JPH05310423A - Production of zns crystal having controlled particle diametfr - Google Patents

Abstract

PURPOSE:To provide a ZnS crystal having large crystal particle size and suitable as an infrared transmission material. CONSTITUTION:Iodine vapor is introduced together with raw material gas consisting of H2S and Zn vapor into a reaction zone in the synthesis of polycrystalline ZnS on the surface of a substrate by the reaction of H2S+Zn=ZnS+H2. The feeding rate of iodine may be changed during the CVD reaction. The particle diameter of the produced ZnS crystal increases nearly proportional to the feeding rate of iodine. The process gives a ZnS crystal having particle size almost comparable to that of commercially available infrared transmission material such as ZnSe and CdS and excellent infrared transmission properties and scratch resistance.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing ZnS polycrystals having excellent infrared transmission properties.

[0002]

2. Description of the Related Art With the development of infrared optics, the development of infrared lenses and window materials has been promoted. As a material of this type, a halogen-based crystal such as CaF ₂ has been conventionally used. However, the halogen-based crystal has a deliquescent property and is extremely brittle.

On the other hand, ZnSe, Z which is a II-VI group compound
Although nS, CdS and the like are excellent in infrared ray transmission characteristics, they are very difficult to prepare crystals, and thus have not been used so far. However, the adoption of the CVD method has enabled the production of large-scale polycrystals.
Polycrystals of Group I-VI compounds are increasingly being used. Among them, ZnS has high mechanical strength and is particularly excellent in scratch resistance, and therefore has an advantage that it can be used in a severe environment such as a dusty place or outdoors.

[0004]

However, unlike ZnSe and CdS, ZnS produced by the CVD method does not transmit visible light in the state where it is deposited by CVD. Therefore, since laborious work such as optical axis alignment is required, there are few examples of using ZnS as an infrared transmitting material, and ZnSe that transmits visible light and has excellent operability is widely used.

The reason why ZnS does not transmit visible light is
This is not due to the physical properties peculiar to ZnS, but because the precipitated ZnS crystal grains are as small as about 10 μm and the light scattering at the crystal grain boundaries is very large. Therefore, if the ZnS crystal grains can be made large, it is expected to be used as an infrared transmitting material having excellent durability.

For example, ZnS deposited by the CVD method is converted into H
When the IP treatment is performed, ZnS crystal grains having a size of 100 μm or more are obtained. The obtained ZnS crystal is transparent and has a particle size comparable to that of a crystal of ZnSe, CdS or the like which is generally marketed as an infrared transmitting material. However, since the HIP process is required after the CVD, the process is complicated and the manufacturing cost is increased. In this respect, large ZnS without requiring post-treatment such as HIP treatment
A method of producing crystals is desired.

If the grain size of ZnS crystals to be deposited by the CVD method itself can be 100 μm or more, HI
It is possible to obtain a ZnS crystal with excellent performance at a low manufacturing cost without requiring post-treatment such as P treatment.
In the CVD method, it is generally known that increasing the reaction temperature increases the grain size of the obtained crystal. However, as the reaction temperature rises, pores are more likely to be generated, and the characteristics of the obtained crystal are significantly deteriorated. Therefore, it is practically impossible to obtain crystals with a large grain size by increasing the reaction temperature.

The high mechanical strength, which is an excellent characteristic of ZnS, is also due to the size of crystal grains. Therefore, it is desirable not only to simply increase the crystal grain size, but also to prepare a ZnS crystal having a grain size of a predetermined size at an arbitrary position. For example, Zn having a crystal grain structure in which fine crystal grains are formed in the vicinity of the surface to improve scratch resistance, and large crystal grains are formed in the central portion to improve infrared ray transmission characteristics.
If S crystals are obtained, it is expected to become a very excellent infrared transparent material.

The present invention has been devised in order to meet such a demand, and by introducing iodine into the reaction zone to promote crystal growth, a large ZnS crystal suitable as an infrared transmitting material can be obtained only by the CVD method. It is intended to be manufactured in.

[0010]

In order to achieve the object, the method for producing a ZnS crystal according to the present invention is H ₂ S + Zn = Zn
When synthesizing ZnS polycrystal on the substrate surface by the reaction of S + H ₂ , iodine vapor is introduced into the reaction zone together with source gases of H ₂ S and Zn vapor. Further, when the supply amount of iodine introduced into the reaction zone is changed according to the transition of the CVD reaction, ZnS crystal having a controlled crystal structure can be obtained.

[0011]

[Operation] The inventors of the present invention have made Z produced by the CVD method.
The effects of various gases on the properties of nS crystals were investigated. As a result, it was found that when iodine was added to the raw material gas, the grain size of the crystal was significantly increased, and iodine was hardly incorporated in the obtained ZnS crystal. Therefore, when the influence of iodine on the size of the ZnS crystal grains produced by the CVD method was investigated in detail, there was almost no correlation between the concentration of iodine contained in the ZnS crystal and the size of the crystal grain size, and the iodine supplied. The larger the partial pressure P _{I2 of the} gas, the more Zn
It was found that the hydrogen concentration contained in the S crystal was reduced.

From this, it is presumed that it is hydrogen that determines the grain size of the ZnS crystal, and the hydrogen that is normally incorporated in the ZnS crystal is removed by the introduced iodine and the crystal grain becomes large. Hydrogen in ZnS crystals is a hydride that absorbs light at a wavelength of about 6.3 μm ZnH ₂
And deteriorates the infrared transmission characteristics. This defect due to hydrogen or hydride can be eliminated by removing hydrogen from the ZnS crystal by introducing iodine.

[0013]

EXAMPLE In this example, the CVD apparatus shown in FIG. 1 was used. In this CVD apparatus, a quartz reactor 2 is installed in a heating furnace 1 having three heating zones, and each heating zone is heated and maintained at a predetermined temperature. In the reactor 2, Z
A quartz tube 3a for introducing n-vapor, a quartz tube 3b for introducing H ₂ S, and a quartz tube 3c for introducing iodine vapor are exposed.

In the basin 4 provided in the middle of the quartz tube 3a, Z
n raw material 5 is filled. The Zn vapor gasified by heating is sent to the substrate 6 through the quartz tube 3a with Ar as a carrier gas. The other reactive gas, H ₂ S, is supplied to the substrate 6 via the quartz tube 3b. The iodine 7 is filled in a stainless steel container 8 and heated to a predetermined temperature by a ribbon heater 9 wound around the container 8 to be gasified. The gasified iodine vapor is sent to the substrate 6 via the quartz tube 3c using Ar as a carrier gas.

Reaction temperature 923 to 1023K, reaction pressure 6
Iodine supply amount of 0 to 0.02 under the conditions of 650 Pa, reaction time of 10 hours and iodine carrier gas flow rate of 100 cc / min.
ZnS crystals were prepared while changing the range of 5 g / min.

FIG. 2 shows a ZnS crystal obtained when the reaction temperature was 973 K and iodine was not added. This ZnS crystal had an average particle size of about 5 μm. Further, FIG. 3 shows a ZnS crystal obtained when iodine was introduced at a supply rate of 0.015 g / min. This ZnS crystal had an average particle size of 200 μm. As is clear from this comparison, it is understood that the crystal grain size is increased about 50 times by the introduction of iodine.

ZnS crystals were produced at the same reaction temperature while changing the amount of iodine supplied. When the relationship between the size of the obtained ZnS crystal and the iodine supply amount was investigated, it was found that there was the relationship shown in FIG. That is, the grain size of the ZnS crystal grains is increased almost in proportion to the iodine supply amount. The relationship between the crystal grain system and the amount of iodine supplied had a similar tendency when the CVD reaction was performed while changing the reaction temperature.

The results shown in FIG. 4 indicate that not only the grain size of ZnS crystal is increased by introducing iodine into the reaction zone, but also the ZnS crystal having an arbitrary grain size is controlled by controlling the supply amount of iodine. It shows that it can be manufactured.
Moreover, the supply amount of iodine can be easily controlled by adjusting the heating condition of iodine and the flow rate of carrier gas.

Therefore, in order to confirm the effect of controlling the flow rate of iodine gas, a ZnS crystal having a crystal structure in which the substrate side half and the surface side half consist of a large crystal and a fine crystal, respectively, was prepared as follows. Reaction temperature 923K, reaction pressure 6
650 Pa, Ar flow rate of 10 as iodine carrier gas
Set reaction conditions to 0 cc / min, feed rate 0.025 g
The CVD reaction was continued for 3 hours while introducing iodine at a flow rate of 1 / min. Next, the CVD reaction was continued for 3 hours under the same reaction conditions except that iodine was not introduced, and ZnS was deposited on the substrate surface by CVD in a total of 6 hours.

FIG. 5 showing the structure of the prepared ZnS crystal.
As is apparent from the above, fine crystal grains are stacked on the crystal grains that have been enlarged by the introduction of iodine. From this, it is understood that a ZnS crystal having a predetermined grain size at a predetermined position can be produced by controlling the introduction and supply amount of iodine. Further, the obtained ZnS crystal exhibited excellent infrared ray transmission characteristics due to the large crystal on the substrate side, and exhibited excellent scratch resistance due to the fine crystal on the surface side.

The amount of iodine taken into the obtained ZnS crystal hardly changed even when the iodine supply rate was changed. That is, the iodine supply amount is 0 to 0.025 g /
Even if it is changed within the range of minutes, the amount of iodine taken into the ZnS crystal is about 0.0002 atomic% regardless of the size of the crystal grain size.
Was almost constant at.

[0022]

As described above, in the present invention, ZnS crystal having a predetermined size is produced by introducing iodine into the reaction zone. The obtained ZnS crystal has a conventional ZnSe, Cd structure without requiring HIP treatment or the like.
It has a particle size comparable to that of S, etc., and exhibits excellent infrared transmission characteristics. Further, by controlling the iodine supply amount, the crystal grain size can be adjusted, for example, by increasing the crystal grain size in the lower layer portion and decreasing the crystal grain system in the surface layer portion. A ZnS crystal excellent in both physical properties can be obtained. Thus, according to the present invention, high quality ZnS crystals can be produced with a high yield by a relatively simple operation.

[Brief description of drawings]

FIG. 1 is a CVD apparatus used in an embodiment of the present invention.

FIG. 2 Structure of ZnS crystal prepared without introducing iodine

FIG. 3 Structure of ZnS crystal prepared by introducing iodine

FIG. 4 is a graph showing the relationship between the grain size of ZnS crystals and the iodine supply amount.

FIG. 5: Structure of ZnS crystal obtained when the introduction of iodine was stopped during the CVD reaction

[Explanation of symbols]

1 heating furnace 2 reactor 3a quartz tube (for introducing Zn vapor) 3b quartz tube (for introducing H ₂ S) 3c quartz tube (for introducing iodine vapor) 4 hot water pool 5 Zn raw material 6 substrate
7 iodine 8 container 9 ribbon heater

Claims (2)

[Claims] 1. When synthesizing ZnS polycrystal on the substrate surface by the reaction of H ₂ S + Zn = ZnS + H ₂ , H ₂ S and Z
A method for producing a ZnS crystal having a controlled particle size, which comprises introducing iodine vapor into a reaction zone together with a source gas of n vapor. 2. The supply amount of iodine introduced into the reaction zone is CV
The method for producing a ZnS crystal according to claim 1, wherein the method is changed during the D reaction.