1. Field of the Invention
The present invention relates to a cluster-included material comprising granular or thin linear clusters, each cluster having a preferable size, and a method for producing the same.
2. Related Art
An intensive study on practical application of a technique of utilizing the quantum effect by micronizing the size of substances to such a degree that the quantum effect is obtained by the substances has recently begun. For example, when the thickness of an active layer of a semiconductor laser is reduced to a value smaller than that of the de Broglie's wavelength of carriers, a quantum well laser is obtained. According to this quantum well laser, various characteristics are improved, for example, increase in differential gain and relaxation of oscillation frequency, decrease in spectral line width and the like.
In case of the above quantum well laser, the thickness of the layer called the active layer is reduced but the area thereof becomes larger. A trial of increasing the number of dimensions to be micronized is made, and a study of realizing those for micronizing the region or substance to the thin linear form (referred to as a "quantum wire")and those for micronizing to the dot form (referred to as a "quantum dot") is made. In the quantum wire, substance is micronized in two-dimension and a one-dimensional electron system is obtained. In the quantum dot, substance is micronized in three-dimension and a zero-dimensional electron system is obtained. By making the line thin to such a degree that the quantum effect is obtained (quantum wire) or making the particle small to such a degree that the quantum effect is obtained (quantum dot), characteristics of electron devices are improved or realization of electron devices based on a quite new physical phenomenon is expected.
For example, when the quantum dot laser is realized, not only the above mentioned characteristics of the quantum well laser is further improved but also the other characteristics are improved, e.g. decrease in threshold current, and temperature dependence of the threshold current and the like.
As the method of realizing the microstructure of the substance wherein the improvement of various characteristics are expected, for example, there are suggested use of lithography (production of quantum wires and quantum dots), deposition of clusters by means of a heat treatment of a mixed crystal substance, metal or semiconductor particles-dispersed glass, etc. (production of quantum dots), direct production of clusters by means of a dry process (production of quantum dots), utilization of a one-dimensional polymer (production of quantum wires), utilization of a porous silicon substance (utilization of quantum wires and/or quantum dots) and the like.
In addition to these techniques, a method of embedding clusters into pores (voids) of a previously prepared porous substance is made.
As one of this kind of trials, a technique described in N. Herron et al., J. Am. Chem. Soc. Vol. 111, No. 2, 530 (1989) is known.
According to this technique, cadmium sulfide (CdS) clusters are deposited in pores in a zeolite crystal by using the zeolite crystal as a porous substance. Each pore in the zeolite crystal has a diameter of not more than 1 nm, and the quantum dot is produced.
Furthermore, another technique includes a technique described in Japanese Patent Kokai Publication No. 7-72520. According to this technique, a compound semiconductor is embedded into voids of a zeolite crystal by utilizing ion exchange and/or gas adsorption. Particularly, the compound semiconductor is embedded into the above voids by applying visible light or ultraviolet light to the above zeolite crystal.
These techniques have an advantage that, since clusters are embedded into pores of the zeolite crystal wherein the pores are regularly arranged, a microstructure of clusters corresponding to the crystal structure of the zeolite crystal can be obtained.
Particularly, according to the technique described in Japanese Patent Kokai Publication No. 7-72520, since visible light or ultraviolet light is applied to compound introduced into voids in the zeolite crystal, bonding between components of the compound is accelerated by the photochemical reaction and clusters of a compound semiconductor are formed in the zeolite crystal in high efficiency. Consequently, the compound semiconductor is embedded into the above void, easily and efficiently.
However, these prior arts had the following problems because the zeolite crystal is used as a host for forming the cluster.
The diameter of the pore of the zeolite crystal is not more than several nm, normally not more than 1 nm. Since the diameter of this pore is too small, the embedding rate of the cluster into the pores is reduced. That is, the cluster density in the zeolite crystal could not be increased sufficiently and, therefore, characteristics required for practical application could not be obtained.
There sometimes arises a problem that, since the pore is too small, the size of the cluster to be formed in the pore of the zeolite crystal is also too small.
The present invention is based on the fact that the above knowledge has been found as a result of intensive study about the cause of the problems which arise in case of utilizing the zeolite crystal.