JP2742366B2 - Method for producing glass containing CdSxSe (1-x) semiconductor microcrystals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a process for the preparation of CdS _x Se _(1-x) semiconductor nanocrystals containing glass. The CdS _x Se _(1-x) semiconductor microcrystal-containing glass obtained by the present invention is used as a glass material having a large nonlinear effect used in the optical information field, such as an optical switch and an optical wavelength conversion element.

[0002]

2. Description of the Related Art CdS _x Se _(1-x) , CuCl, CuB
Glass containing semiconductor microcrystals such as r has optical bistability, has optical relaxation time on the order of ps (picoseconds), and has a quantum size effect. It is attracting attention as a nonlinear optical material that can be used for devices and the like. Glass containing such semiconductor microcrystals has a Cd content of about 1%.
Multicomponent glasses containing S _x Se _(1-x) microcrystals are generally known and are commercially available as filter glasses. The semiconductor microcrystal-containing glass is manufactured by heating a glass material serving as a matrix and a semiconductor material to form a glass melt, and then rapidly cooling and reheating the glass melt.

However, the conventional glass containing semiconductor microcrystals produced by such a melting method has a low content of semiconductor microcrystals due to oxidation, volatilization and decomposition of the semiconductor raw material during the preparation of the glass melt. Because the semiconductor microcrystals grow randomly in the reheating treatment, the size of the semiconductor microcrystals is not uniform, it is difficult to reduce the thickness, and there are restrictions on the types of compound semiconductors that can be contained. Therefore, it is hard to say that it is useful as a nonlinear optical material.

For this purpose, sol-gel methods, CVD methods, sputtering methods, simultaneous vapor deposition methods, lithography methods, etc. have been used for the purpose of improving the content concentration of semiconductor microcrystals, making the size of semiconductor microcrystals uniform or thinning, and the like. Various attempts have been made to produce glass containing semiconductor microcrystals using a new amorphous material production technique such as the use of porous glass.

[0005] Among them, a method for producing CdS _x Se _(1-x) semiconductor microcrystal-containing glass is disclosed in Japanese Unexamined Patent Application Publication No. 3-18 / 1991.
No. 7950, Zarzyki (Zarzy)
cki) et al. (Journal of
Non-Crystalline solids, 1
21 221 (1990), SPIE Proceed
ins of Sol-Gel Optics, 13
28 108 (1990)).

In the former method, a solidified gel containing a Cd element and a Se element (or an S element) is heated in a reducing atmosphere to precipitate CdSe semiconductor microcrystals (or CdS semiconductor microcrystals) in a glass matrix. Then, it reacts with H ₂ S gas (or H ₂ Se gas) to form CdS _x Se having a small particle size and a uniform particle size distribution in the glass matrix.
_(1-x) A semiconductor-containing glass doped with semiconductor microcrystals is obtained.

On the other hand, the latter method uses potassium selenate (K ₂ SeO ₄ ) and cadmium nitrate (Cd (N
A wet silica gel containing Cd element and Se element prepared using O ₃ ) ₂ ) as a raw material of semiconductor microcrystals is immersed in a thioacetamide (CH ₃ CSNH ₂ ) solution to diffuse S ²⁻ into the wet gel. The purpose is to obtain silica gel in which CdS _x Se _(1-x) semiconductor microcrystals are dispersed.

[0008]

However, in these methods, it is difficult to control the ratio of S to Se, there is a possibility that the distribution of elements in the semiconductor microcrystal may not be uniform, and the size of the semiconductor microcrystal may be small. There are problems such as difficult control. Also, the former method disclosed in Japanese Patent Application Laid-Open No. 3-187950 uses toxic H ₂ S gas or H ₂ Se gas, so that it is necessary to give due consideration to safety.

[0009]

Means for Solving the Problems The present invention has been made to solve the above problems, CdS _x S of the present invention
e _(1-x) (where 0 <x <1) A method for producing a semiconductor microcrystal-containing glass comprises the steps of: mixing an acidic solution containing Cd, S, and Se elements with a compound component that eventually becomes glass. After mixing, the mixture is gelled and dried to obtain a solidified gel, and the solidified gel is heat-treated in a reducing atmosphere to precipitate CdS _x Se _(1-x) semiconductor microcrystals in a glass matrix. It is assumed that.

Hereinafter, the present invention will be described in detail. In the method for producing glass containing CdS _x Se _(1-x) semiconductor microcrystals of the present invention, an acidic solution (A) containing Cd, S, and Se elements as a starting material and a compound component that finally becomes glass
(B) is used.

Here, an acidic solution containing Cd, S and Se elements
(A) is obtained by dissolving one or more compounds containing at least one of Cd, S, and Se elements in an acid and reacting them. Here, examples of the compound containing at least one of Cd, S, and Se elements include Cd element-containing compounds such as cadmium alone, cadmium acetate, cadmium nitrate, cadmium chloride, and cadmium perchlorate;
Se element-containing compounds such as selenium alone, selenic acid, selenous acid, ammonium selenate, selenourea, sulfur alone, S element-containing compounds such as ammonium thiocyanate, thiourea, sulfuric acid, and ammonium sulfate; Cd such as cadmium selenate; Examples include Se element-containing compounds and Cd and S element-containing compounds such as cadmium sulfate.

As an acid for dissolving a compound containing at least one of the elements Cd, S and Se, inorganic acids such as nitric acid and perchloric acid can be mentioned.
Organic solvents (such as alcohols) are mentioned.

Compounds containing at least one of the elements Cd, S and Se react with each other in an acidic solution to form Cd,
A reaction system in which S and Se elements are uniformly dispersed is formed. For example, when cadmium selenate and ammonium thiocyanate are used as starting materials and these are dissolved in concentrated nitric acid, ammonium thiocyanate is converted to Se by concentrated nitric acid.
(NH ₂ ) ₂ and reacts with cadmium selenate to form a complex Cd [Se (NH ₂ ) ₂ ] _n SeO ₄ .

According to a preferred embodiment of the present invention, the above C
By adjusting the pH by adding a pH adjuster such as aqueous ammonia to the acidic solution (A) containing d, Se, and S elements, the ratio of Se to S in the acidic solution (A) can be appropriately controlled. . That is, when the pH is lowered, Se goes out of the system, and the proportion x of S in the finally obtained CdS _x Se _(1-x) semiconductor fine particles is relatively large, and Se
(1-x) becomes relatively small. Conversely, pH
Is high, Se tends to remain in the system, so CdS _x S
e The proportion of S in the _(1-x) fine particles is relatively small,
The ratio of e becomes relatively large. For example, concentrated nitric acid 40g
Cadmium selenate (CdSe)
O ₄ ) and ammonium thiocyanate (NH ₄ SCN) are dissolved, and ammonium thiocyanate is converted to SC (NH
₂ ) changes to ₂ and forms a complex Cd [SC with CdSeO ₄
(NH ₂ ) ₂ ] _n · SeO ₄ is formed. The value of n of this complex is in the range of 1 to 3, and the ratio of S in the complex is higher than that of Se. Se that does not participate in complex formation goes out of the system during gelation, and eventually the proportion of S also increases.

On the other hand, if the pH of the solution is increased with ammonia water or the like, NH ₄ SCN does not become SC (NH ₂ ) ₂ but Cd
No complex is formed with SeO ₄ . Therefore,
At the time of gelation, all of the prepared components are included in the gel without being separated out of the system, so that the Se ratio is increased.

In the present invention, the compound component (B) that finally becomes glass is mixed with the acidic solution (A) containing the Cd, S, and Se elements. As), alkoxides having a glass constituent metal or a hydrolyzate thereof are used. That is, for example, when the glass to be obtained is a silica single-component glass, silicon tetraalkoxide (tetraalkoxysilane), a partial or complete hydrolyzate thereof is used. When the glass to be obtained is a multi-component glass, silicon, boron, zirconium,
Alkoxides such as titanium and aluminum or their partial or complete hydrolysates are used. As the compound component (B) which finally becomes glass, an inorganic salt such as a nitrate, a carbonate, a phosphate or a borate of a glass constituent metal, or an organic salt such as an acetate may be used. Further, the glass constituent metal oxide itself can be partially used.

In the present invention, a mixture of the acidic solution (A) containing the Cd, Se, and S elements and the glass-forming compound component (B) is gelled and dried to obtain a solidified gel. This gelling and drying treatment is performed as follows. That is, after a mixture of the solution (A) and the component (B) is stirred to prepare a sol solution, the solution is transferred to a container such as polymethylpentene or polypropylene and left. By this standing, the glass-forming compound component (B) in the sol solution undergoes hydrolysis and polymerization reaction to form a gel, and by careful drying, excess water and an organic solvent volatilize to solidify the gel containing Cd, S, and Se elements. The body is obtained.

In the present invention, the obtained solidified gel is heat-treated in a reducing atmosphere to disperse CdS _x Se _(1-x) semiconductor microcrystals in a glass matrix.
The desired semiconductor microcrystal-containing glass can be obtained. The heat treatment in a reducing atmosphere is performed, for example, by placing the solidified gel in a mixed gas of a hydrogen gas and an inert gas (such as a nitrogen gas or a helium gas) and heating it at a temperature of, for example, 300 to 1100 ° C. for 1 to 10 hours. Done. By this heat treatment, the solidified gel becomes vitrified and CdS _x S
e _(1-x) microcrystals precipitate in the glass. In the above heat treatment, if the heating temperature is lower than 300 ° C., an organic substance, CN
Group, NH ₂ group, etc. do not desorb and decompose, vitrification becomes insufficient, and CdS _x Se _(1-x) microcrystals hardly precipitate,
If the temperature exceeds 1100 ° C., the proportion x of S decreases, and in some cases, crystallization of the glass itself as a matrix may occur.
The temperature is preferably set to 1100 ° C. In the heat treatment, if the heating time is less than 1 hour, vitrification and C
Precipitation of dS _x Se _(1-x) semiconductor microcrystals becomes insufficient.
On the other hand, heating for too long is meaningless, for example, 10
No change was observed anymore when heating was performed for more than an hour.

According to a preferred embodiment of the present invention, by appropriately changing the heat treatment conditions, the ratio x of S and the ratio of Se _{(1-x) in the} CdS _x Se _(1-x) semiconductor microcrystals.
Can be varied appropriately. To elaborate on this point,
CdS _x Se ₍₁ ) was prepared by heating the gel obtained by mixing and forming a complex under the condition of an acidic solution (about pH 2).
The value of x in _-x) is x = 0.52, 0.49 when heated at 400 ° C. for 2, 5, and 10 hours, respectively.
And 0.40, and the value of x became smaller as the time became longer. Further, when heated at 400 ° C. and 500 ° C. for 2 hours, x = 0.52 and 0.29, respectively.

The crystal size did not change so much even when the heat treatment conditions were changed. However, as the pH value increases, it tends to decrease, but rather CdS _x S
It strongly depends on the amount of e _{(1 -x), and as} the amount increases, the crystal diameter tends to increase. The preferred particle size of the semiconductor microcrystal obtained by the present invention is 20 to 100 Å.

[0021]

The present invention will be further described with reference to the following examples. Example 1 3.8 g of cadmium selenate (CdSeO ₄ ) was added to a mixed solution of 40.0 g of concentrated nitric acid (HNO ₃ ) and 30.0 g of water (H ₂ O), and the mixture was stirred at room temperature to be dissolved. 0.6 g of ammonium acid (NH ₄ SCN)
An acidic solution containing d, S and Se elements was prepared. When the pH of this solution was measured, it was pH = 2. To this solution is added tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ )
177.0 g was added with stirring, and stirred for 1 hour to prepare a sol solution.

The obtained sol solution was transferred to a container such as polymethylpentene or polypropylene and allowed to stand. The sol solution gels as the hydrolysis and polymerization reaction progresses,
By careful drying, excess water and organic solvent were volatilized, and a solidified gel containing Cd, Se, and S was obtained.

The obtained solidified gel is placed in an electric tube furnace,
By heating at 500 ° C. for 2 hours while flowing a mixed gas of hydrogen and nitrogen (H ₂ : N ₂ = 3: 97), CdS
A glass on which _x Se _(1-x) semiconductor microcrystals were precipitated was manufactured.

The composition of the semiconductor-containing glass is 10.0
Silica (SiO ₂ ) containing CdS _x Se _(1-x) by weight
It is glass, and hexagonal Cd is obtained by X-ray diffraction of the sample.
Only S _x Se _(1-x) crystals were observed, and no other crystals were found. Furthermore, the ratio x of S in the CdS _x Se _(1-x) crystal, the size of the crystal, and the energy gap value were determined. The ratio x of S in the CdS _x Se _(1-x) crystal was determined from the lattice constant of the X-ray diffraction measurement and the Raman spectroscopy, and was both x = 0.29. When the size of the crystal was determined using a peak width of X-ray diffraction (using the Scherrer equation) and a transmission electron microscope, both values were 63 Å (average). The energy gap value (Eg) determined from the visible ultraviolet absorption spectrum was 1.79 eV.

Examples 2 to 10 CdS _x Se _(1-x) semiconductor microcrystal-containing glass in the same manner as in Example 1 except that the content of CdS _x Se _(1-x) and / or the heating conditions were changed. Was prepared. The results are shown in Table 1 together with the results of Example 1.

[0026]

[Table 1] From Table 1, by appropriately changing the content of CdS _x Se _(1-x) and / or the heating conditions (temperature and time),
It has been clarified that the ratio x of S in the CdS _x Se _(1-x) semiconductor microcrystal (in other words, the ratio of Se (1-x)) and the particle diameter can be appropriately changed. Further, the energy gap value (Eg) was in the range of 1.79 to 1.90 eV, showing an excellent value.

Examples 11 to 13 Ammonia water (NH ₄ OH) was added to an acidic solution containing Cd, Se and S elements prepared in the same procedure as in Example 1 to adjust the pH to 5.3. A CdS _x Se _(1-x) semiconductor microcrystal-containing glass was produced in the same manner as in Example 1. Table 2 shows the results.

[0028]

[Table 2] From Table 2, it can be seen that by increasing the pH of the acidic solution,
It has been found that it is possible to reduce the ratio x of S in the dS _x Se _(1-x) semiconductor microcrystal and increase the ratio (1-x) of Se. In addition, the energy gap value (Eg) was in the range of 1.79 to 1.82 eV, showing an excellent value.

[0029] Examples 14, 15 cadmium acetate dihydrate _{(Cd (CH 3 COO) 2} · 2H
₂ O), selenium (Se) powder, thiourea (SC (N
An acidic solution containing Cd, S and Se elements was prepared using H ₂ ) ₂ ) as a raw material. When the pH of this solution was measured, it was pH = 1.5. Using this acidic solution, a glass containing CdS _x Se _(1-x) semiconductor microcrystals was produced in the same manner as in Example 1. Table 3 shows the results.

[0030]

[Table 3] From Table 3, it can be seen that even when a compound (cadmium acetate dihydrate, selenium powder, thiourea) different from those used in Examples 1 to 10 is used as a source of the Cd, S, Se elements in the acidic solution, the energy is also increased. The gap value (Eg) is 1.94 to 1.
It is clear that a CdS _x Se _(1-x) semiconductor microcrystal-containing glass having a high value of 98 can be obtained.

[0031]

As described above, according to the present invention,
CdS _x Se _(1-x) semiconductor microcrystal-containing glass having excellent nonlinear optical characteristics can be obtained.

Claims (6)

(57) [Claims] 1. An acidic solution containing Cd, S and Se elements is mixed with a compound component which finally becomes glass, and then gelled and dried to obtain a gel solidified product. CdS and heat-treated in a reducing atmosphere in a glass matrix _x Se _(1-x) (where, 0 <x <a 1) CdS _x Se, characterized in that to precipitate the semiconductor nanocrystals
_{(1-x) A} method for producing glass containing semiconductor microcrystals. 2. The pH of an acidic solution is adjusted to adjust CdS _x Se.
The method according to claim 1, wherein the ratio of S and Se in the _(1-x) semiconductor microcrystal is controlled. 3. CdS _x Se by changing heat treatment conditions.
The method according to claim 1, wherein the ratio of S and Se in the _(1-x) semiconductor microcrystal is changed. 4. The method according to claim 1, wherein cadmium alone, cadmium acetate, cadmium nitrate, cadmium chloride, cadmium perchlorate, cadmium selenate, or cadmium sulfate is used as a source of the Cd element in the acidic solution. The method described in. 5. A source of the S element in the acidic solution,
2. The method according to claim 1, wherein sulfur alone, ammonium thiocyanate, thiourea, sulfuric acid, ammonium sulfate or cadmium sulfate are used. 6. The method according to claim 1, wherein selenium alone, selenic acid, selenite, ammonium selenate, selenourea or cadmium selenate is used as a source of Se element in the acidic solution.