JPH03266393A - Complex luminous body thin film and thin film el element - Google Patents

Abstract

PURPOSE:To obtain ultraviolet light emission of high efficiency by alternately laminating a phosphor layer mainly composed of liquid crystal of zinc sulfide having specific thickness and a barrier layer mainly composed of mixed crystal of magnesium and calcium sulfide to form a luminous body thin film. CONSTITUTION:An insulating layer 2 of CaF2 is formed on an Si base board 1, and barrier layers 3 are formed thereon by using a K cell, in which CaS, MgS are contained, further phosphor layers 4 consisting of ZnS having thickness not exceeding 50nm and not less than 1nm are formed. Then, a prescribed number of the layers 3, 4 are alternately laminated to form complex luminous body layers 5, whereon a transparent electrode 7 consisting of an insulating layer 6 and ITO is provided to form a thin film EL element. Since this EL element uses ZnS for the layer 4, Si and CaF2 having a close lattice constant to ZnS can be used for the board 1 and the layer 2, and mixed crystal of MgS and CaS for lattice matching can be used for the layer 3. Thereby, an ultraviolet luminous element of high efficiency can be obtained.

Description

[Detailed description of the invention] Industrial field of application The present invention (Friend) A light-emitting thin film that has high luminous efficiency and emits bright light in the blue or ultraviolet wavelength range, and an EL using the same
2. Description of the Related Art Related to Elements Thin film EL elements are being actively researched as flat displays used in computer terminals and the like.

Although monochrome thin-film EL displays using phosphor thin films made of manganese-doped zinc sulfide that emit yellow-orange light have already been put into practical use, full-color displays are essential for wide-ranging applications, and three colors of red, green, and blue are used. Although a great deal of effort has been put into the development of EL phosphors that emit light in primary colors, blue light emitting phosphors (Tomo ZnS
: Trn'P, SrS: Ce, as red phosphor (L ZnS: Sm, CaS: E
u, ZnS as a green phosphor: Tb, CaS:
Even though there is active research on Ce, etc.-X In light-emitting diodes, research on shortening wavelengths is also being actively conducted with the aim of achieving full color.
5iCS GaN5 ZnS, Zn5e, etc. Although attempts have been made to increase the brightness of blue LEDs by forming PN junctions and MIS junctions using semiconductor materials with a wide band gap, the invention aims to solve the above-mentioned phosphor thin film for electroluminescence. For red and green, there is a problem with luminescence efficiency, and for blue, there is a problem with color purity, and currently there are no color EL panels of a practical level. A light-emitting device with high brightness has been obtained and put into practical use.About blue color?!It is insufficient for practical use, and it is too late.A solid-state light-emitting device with an emission wavelength range of shorter ultraviolet wavelengths has yet to be realized. (X.

The present invention aims to realize a blue or ultraviolet light-emitting device with high luminance and efficiency of 1.X. A phosphor layer mainly composed of a mixed crystal with another IIb VI group compound semiconductor has an energy gap larger than that of the phosphor layer. A mixed crystal of at least magnesium sulfide and another alkaline earth metal sulfide is A composite light-emitting thin film is formed in which one or more units of structural units sandwiched between barrier layers as main components are repeated.

Effect By forming a composite light emitting thin film with the above structure, a material with a wide band gap that emits light in the wavelength range from blue to ultraviolet is used for the phosphor layer, and a material with a sufficiently wide energy gap is used as a barrier. Electrons and holes generated or injected by the high electric field are sufficiently confined in the phosphor layer, and they recombine efficiently either directly or via recombination centers, resulting in high emission efficiency. (Although it is thought that a blue or ultraviolet light-emitting device has been realized, Example 1 shows the device structure as an example of the thin film EL device of the present invention. Molecular beam epitaxial vapor deposition is performed on a low-resistance Si substrate 1. CaF2 with a thickness of 150 nm by
An insulating layer 2 made of a thin film was epitaxially grown.9 Furthermore, a barrier layer 3 made of Cas, eMgm, and aS with a thickness of 50 nm was grown epitaxially using a cell containing E, CaS, and MgS. Upper version: A phosphor layer 4 made of ZnS with a thickness of 20 nm is epitaxially grown.
Barrier layer consisting of Ca s, @Mg 1.4 S and Zn
The phosphor layers made of S were epitaxially grown alternately in order to complete a composite phosphor layer 5 with a total thickness of 10 layers of 700 nm. 4 Thickness 20
An insulating layer 6 of 0 nm thickness was formed, and finally a thickness of 200 nm was formed.
A transparent electrode 7 made of ITO was formed by electron beam evaporation to complete a thin film EL device.
An insulating layer 2 and an insulating layer 6 are formed between the composite light emitter layer 5 and the transparent electrode 7, respectively.
z, by applying an AC voltage of 150 V between the substrate 1 and the transparent electrode 7, the wavelength of 350 nm to 380 nm
The main point of the present invention that achieved the strong ultraviolet emission of m The point is that the semiconductor material can be used for the phosphor layer. The reason why this became possible for the first time in the present invention will be described below.

In order to realize a highly efficient short-wavelength light emitting device in the structure of the thin film EL device represented by the first example (Table 1), magnesium sulfide and other alkalis can be used as barrier layer materials that satisfy the following two conditions. This is due to the adoption of a material whose main component is a mixed crystal with earth metal sulfides. 3.8 ~
5.4 eV and 3.5 eV of ZnS adopted as the phosphor layer.
The second point is that we were able to efficiently confine carriers in the phosphor layer, which is sufficiently wide compared to eV. In order to maintain high luminous efficiency, it is important to reduce as much as possible lattice defects, which are one of the causes of non-luminescent centers of carriers. When the insulating layer 2 is provided as shown in the first embodiment, lattice matching is possible between these materials including the insulating layer 2, and the concentration of non-emissive centers can be reduced. In the example, Zns was used for the phosphor layer.Substrate material Si and CaF2, which have lattice constants similar to LZnS, were used for the insulating layer 2, and barrier layer materials were also used for lattice matching. When a mixed crystal of MgS and CaS is used and lattice-matched to a Si substrate, the band gap of the barrier layer is sufficiently wide (approximately 4.8 eV), and both electrons and holes are sufficiently confined in the phosphor layer, resulting in highly efficient ultraviolet light emission. It is thought that it was possible to obtain

In the first embodiment, a camera using Si as the substrate material is used.
For example, a similar effect can be obtained by using GaP, which has a similar lattice constant.9 Also, CaS and Mg can be used as barrier layer materials.
Cami using mixed crystal of S Instead, 42M g S and S
A film with a composition ratio that matches the L lattice using rS or a mixed crystal of MgS and BaS would have the same effect. Q The material of the phosphor layer is ZnS with a predetermined composition ratio.
In the case of using a semiconductor material whose main component is a mixed crystal of and another IIbVI group compound semiconductor L. By using the above-mentioned lattice-matched mixed crystal of alkaline earth metal sulfide as the barrier layer material, the same as in the first embodiment can be obtained. Effects of the invention in which a highly efficient short-wavelength thin film EL device with a desired wavelength corresponding to the bandgap of the phosphor layer could be obtained.By the present invention, a composite light-emitting thin film that emits light at short wavelengths from blue to ultraviolet can be obtained. Furthermore, when a thin film EL device is formed using this composite light emitting thin film, a high efficiency, high brightness, short wavelength thin film EL device can be realized. Or it has great practical value (
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[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an element of an embodiment of the thin film EL element of the present invention.
Barrier layer 4... Phosphor layer 5... Composite light emitter F#
7...Transparent electrode

Claims (4)

[Claims] (1) A phosphor layer whose main component is zinc sulfide or at least a mixed crystal of zinc sulfide and another IIbVI group compound semiconductor with a thickness of 50 nm or less and 1 nm or more, with an energy gap larger than that of the phosphor layer. , a composite luminescent thin film characterized in that one or more units of structural units sandwiched between barrier layers mainly composed of mixed crystals of at least magnesium sulfide and sulfides of other alkaline earth metals are provided. . (2) A thin film EL device comprising the composite light emitter thin film according to claim 1 and means for applying a voltage from the outside of the composite light emitter thin film. (3) The thin film EL device according to claim 2, wherein a dielectric thin film is formed on at least one surface of the composite light emitting thin film, and means for applying a voltage from outside the dielectric thin film is further provided. (4) The composite light-emitting thin film according to claim 1, wherein the difference in lattice constant between the phosphor layer and the barrier layer is within 5%.