JPH0695188A - Organic superlattice photoelectronic element and its production - Google Patents

Abstract

PURPOSE:To provide the novel element for which the characteristics of elementary excitons, such as excitons and polarons, are utilized and to provide the optical third higher harmonic wave generating element and photo-photo switching element by providing an org. superlattice structure periodically laminated with plural org. ultrathin film layers on a substrate. CONSTITUTION:This org. superlattice photoelectronic element is constituted by having media which can be modulated by exit and incidence of light, charge implantation or electric field magnetic field. The element has the org. superlattice structure periodically laminated with >=2 kinds of the org. ultrathin film layers on the substrate. Namely, the org. superlattice photoelectronic element consisting of highly crystalline hetero ultrathin films of about several nm film thickness which are heretofore difficult with the conventional film forming technique has the superlattice structure of the org. molecules consisting of the high-grade hetero-ultrathin films. The novel superlattice electronic state is thus attained by the quantum confining property and tunnel effect possessed by the org. molecules. The novel org. superlattice photoelectronic element is obtd. by the elementary exciton characteristics, such as excitons and polarons, stabilized in the superlattice structure of the org. molecules.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic superlattice optoelectronic device, and more particularly to an organic superlattice optoelectronic device having nonlinear optical effects such as light mixing, optical parametric oscillation, generation of optical harmonics, Pockels effect and Kerr effect. .

[0002]

2. Description of the Related Art A superlattice is, for example, an MBE (Molecular
Thin film forming technology such as Beam Epitaxy) or ALE (Atomic Layer Epitaxy) method, in a clean environment under ultra-high vacuum of 10 to ⁹ Torr or more, an inorganic semiconductor such as GaAs at an arbitrary atomic ratio on a Si substrate. It is defined as a material system in which epitaxial growth is performed and heterojunctions of different structures are repeated to form a superstructure of atoms or molecules that does not exist naturally, thereby artificially changing the electronic state of the material or its wave function ( "Superlattice heterostructure device", edited by Hirona Ezaki and edited by Hiroyuki Sakaki).

The first idea of the semiconductor superlattice was 196
From 9 to 1970, at that time IBM's Esaki
And proposed by Tsu [L. Esaki and R. Tsu, "S
uperlattice and negative conductivity in semicondu
ctors ", IBM Research Note (1969), RC-2418 and the same name, IBM J. Res. Develop. 14 , 61 (1970)].

In the 1970s, MBE, MOCVD (Meta
lorganic Chemical VaporDeposition), MONBE (M
etalorganic Molecular Beam Epitaxy, CBE: Chemica
With the progress of thin film growth technology such as l Beam Epitaxy, it has become possible to fabricate extremely high-quality heterojunctions, and high electron mobility transistors (HEMT: High Elect
ron Mobility Transistor), Hetero Bipolar Transistor (HBT), Resonant Tunneling Diode, Quantum Well Laser, Optical Bistable Device (SEED: Self-Electro-optic Effect Device, CS)
F-OB: Charge-induced Self Feedback Optical Bis
Many superlattice devices such as table devices have been proposed.

In recent years, research on superlattice devices started with such inorganic semiconductors has been made to reduce the dimension of a conventional two-dimensional quantum well structure by a planar heterojunction by means of high-definition lithography technology and particle dispersion technology. The interest is shifting to the realization of quantum well wires (one-dimensional) and quantum well boxes (zero-dimensional).

On the other hand, research on the improvement of the physical properties of heterojunction thin films composed of organic molecules has been started mainly in the 1960s, mainly in relation to organic semiconductor thin films [F. Gutmann and L.
E. Lyons, "Organic Semiconductors", John Wiley & So
ns, Inc. (1967)].

In the case of an inorganic crystal such as silicon or germanium, the energy level of one semiconductor layer is represented by a band structure in which atomic orbitals of atoms constituting the crystal are superposed by the periodic structure of the crystal. In the ground state, the valence band filled with electrons and the conduction band above it are separated by a constant band gap. Junctions of different semiconductors cause band discontinuities at their boundaries, and repeating such junctions form a band confinement structure (ie, quantum wells or tunnel barriers). The confined band exhibits a wave function like an isolated atom.

In the case of a crystal composed of organic molecules, one complete molecular orbital is formed within one molecule, but the whole crystal is a weak molecular crystal composed of van der Waals forces, and the intermolecular interaction is weak. The band width is narrow and the energy gap is larger than that of semiconductors. Therefore usual organic crystal is an insulator (electric conductivity ¹⁰ ~ 10 Ω ~ ¹ c
m ~ ¹ or less in many ^{10 ~ 20 ~10 ~ 14 Ω ~} 1 cm ~ 1), no reforming of electronic properties even heterojunction such organic molecules.

Therefore, in order to form a superlattice from organic molecules, the molecules are enlarged to expand the molecular orbital to a size where one molecule can be regarded as one quantum box or quantum wire, or some kind of intermolecular interaction. Band structure must be created in the crystal.

As an example of the former, one-dimensional conjugated polymers such as polyacetylene and polydiacetylene and planar conjugated molecules such as porphyrin and phthalocyanine show electric characteristics in the semiconductor region (electric conductivity 10 to ⁹ to 10).
~ ⁵ Ω ~ ¹ cm ~ ¹ ), and as an example of the latter, in a dopant type hetero film such as poly-p-phenylene / iodine or a charge transfer complex crystal such as tetrathiafulvalene / tetracyanoquinodimethane, a semiconductor is used. It is known to show electric characteristics from the region to the conductor region (electrical conductivity 10 to ⁴ to 10 ⁴ Ω to ¹ cm to ¹ ).

However, in these early studies on organic semiconductors, the purity was lower than that of inorganic semiconductors, and the process technology such as single crystal production and thin film production by the vacuum deposition method was undeveloped. It was poor in properties, and there were problems such as drastic changes in electrical characteristics due to the influence of moisture and oxygen in the air, and marked deterioration of the sample.

As a method aiming at more complete control of molecular orientation of an organic molecular thin film, a solvent evaporation method, a spin coating method, in addition to a dry process such as the vacuum evaporation method described above,
Wet processes such as the Langmuir-Blodgett film method are being studied. Among them, the Langmuir-Blodgett method is the only method that can control the array at the molecular level, because it can form a thin film on the molecular order and control the array in the thin film layer direction. To the first half of the same generation [FL Carter, "Molecular Electronic Devi
ces ", Marcel (1982)].

However, in this method, since the molecular arrangement at the gas-liquid interface is utilized, solvent molecules are mixed in the film, no ordering is obtained in the plane of the thin film, and a long time for the molecular arrangement is required. There is a problem that intermolecular interaction in the layer direction cannot be achieved because an alkyl chain is required in the molecule.

On the other hand, as a technique for forming a multilayer of an organic thin film, there is a film forming technique by a laminating method of a functional polymer film. However, with this method, it is difficult to control the array at the molecular level, and it is impossible to form a multilayer film with a quantum size that exhibits superlattice properties.

From the late 1980s, MBE (Molecula
r Beam Epitaxy) technology is being actively used for epitaxial growth of organic molecules in an extremely clean environment.
It has been reported that ultra-thin films prepared by the MBE method are extremely uniform and of high quality [JC Buchholz and GA Som
orjai, J. Chem. Phys. 66 , 573 (1977): M. Komiyama,
Y. Sakakibara, and H. Hirai, Thin Solid Films 15
1 , L109 (1987): A. Yamada, K. Shigehara, and M. H
ara, Synth. Met. 18 , 821 (1987): M. Hara, H. Sas
abe, A. Yamada, and AF Garito, Jpn. J. Appl. Ph
ys. 28 , L306 (1989), etc.]. Most of them are related to the examination of epitaxial growth conditions of phthalocyanine compounds on various crystal substrates.

In the 1990s, it was confirmed that many other organic molecules were epitaxially grown on an alkali halide substrate or a MoS ₂ substrate [Hirichi Tada,
Atsushi Koma, "Chemistry and Industry" 44 , 2109 (1991)
)], It is expected that various properties, which have been inferior due to poor film quality, are remarkably improved.

Due to such advances in vacuum deposition technology, the production of heteroepitaxial structures of organic molecules, which has been incomplete in the past, has been active again since 1991. For example, a report on the relationship between fluorescence lifetime and film thickness for perylene / naphthalene hetero films [FF So and SR For
rest, Phys. Rev. Lett. 66, 2649 (1991)] and confirmation of artificial periodic structure of pentacene / hexacene hetero films [Hitomi Akimichi, Hiroyuki Sakaki, "Creative Science and Technology Promotion Project '91 Research Report Meeting II""Abstracts of Part Lectures", p. 69, New Technology Agency (1991)], etc., have begun research on polycyclic aromatic derivative laminated films with high crystallinity. With the progress of the hetero thin film forming technology by such a dry process of organic molecules, the concept of a superlattice composed of organic molecules has been studied.

[0018]

As described above, in the case of a conventional thin film optical device having a simple ultra-thin film laminated structure composed of organic molecules, the film quality itself of a single kind of thin film is incomplete and Growth techniques such as the control of molecular orientation and the epitaxial growth between the substrate and the thin film were also incomplete. Moreover, the structure of the obtained thin film is the same as that of a bulk crystal and does not take an artificial lattice structure, and the electronic states of the constituent molecular aggregates having such a structure could not be modulated.

In order to realize the organic superlattice technology, it is necessary to study the problems such as model of the material system, quantum mechanical consideration, superlattice structure fabrication technology and characterization, and evaluation of optical and electronic properties peculiar to the superlattice structure. Despite that,
There was no study example of the organic ultra-thin film device which investigated the superlattice property of the organic molecule.

Then, I will sort out what is what characterizes the optical and electronic properties of superlattices based on a review article [Physics and Applications of Semiconductor Superlattices, edited by the Physical Society of Japan, Baifukan (1984)].

Superlattices are realized by heteroepitaxial junctions of semiconductor compounds having different electronic states. The energy level of one semiconductor layer is represented by a band structure in which atomic orbitals of atoms constituting a crystal are superposed by the periodic structure of the crystal. Among these, the valence band filled with electrons in the ground state and the conduction band above it are
They are separated by a constant bandgap.

Therefore, electrons are put in the conduction band, or
When holes are created by removing electrons from the valence band,
These electrons or holes have an effective mass m under an external field.
[Electron] or m [hole (hole)] moves around in the crystal relatively freely. Junctions of different semiconductors cause band discontinuities at their boundaries, and repeating such junctions form a band confinement structure (ie, quantum wells or tunnel barriers). The confined band exhibits a wave function like an isolated atom.

The electronic state of such a superlattice has four parameters, namely, the conduction band at the hetero interface of two semiconductors, the energy band discontinuity ΔEc and ΔEv at the valence band, the quantum well and the tunnel barrier. Width Lw of
Characterized by Lb.

First, the tunnel barrier width Lb is infinite and the height Vo is
Consider the case of a single quantum well (Vo = ΔEc or ΔEv). The electrons in the well behave as free electrons having wave number vectors kx and ky in the plane (x, y) perpendicular to the well, but there is a potential barrier of Vo in the direction (z) along the well and the electrons are well. Localized in the vicinity, the wave function decreases exponentially. Therefore, when the height Vo is sufficiently high, the energy eigenvalue En in this direction is

[0025]

[Equation 1]

It is represented by Here, n is a quantum number (n =
, 1, 2, 3, ...), π is the circular constant, h is the Plank constant, and m is the effective mass of the electron. Therefore, the total energy of the electron is

[0027]

[Equation 2]

It is represented by This is because the total energy of electrons in a bulk crystal without quantum confinement is

[0029]

[Equation 3]

Comparing with, it can be seen that the electronic state which was continuous in the bulk becomes discrete in the quantum well.
Where p is the momentum of the electron, and the electron de Broll
It is related to the ie wavelength λ by λ = h / p. Therefore, in order for the energy levels to become discrete and the quantum effect to be significant, the following formula must be satisfied.

[0031]

## EQU00004 ## Next, consider the case where the tunnel barrier width Lb becomes thin. At this time, the wavefunctions in adjacent quantum wells overlap,
When the well potential exists alone, the degenerate quantum level splits due to the tunnel effect, forming a miniband (or subband). In the superlattice composed of semiconductors GaAs and AlGaAs, the GaAs layer and AlG
Since the unit cell is formed by the aAs layer, the length of the periodicity in the real space is repeated by Lb + Lw, and the first Brill
The size of the ouan area is 2π / (Lb + Lw).

In the case of a bulk crystal, the unit cell size a is about the lattice spacing, and if this semiconductor superlattice is composed of 10 layers of GaAs and 10 layers of AlGaAs, Lb + Lw is 2
The size of the first Brillouan region of the superlattice is 1/20 of the size 2π / a in the case of the bulk crystal.
It will be about. Therefore, the band structure of the bulk crystal is 2π
Corresponding to the folding back of the energy band at a cycle of / a, this energy band is folded back at a finer 1/20 interval to form a miniband.

From the above, it can be seen that the electronic state of the superlattice system can be greatly changed by changing the quantum well width Lw and the tunnel barrier width Lb. In particular, the quantum effect becomes remarkable when Lw is equal to or less than the de Brolie wavelength (about 300Å in the case of GaAs).

Further, if Lw is made sufficiently thicker than Lb, electrons can be confined, and if Lb is made sufficiently thin, a miniband is formed (several hundreds of liters or less). If Lw is 10 Å or less and a few atomic layer thickness or less, the Kronig-Penny model using the electronic structure of the bulk crystal cannot be used, and band calculation with a large unit cell is required.

In the case of a crystal composed of organic molecules, one complete molecular orbital is formed within one molecule, but the whole crystal is a weak molecular crystal composed of van der Waals forces, and the intermolecular interaction is weak. The band width is narrow and the energy gap is larger than that of semiconductors. Moreover, when the above semiconductor superlattice model is applied, each molecule is a quantum well, and each quantum well is in an isolated state because intermolecular interaction is poor.

Therefore, in order to form a superlattice from organic molecules, the molecules are enlarged to expand the molecular orbital to a size where one molecule can be regarded as one quantum box or quantum wire, or some kind of intermolecular interaction. Band structure must be created in the crystal. Furthermore, in an organic molecule, a molecule is formed by combining a plurality of atoms, and the distribution of electrons throughout the molecule forms a molecular orbital peculiar to the molecule and has anisotropy. Therefore, the molecular orbital of one molecule and the arrangement of molecular aggregates have a great influence on the physical properties of the whole substance. That is, in designing an organic superlattice, selection of molecular species, control of electronic state of each molecule,
A molecular assembly called a superlattice cannot be formed without considering the control of the molecular orientation and the optimization of the molecular layer thickness.

In order to solve the above-mentioned problems, the present invention provides a design guideline for a molecular orientation and a superlattice structure, which was conventionally overlooked in a thin film optical element composed of a laminated structure of organic thin films, and its specific fabrication. The object is to provide an organic superlattice optoelectronic device comprising a laminated structure of organic thin films.

Another object of the present invention is to provide a method for manufacturing the above organic superlattice optoelectronic device.

[0039]

The gist of the present invention for solving the above problems is as follows.

(1) An organic superlattice optoelectronic device comprising a medium capable of being modulated by light incident / incident light, charge injection or electric field / magnetic field, wherein the device comprises two or more kinds of organic ultrathin film layers periodically formed on a substrate. An organic superlattice optoelectronic device characterized by having an organic superlattice structure that is laminated physically.

(2) Each ultrathin film layer constituting the organic superlattice structure is composed of two or more kinds of organic films, and the thickness of one thin film is 1 to 100000Å, and different thin film layers are repeatedly laminated. An organic superlattice optoelectronic device comprising an organic superlattice structure having at least three layers.

(3) Each of the ultrathin film layers constituting the organic superlattice structure is composed of two or more kinds of organic films, and the thickness of one thin film is 1 to 100 molecular layers. An organic superlattice optoelectronic device having an organic superlattice structure in which the number of repeated layers is at least three.

(4) An organic superlattice optoelectronic device having a molecular alignment assembly structure in which the organic molecules constituting the ultrathin film layer are coordinated at a specific position to modulate the electronic state of the organic molecules.

(5) The organic superlattice layer has a molecular orientation aggregate structure in which the orientational state or electronic state of each constituent molecule of the organic ultrathin layer is modulated by an adjacent substrate or a different thin film layer. Organic superlattice optoelectronic device.

(6) An organic superlattice optoelectronic device in which an electrode for applying an electric field or moving an electric charge is provided at or near a part of the organic ultrathin film layer constituting the organic superlattice structure.

A molecular orientation aggregate structure is formed by modulating the orientation state or electronic state of the organic molecules constituting the thin film layer by applying the above electric field or transferring charges.

The term "modulation of the orientation state or electronic state of a molecule" as used herein means to form a new bond, charge transfer, electrostatic potential in the vicinity of a hetero interface by stacking molecules on the substrate surface and stacking different molecules. Due to intermolecular interactions such as, and geometrical factors such as stereospecific structure, steric hindrance, and optical activity of the molecule or substrate surface, the molecular orientation of the molecule in the crystalline state or the glass state in the case of only the same molecule, and It indicates that its electronic state is subject to change.

In order to fabricate the organic superlattice optoelectronic device of the present invention, various dry-process thin film forming techniques capable of epitaxial growth, for example, MBE (Molecular Beam E) are used.
pitaxy) method, ALE (Atomic Layer Epitaxy) method, ML
E (Molecular Layer Epitaxy) method, MO-ALE (Met
alorganic Atomic Layer Epitaxy method, MOCVD (Me
talorganic Chemical Vapor Deposition) method or the like.

As the organic substance, polycarbonate, polysulfone, polyarylate, polyester, polyamide, polyimide, polysiloxane, polyethylene terephthalate, polyvinyl acetate, polyethylene, polypropylene, acrylic resin, polybutadiene, polyvinyl chloride, polyvinylidene chloride, petroleum resin, Melamine resin, epoxy resin, phenol resin, isoprene rubber, ethylene-propylene rubber, norbornene resin, cyanoacrylate resin, styrene resin and copolymers thereof, cellulose, starch, chitin, agar, silk thread, cotton thread, nylon thread,
Albumin, globulin and other proteins, wood, bone powder and the like, and examples of low molecular weight organic substances include condensed aromatic compounds such as naphthalene and anthracene, dyes, pigments, urea, tartaric acid and optically active amino acids.

The organic thin film inorganic material such as glass, crystal, diamond, silicon dioxide, mica, marble, calcite, single crystal silicon, amorphous silicon, GaAs, Cd.
S, KDP, KTP, lithium niobate, charismum bromide, Rochelle salt, copper sulfate, calcium fluoride, graphite, tin dioxide, barium titanate, red blood salt, ceramics, ceramics, bentonite, cement, metal or alloy Can coexist or coexist.

The organic superlattice optoelectronic device of the present invention can be used by forming a superlattice structure, or adding an appropriate dopant to the superlattice structure, and forming it into a lump, a plate, a fiber, a powder or a thin film. . Further, in the above-mentioned shape, other materials having different structures of the present invention or different kinds of materials can coexist or be mixed and used.

The organic superlattice optoelectronic device of the present invention is
In order to improve its characteristics and extend its life, post-treatments such as thermal annealing, radiation irradiation, electron beam irradiation, light irradiation, radio wave irradiation, magnetic force line irradiation, and ultrasonic wave irradiation may be performed.

The organic superlattice optoelectronic device of the present invention is, for example, an optical waveguide, an optical mixer, an optical phase discriminator, an optical modulator, an optical deflector, an optical selective wavelength plate, a phase conjugate mirror, an optical switch, a light emitting device. , A laser emitting element, a photo-electron conversion element, a light-sound wave conversion element, a piezoelectric element, an optical logic element, a memory element, a display element and the like.

[0054]

The organic superlattice optoelectronic device of the present invention comprising a highly crystalline hetero ultrathin film having a film thickness of about several nm, which has been difficult to achieve by the conventional film forming technique, is an organic superlattice composed of a high quality hetero ultrathin film. By having a lattice structure, a new superlattice electronic state can be realized due to the quantum confinement property and the tunnel effect of organic molecules. In addition, a novel organic superlattice optoelectronic device is provided by the characteristics of elementary excitons such as excitons and polarons stabilized in the superlattice structure of the organic molecule.

[0055]

EXAMPLES The organic superlattice optoelectronic device of the present invention will be described based on examples.

[Example 1] A molecular beam deposition apparatus [MBE for organic substances] which is an example of an apparatus for producing an organic superlattice structure of the present invention.
(Molecular Beam Epitaxy) device, hereinafter referred to as MBE device] is shown in FIG.

The MBE apparatus comprises an exchange chamber 1 for introducing a substrate into the apparatus, a pretreatment chamber 2 for cleaning the substrate by heating and UV irradiation, a growth chamber 4 for depositing and forming an organic superlattice structure, and an organic superlattice. There are a pre-deposition chamber 3 for depositing a gold electrode or the like on a lattice structure, a structure analysis chamber 5 for analyzing a superlattice structure, and an optical evaluation chamber 6 for measuring and evaluating optical characteristics, each chamber via a gate valve 7. It is connected. Each of the above chambers is individually connected to an ultra high vacuum pump (not shown). The arrangement of each chamber is not limited to that shown in FIG.
Further, a chamber other than this may be attached if necessary.

An example of the structure of the growth chamber 4 forming the above organic superlattice structure is shown in FIG.

The growth chamber 4 is constantly evacuated to the main exhaust system by an ultrahigh vacuum pump (not shown) via the gate valve 7. The substrate 11 forming the organic superlattice structure is held by the substrate holding means 9, and the substrate holding means 9 includes means (not shown) for changing the orientation of the substrate surface and substrate heating means 10. The substrate heating means 10 can arbitrarily control the temperature of the substrate 11 in the range of + 1000 ° C. to −271 ° C. by using both the heater and the coolant.

During the vapor deposition, the growth chamber 4 conducts liquid nitrogen to maintain the degree of vacuum in the chamber and traps extra molecular beams. In this embodiment, there are three molecular beam sources, each of which has a Kn
A vapor deposition sample is held in an udsen cell (hereinafter referred to as K-cell) 15. The K-cell is moved in and out of the growth chamber 4 by the K-cell moving means 18, and its entrance and exit is partitioned by the gate valve 7 '. The K-cell 15 held by the K-cell moving means 18 is first degassed by the auxiliary exhaust system connected via the valve 17, and then transferred into the growth chamber 4.

K-K carried by the cell moving means 18
-The cell 15 is heated to the evaporation temperature of the sample or higher by the K-cell heating means 16 and ejects the molecular beam of the sample toward the substrate 11 at a constant evaporation rate. The vapor deposition time of the sample molecular beam is controlled by opening and closing the shutter 13. In addition,
A molecular beam control means 14 is provided on the way to improve the directivity of the ejected sample molecular beam. Further, the growth chamber 4 is additionally provided with a means for sequentially monitoring the molecular beam injection speed, residual gas concentration, thin film crystallinity, etc. (not shown).

FIG. 3 shows an example of the film thickness distribution of the organic molecule ultra-thin film produced by using the above MBE apparatus. Figure 3 shows copper phthalocyanine on a silicon substrate with a vacuum of 10 to ⁶ Torr.
r unit (substrate temperature 200 ° C) and vacuum degree 10 ~ ¹⁰ Torr
The film formed on the table (substrate temperature of 200 ° C) was accelerated at an accelerating voltage of 5
SEM (Scanning Electron Microscopy) observed by emphasizing the unevenness in the thickness direction of the thin film at kV and sample horizontal inclination angle of 60 °.
pe: Hitachi S-800 type field emission scanning electron microscope). 3A shows the film thickness distribution in the plane, and FIG. 3B shows the film thickness distribution on the line AA ′ in FIG.

In the case of a normal vacuum deposited film, it is about 10 to 20 n.
Although the unevenness of m is observed, the molecular beam vapor deposition film of this example has an extremely smooth and uniform film thickness, and even within an extremely wide range of 3 cm × 4 cm, the unevenness is only about 3 to 4 molecular layers. It can be seen that it is a uniform film that cannot be seen. This is
This indicates that the molecular beam strengths are extremely uniformly distributed and formed. As described above, according to the MBE method, it is almost impossible to use ordinary vacuum deposition.
It can be seen that it is possible to manufacture a film in which the unevenness has a uniform film thickness on the molecular order.

Example 2 Next, an example is shown in which two different kinds of raw material organic compounds are used to control the molecular orientation and form an alternating laminated film of several molecular layers.

As the raw material organic compound for the organic superlattice,
In order to increase the intermolecular interaction due to the d-orbital of the central metal and to facilitate the epitaxial growth control due to the similarity of the molecular skeleton, two types of metal phthalocyanines, copper phthalocyanine (CuPc) and zinc phthalocyanine (ZnPc), are used.
Select organic compounds of the species and select CuPc / ZnPc / Si and ZnPc / CuPc / S on a single crystal silicon (Si) substrate.
The conditions for forming an ultrathin film of an organic superlattice were examined by alternately stacking two combinations of i.

The above copper phthalocyanine and zinc phthalocyanine are commercial products (manufactured by Tokyo Kasei) and heated and degassed in a glass tube oven (manufactured by Shibata Scientific Instruments) at about 250 ° C. under reduced pressure by an aspirator to obtain adsorbed water and volatile impurities. (Unreacted raw materials such as phthalonitrile) were removed as much as possible.

The substrate is a silicon single crystal substrate (manufactured by Shin-Etsu Chemical,
35 mm x 35 with p type, 100 sides) with a diamond pen
Cut to a size of mm and read the document [S. Hattori, et al., JA
ppl.Phys. 67 , 237 (1990)] method (UV / HF method)
After cleaning the surface, the sample was subjected to molecular beam deposition. That is, set the silicon substrate on a hot plate set to 200 ° C. in air and covered with aluminum foil,
Ultraviolet rays were applied to the front and back of the substrate for 10 to 20 minutes from a distance of cm using a high pressure mercury lamp (440 W) to remove the organic contaminant layer on the surface. Next, sodium persulfate (Na
₂ S ₂ O ₈ (manufactured by Wako Pure Chemical Industries, Ltd.) was boiled in a saturated solution of pure water, carefully washed with pure water to remove adhered organic contaminants, and then used a Teflon-made instrument to prepare 1 wt% diluted hydrogen fluoride (Morimoto Chemical Co., Ltd.). Made by
A substrate holder made of molybdenum that has been cleaned by UV irradiation in the same state (with some water droplets attached) without removing the natural oxide film on the surface by etching with (diluting a semiconductor grade product) to remove the surface natural oxide film I attached it to.

This was quickly set in the exchange chamber 1 of the MBE apparatus, exhausted to 1 × 10 to ⁸ Torr or less by a turbo molecular pump, and the structure analysis chamber 5 and the growth chamber 4 were kept in an ultrahigh vacuum state. Introduced in.

Next, the conditions for molecular beam deposition of metal phthalocyanine will be described. Base pressure of growth chamber 3.8 × 10 ~ ¹¹
Torr, pressure during vapor deposition (7 to 11) x 10 to ¹⁰ Torr
K-made of fused silica glass loaded with about 0.2 to 0.3 g of sample under the condition of (value according to the apparatus attached nude ion gauge)
After degassing the cell in advance at 10 to ⁹ Torr level, differential evacuation by the turbo molecular pump (pressure 7 to 9 × 10
~ ⁹ Torr) and 400 ℃ with tantalum heater
Heated to. In addition, the substrate temperature is X-ray of the literature [Shintaro Hattori, "Structural control of organic ultra-thin film", New Technology Corporation Creative Science Promotion Business 1989 Research Report Meeting, Part 2 Lectures, page 22 (1989)] With reference to the results of diffraction (XRD) and RHEED analysis, the temperature was set to 200 ° C. at which the crystallinity of the ultrathin film was estimated to be highest. Under these conditions, the ultrathin film was grown for about 2 hours. During the ultra-thin film growth, the molecular beam intensity was monitored with a crystal oscillator type film thickness meter attached to the device, and the analysis and evaluation described below were performed as necessary.

AES (Auger Electron Spectroscopy) was used before and after the molecular beam deposition to confirm and evaluate the cleanliness and thin film formation of the substrate.
scopy) and XPS (X-ray Photoelectronspectrosco
py) The measurement was performed. These measurements were conducted in the structural analysis room 5 connected to the MBE growth room and maintained in an ultrahigh vacuum state of 10 to ¹⁰ Torr level.

AES measurement is performed by PHI ESCA / AE
The S255 system (equipped with a coaxial electron gun and a cylindrical double-pass type energy analyzer) was set in the AES measurement mode, and measurement was performed at a primary electron acceleration voltage of 3 kV.

The XPS measurement was carried out by using the same device in the XPS measurement mode and using MgKα rays (1253.6 eV) as the X-ray source. The measurement was performed at room temperature, and temperature control such as heating and cooling for protecting the sample was not particularly performed.

The spectrum thus obtained was obtained from the literature [C.
D. Wagner et al., "Handbook of X-ray Photoelectron
Spectroscopy ", Perkin-Elmer Co. (1979), and L.
E. Davis et al., "Handbook of Auger Electron Spectr
oscopy ", Physicalelectronics industries, Inc. (197
6 years)] The attribution was identified with reference to the standard spectrum described.

The thickness of the produced thin film was determined by ellipsometry in the atmosphere. Since the phthalocyanine compound vapor-deposited film shows absorption at the He-Ne laser wavelength (632.8 nm) of the light source, which cannot be ignored in normal film thickness calculation, the incident angles to the sample are set to 70 degrees and 58 degrees, respectively. The phase difference Δ and the arc tangent Ψ of the reflection coefficient ratio were measured at the incident angle, and the film thickness was calculated from them.

FIG. 4 shows ZnPc / CuPc / Si and CuP.
It is a graph which shows the time-dependent change of the XPS intensity in the formation process of the alternating laminated film (two layers) of c / ZnPc / Si.

In the case of the ZnPc / CuPc / Si film of FIG. 4A, in the growth process of CuPc of the first layer, the signal from the substrate Si atoms drastically decreases during the first 2 hours, and C and N of the CuPc layer are reduced. , The signal from the Cu atom increases. The ratio does not change after 4 hours. Even if the second layer of ZnPc is vapor-deposited thereon for 4 hours, the signals of Si, C and N do not change so much. The central metal signal is C over time
u is slightly decreased and Zn is increased. From this fact, the CuPc of the first layer was added to the first 2
It was found that it grew uniformly over time and almost no growth in the other portions, and almost all of the second layer ZnPc also grew on the first layer CuPc.

On the other hand, CuPc / Z shown in FIG.
In the case of the nPc / Si film, the Si signal gradually decreases and the C, N, and Zn signals continue to increase during the growth process of the first layer ZnPc. On top of this, the second layer C
When uPc is grown, the Si signal is significantly decreased and the C and N signals are further increased. The signal of the central metal was increased in Cu, whereas Zn was considerably decreased. From this, ZnPc of the first layer grew only slightly sparsely on the surface of the substrate even after the vapor deposition for 4 hours, and CuPc of the second layer was not deposited on the surface of the substrate other than ZnPc. I also found that I was growing.

It is considered that the difference in the growth state of the first layer reflects the difference in the average residence time of the organic molecules under the experimental substrate temperature condition, that is, the difference in the sticking coefficient. When the film thickness of these ultra-thin films was determined by ellipsometry, CuP
c / Si (2 hours) about 46Å, ZnPc / Si (2 hours) about 15Å, ZnPc / CuPc / Si (4 hours /
It was about 67Å in 4 hours) and about 70Å in CuPc / ZnPc / Si (4 hours / 4 hours).

Next, the molecular orientation of the ultra-thin film of about several molecular layers as described above was determined from the dependence of the XPS signal intensity on the escape angle (θ).

FIG. 5 shows XPS charts of the CuPc / ZnPc / Si film with the escape angles of 90 ° and 30 ° with respect to the substrate surface.

As the escape angle becomes smaller, signals of atoms closer to the surface of the thin film are emphasized and signals of atoms deeper than the surface are attenuated. It can be seen that the signals of Si of the substrate and Zn of the first layer are considerably attenuated.

[0082]

[Table 1]

Table 1 shows CuPc / Si and ZnPc / S.
i, CuPc / ZnPc / Si, ZnPc / CuPc /
The escape angle dependence of the XPS signal of Si is shown by the relative value to the signal of the C atom. Looking at the molecular orientation of a single layer,
The signals of C, N, and Cu constituting CuPc have almost no dependence on the exit angle, and the molecular planes are oriented almost at the same depth from the surface, that is, the substrate.

On the other hand, in ZnPc, the smaller the escape angle, the weaker the signals of N and Zn as compared with the C atom,
Since the N and Zn atoms are located under the C atom, it can be seen that the molecular surface stands on the substrate.

When the second layer is laminated, CuPc / ZnP
In the c / Si film, the Zn signal was remarkably reduced, but
u shows almost the same dependence as that of the single-layer CuPc film, and most of CuPc have an orientation different from that of the first layer. On the other hand, in the ZnPc / CuPc / Si film, the Cu signal showed some dependence on the escape angle, but the Zn signal did not have such an exit angle and the orientation was almost the same as the horizontal orientation of CuPc in the first layer. It was found that the ZnPc of the second layer was also generated.

FIG. 6 shows a model of the molecular orientation of the present alternate laminated film predicted from these findings.

When the first layer is CuPc as shown in FIG. 6 (b), the molecular surface is horizontally oriented with respect to the substrate surface, and ZnPc on this has the same horizontal orientation as CuPc. On the other hand, when the first layer is ZnPc as shown in FIG. 6A, the molecular surface is oriented almost perpendicular to the substrate surface. In particular, no one molecular layer has grown during the growth time this time, and most of CuPc grown on it grows on the Si substrate not covered with ZnPc.

From the above results, it is possible to manufacture a heteroepitaxial ultrathin film of tens of liters of phthalocyanine having different central metals.

[Embodiment 3] Next, an example of forming a superlattice structure by forming three or more layers of organic ultrathin films will be described.

As described in Example 2, by using copper phthalocyanine as the first layer on the cleaned silicon single crystal plate, the expected molecular orientation and the zinc phthalocyanine in the second layer were oriented. I found that I could grow. Therefore, a new organic superlattice structure in which a plurality of layers are alternately laminated by repeating the same film forming condition, that is, the combination of CuPc for the first layer and ZnPc for the second layer is manufactured.

FIG. 7 shows a film in which copper phthalocyanine and zinc phthalocyanine are alternately laminated three times, for a total of six layers [hereinafter referred to as (Zn
[Pc / CuPc) x / Si (x = 3)] XP
It is an S chart. Total film thickness by ellipsometry is about 2
0 to 300Å, the film thickness per layer is 30 to 40Å
Is. The metal phthalocyanine from the third layer onward does not lose the signals of copper and zinc and does not lose the signal derived from the oxide film of the substrate. You can see that they are stacked on top.

In the same manner as above, 50 times with the same combination,
A total of 100 layers are laminated on a silicon substrate [Si (100)] and a potassium chloride substrate [KCl (100)] to form an organic superlattice thin film [hereinafter, (ZnPc / CuPc) x / S, respectively.
i (x = 50) and (ZnPc / CuPc) x / KCl
(Denoted as (x = 50)] was produced. The total film thickness by the ellipsometry method was about 4000 to 5000Å in all cases.

As shown in this example, it is possible to form a superlattice structure composed of organic molecules by the above method.

[Embodiment 4] Next, the third-order nonlinear optical characteristic, which is one of the performance indexes when the organic superlattice structure is used as an optical third harmonic generating element which is one of optoelectronic elements, was evaluated. .

The above-mentioned optical third harmonic wave generating element is to provide a coherent micro light source used in optical communication, an optical computer, etc., and when a laser beam having a specific wavelength is incident on the element, it is applied to the element medium. Since non-linear polarization occurs and light having a wavelength ⅓ of the wavelength of incident light is generated, it can be used as a light wavelength conversion element.

FIG. 8 is a block diagram showing an optical system for evaluation thereof. Q-switch YAG laser system (Quanta-
106, generated by Ray, DCR-3) 22
Laser light having two wavelengths of 4 nm and 532 nm is a dye laser system (PDL-2, manufactured by Quanta-Ray) 23
Laser light of 532 nm was introduced into the excitation light source of the dye laser (the dye used was Quanta-Ray, LDS69).
8) used to generate 681 nm light. This 6
81 nm light and 1064 nm light are generated by a difference frequency generator (Q
Quanta-Infrared Wavelength Extens
ion system) 24 and converted into infrared light of 1900 nm.

This 1900 nm infrared light is reflected by two mirrors.
The sample 28 is irradiated through 25, 25 ', a filter 26 for adjusting the intensity, and a lens 27 for condensing.

The sample 28 was produced in the third embodiment.
(ZnPc / CuPc) x / Si (x = 50) and (ZnPc
/ CuPc) x / KCl (x = 50), and CuPc / Si prepared by the vacuum deposition method as these comparative samples.
And ZnPc / Si were used. A fused quartz substrate was used as a standard sample.

The incident angle of 1900 nm infrared light on the sample 28 is controlled by the rotary stage 29. Sample 28
The light of 1900 nm out of the light transmitted through the filter 26 '
And the third harmonic (633 nm) generated in the sample is separated by the monochromator 30 and detected by the photomultiplier tube 31.

Table 2 shows the intensity of the measured third harmonic. As can be seen from Table 2, the superlattice structure was observed to generate 4 to 5 times the number of third harmonics as compared with a normal vacuum deposited film.

[0101]

[Table 2]

[Embodiment 5] Next, characteristics when the organic ultrathin film is used as an optical-optical switching element which is one of optoelectronic elements will be described.

The optical-optical switching element referred to here is used for optical communication, optical computer, etc., and when the probe light transmitting information is transmitted through the switching medium, the transmittance is controlled by the gate light. , High-speed optical calculation, etc. are realized. The magnitude of the effect is evaluated by the above-mentioned third-order nonlinear optical characteristics of the switching medium used and physical properties such as changes in absorption spectrum with time.

In this embodiment, an example in which the produced organic ultrathin film is used as a switching medium and the probe light transmittance is controlled by gate light will be described.

FIG. 9 is a block diagram of an optical system for evaluating the characteristics of the light-light switching element. A semiconductor laser (peak wavelength 900 nm) is used as the probe light source 37, and the gate light source 3 is used.
For No. 8, a nanosecond pulse dye laser (wavelength 700 nm) was used.

The probe light is first split into a specific polarization component by the polarizer 39, passes through the half mirror 40 without loss, is condensed by the lens 41, and is applied to the sample 28. The gate light is reflected by the half mirror 40, is coaxially combined with the probe light, and is similarly condensed by the lens 41 and applied to the sample 28. Sample 28 contains the organic superlattice (ZnPc / CuPc) x / KCl (x = 5) prepared in Example 3.
0) was used.

When there is no gate light from the gate light source 38, the probe light from the probe light source 37 is transmitted without changing the polarization direction by the polarizer 39, but when the gate light is introduced, it is caused by the third-order nonlinear optical effect. A polarization component that is orthogonal to the incident probe light appears.

The probe light and the gate light which have passed through the sample 28 are returned to parallel light by the lens 41 ', and the half mirror 40'.
Then, the gate light is reflected and reaches the damper 44, and the probe light is transmitted as it is through the half mirror 40 ′ to the analyzer 43.
To reach. In the analyzer 43, only the component orthogonal to the incident probe light generated in the sample part is transmitted and detected by the photometer 45.

Table 3 shows the relationship between the gate light intensity and the probe light transmittance of the analyzer. As described above, it can be seen that the transmittance of the probe light in the sample portion changes corresponding to the gate light, and that it has switching characteristics.

[0110]

[Table 3]

[0111]

According to the present invention, a novel organic superlattice optoelectronic device using the characteristics of elementary excitons such as excitons and polarons stabilized in the superlattice structure of organic molecules can be obtained.
By using this, it is possible to provide an optical third harmonic generation element and an optical-optical switching element.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a molecular beam deposition apparatus for producing an organic superlattice structure.

FIG. 2 is a configuration diagram of a growth chamber of a molecular beam deposition apparatus.

FIG. 3 is a film thickness distribution diagram of a molecular beam deposition film of copper phthalocyanine.

FIG. 4 is a graph showing changes with time of XPS signals of an alternating bilayer film of copper phthalocyanine and zinc phthalocyanine.

FIG. 5: X at an escape angle of 90 ° and 30 ° with respect to the substrate surface of an alternating bilayer film of copper phthalocyanine and zinc phthalocyanine.
It is a PS chart figure.

FIG. 6 is a model diagram of the molecular orientation of an alternating bilayer film of copper phthalocyanine and zinc phthalocyanine.

FIG. 7 is an XPS chart diagram of a copper phthalocyanine and zinc phthalocyanine alternating 6-layer film.

FIG. 8 is a configuration diagram of an optical system for evaluating an optical third harmonic generation element of an organic superlattice.

FIG. 9 is a configuration diagram of an optical system for evaluating light-light switching characteristics.

[Explanation of symbols]

1 ... Exchange room, 2 ... Pretreatment room, 3 ... Preliminary evaporation room, 4 ... Growth room, 5 ... Structural analysis room, 6 ... Optical evaluation room, 7, 7 '... Gate valve, 9 ... Substrate holding means, 10 ... Substrate heating means, 1
DESCRIPTION OF SYMBOLS 1 ... Substrate, 13 ... Shutter, 14 ... Molecular beam control means, 1
5 ... K-cell, 16 ... K-cell heating means, 17 ... Valve, 18 ... K-cell moving means, 19, 19 '... Copper phthalocyanine molecule, 20, 20' ... Zinc phthalocyanine molecule, 21, 21 '... Silicon Substrate, 22 ... Q switch Y
AG laser system, 23 ... Dye laser system, 24 ... Difference frequency generator, 25, 25 '... Filter, 26, 26' ... Miller, 2
7 ... Lens, 28 ... Sample, 29 ... Rotation stage, 30 ...
Monochromator, 31 ... Photomultiplier tube, 32 ... High-voltage power supply, 33 ... Delay circuit device, 34 ... Boxcar integrator, 3
5 ... GB-IB, 36 ... Personal computer, 37
… Probe light source, 38… Gate light source, 39… Polarizer, 4
0,40 '... Half mirror, 41,41' ... Lens, 43
… Analyzer, 44… Damper, 45… Light meter.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication location H01S 3/10 Z 8934-4M 3/109 8934-4M // H01L 31/10 (72) Inventor Gentaro Hattori 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Atsushi Tsunoda 4026 Kuji Town, Hitachi City, Hitachi City, Ibaraki Hitachi Research Laboratory, Hitachi Ltd.

Claims (8)

[Claims] 1. An organic superlattice optoelectronic device comprising a medium capable of being modulated by light emission / incidence, charge injection or electric field / magnetic field, wherein the device comprises two or more organic ultrathin film layers periodically formed on a substrate. An organic superlattice optoelectronic device having an organic superlattice structure laminated on a substrate. 2. Each of the ultrathin film layers constituting the organic superlattice structure is composed of two or more kinds of organic films, and the thickness of one thin film is 1 to 100,000Å, and the number of repeated laminated thin film layers is different. 2. The organic superlattice optoelectronic device according to claim 1, wherein the organic superlattice structure has at least three layers. 3. Each ultrathin film layer constituting the organic superlattice structure is composed of two or more kinds of organic films, and one thin film has a thickness of 1 to 100 molecular layers, and different thin film layers are repeated. The organic superlattice optoelectronic device according to claim 1, wherein the organic superlattice device is configured by an organic superlattice structure having at least three layers. 4. The organic superlattice according to claim 1, which has a molecular orientation assembly structure in which organic molecules that constitute the ultrathin film layer are coordinated at a specific position that modulates an electronic state of the organic molecule. Optoelectronic device. 5. A molecular orientation aggregate structure in which an orientation state or an electronic state which a constituent molecule of the organic ultrathin film layer constituting the organic superlattice structure has independently is modulated by an adjacent substrate or a different thin film layer. Item 5. An organic superlattice optoelectronic device according to any one of items 1 to 4. 6. The organic superlattice photoelectron according to claim 1, wherein an electrode for applying an electric field or moving an electric charge is provided at or near a part of the organic ultrathin film layer constituting the organic superlattice structure. element. 7. The organic superlattice optoelectronic device according to claim 1, wherein the organic ultrathin film layer constituting the organic superlattice structure contains an inorganic molecule. 8. An ultrathin film of at least two kinds of organic ultrathin films, wherein a substrate from which surface impurities have been removed is held in a container kept in an ultrahigh vacuum of 10 to ⁶ Torr or less, and the substrate is heated to 200 ° C. or higher. By loading each cell containing the material into a cell moving means provided with a heating means, a molecular beam control means and a shutter, heating the cell above the evaporation temperature of the organic ultra-thin film material, and opening and closing the shutter for a predetermined time. A method for manufacturing an organic superlattice optoelectronic device, which comprises forming an organic superlattice structure by stacking organic ultrathin films made of different materials by alternately irradiating a substrate with a molecular beam of the organic ultrathin film material.