JPH0433120B2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Application of the Invention) The present invention relates to an EL display device,
More specifically, the present invention relates to an EL display device that utilizes a superlattice structure to improve light emitting characteristics.

(Prior Art) FIG. 1 is a configuration explanatory diagram showing an example of a conventional EL display device, in which transparent electrodes 2 are placed on a glass substrate 1.
ZnS, etc., on which deactivator impurities such as Mn and Tb and coactivators such as Cl ^- and Al ⁺ are diffused. An EL semiconductor compound layer (S) 3 is formed, the outer periphery of this EL semiconductor compound layer 3 is covered with an insulating layer (I) 4, and a metal electrode (M) 5 is formed on the top surface of the insulating layer 4, From the top: metal electrode (M), insulating layer (I), and EL semiconductor compound layer
It is called MIS structure because (S) is stacked. FIG. 2 is a configuration explanatory diagram showing another example of a conventional EL display device, in which a transparent electrode 2 is formed on a glass substrate 1, a transparent insulating layer (I) 6 is formed thereon, On this insulating layer 6, an EL semiconductor compound layer (S) 3 such as ZnS in which impurities such as Mn and Tb as a light emission center are diffused is formed, and the outer periphery of this EL semiconductor compound layer 3 is formed as an insulating layer (I). 4, and a metal electrode (M) 5 is formed on the top surface of the insulating layer 4. From above, the metal electrode (M), the insulating layer (I), the EL semiconductor compound layer (S), and the insulating layer (I ) are stacked, so MISI
It is called structure.

However, as shown in Figures 1 and 2,
In the EL display device, since the metal electrodes 5 are exposed to the external atmosphere, the function deteriorates very quickly when used in an atmosphere containing water vapor. Further, since the activator and coactivator are mixed and diffused in the EL semiconductor compound layer 3, the activator and coactivator often form a pair in the closest proximity and do not function as a luminescent center.
In addition, the MIS structure has a relatively low voltage (several 10s to 100V)
However, when oxygen ions move and enter the EL semiconductor compound layer 3 from the transparent electrode 2 side, a deep electron trapping level is formed and the characteristics may be deteriorated. On the other hand, in the MISI structure, a relatively high voltage (200 to several
100V), which makes the drive circuit complicated. In order to solve these drawbacks of the MISI structure, attempts have been made to increase the efficiency of the electric field applied to the EL semiconductor compound layer 3 by using ferroelectric materials as the insulating layers 4 and 6, but they have not been sufficiently effective. I'm not used to getting it.

(Object of the Invention) The present invention has focused on such points, and its object is to provide an EL display device that can be driven at a relatively low voltage and has a long life.

(Summary of the Invention) The present invention achieves the above object by forming a plurality of EL semiconductor compound layers in which P-type impurities are diffused and a plurality of EL semiconductor compound layers in which N-type impurities are diffused, in which these impurities are not diffused. It is characterized by being sequentially stacked with pure EL semiconductor compound layers sandwiched therebetween.

(Example) Hereinafter, it will be explained in detail using the drawings.

FIG. 3 is a configuration explanatory diagram showing an embodiment of the present invention;
FIG. 4 is an enlarged sectional view of the main part thereof, and the same parts as in FIGS. 1 and 2 are given the same reference numerals.
In Figure 3, 7 is a region in which P-type impurities are diffused.
EL semiconductor compound layer (hereinafter referred to as P-type layer), 8 is N
9 is a pure EL semiconductor compound layer in which these impurities are not diffused (hereinafter referred to as a pure layer).
The P-type layer 7 and the N-type layer 8 are sequentially laminated with a pure layer 9 in between.

Such a device can be made as follows.

First, a 50 nm film was deposited on the glass substrate 1 by sputtering.
A transparent electrode 2 with a thickness of ~60 nm is formed. next,
An insulating layer 6 is formed on the transparent electrode 2 by sputtering.
Form with a thickness of about 100 nm. As this insulating layer 6, La ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , Y ₂ O ₃ , Sm ₂ O ₃ or the like is used. Note that when forming the insulating layer 6, sputtering is performed in a He atmosphere while heating the substrate 1 to several hundred degrees. Compared to Ar, He enters the sputtered film at a much lower rate, and a more complete insulating layer can be obtained than when sputtering is performed in an Ar atmosphere. Subsequently, a P-type layer 7 is formed on the insulating layer 6 by sputtering to a thickness of several nm to several tens of nm. In forming this P-type layer 7, for example, Mn, Tb, which acts as an activator on ZnS,
Using a target to which impurities such as Cu are added as sulfide, the substrate 1 is coated several hundred times in the same manner as the insulating layer 6.
Sputtering should be performed in a He atmosphere while heating to a certain degree. At this time, the impurity acting as an activator is diffused more than in conventional EL display devices so that it can be characterized as a P-type semiconductor, and the impurity acting as a coactivator is prevented from entering. The activator thus diffused into the P-type layer 7 enters the Zn ⁺⁺ site and becomes an acceptor. Subsequently, a pure layer 9 with a thickness of several nm to 15 nm is formed on the P-type layer 7 by sputtering. In forming this pure layer 9, pure ZnS to which no impurities are added is used as a target, and like the insulating layer 6 and the P-type layer 7, the substrate 1 is
Sputtering should be performed in a He atmosphere while heating to a certain degree. This pure layer 9 prevents the activator and coactivator from forming a pair in their closest proximity and failing to function as a luminescent center, thereby forming a field that accelerates electrons. Next, an N-type layer 8 is formed on the pure layer 9 by sputtering to a thickness of several nanometers to several nanometers.
Form with a thickness of 10 nm. In forming this N-type layer 8, for example, a target in which impurities such as Te and Cl, which act as coactivators, are added to ZnS in the form of sulfide or chloride is used, and the substrate 1 is coated several times in the same manner as in the above-mentioned layers. Sputtering is performed in a He atmosphere while heating to 100 degrees. At this time, the impurity acting as a coactivator is formed to diffuse more than in conventional EL display devices so that it can be characterized as an N-type semiconductor. Similarly below,
A plurality of layers are sequentially stacked such that the pure layer 9 is sandwiched between the P-type layer 7 and the N-type layer 8. As a result, an EL semiconductor compound layer having a superlattice structure with a continuous crystal structure is obtained. After laminating a plurality of EL semiconductor compound layers in this manner, an insulating layer 10 similar to the insulating layer 6 is formed by sputtering to a thickness of several tens of nanometers to several hundreds of nanometers so as to cover these EL semiconductor compound layers. Then, a metal electrode 5 is formed on this insulating layer 10, and a protective layer 11 of, for example, SiO ₂ is formed thereon to a thickness of several μm by sputtering.

In such a configuration, each pure layer 9 acts similarly to a depletion layer in a PN junction and accelerates electrons when a voltage is applied. And the accelerated electron is each P
The activator in the mold layer 7 is excited to form a level necessary for light emission. As a result, even at a relatively low driving voltage of several tens of volts, a high electric field is generated in the region including the pure layer 9, electrons are efficiently accelerated, and extremely high luminous efficiency can be obtained. Furthermore, since the depletion layer prevents the activator and coactivator from forming a pair in their closest proximity, a longer life can be achieved. In addition, when forming each EL semiconductor compound layer 7, 8, 9, the substrate 1 is heated to several hundred degrees.
Since sputtering is performed in a He atmosphere, a superlattice structure with few crystal defects can be realized, and the movement of each ion in the crystal can be suppressed. Furthermore, metal electrode 5
Since the protective layer 11 is provided thereon, the water resistance and environmental resistance of the metal electrode 5 side can be improved, and a long life can be achieved.

In the above example, an example was explained in which the EL semiconductor compound layer is made up of three layers: a P-type layer, an N-type layer, and a pure layer. However, it is also possible to further increase the luminous efficiency by adding two more P-type layers. can. In other words, the P-type layer is divided into a first layer in which a P-type impurity such as Mn, which becomes a luminescent center, is diffused, and a second layer, in which a large amount of P-type impurity such as Cs, which does not directly become a luminescent center, is diffused. It consists of layers. With this configuration, holes generated in the second P-type layer enter the first P-type layer and combine with electrons at the luminescence center, thereby emptying the electrons at the luminescence center. Here, electrons from the N-type layer are injected through the pure layer and light is emitted, making it possible to further increase the luminous efficiency.

Furthermore, the emission threshold and emission intensity can be set to arbitrary values depending on the number of these layers.

(Effects of the Invention) As described above, according to the present invention, an EL display device that can be driven at a relatively low voltage and has a long life can be realized.

[Brief explanation of drawings]

1 and 2 are structural explanatory diagrams showing an example of a conventional EL display device, FIG. 3 is a structural explanatory diagram showing an embodiment of the present invention, and FIG. 4 is an enlarged sectional view of the main part thereof. 1... Gaki, 2... Transparent electrode, 4, 6, 10...
...Insulating layer, 5...Metal electrode, 7...P-type layer, 8...
...N-type layer, 9...pure layer.

Claims (1)

[Claims] 1 A plurality of EL semiconductor compound layers in which P-type impurities are diffused and a plurality of EL semiconductor compound layers in which N-type impurities are diffused are separated into pure layers in which these impurities are not diffused.
An EL display device characterized in that EL semiconductor compound layers are sequentially laminated with sandwiching them.