JPH05158094A - Nonlinear optical material - Google Patents

Abstract

PURPOSE:To improve the heat stability of the material by providing a diffusion barrier layer in the superfine grain dispersed thin film. CONSTITUTION:A diffusion barrier layer is provided in the superfine grain dispersed thin film contg. a semiconductor and/or fine metallic grain. This thin film contains the semiconductor and/or metallic grain having the diameter in the quantum size effect range, preferably <=100Angstrom diameter, in its matrix. The barrier layer is formed in the thin film, for example, by forming a diffusion barrier layer on the superfine grain dispersed thin film and further forming a diffusion barrier layer on the barrier layer. Although one or multiple barrier layers can be formed, the thickness of one layer is preferably controlled to several to 50Angstrom so that the nonlinear characteristic is not deteriorated. The metal silicide, TiN, TiW the nitride, carbide, boride, etc., of transition metals, etc., which are chemically stable and have a high barrier effect are used as the material for the barrier layer.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The non-linear optical material of the present invention is used as a thin film in the fields of optical bistable elements, optical gate optical switches, wavelength conversion elements and the like.

[0002]

2. Description of the Related Art As a conventional technique of a nonlinear optical thin film, semiconductor ultrafine particles having a particle size of 100 Å or less in a transparent insulator (eg, amorphous Al ₂ O ₃ or amorphous SiO ₂ ) [C
dS, CdSe, CuCl, GaAl, ZnSe, In
Sb, InP, CdTe, CdSxSey (y = 1−
x) etc.] or metal ultrafine particles (Au, Ag, etc.) dispersed therein were used. However, the conventional ultrafine particle-dispersed thin film has a basic defect that the particle size increases when heated. Originally, the particle size was controlled and produced, and this led to the appearance of nonlinear optical characteristics. However, the particle size stability due to heat was poor, and there was a problem with repeated use. That is, in the conventional ultrafine particle-dispersed thin film, the method of heating the substrate was used to control the particle size. This is because the particles dispersed in the matrix in the film are aggregated by the diffusion of atoms and become large. Means Therefore, the particle size of these films can be controlled immediately after production, but it means that the long-term thermal stability is poor.

[0003]

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a non-linear optical material comprising an ultrafine particle dispersed thin film having excellent thermal stability.

[0004]

The present invention relates to a non-linear optical material exhibiting a so-called quantum size effect in which electrons and excitons exhibit zero-dimensional behavior due to a three-dimensional confinement effect.

Here, the non-linear optical effect is a phenomenon in which, when a substance is irradiated with light, the optical characteristics such as the absorption coefficient and the refractive index of the substance change according to the intensity of the light. Can be controlled, and an all-optical logic element that uses only light for input and output can be realized.

The quantum size effect means that the electrons and holes of semiconductor particles embedded in transparent glass in the visible light region are three-dimensionally confined by the deep potential created by the glass. If you think
In a small box, the wave pattern is limited to a specific one, so the electronic states become discrete and the oscillator strength and nonlinear susceptibility increase.

The quantum size effect of this fine particle-dispersed glass has recently been discovered (7 to 8 years ago) and has come to the forefront, and 100 Å in an insulating material such as glass.
The following semiconductor fine particles are dispersed.

These technical matters are described in, for example, [JAP
ANESE JOURNAL OFAPPLIED P
HYSICS, Volume 28, No. 10, 1928-1933.
P.] And "Optics, Vol. 19, No. 1 (1990, 1
Mon) 10-16 ”.

In the present invention, it is considered that the conventional instability of the particle diameter of the ultrafine particles due to heat is due to the atoms of the fine particles diffusing and assembling in the matrix, or due to the atoms dispersed in the matrix. For example, the diffusion of Al atoms in SiO ₂ is a well known phenomenon. The present invention is characterized in that a diffusion barrier layer is provided in an ultrafine particle-dispersed thin film in order to prevent the diffusion of atoms, which are considered to be the cause of ultrafine particles, to solve the above-mentioned drawbacks. The barrier layer may be provided in any direction as long as it has a function of diffusing the atoms, and may be provided in the vertical direction, for example. The ultrafine particle-dispersed thin film provided with the diffusion barrier layer in the present invention has a particle size in the range of the quantum size effect,
Preferably a semiconductor having a particle size of 100Å or less and /
Alternatively, the metal fine particles are contained in the matrix. Examples of the method of forming the diffusion barrier layer in the ultrafine particle dispersed thin film include a method of forming a diffusion barrier layer on the ultrafine particle dispersed thin film and further forming an ultrafine particle dispersed thin film on the barrier layer. The barrier layer may be provided not only in one layer but in any number of layers, but the thickness of one layer is preferably several Å to 50Å so as not to deteriorate the nonlinear characteristics. As a material for forming the barrier layer, a metal silicide (for example, Ti, V, Cr, Z) that is chemically stable and has a high barrier effect is used.
r, Nb, Mo, Hf, Ta, W, etc., IVA, VA, VIA
It is preferable to use silicide of group elements), TiN, TiW, nitrides of other transition metals, carbides, borides, or the like. In the present invention, the method for forming the ultrafine particle-dispersed thin film and the barrier layer is not particularly limited, and both PVD and CVD can be used. However, as a method for forming the ultrafine particle-dispersed thin film, an ion beam with good crystallization is used. The sputtering method is preferred. The film thickness is also not particularly limited, but 100 Å ~
1 μm is suitable. The total thickness of the ultrafine particle dispersed thin film and the barrier layer can be arbitrarily determined in consideration of transparency and the like, but is preferably about 1 μm, for example.

The substrate on which the ultrafine-particle-dispersed thin film and the barrier layer are formed is not particularly limited as long as it is transparent to visible light, and glass, quartz, or plastic such as polycarbonate or polyester can be used.

[0011]

Example 1 A transparent thin film having a thickness of about 200 Å was formed on a quartz substrate by using the RF sputtering method. Introduced gas Ar (99.999%) with introduced Au chip on target SiO ₂ Introduced gas pressure 5 × 10 ⁻³ Torr Quartz substrate temperature 150 to 300 ° C. Base pressure 8 × 10 ⁻⁷ Torr Target-substrate distance 50 mm high frequency power 200 to 300 W As described above, the quartz substrate temperature and the high frequency power were changed to form three types of films. Then, a TiN layer was formed on these films under the following conditions. The thickness was about 20Å. Target Ti (99.99%) Introduced gas Ar + N ₂ (1: 1) Introduced gas pressure 3 × 10 ⁻⁴ Torr Quartz substrate temperature 300 ° C. Base pressure 5 × 10 ⁻⁷ Torr Target-substrate distance 50 mm High frequency power 200 W 2 transparent thin films and TiN film
Layer by layer, about 1300Å thin film was obtained. When examined by an X-ray diffraction method, minute diffraction peaks of Au and TiN were observed. When examined by a cross-sectional TEM method, the fine particle diameter of Au was 18Å, 26% and 39%. A high energy shift (blue shift) was observed from the measurement results of the optical absorption edge of these three types of thin films examined at room temperature using a spectrophotometer, and the size is proportional to the square of the average particle size of the fine particles. And showed the quantum size effect. There was no change in particle size or quantum size effect after the film was placed in a 450 ° C. oven for 30 minutes. Comparative Example 1 The RF sputtering method was performed in the same manner as in Example 1 to obtain about 1
A 500 Å thick transparent thin film was prepared. In this case, no TiN layer was provided. The average particle size of each sample is 20Å, 26
Å and 37Å were almost the same as in the example. X-ray diffraction and T
From the EM method, the thin film was an amorphous film of SiOx as in the example. From the measurement result of the optical absorption edge, the same blue shift as in Example 1 was recognized. However, after being placed in a furnace at 450 ° C for 30 minutes, the particle size increased by about 10Å, the energy at the absorption edge moved, and the blue shift decreased.

[0012]

[Effects] According to the present invention, since the barrier layer for preventing the diffusion of the atoms of the ultrafine particles is provided in the ultrafine particle-dispersed nonlinear optical thin film, it is possible to prevent the ultrafine particles from increasing in particle size due to heat absorption and the like. Stable performance can be maintained as an optical material.

Claims (2)

[Claims] 1. An ultrafine particle dispersed thin film in which ultrafine particles of a semiconductor and / or a metal are contained in a matrix,
A nonlinear optical material comprising an ultrafine particle-dispersed thin film, wherein a diffusion barrier layer for preventing the diffusion of atoms, which causes variation in the particle size of the ultrafine particles, is provided in the ultrafine particle-dispersed thin film. 2. The nonlinear optical material according to claim 1, wherein a plurality of diffusion barrier layers are provided.