thin 11L4, 11... Composite light emitter ML
5... Dielectric thin trap 6, 12... Electric wire

Claims (8)

[Claims] (1) A phosphor thin film characterized by having a composite structure in which a phosphor thin film with a thickness of 50 nm or less and 1 nm or more is sandwiched between barrier layers made of a material with an energy gap larger than the energy gap of the phosphor thin film. (2) A light-emitting thin film characterized in that the composite structure according to claim 1 is repeated multiple times. (3) A thin film EL device comprising the light emitting thin film according to claim 1 and means for applying a voltage from the outside of the light emitting thin film. (4) The thin film E according to claim 3, wherein a dielectric thin film is formed on at least one surface of the light-emitting thin film, and means for applying a voltage from the outside is further provided.
L element. (5) A thin-film EL device comprising the light-emitting thin film according to claim 2 and means for applying a voltage from outside the light-emitting thin film. (6) The thin film E according to claim 5, characterized in that a dielectric thin film is formed on at least one surface of the light-emitting thin film, and a means for applying a voltage from the outside is provided.
L element. (7) The phosphor thin film according to claim 1, wherein the phosphor thin film contains zinc sulfide, cadmium sulfide, zinc telluride, zinc selenide, or a mixed crystal thereof as a main component. (8) The phosphor thin film according to claim 1, wherein the barrier layer contains zinc sulfide, cadmium zinc sulfide, alkaline earth metal sulfide, or alkaline earth metal fluoride as a main component.