JPH0618947A - Nonlinear optical thin film - Google Patents

Abstract

PURPOSE:To provide a nonlinear optical thin film contg. fine semiconductor particles having a uniform particle diameter dispersed uniformly in glass at high density and having high tertiary nonlinear optical sensitivity. CONSTITUTION:When fine semiconductor particles 12 and glass 11 are alternately deposited on a substrate 13 to obtain a nonlinear optical thin film, the height (a) of the fine semiconductor particles per one period 14 and the height (b) of the glass per one period are allowed to satisfy the relation of 0.5mm<=a<=10 mm and b/2<=a<=4b. For example, fine CdSe particles and quartz glass are alternately sputtered 500 times with 2nm height (a) and 2nm height (b) and they are heat-treated at 400 deg.C for 10min to obtain the objective nonlinear optical thin film satisfying *=6mum10<-7>esu.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonlinear optical thin film used in an optical device utilizing the nonlinear optical effect.

[0002]

2. Description of the Related Art Conventionally, as this type of technology, for example, Journal of Optical Society of America, Vol. 73, p. 647 (Journal of Optical Society of
CdS _x S described in America 73, 647 (1983))
There is a filter glass in which e _1-x is dispersed in borosilicate glass. This filter glass is made of CdS _x S with a particle size of 1-10 nm.
e _1-x fine particles are dispersed in a borosilicate glass material in an amount of about 2% by weight.

In addition, the Journal of Applied Physics, Vol. 63, page 957 (Journal of Applied Phys
There is a CdS fine particle dispersed glass thin film as shown in ics 63, 957 (1988)). This glass thin film is Cd on the target
Corning "7059 glass" (B
a) -containing borosilicate glass) and produced by high frequency magnetron sputtering in argon gas, in which 2 to 4% by weight of CdS is dispersed in "7059 glass".

[0004]

In the conventional semiconductor fine particle-dispersed glass, the amount of semiconductor fine particles dispersed is about 2% by weight, and the value of the third-order nonlinear optical susceptibility χ ⁽³⁾ , which is an index of nonlinear optical characteristics, is obtained. is 10 ^{-1 1} esu about. This χ ⁽³⁾
Attempts have been made to increase the dispersion amount of semiconductor fine particles in order to increase the value of.

However, in the manufacture of filter glass
In bulk manufacturing method, such as 1200 ℃
Because of the need to melt at higher temperatures,
Can be easily volatilized, decomposed or oxidized depending on the type and can be dispersed
There are restrictions on semiconductors. Especially for low melting point materials.
It is fatal because it is usually volatilized, decomposed or oxidized.
At such high temperatures, volatilization is likely to occur and the amount of dispersion is limited.
Therefore, for example, CdS _xSe_1-xBorosilicate glass
It is difficult to uniformly disperse 2 to 4% by weight or more
It This kind of problem is solved and the dispersion amount of semiconductor particles is reduced.
As a way to increase it, lower the melting temperature as much as possible.
The search for possible glass compositions is ongoing.

In the case of a thin film, there are less restrictions on the type and dispersion amount of semiconductor fine particles than in bulk, and it is possible to disperse CdSe fine particles in silica glass by 10% or more.
However, there is a problem that the particle size of the semiconductor fine particles varies greatly. By heating the substrate, it is possible to reduce variations in particle size to some extent.
It is still insufficient at present. Furthermore, as the dispersion amount increases, the particle size of the semiconductor fine particles increases,
It is difficult to uniformly disperse the semiconductor fine particles having a uniform particle size in the glass at a high concentration because the dispersion of the particle size becomes large such that adjacent semiconductor fine particles stick to each other. If the variation in particle size becomes large, the nonlinear characteristics of the output light due to each fine particle will vary, resulting in a nonlinear optical thin film with low conversion efficiency.

According to the present invention, semiconductor fine particles having a uniform particle size can be uniformly dispersed in glass at a high concentration,
An object of the present invention is to provide a non-linear optical thin film having a third-order non-linear optical susceptibility higher than that of a conventional one.

[0008]

In order to solve the above-mentioned problems, the nonlinear optical thin film of the present invention is a nonlinear optical thin film formed by alternately depositing semiconductor fine particles and glass on a substrate. The height a of the semiconductor fine particles per one cycle and the height b of the glass per one cycle satisfy the relations of 0.5 nm ≦ a ≦ 10 nm and b / 2 ≦ a ≦ 4b.

In the nonlinear optical thin film, it is preferable that the nonlinear optical thin film is further subjected to heat treatment.

[0010]

The non-linear optical thin film in the present invention utilizes the fact that the vapor-deposited particles that reach the substrate are fine particles that are formed before the thin film is formed. By selecting the conditions, the fine particles can be uniformly dispersed with a uniform particle size on the substrate. Moreover, when the semiconductor fine particles and the glass are alternately deposited to form a nonlinear optical thin film, the height a of the semiconductor fine particles per one cycle of deposition and the height b of the glass per cycle are b / 2 ≦ a ≦ 4b. By satisfying the relationship of, it is possible to distribute the particles on the substrate in a high concentration with the particle diameters made uniform. If a is larger than 4b, the probability that the semiconductor fine particles are continuous becomes extremely high, and if a is smaller than b / 2, the dispersion amount of the semiconductor fine particles is reduced and the third-order nonlinear optical susceptibility is extremely reduced. For,
a is set to be b / 2 or more.
The size of the semiconductor particles needs to be larger than the Bohr radius of excitons and small enough to cause the quantum size effect to appear remarkably. The specific size depends on the type of semiconductor, but is usually about 1 nm to 30 nm. The size of is appropriate. By setting the value of a within the range of 0.5 nm to 10 nm, the size of the semiconductor fine particles dispersed in the glass matrix can be adjusted within the above range.
With such a structure, a semiconductor fine particle-dispersed glass thin film in which semiconductor fine particles having a uniform particle size are uniformly dispersed in glass at a high concentration can be obtained, so that a material having a large third-order nonlinear optical susceptibility Is obtained.

In the non-linear optical thin film, it is preferable that the non-linear optical thin film is a non-linear optical thin film formed by further heat treatment, so that the crystallinity of the semiconductor fine particles is improved and the third-order non-linear optical film is formed. The susceptibility can be further improved.

[0012]

1 is a schematic view showing the cross-sectional structure of a nonlinear optical thin film according to the present invention. In FIG. 1, 11 is semiconductor fine particles, 12 is glass, and 13 is a substrate. Further, 14 indicates a unit of one deposition cycle. 2 is a partially enlarged view of FIG. 1. In FIG. 2, a indicates the height of semiconductor fine particles per cycle, and b indicates the height of glass per cycle.

The nonlinear optical thin film according to the present invention has a structure in which semiconductor particles and glass are alternately deposited, and the height a of the semiconductor particles per cycle and the height b of the glass per cycle are included. Must satisfy the relationship of b / 2 ≦ a ≦ 4b. If the height a is larger than 4b, the probability that the semiconductor fine particles continuously grow increases, and the particle size of the fine particles becomes too large, which is not preferable. Therefore 4
It is preferably smaller than b. When a is smaller than b / 2, the amount of semiconductor fine particles dispersed is reduced, and the third-order nonlinear optical susceptibility is extremely small. Therefore, a is preferably b / 2 or more. The size of the semiconductor fine particles must be larger than the Bohr radius of the excitons and small enough to cause the quantum size effect to appear remarkably. The specific size is usually 1 nm to 30 nm although it varies depending on the type of semiconductor.
The size is appropriate. In the deposited thin film according to the present invention, the height of the deposited fine particles is generally smaller than the width in the perpendicular direction when the semiconductor fine particles are deposited by a method such as vapor deposition or sputtering.
By adjusting the size in the range of 5 nm to 10 nm, the size of the semiconductor fine particles dispersed in the glass matrix can be adjusted within the above range.

In vacuum vapor deposition or sputtering, generally, vapor deposition particles that have reached a substrate are first deposited in the form of fine particles before forming a thin film. The particles have a uniform particle size, and can be uniformly distributed on the substrate by selecting the conditions.

The particle size and dispersion state of the semiconductor fine particles differ depending on the substrate temperature at the time of manufacturing the thin film. The lower the substrate temperature, the smaller the particle size of the semiconductor fine particles. However, if the substrate temperature is too low, the crystallinity of the semiconductor fine particles deteriorates. Therefore, in the present invention, the substrate temperature in the case of forming a deposited thin film by vacuum deposition or sputtering is -5.
0 ° C to 250 ° C is preferable. Further, if the thin film is heat-treated after the deposited thin film is manufactured, the crystallinity of the semiconductor fine particles is improved,
It was found that the following nonlinear optical susceptibility also increases. In this case, the heat treatment temperature is preferably in the range of about 300 ° C. to 700 ° C., and the heat treatment time is preferably set to a time at which crystallinity improves but grain growth does not proceed. For example, for a CdSe fine particle-dispersed glass thin film manufactured at a substrate temperature of 100 ° C., 400 ° C. for about 10 minutes was suitable.

The semiconductor particles used are CuCl, C
I-VII group compound semiconductors such as uBr, CdS, CdSe, CdO, CdTe,
II-VI group compound semiconductors such as ZnSe, ZnO, ZnTe, HgTe, CdSSe, HgCdTe, GaAs, GaN, GaP, GaSb, InAs, InP, InSb, GaAlAs, InA
III-V group compound semiconductors such as lAs, or Si, Ge, etc.
Group IV semiconductors are preferred.

The glass is not particularly limited, but quartz glass (SiO ₂ ) and borosilicate glass are suitable. When the semiconductor particles and the glass are alternately deposited on the substrate by the above-mentioned sputtering or vacuum evaporation method, the substrate is preferably an optically transparent substrate, for example, quartz glass (SiO ₂ ) or borosilicate. Glass or the like is suitable.

When the thin film of the present invention is formed by sputtering, the pressure of the inert gas such as argon introduced into the vacuum chamber is usually in the range of 0.1 to 10 Pa,
It is used at an appropriate pressure according to various conditions. Although the substrate temperature is within the above range, it is preferably 200 ° C. or lower because the particle size can be made smaller, and it is usually convenient to carry out at room temperature. The input power to the glass target is not particularly limited but is usually about 50 W to 1 kW, and the input power to the semiconductor target is not particularly limited and is usually about 10 W to 100 W.

The number of cycles for forming the thin film of the present invention is not particularly limited and varies depending on the thickness of each cycle, but the final total thickness of the thin film is usually 0.1 μm or more. Therefore, the number of cycles is about 20 or more.

Specific examples of the manufacturing method of the present invention will be described. FIG. 3 shows a schematic diagram of a two-component sputtering apparatus. However, the outer wall of the vacuum chamber that covers the outer periphery of this apparatus, the power source, and the like are the same as those in a normal sputtering apparatus, and therefore are not shown. The sputtering target 23 is quartz glass.
23a and CdSe23b. In the figure, 21 is a substrate and 22 is a heater. Shutter 24 between substrate and target
(24a is a shutter for quartz glass, and 24b is a shutter for CdSe) are arranged, and the element for irradiating the substrate can be changed by opening and closing the shutter. The height of vapor deposition particles per cycle can be changed by opening and closing the shutter. In the figure, 25a and 25b are the rotation axes of the shutter. Quartz glass was used for the substrate 21.

In an argon atmosphere, the gas pressure was 1 Pa, the substrate temperature was 50 ° C., the input power to the quartz glass target 23a was 200 W, and the input power to the CdSe target 23b was 30 W.

First, in order to cover the surface of the substrate 21 with the SiO ₂ film to make it flat, an SiO ₂ film was deposited to 100 nm on the substrate 21 by the shutter 24a of the quartz glass target 23a. Next, the shutter 24b of the CdSe target 23b
Opened to deposit CdSe fine particles. The CdSe fine particles rapidly increase with time and the size of the fine particles increases. When the height of the semiconductor particles reaches 2 nm, the shutter 24b is closed, the shutter 24a of the quartz glass target 23a is opened, and the SiO 2
_Two films were deposited to about 2 nm. Substrate made of SiO ₂ and CdSe
By repeating the operation of alternately irradiating 21, CdS
e A thin film having a structure in which fine particles and SiO ₂ films were alternately deposited was formed. This operation was repeated 500 times to produce a nonlinear optical thin film of about 2 μm. The doping amount of CdSe in this thin film was 25% by volume.

When the light absorption spectrum of this thin film was measured, a spectrum as shown at 31 in FIG. 4 was obtained. The bandgap obtained from this is 0.3e compared to the bulk semiconductor.
The V blue shift revealed that the semiconductor is a quantum dot. The third-order nonlinear optical susceptibility χ ⁽³⁾ of this thin film was measured at room temperature by the degenerate four-wave mixing method. Χ ⁽³⁾ at a wavelength of 575 nm was 3 ×
It was 10 ^-7 esu.

By heat-treating this thin film at 400 ° C. for 10 minutes in the atmosphere, 575 nm as shown by 32 in FIG.
A structure with a shoulder in the vicinity was obtained. From this, CdSe
It can be seen that the particle size distribution of the fine particles is smaller. Χ ⁽³⁾ at wavelength 575nm of this thin film is 6 × 1
It was 0 ^-7 esu. From the above, χ ⁽³⁾ is larger in the heat-treated thin film. It is considered that this is because the crystallinity of the fine particles is improved by the heat treatment.

[0025]

The non-linear optical thin film of the present invention can disperse semiconductor fine particles having a uniform particle size in glass uniformly and in a high concentration, and has a third-order non-linear optical susceptibility larger than that of the conventional one. An optical thin film can be provided.

Further, by adopting a preferred embodiment in which the non-linear optical thin film is a non-linear optical thin film further heat-treated, the crystallinity of the semiconductor fine particles is improved, and the third-order non-linear optical susceptibility is further improved. A thin film can be provided.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a cross-sectional structure of a nonlinear optical thin film of the present invention.

FIG. 2 is a partially enlarged view of FIG.

FIG. 3 is a schematic view of a binary sputtering apparatus used in an example of the present invention.

FIG. 4 is a diagram showing light absorption characteristics of a nonlinear optical thin film according to an embodiment of the present invention.

[Explanation of symbols]

 11 Semiconductor fine particles 12 Glass 13 Substrate 14 Unit of one cycle of deposition 21 Substrate 22 Heater 23 Target 23a Quartz glass target, 23b CdSe target 24, 24a, 24b Shutter 25a, 25b Shutter axis 31 Spectrum before heat treatment 32 Spectrum after heat treatment

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuneo Mikuro 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. In a nonlinear optical thin film formed by alternately depositing semiconductor particles and glass on a substrate, the height a of semiconductor particles per deposition cycle and the height b of glass per cycle are set. And satisfying the relations of 0.5 nm ≦ a ≦ 10 nm and b / 2 ≦ a ≦ 4 b. 2. The nonlinear optical thin film according to claim 1, wherein the nonlinear optical thin film according to claim 1, which is formed by alternately depositing semiconductor fine particles and glass, is a nonlinear optical thin film that has been further heat-treated.