JP7109062B2 - Quantum dot sheet, optoelectronic device using the same, and method for producing quantum dot sheet - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Law 1. (1) Date: February 6, 2018 (2) Meeting name: University of Electro-Communications Graduate School of Engineering Science, Master's Thesis Presentation Examination (3) Publisher: WICKRAMANAYAKA PRAVEEN RASHMI ) (4) The title of the publication "Fabrication of InAs Quantum Nanostructures on SiO2/Si Substrates by Molecular Beam Deposition"2. (1) Publication date, etc.: March 5, 2018 (proceedings publication date) / March 17, 2018 to March 20, 2018 (lecture period) (2) Publications, etc.: 65th country, 2018 The Japan Society of Applied Physics Spring Conference [Proceedings] (DVD) (3) Publisher: The Japan Society of Applied Physics (4) Publishers: Uikramanayaka Rashimi Praveen, Kageyoshi Makai, Katsuyoshi Sakamoto, Koichi Yamaguchi (5) Publication Title: Self-Formation of InAs Quantum Dots on SiO2/Semiconductors by Molecular Beam Deposition. (1) Publication date, etc.: May 26, 2018 (proceedings publication date) / May 29, 2018 to June 1, 2018 (conference held) (2) Meeting name and venue: CSW2018 (COMPOUND SEMICONDUCTOR WEEK 2018)・Cambridge/Boston, Massachusetts (Massachusetts Institute of Technology) (3) Published by: Kageyoshi Makaino, Katsyoshi Sakamoto, Touma Sogabe, Koichi Yamaguchi (4) Published title: “Self-Formation of InAs Quantum Dots on Oxide/Semiconductor Substrates by Molecular Beam Deposition” (Self-formation of InAs quantum dots on oxide semiconductor substrates by molecular beam deposition)

TECHNICAL FIELD The present invention relates to a quantum dot sheet, an optoelectronic device using the same, and a method for manufacturing the quantum dot sheet.

Quantum dots are widely applied to solar cells, display technology, etc., and generally, a method of self-forming quantum dots on a semiconductor single crystal substrate by the SK growth mode or the droplet epitaxy method is utilized. The self-assembled quantum dots are embedded in another semiconductor single crystal with a larger energy bandgap than the single crystal of quantum dots. By controlling the growth conditions of quantum dots, it is possible to form uniform and highly crystalline quantum dots at high density.

On the other hand, a sheet in which colloidal quantum dots produced by a chemical method are embedded in an organic thin film has also been developed. Colloidal quantum dots are dispersed in an organic solvent, and a coating film can be obtained by spin coating, spraying, or the like.

A method of growing GaAs microcrystals on a quartz substrate that has been surface-cleaned is known (see, for example, Patent Document 1). Also, formation of InAs nanocrystals embedded in _SiO2 matrix (see, for example, Non-Patent Document 1), growth of InAs nanocrystals on _SiO2 /Si (see, for example, Non-Patent Document 2), _SiO2 / Formation of ZnO quantum dots on Si (for example, see Non-Patent Document 3) is also known.

JP-A-5-251352

"Ultraviolet (340-390 nm), room temperature, photoluminescence from InAs nanocrystals embedded in SiO2 matrix," Jianzhong Shi, et al., Appl. Phys. Lett. 70(19), 2586-2588, 12 May 1997 "InAs nanocrystals on SiO2/Si by molecular beam epitaxy for memory applications," Moira Hocevar, et al., Appl. Phys. Lett. 91, 133114(2007) "Self-organized ZnO quantum dots on SiO2/Si substrates by metalorganic chemical vapor deposition," Sang-Woo Kim, et al., Appl. Phys. Lett.81, 5036(2002)

When self-forming quantum dots by epitaxial growth using a lattice mismatch system on a semiconductor substrate, the combination of the substrate crystal and the growth crystal is limited. In the case of droplet epitaxy, the selection range of materials is wider than in the method using a lattice-mismatched system, but it is difficult to control the arrangement of quantum dots. Both methods are limited to applications in which quantum dots are formed on a substrate.

Colloidal quantum dots are unstable in the atmosphere and are less crystalline than self-assembled (self-assembled) quantum dots. Since the organic film in which colloidal quantum dots are dispersed is produced by a coating method, its thickness is on the order of micrometers. When injecting carriers into colloidal quantum dots, carriers are injected from a metal electrode deposited on the organic thin film through the conductive organic thin film. Injection of carriers is greatly affected by the characteristics of the organic thin film, and the injection efficiency may decrease. If a stable inorganic thin film sheet with quantum dots with good crystallinity is realized, it should be possible to expand the range of applications for optoelectronic devices that make use of the characteristics of quantum dots.

An object of the present invention is to provide a quantum dot sheet that enables diversification of substrate materials for forming quantum dots and that has stable properties and structure.

To this end, embodiments self-assemble quantum dots on dielectric thin films of inorganic materials. A sheet of inorganic dielectric layer with embedded quantum dots is obtained by removing at least part of the growth substrate after the quantum dots have been coated with a dielectric thin film of inorganic material.

In a first aspect of the present invention, a quantum dot sheet has an inorganic dielectric layer and quantum dots distributed within a predetermined plane inside the dielectric layer.

In one configuration example, one surface of the inorganic dielectric layer may have a supporting thin film. When this support thin film is a thin film of a layered substance, it may have a cleavage plane substantially parallel to the distribution plane of quantum dots.

Another aspect of the present invention provides a method for producing a quantum dot sheet. The manufacturing method of the quantum dot sheet is
Quantum dots are formed on an inorganic dielectric thin film on a substrate by molecular beam deposition,
coating the quantum dots with a second inorganic dielectric thin film to form a stack comprising a quantum dot layer;
separating the laminate from the substrate;
A process may be included.

As one example, when a layered substance substrate is used as the substrate, the laminate may be separated from the substrate by cleaving the layered substance.

A quantum dot sheet made of an inorganic material with stable characteristics is realized by the above configuration and method. Unlike the conventional self-formation of quantum dots based on lattice-mismatched epitaxial growth, it is not restricted by the combination of semiconductor single crystal substrate and quantum dot material, and various device applications are expected. In addition, even if the quantum dot sheet of inorganic material has a multilayer structure, it is thin on the order of nanometers and is elastically deformable. Application development as a flexible sheet is also expected.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram of the quantum dot sheet of embodiment. It is a production process drawing of a single-layer quantum dot sheet. It is a manufacturing process drawing of a multilayer quantum dot sheet. It is a schematic diagram which shows another example of a quantum dot sheet. It is a schematic diagram which shows another example of a quantum dot sheet. 4 is an AFM image of quantum dots formed on a dielectric thin film; It is a TEM image of quantum dots formed on a dielectric thin film. It is a RHEED pattern of quantum dots formed on a dielectric thin film. FIG. 4 is a diagram showing the relationship between dot size and temperature for InAs dots grown at different temperatures; FIG. 4 is a diagram showing the effect of temperature on the growth of InAs dots; PL spectra of InAs dots grown on SiOx/GaAs substrates at different growth temperatures. It is a figure which shows the application example 1 to the display of a quantum dot sheet. FIG. 10 is a diagram showing an application example 2 of a quantum dot sheet to a display; FIG. 10 is a diagram showing an application example 3 of a quantum dot sheet to a display;

In embodiments, a dielectric thin film of an inorganic material such as SiO ₂ is deposited on an arbitrary substrate, and quantum dots of a compound semiconductor such as InGaAs or AlGaAs are self-formed on the dielectric thin film. By embedding the quantum dots in a dielectric thin film of an inorganic material and removing part or all of the substrate, a quantum dot sheet with a thickness on the order of nanometers can be obtained. When a layered substance substrate is used as the substrate, the quantum dot sheet can be easily separated using cleavage.

FIG. 1 is a schematic diagram of a quantum dot sheet of an embodiment. FIG. 1A is a schematic diagram of a quantum dot sheet 10A containing a single layer of quantum dots, and FIG. 1B is a schematic diagram of a quantum dot sheet 10B containing multiple layers of quantum dots. Hereinafter, these quantum dot sheets are collectively referred to as "quantum dot sheet 10" as appropriate.

1A, the quantum dot sheet 10A has an inorganic dielectric layer 21 and quantum dots 15 embedded in the inorganic dielectric layer 21. In FIG. The quantum dots 15 are distributed within a predetermined plane inside the inorganic dielectric layer 21, unlike a quantum dot sheet of an organic material formed by a coating method. The quantum dots 15 are self-assembled on the dielectric thin film 12 of inorganic material, unlike colloidal quantum dots dispersed in an organic solvent. Compared to colloidal quantum dots coated with ligands, surfactant molecules, etc., their crystallinity is good and their structures are stable. The inorganic dielectric layer 21 itself containing the quantum dots 15 is also less susceptible to deterioration in the atmosphere than organic films. Furthermore, the properties of the inorganic dielectric layer 21 are uniform and can efficiently inject carriers into the quantum dots 15 compared to organic quantum dot films.

The support thin film 11P may remain on one surface of the inorganic dielectric layer 21 . The supporting thin film 11P is part of the substrate used for growing the quantum dots 15, for example. When a layered material substrate is used, the back surface of the supporting thin film 11P is a cleaved plane that is substantially parallel to the distribution plane of the quantum dots 15 . Instead of the support thin film 11P, or together with the support thin film 11P, a polymer material thin film may be attached to the inorganic dielectric layer 21. FIG. When an ultra-thin light-transmitting resin film having a thickness of 1 to several μm is used as the thin film for bonding, the quantum dot sheet 10A may be used with the resin film bonded. When using a resin film with a thickness of several tens to several hundreds of μm as the support thin film, the resin film is attached to the quantum dot sheet 10A in a peelable state, and the resin film is peeled off during use to use the quantum dot sheet 10A. can be

However, the supporting thin film 11P is not essential, and the quantum dot sheet 10A may be composed only of the inorganic dielectric layer 21 embedded with the quantum dots 15 distributed in the plane. In this case, the layered substance remaining on the inorganic dielectric layer 21 may be removed after the layered substrate is separated by cleavage near the interface of the inorganic dielectric layer 21 .

The thickness of the quantum dot sheet 10A is, for example, several hundred nm to 1 μm, and is a sheet that is uniform and remarkably thin compared to an organic solvent coating film in which colloidal quantum dots are dispersed. Even a dielectric layer made of an inorganic material can maintain elastic deformation up to a certain curvature when it becomes a thin film on the order of nanometers. The curvature can be increased (the radius of curvature can be decreased) as much as possible.

FIG. 1B shows a multi-layered quantum dot sheet 10B. Quantum dot sheet 10B has a plurality of quantum dot layers 16-1 to 16-n inside inorganic dielectric layer 21. FIG. In any quantum dot layer 16, the quantum dots 15 are distributed within a specific plane. The number of quantum dot layers 16-1 to 16-n and the thickness of the dielectric thin films 14-1 to 14-n in which the quantum dots 15 are embedded in each layer can be appropriately designed according to the application. The inorganic dielectric layer 21 is formed of a laminate of dielectric thin films 14-1 to 14-n, has high mechanical strength, and is resistant to deterioration in the atmosphere.

FIG. 2 is a manufacturing process diagram of the quantum dot sheet 10A. In FIG. 2A, a dielectric thin film 12 is formed on a substrate 11 of layered material. As the layered substance substrate 11, for example, a substrate of a monatomic layered substance such as graphite, a substrate of a transition metal dichalcogenide such as molybdenite, a substrate of a layered silicate such as mica, a substrate of a layered oxide, or the like can be used. can.

In the case of a graphite substrate, a commercially available HOPG (Highly Oriented Pyrolytic Graphite) substrate may be used. In the case of layered silicate substrates, commercially available mica plates may be used. In the case of a layered oxide substrate, a titanium oxide-based or perovskite-based substrate may be used.

A SiOx film is sputter-deposited as a dielectric thin film 12 to a thickness of several nm to 500 nm on a substrate 11 made of a layered material. The dielectric thin film ₁₂ is not limited to a SiOx film, and oxide dielectrics such as _TiO2 , ZnO and ZrO2 may be used, and nitride dielectrics such as SiN, WN and MoN may be used. If a layered material substrate is not used, a thinned SiO ₂ /Si substrate may be used. In either case, a thin film is formed from an inorganic dielectric material.

In FIG. 2B, quantum dots are formed on the dielectric thin film 12 by molecular beam deposition (MBD). Since it is not necessary to consider the combination of lattice constants, quantum dots can be made of suitable materials such as InGaAs, AlGaAs, and InGaN, depending on the purpose. As will be described later, the growth of the quantum dots 15 on the dielectric thin film 12 differs from the conventional epitaxial growth in the SK mode (three-dimensional dot growth mode after layer growth from two-dimensional nuclei), unlike VW (Volmer-Weber ) mode (three-dimensional core growth mode from the initial stage of growth).

In FIG. 2C, a dielectric thin film 14 is sputter-deposited on the quantum dots 15 . Dielectric thin film 14 is, for example, a SiOx film. The thickness of the dielectric thin film 14 may be any thickness that allows the quantum dots 15 to be completely embedded, and is, for example, about 10 nm to 500 nm.

In FIG. 2D, part or all of the substrate 11 is removed as required. When the substrate 11 of a layered material is used, the inorganic dielectric layer 21 embedded with the quantum dots 15 can be peeled off near the interface with the substrate 11 by cleaving. The cleavage may leave a supporting thin film 11P of the substrate material at the interface with the inorganic dielectric layer 21 . The supporting thin film 11P may be left as it is, or may be removed by etching. For example, when a graphite substrate 11 is used, a sacrificial layer such as AlAs is formed between the substrate 11 and the dielectric thin film 12, and the substrate 11 is separated by cleavage near the interface between the substrate 11 and the sacrificial layer. Removing the sacrificial layer with a solution etch removes the remaining layered material. When the quantum dots 15 are formed using a SiO ₂ /Si substrate, the quantum dots may be grown after thinning the Si substrate in advance, and then only the Si substrate may be removed by etching.

It should be noted that the removal of the substrate 11 is not essential, and it may be left as a part of the quantum dot sheet as long as it has a thickness that can maintain the elastic deformation of the quantum dot sheet. The quantum dots 15 are distributed in a predetermined plane inside the inorganic dielectric layer 21, and the thickness of the entire inorganic dielectric layer 21 can be made nanometer order. The function as a dot sheet can be maintained. Optionally, at least one side of the inorganic dielectric layer 21 may be laminated with an ultra-thin resin film, as described above.

FIG. 3 is a manufacturing process diagram of the quantum dot sheet 10B having a multilayer structure. In FIG. 3A, similarly to FIG. 2A, a dielectric thin film 12 is formed on a substrate 11 of layered material, for example. _The layered substance substrate 11 is advantageous in that the inorganic dielectric layer 21 containing quantum dots can be easily peeled off, but it is not essential. Other substrates, such as substrates, may be used. A dielectric thin film 12 having a thickness of several nm to 500 nm is formed on a substrate 11 . Dielectric thin film 12 may be an oxide dielectric, nitride dielectric, or the like using a suitable material, but as an example, a SiOx film is sputter-deposited.

In FIG. 3B, quantum dots are formed on the dielectric thin film 12 by molecular beam deposition (MBD). Materials for the quantum dots are appropriately selected according to the purpose, such as InGaAs, AlGaAs, and InGaN.

In FIG. 3C, a dielectric thin film 14-1 is deposited on the quantum dots 15 by sputtering to form a quantum dot layer 16-1 in which the quantum dots 15 are embedded within a predetermined plane. A second layer of quantum dots 15 is formed on the dielectric thin film 14-1 of the quantum dot layer 16-1, the second layer of quantum dots 15 is embedded in the dielectric thin film 14-2, and a quantum dot layer 16-2 is formed. to form The formation of the quantum dots 15 and the formation of the dielectric thin film 14 are repeated by a desired number to form a laminate of a plurality of quantum dot layers 16-1 to 16-n.

As will be described later, the height and in-plane size of the quantum dots can be appropriately designed by controlling the growth conditions. Each of the sputter-deposited dielectric thin films 14-1 to 14-n is a uniform thin film. , or on the order of 1 μm.

In FIG. 3D, the substrate 11 is removed if necessary. When a layered material substrate 11 is used, cleaving can be used to separate the inorganic dielectric layer 21 having multiple quantum dot layers 16-1 to 16-n. Quantum dot sheet 10B having multiple quantum tod layers 16-1 to 16-n inside inorganic dielectric layer 21 is superior in optical specificity to quantum dot sheet 10A obtained in the process of FIG. 2, and has greater bending elasticity. .

FIG. 4 shows a schematic diagram of a quantum dot sheet 10C as another configuration example. The quantum dot sheet 10C has regions of different types of quantum dot groups 15-1, 15-2, 15-3 in the in-plane direction, that is, in the XY plane perpendicular to the stacking direction (Z direction).

In quantum dot group 1 , quantum dots 251 with a first composition are formed in a first region of inorganic dielectric layer 21 . In quantum dot group 2 , quantum dots 252 with a second composition are formed in a second region of inorganic dielectric layer 21 . In quantum dot group 3, quantum dots 253 with a third composition are formed in a third region of inorganic dielectric layer 21 . When quantum dots are formed in multiple layers, regions in which three different types of quantum dots 251, 252, and 253 are distributed are provided in the plane of each layer.

The number of types of quantum dots is not limited to three, and may be two, or four or more. The type, composition, etc. of the quantum dots can be designed according to the purpose of the quantum dot sheet 10C.

In this example, the substrate 11 of layered material is left intact. Alternatively, the substrate 11 may be cleaved in the horizontal direction (in-plane direction) at an appropriate position in the thickness direction of the substrate 11 to leave a supporting thin film 11P (see FIG. 1) with a desired thickness. When substrate 11 is a graphite substrate, substrate 11 may be used as a graphite electrode.

When fabricating the quantum dot sheet 10C, the portion other than the first region is covered with a mask, and the quantum dots 251 of the first composition are formed in the first region. Next, portions other than the second region are masked to form quantum dots 252 of the second composition in the second region. Further, portions other than the third region are masked to form quantum dots 253 of the third composition in the third region. Even in the case of multiple layers, three types of quantum dots can be distributed in substantially the same plane by controlling the thickness of the dielectric thin film of each layer.

FIG. 5 shows a schematic diagram of a quantum dot sheet 10D as still another configuration example. In FIG. 4, quantum dot groups 15-1, 15-2 and 15-3 containing quantum dots 251, 252 and 253 with different compositions are arranged in the direction orthogonal to the stacking direction. In FIG. 5, quantum dot groups 15-1 and 15-2 with different compositions are arranged in the stacking direction.

In the example of FIG. 5, a predetermined number of layers of quantum dots 251 of the first composition are repeatedly laminated on the substrate 11 to form the first quantum dot group 15-1. A predetermined number of layers of quantum dots 252 of the second composition are repeatedly laminated on the upper layer of the first quantum dot group 15-1 to form the second quantum dot group 15-2.

A dielectric thin film 141 having a predetermined thickness is formed on the second quantum dot group 15-2. The first quantum dot group 15-1, the second quantum dot group 15-2, and the dielectric thin film 141 are set as one set, or a plurality of sets may be repeatedly stacked as one unit.

This quantum dot sheet 10D is obtained by sequentially forming quantum dot groups 15-1 and 15-2 having different compositions in the stacking direction and a dielectric thin film 141 on a large substrate, and then forming a predetermined amount in a direction perpendicular to the stacking direction. It may be sliced widthwise and made into a thin film. In that case, the quantum dot groups 15-1 and 15-2 with different compositions are arranged in the plane of the thin film as in FIG.

In FIG. 5 as well, the number of quantum dot groups is not limited to two groups, and the composition and type of quantum dots can be designed such as one group, three groups, etc., according to the purpose of use.

<Characteristic evaluation of quantum dots on _SiO2 film>
A sample of quantum dots formed directly on a dielectric thin film is fabricated, and the properties of the quantum dots are evaluated. As samples, quantum dots are formed on two different substrates.

Sample 1 uses a substrate obtained by forming a 1 μm-thick SiO ₂ film on a Si (001) substrate by a thermal oxidation process. This is called "SiO ₂ /Si substrate". Sample 2 uses a GaAs (001) substrate on which a 0.5 μm SiOx film is formed by radio frequency (RF) magnetron sputtering. This is called a "SiOx/GaAs substrate". InAs quantum dots are formed on the SiO ₂ /Si substrate of sample 1 and the SiO x /GaAs substrate of sample 2, respectively, by molecular beam deposition (MBD).

Prior to InAs growth, the SiO ₂ /Si substrate of sample 1 and the SiO x /GaAs substrate of sample 2 are thermally cleaned at 590° C. under As pressure in a solid source MBE chamber.

InAs is formed by changing the growth temperature in the range of 350 to 400° C. and simultaneously supplying molecular beams of In and As ₄ or As ₂ . The In supply rate is precisely controlled to set the InAs growth rate to be 0.01-0.1 ML/s (monolayer/sec) for heteroepitaxial growth on GaAs(001) substrates. After the InAs growth, samples 1 and 2 are annealed under As pressure for 4 minutes at the growth temperature.

FIG. 6 shows Atomic Force Microscopy (AFM) images of Sample 1 and Sample 2. FIG. Figure 6(A) is an AFM image of InAs dots grown on sample 1, i.e., _SiO2 /Si, at 370°C for 120 seconds, and Figure 6(B) is an AFM image of sample 2, i.e., on SiOx/GaAs under the same conditions. 4 is an AFM image of formed InAs dots. In both images, almost all InAs dots are formed independently of each other on the oxide film.

The average density of InAs dots is 6.7×10 ¹⁰ cm ⁻² for sample 1 in FIG. 6A and 5.9×10 ¹⁰ cm ⁻² for sample 2 in FIG. 6B.

FIG. 7 is an image of the surface of InAs dots grown at 370° C. on the SiOx/GaAs substrate of Sample 2, observed with a transmission electron microscope (TEM). A lattice image is observed with three InAs dots A, B, and C on the growth surface. The lattice spacing of the observed InAs dots is about 0.33 nm, but each dot has a different crystal orientation. In dots other than A, B, and C, a lattice image appears by adjusting the incident angle of the electron beam. This means that each InAs dot is a single crystal grain with a different crystal orientation.

FIG. 8 is a RHEED pattern obtained by in-situ monitoring of InAs dots growing on the SiOx film by RHEED (Reflection High Energy-beam Electron Diffraction). A double ring pattern is observed near the top of the image. This RHEED ring pattern was clearly observed from the initial growth stage, indicating that the growth of InAs dots on the SiOx film was VW growth.

The double ring pattern of RHEED in FIG. 8 indicates InAs crystallization with {111} and {100} faces. Combined with the TEM observation results in FIG. 7, it can be seen that the InAs dots on SiOx are single crystal grains randomly arranged in different directions.

FIG. 9 is a diagram showing the relationship between dot size and temperature when InAs dots are formed at different growth temperatures. InAs dots are formed by changing the growth temperature to 350° C., 370° C., and 400° C. for sample 1 and sample 2, respectively. The quantum dot size is plotted in the in-plane (horizontal) direction (horizontal axis) and in the height direction (vertical axis).

Since the curvature of the AFM tip can affect the in-plane (lateral) size of the nano-islands, the in-plane size is calibrated with TEM data. Bold numbers on the horizontal axis are values after calibration. The effect of size expansion in the in-plane direction of the AFM apparatus used in this evaluation experiment is estimated to be about 5 nm from the TEM image. Based on the post-calibration abscissa values, the size of the nano-islands increases linearly from the zero point, and three-dimensional (3D) islands of InAs grow immediately from the surface of SiO without two-dimensional growth. I understand. The growth of InAs islands on this SiOx film is not the SK mode but the VW growth mode.

In FIG. 9, the InAs dots grown on the SiOx film at 370° C. have an in-plane (horizontal) size of 5 to 13 nm and a height of 3 to 8 nm. InAs dots have an aspect ratio of 0.35 to 0.70 and are taller than InAs quantum dots self-assembled on GaAs(001) substrates. Since the size of the obtained dots is smaller than the de Broglie wavelength of InAs, single-crystal InAs dots grown on oxide films are expected to have the properties of quantum dots based on the zero-dimensional electron system.

FIG. 10 is a diagram showing the effect of temperature on the growth of InAs dots. FIG. 10A shows the relationship between InAs dot growth temperature and the product of average volume and density, and FIG. 10B shows the relationship between growth temperature and desorption rate. AFM is used to estimate the volume and density of InAs dots at temperatures of 350° C., 370° C., and 400° C., and investigate the re-evaporation of adsorbed In atoms on the SiOx film surface.

In FIG. 10A, the product of the average volume and density of InAs dots is equivalent to the average thickness of the virtual two-dimensional layer. As the growth temperature increases, the value of (average volume)×(density) of InAs dots decreases exponentially. This is thought to be due to re-evaporation of adatoms. In the demonstration experiment, the growth amount of InAs dots on SiOx was adjusted to a thickness of 6 ML (1.8 nm) in the case of heteroepitaxial growth on a GaAs (001) substrate. The amount of growth is reduced to about 3ML at 370°C.

In FIG. 10B, the desorption rate is 50% when the growth temperature is 370.degree. The desorption rate increases exponentially with increasing growth temperature. The re-evaporation rate (R) of adatoms is represented by equation (1).

R=1/τ= _νexp ( _-Ea /kBT) (1)
where τ is the average residence time on the surface and ν is the vibrational frequency of the adatoms. From FIG. 10(B), the activation energy E _a for re-evaporation of In adatoms on the SiOx surface is estimated to be 0.43 eV. This value is smaller than the activation energy on the As-terminated Si surface, which means that re-evaporation of In adatoms is strong on the SiOx surface. Thereby, the growth temperature of InAs dots by the MBD method is set to a low temperature of 350 to 400.degree.

When the substrate temperature is low, the surface diffusion coefficient is small, the surface residence time is short, and the surface migration length is short. That is, the rate of incorporation of In adatoms into the initial InAs nuclei is limited, and as a result, single nuclei of individual InAs islands can be obtained by controlling the growth rate.

The re-evaporation of As adatoms on the SiOx surface is further enhanced by its low sticking coefficient. Therefore, a high V/III flux ratio of 286 is maintained during MBD growth of InAs. The SiOx film is exposed to As ₄ or As ₂ irradiation for 4 minutes at the growth temperature during the growth of the InAs islands to maintain the InAs stoichiometry.

FIG. 11 is the photoluminescence (PL) spectra at 15K of InAs dots grown on SiOx/GaAs substrates at different temperatures. An emission peak is observed near 1.2 to 1.25 eV. In particular, when grown at 350° C., a narrow PL half width and strong light emission can be obtained.

In FIG. 11, the emission from InAs dots grown on SiOx/GaAs substrates at 350° C. and 400° C. is captured by two photodiodes, a PbS photodiode (measurement range 0.4-0.7 eV) and an InGaAs photodiode ( Measurement range is 0.73 to 1.33 eV).

Although not shown in FIG. 11, the PL spectrum of the SiOx/GaAs substrate on which InAs dots are not formed is also measured at the same time. In this measurement result, the broad PL peak from 0.8 to 1.0 eV is the spectrum caused by the SiOx/GaAs substrate.

To investigate the origin of these PL peaks, the optical transition energies in the vacuum/InAs quantum dots/SiO ₂ configuration are theoretically calculated using APSYS simulation software. Distortion of the InAs quantum dots is ignored in this calculation, and the quantum dot size is based on the measurement results of FIG. The calculated transition energies for the vacuum/InAs quantum dots/SiO ₂ structure are shown at the top of FIG. The range in the calculated energies is due to the size variation of the InAs quantum dots.

From the calculation results, the small PL peak at 0.6-0.7 eV is the emission from the ground level (GS) of the heavy hole (hh), and at 1.0-1.3 eV, the heavy hole (hh) Emission from the first excitation level (ES) of is observed. By passivating (inactivating) the surface of the InAs quantum dots formed on the SiOx film, non-radiative recombination (recombination without light emission) at the surface and interface of the InAs dots is suppressed, and PL Characteristics are further improved.

<Application example of quantum dot sheet>
FIG. 12 shows application to a display device 300A as an application example 1 of the quantum dot sheet 30A. The display device 300A is an example of an optoelectronic device, and uses the quantum dot group included in the quantum dot sheet 30A as light emitting elements.

The quantum dot sheet 30A is an inorganic sheet in which quantum dots are distributed within a predetermined plane within the inorganic dielectric layer 31 . The crystallinity of the quantum dots VW-grown on the inorganic dielectric thin film 12 is better than that of the colloidal quantum dots. In the quantum dot sheet 30A, quantum dot groups 35R, 35G, and 35B with different compositions are repeatedly arranged in the in-plane direction of the sheet, as in FIG.

Inside the inorganic dielectric layer 31, each quantum dot group 35 has multiple quantum dot layers. The first quantum dot group 35R has, for example, AlGaAs quantum dots 351 stacked in multiple layers. The second quantum dot group 35G has, for example, In _x Ga _1-x N quantum dots 352 stacked in multiple layers. The third quantum dot group 35B has, for example, In _y Ga _1-y N quantum dots 353 stacked in multiple layers. Quantum dot groups 35R, 35G, and 35B can be formed in predetermined regions by selective growth using a mask pattern.

A graphite electrode is arranged as a common electrode 111 on one surface of the quantum tod sheet 30A, and a transparent electrode 33 patterned into a predetermined shape is arranged on the other surface at a position corresponding to each quantum dot group 35. ing. In this example, after forming an inorganic dielectric layer 31 containing different types of quantum dot groups 35 on a graphite substrate, the graphite substrate is cleaved at predetermined positions in the thickness direction to leave a supporting thin film, and the supporting thin film is used as a graphite common electrode 111 .

Although only one set of RGB pixels is shown in FIG. 12, a matrix pattern of RGB cells is formed on the quantum dot sheet 30A. A set of RGB constitutes one pixel, and each quantum dot group 35 in the pixel is individually driven by a switching element (not shown).

When this pixel is selected and the quantum dot group 35R is switched and driven, carriers are injected into the quantum dot 15R from the corresponding transparent electrode 33 and common electrode 11, and light in the red wavelength region is output. Further, carriers are injected into the quantum dots 15G from the corresponding transparent electrode 33 and the common electrode 11 of the quantum dot group 35G, and light in the green wavelength range is output. When carriers are injected into the quantum dots 15B from the corresponding transparent electrode 33 and the common electrode 111 of the quantum dot group 35B, light in the blue wavelength region is output. The switching drive of the three quantum dot groups 35 is so fast that the composite light color is perceived as being output from this pixel.

Polysilicon or amorphous silicon is generally used as the active layer of the switching element, but since there is no significant difference in thermal expansion coefficient between the active matrix drive circuit and the quantum dot sheet 30A, damage due to the difference in thermal expansion coefficient etc. can be suppressed.

FIG. 13 shows Application Example 2 of the quantum dot sheet 30B to the display device 300B. The quantum dot sheet 30B used in the display device 300B has quantum dot groups 35R and 35G with different compositions and a region 35N where no quantum dots are formed in the in-plane direction of the sheet.

Quantum dot group 35R has AlGaAs quantum dots 351, for example. Quantum dot group 35G includes, for example, In _x Ga _1-x N quantum dots 352 . The size of the region 35N where no quantum dots are formed is substantially the same as the size of each region where the quantum dot groups 35R and 35G are formed. Quantum dot groups 35R and 35G and a region 35N where no quantum dots are formed form one pixel.

The quantum dot sheet 30B is a quantum dot sheet consisting only of multiple quantum dot layers and an inorganic dielectric layer 31 containing the quantum dot layers. For example, after forming a sacrificial layer on a graphite substrate 11, the dielectric thin film 12 is formed, and after the substrate 11 is separated by cleavage, the sacrificial layer is removed by solution etching. A sheet 30B can be obtained.

Quantum dot sheet 30B is arranged on blue LED substrate 41 . A number of blue LED elements corresponding to the three regions of each pixel of the quantum dot sheet 30B are arranged in a matrix on the blue LED substrate 41 . When this pixel is selected, the blue LED element at the position corresponding to quantum dot group 35R is driven, and the blue light from the LED element photoexcites quantum dot 15R. Red light is extracted from the quantum dot groups 35R by radiative recombination after photoexcitation. When the blue LED element at the position corresponding to the quantum dot group 35G is driven, blue light from the LED element optically excites the quantum dot 15G. Due to radiative recombination after photoexcitation, green light is output from the pixels of the quantum dot group 35G. Blue light from the LED element corresponding to the region 35B where no quantum dots are formed is transmitted through the inorganic dielectric layer 31 as it is. The RGB cells are arranged in a matrix over the entire surface of the substrate.

Even with this configuration, there is no large difference in thermal expansion coefficient between the active matrix drive circuit and the quantum dot sheet 30B, so damage or the like due to the difference in thermal expansion coefficient can be suppressed.

FIG. 14 shows Application Example 3 of the quantum dot sheet 30C to the display device 300C. The quantum dot sheet 30C used in the display device 300C is of the same type as the quantum dot sheet 10D in FIG. 5, and is used with the quantum dots stacked sideways.

The quantum dot sheet 30C itself is formed by depositing the dielectric thin film 12 on the substrate 11 such as graphite, and forming the quantum dots 15R in multiple layers on the dielectric thin film 12 to form the quantum dot groups 35R. A quantum dot group 35G is formed on the quantum dot group 35R, and a dielectric film 42 containing no quantum dots is formed on the quantum dot group 35G. The dielectric film 42 becomes the regions 35N that do not contain quantum dots.

The stacking direction of the quantum dot sheet 30C is oriented horizontally and attached to the blue LED substrate 41. Blue light excites the quantum dot groups 35R and 35G, respectively, to emit red light and green light. In the region 35 of the quantum dot sheet 30C, blue light passes through the dielectric film 42 and is output as it is.

With RGB in FIG. 14 as one pixel, a large number of pixels are arranged in a matrix on the substrate to form the display device 300C. Even with this configuration, there is no large difference in thermal expansion coefficient between the active matrix drive circuit and the quantum dot sheet 30B, so damage or the like due to the difference in thermal expansion coefficient can be suppressed.

Although the quantum dot sheets 30A-30C are inorganic films, they are flexible, and the display devices 300A-300C can be placed on curved walls in shops or on streets. The use of the quantum dot sheets 30A to 30C is not limited to use as a light-emitting sheet, but can be applied to optoelectronic devices that operate based on the interaction of light and electrons, and can also be applied to light-receiving sheets, solar cell panels, etc. .

10, 10A to 10D, 30A to 30C Quantum dot sheet 15, 151, 152, 153, 351, 352, 353 Quantum dot 21, 31 Inorganic dielectric layer 12, 14, 14-1 to 14-n Dielectric thin film 15- 1, 15-2, 15-3, 35R, 35G, 35B quantum dot groups 16-1 to 16-n quantum dot layer 33 transparent electrode 111 common electrode 300A to 300C display device (optical electronic device)

Claims (10)

an inorganic dielectric layer;
quantum dots self-formed on an inorganic dielectric thin film constituting a part of the inorganic dielectric layer and distributed within a predetermined plane inside the inorganic dielectric layer;
has
The quantum dots are formed in a first quantum dot group formed in a first region of the inorganic dielectric layer and in a second region different from the first region in the in-plane direction of the inorganic dielectric layer. a second group of quantum dots comprising
A quantum dot sheet, wherein the composition of the first quantum dot group and the composition of the second quantum dot group are different . an inorganic dielectric layer;
quantum dots self-formed on an inorganic dielectric thin film constituting a part of the inorganic dielectric layer and distributed within a predetermined plane inside the inorganic dielectric layer;
a supporting thin film disposed on one side of the inorganic dielectric layer;
has
The quantum dot sheet , wherein the supporting thin film is a transition metal dichalcogenide or layered silicate thin film . a supporting thin film disposed on one side of the inorganic dielectric layer;
The quantum dot sheet according to claim 1 , further comprising: and the supporting thin film is a graphite layer. a supporting thin film disposed on one side of the inorganic dielectric layer;
2. The quantum dot sheet according to claim 1 , wherein the support thin film is a resin film bonded to the inorganic dielectric layer. A quantum dot sheet according to any one of claims 1 to 4 ,
a common electrode provided on one surface of the quantum dot sheet;
A transparent electrode provided on the other surface of the quantum dot sheet and processed into a predetermined shape;
An optoelectronic device comprising: 6. An optoelectronic device as recited in claim 5 , wherein said common electrode is a graphite electrode. A quantum dot sheet according to any one of claims 1 to 4 ,
a light-emitting element substrate arranged on one surface of the quantum dot sheet and outputting light of a first wavelength;
has
An optoelectronic device, wherein the quantum dots included in the quantum dot sheet are photoexcited by the light of the first wavelength to emit light of a second wavelength different from the first wavelength. The inorganic dielectric layer has a first zone in which the quantum dots are arranged and a second zone in which the quantum dots are not arranged,
8. The optoelectronic device of Claim 7 , wherein light of the first wavelength photoexcites the quantum dots in the first zone and is transmitted through the inorganic dielectric layer in the second zone . Quantum dots are formed on an inorganic dielectric thin film on a substrate by molecular beam deposition,
coating the quantum dots with a second inorganic dielectric thin film to form a stack comprising a quantum dot layer;
separating the laminate from the substrate;
A method for producing a quantum dot sheet, characterized by: the substrate is a substrate of a layered material,
separating the laminate from the substrate by cleaving the layered material;
The method for producing a quantum dot sheet according to claim 9 , characterized in that:

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