JPH05101887A - Manufacture of electroluminescent thin film - Google Patents

Abstract

PURPOSE:To manufacture rare earth element-doped ZnS thin film with good crystal property by depositing ZnS or Zn with S as a matrix material and a rare earth element as a luminescent center material on a substrate under heating by leading a hydrogen halide gas. CONSTITUTION:A ZnS powder as a matrix material and a rare earth metal element (e.g. Tb) as a light-emitting center material are stored in quartz tubes 2. 3, respectively, in a quartz tube 1. The ZnS powder and the rare earth metal element are heated at 900-1000 deg.C and 700-900 deg.C, respectively by resistance heating furnaces 6, 7. Hydrogen gas and a hydrogen halide gas (e.g. hydrogen chloride) are led through a leading tube 9 and a leading tube 10, respectively to transport the ZnS and halide compound of the rare earth metal to a substrate and deposit them on the substrate heated to 500-600 deg.C by a resistance heating furnace 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electroluminescent thin film used for a light emitting layer of an electroluminescent device applied as a flat thin display.

[0002]

2. Description of the Related Art A double insulating thin film electroluminescent element (hereinafter referred to as an EL element) is expected to be applied to a high performance flat thin display as a self-luminous display element. The emission color of the thin film EL element is determined by the type of the light emitting layer.
S: Mn, ZnS: Sm, CaS: Eu as the light emitting layer of the red EL element, ZnS: Tb as the light emitting layer of the green EL element, ZnS: Tm, SrS: Ce as the light emitting layer of the blue EL element are known. .. Among these, particularly for the light emitting layer containing ZnS as a base material and a rare earth element such as Sm, Tb, or Tm added, full-color display is possible only with these materials, and therefore manufacturing technology is being actively developed.

As a method for manufacturing the light emitting layer, there are currently a vacuum vapor deposition method, a sputtering method, a chemical vapor deposition (CVD) method, an atomic layer epitaxy (ALE) method, etc., and currently, the vacuum vapor deposition method and the ALE method are used. A yellow EL display using a ZnS: Mn light emitting layer has been put to practical use. Regarding the preparation of ZnS film with rare earth element added, fluoride of rare earth element is used.
Known methods include a vacuum deposition method and a sputtering method using (ReF ₃ ) as a dopant, and an ALE method in which an organic metal compound of Tb is used for doping.

[0004]

When the ZnS host is doped with a rare earth element, the rare earth ion serving as the emission center is often trivalent, and the divalent ion of the zinc element to be substituted is different in valence and ionic radius. The size is different. For this reason, it is difficult to dope the base material with a high concentration of a rare earth element, and further, since the crystallinity of the base material is impaired by the doping, when these thin films are used for an EL element as a light emitting layer, the reliability of light emission brightness, breakdown voltage, etc. In this respect, it is difficult to manufacture a high-performance EL element. In order to solve the problem caused by the difference in the valence of the emission center ion, a method of forming a light emitting layer using a fluoride of a rare earth element as a dopant has been performed, but a sufficient film has not been obtained yet. Absent. In view of the above, it is an object of the present invention to provide a method for manufacturing an electroluminescent thin film made of a rare earth element-containing ZnS thin film having good crystallinity.

[0005]

A method for producing an electroluminescent thin film of the present invention for achieving the above object uses ZnS or Zn and S as a base material,
Using a rare earth element as an emission center material, hydrogen or an inert gas is circulated on the host material while heating the base material, and a hydrogen halide gas is passed on the emission center material while heating the emission center material. The chemical vapor deposition is characterized in that the matrix material and the emission center material are supplied onto the heated substrate arranged in the growth region, and the hydrogen halide gas is directly supplied to the growth region. It is characterized by using the method.

As the base material, for example, ZnS powder, Zn powder, S powder or a molded body of these is used. When Zn and S are used, they are arranged separately. Preferably, solid ZnS is used for thermal sublimation and transportation. The hydrogen halide gas is preferably hydrogen chloride gas.

The crystal structure of the ZnS thin film is preferably a hexagonal wurtzite type, and the hexagonal wurtzite type can be grown by increasing the total introduction amount of the hydrogen halide gas of the above two systems. The total amount of hydrogen halide gas introduced may be controlled so that the number of moles of ZnS per unit time supplied to the region is equal to or more.

[0008]

The hydrogen halide gas introduced directly controls whether the crystal structure of the ZnS film is zinc blende type or wurtzite type by changing the flow rate.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of the thin film growth apparatus used in this example. ZnS powder and metal Tb to be used as raw materials are placed in the quartz inner tubes 2 and 3 provided inside the quartz tube 1, respectively, and the ZnS powder is heated by the resistance heating furnaces 6 and 7 respectively.
The powder is heated to 900 to 1000 ° C and the metal Tb is heated to 700 to 900 ° C. Then, by introducing hydrogen gas from the introduction pipe 9 connected to the quartz inner pipes 2 and 3 and hydrogen chloride gas from the introduction pipe 10, the substrate is heated to 500 to 600 ° C. by the resistance heating furnace 8. ZnS and Tb are transported to the substrate mounting region 12. As a result, ZnS becomes Zn, S, H ₂ S and is transported by hydrogen gas, and Tb becomes TbCl ₃ and is transported. By transporting Tb in this way, T
Uniform doping of b is possible.

Furthermore, in order to increase the hydrogen chloride gas partial pressure in the growth region without affecting the Tb concentration in the film by controlling the Tb concentration in the film for hydrogen chloride gas for Tb transport. , Hydrogen chloride gas is supplied to the substrate installation region without passing through the inner tube in which the metal Tb is installed. This is Figure 2
It was considered based on the data shown in. For this purpose, the introduction pipe 11 is directly connected to the quartz pipe 1, and hydrogen chloride gas (this is called bypass hydrogen chloride) is introduced through the introduction pipe 11. The thin film growth apparatus is used under reduced pressure. By introducing this bypass hydrogen chloride, the amount of ZnCl ₂ in the substrate installation area is controlled.

According to the above method, Zn was formed under the film forming conditions shown in FIG.
An S: Tb thin film was prepared. FIG. 4 shows the growth conditions of two of them, and the actual values of the ZnS transport amount and the Tb transport amount are slightly deviated from the control target. Sample No.1
Indicates that no bypass hydrogen chloride was flown, and sample No. 2 was that where bypass hydrogen chloride was flown. The Tb concentration in the film was controlled by the flow rate of hydrogen chloride for Tb transport, and the Tb content concentration was 2-3 at% in both samples. This is almost the optimum value for the EL device light emitting film.

FIG. 5 shows the X-ray diffraction pattern of the sample film. Sample No. 1 shows a strong diffraction peak on the (311) plane in addition to the main diffraction peak, whereas Sample No. 2 shows only a main diffraction peak and shows a strong diffraction intensity, indicating that the film is a good quality film. .. Also, by combining with the measurement results of the RHEED diffraction pattern, the crystal structure of both is [111] for sample No. 1.
It was found that the zinc-blende type with orientated in the direction of No. 2 and the sample No. 2 were wurtzite type with the orientation in the C-axis direction. Thus, it is understood that the introduction of bypass hydrogen chloride improves the crystallinity and obtains wurtzite type crystals. When a ZnS film containing a rare earth element is produced, it is preferable to use a wurtzite type as described in the previous application (Japanese Patent Application No. 2-214707).

FIGS. 6 and 7 are diagrams showing changes in the crystal structure of the film when the hydrogen chloride flow rates for Tb transport and bypass are variously changed. From this, in order to obtain the hexagonal wurtzite type, it is sufficient to increase the total introduction amount of hydrogen chloride gas of the above two systems, and the amount equal to or more than the number of moles of ZnS per unit time supplied to the growth region. The total amount of hydrogen chloride gas introduced may be controlled so that the number of moles is adjusted. The crystallinity of the wurtzite type crystals was better in all cases. Furthermore, the surface flatness was also improved. In FIG. 7, when the total amount of hydrogen chloride gas introduced is 4 cc / min or more, it is of wurtzite type, and is supplied during growth regardless of Tb concentration, etc., unless the Tb concentration is extremely low. The crystal structure of the film changes depending on the amount of hydrogen chloride formed. The total hydrogen chloride flow rate required for this crystal structure change varies depending on the growth conditions, but the ZnS raw material transport amount is most relevant, and it can be seen from FIG. (Note that 4cc / min is about 1.8mol / mi
n, which is 1.8 to 2.0 mol / m of ZnS transport amount in the example.
almost equal to in).

Next, an EL device using the film manufactured by the above manufacturing method as a light emitting layer will be described. FIG. 8 shows the structure of the manufactured EL element. It is composed of a glass substrate 1, a transparent electrode 2, a first insulating film 3, a light emitting layer 4, a second insulating film 5 and a metal electrode 6, and ITO (tin added indium oxide) as a transparent electrode and SiO as a first insulating film. ₂ and S
i ₃ N ₄ laminated film, Si ₃ N ₄ and Ai ₂ O ₃ as second insulating film
Aluminum is used as the laminated film and the metal electrode. When the zinc blende type ZnS: Tb thin film of sample No. 1 is used as the light emitting layer, the EL emission is weak and the breakdown voltage is low, but sample No. 2
When the wurtzite type ZnS: Tb thin film of
High-luminance EL that can obtain the emission luminance-voltage characteristics shown in FIG.
The device could be manufactured. Also, this device is 300V
The EL element has the above breakdown voltage and high performance in terms of reliability.

Although ZnS: Tb is used as the thin film and hydrogen chloride is used as the hydrogen halide gas to be supplied in the above examples, when a rare earth element (Tm, Sm, Eu, Ce) having similar chemical properties to Tb is applied. It is considered that the same action and effect can be obtained when hydrogen halide (HF, HBr, HI) having similar chemical properties to hydrogen chloride is applied.

When ZnS without any additive is grown by this growth method, the crystal structure does not change even if hydrogen chloride is introduced into the substrate region, and the crystallinity of the film decreases as the supply amount of hydrogen chloride increases. However, research shows that at the end it cannot grow. When manganese is added, it is not necessary to control the hydrogen chloride flow rate because the crystal structure changes to wurtzite type by adding a small amount of manganese. From this, the effect of the present invention is effective when a rare earth element-added ZnS film is manufactured.

[0017]

According to the present invention, an electroluminescent thin film composed of a ZnS thin film containing a rare earth element having good crystallinity can be obtained. By using this thin film as a light emitting layer, an EL element having high withstand voltage and high brightness can be manufactured.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a thin film growth apparatus used in an example.

FIG. 2 is a diagram showing the relationship between Tb transport HCl transport amount, ZnS thin film growth rate, and Tb content.

FIG. 3 is a diagram showing growth conditions used in Examples.

FIG. 4 is a diagram showing growth conditions of Sample No. 1 and Sample No. 2.

FIG. 5 is a diagram showing an X-ray diffraction pattern of a sample.

FIG. 6 is a diagram showing changes in the crystal structure of a ZnS thin film due to changes in the amount of hydrogen chloride supplied.

FIG. 7 is a diagram showing changes in the crystal structure of a ZnS thin film due to changes in the amount of hydrogen chloride supplied.

FIG. 8 is a structural diagram of an EL element.

FIG. 9 is a diagram showing the relationship between the light emission luminance of the EL element of the example and the applied voltage.

[Explanation of symbols]

1. Quartz tube 2,3. Quartz inner tube 6,7,8. Resistance heating furnace 9, 10, 11. Introduction tube 12. Board area

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[Procedure amendment]

[Submission date] April 27, 1992

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Claims (1)

[Claims] 1. ZnS or Zn and S as a base material
And using a rare earth element as the luminescent center material, hydrogen or an inert gas is circulated over the host material while heating the host material, and the hydrogen halide on the luminescent center material while heating the luminescent center material. A chemical method characterized in that a base material and an emission center material are supplied onto a substrate which is placed in a growth region and heated by flowing a gas, and further a hydrogen halide gas is directly supplied to the growth region. Manufacturing method of electroluminescent thin film using vapor phase growth method.