TW202139553A - Laser element - Google Patents

Abstract

This laser element, which has a two-dimensional DFB diffraction grating structure provided with at least two types of linear protruding section arrays that have different array directions, has a low laser oscillation threshold value. The DFB diffraction grating structure is preferably a two-dimensional DFB diffraction grating structure that has a concentric rectangular shape such as a concentric square shape, and an organic layer is preferably formed directly on the DFB diffraction grating structure.

Description

Laser components

The present invention relates to a laser element with a low laser oscillation threshold.

Organic laser elements using organic compounds in the active layer can obtain high photoluminescence (PL) quantum yield and a broad emission spectrum in the visible light region, and can control the characteristics by molecular design of organic compounds, and have the ability to Gives the advantages of component flexibility, so active research has been carried out. In addition, as a result of active research on the development of the current excitation type, the current excitation type laser element using organic compounds has been realized for the first time (refer to Patent Document 1). The current-excited laser element has a structure in which a DFB (distributed feedback) diffraction grating structure as an optical resonator is formed on the surface of the ITO electrode, and an organic gain layer is arranged on the DFB (distributed feedback) diffraction grating structure. The DFB diffraction grating structure here has: a first area in which the strip-shaped convex portions are arranged in one direction at a certain period; and a second area in which the strip-shaped convex portions are arranged in the first area with a grating period different from that of the first area. They are arranged in the same arrangement direction, and the regions have a mixed periodic arrangement alternately arranged. This document describes that in an organic laser element having such a DFB diffraction grating structure, a laser oscillation with a narrow half-width (FWHM) is realized.

[Patent Document 1] International Publication No. 2018/043763 Pamphlet

In order to make organic laser components practical, it is necessary to provide energy-saving organic laser components. Specifically, it is desirable to provide an element that has a low threshold of laser oscillation and performs laser oscillation with low energy. However, in the research so far, it is not clear what conditions are met to provide energy-saving organic laser components.

Under such circumstances, the inventors of the present invention have conducted intensive studies for the purpose of providing a laser element with a low laser oscillation threshold.

In order to solve the above-mentioned problems, the inventors of the present invention have conducted intensive studies and found that a laser can be realized by using a two-dimensional DFB diffraction grating structure with at least two linear convex portions arranged in different alignment directions as an optical resonator. Laser components with extremely low oscillation threshold. The present invention was proposed based on such findings, and specifically has the following structure.

[1] A laser element having a two-dimensional DFB diffraction grating structure with at least two linear convex portions arranged in different alignment directions. [2] The laser element according to [1], wherein the DFB diffraction grating structure has a concentric rectangular shape. [3] The laser element according to [1], wherein the DFB diffraction grating structure has a concentric square shape. [4] The laser element according to [1], wherein the grating period is the same between the arrangement of the two types of linear convex portions. [5] The laser element according to any one of [1] to [4] has a pair of electrodes and performs laser oscillation by energization. [6] The laser element according to any one of [1] to [5], wherein an organic layer is directly formed on the aforementioned DFB diffraction grating structure. [7] The laser device according to [6], wherein the organic layer includes an organic compound having at least one stilbene unit. [8] The laser device according to [6] or [7], wherein the organic layer contains 4,4'-bis[(N-carbazole)styryl]biphenyl (BSBCz). [9] The laser element according to [8], wherein the organic layer contains 4,4'-bis[(N-carbazole)styryl]biphenyl (BSBCz) and 4,4'-bis( N-carbazolyl)-1,1'-biphenyl (CBP). [10] The laser device according to any one of [6] to [9], wherein the organic layer includes a compound having at least one sulphur unit. [11] The laser element according to any one of [6] to [10], wherein the organic layer has a thickness of 80 to 350 nm. [12] The laser element according to any one of [1] to [11], wherein the height of each linear convex portion constituting the DFB diffraction grating structure is less than 75 nm. [13] The laser element according to any one of [1] to [12], wherein the DFB diffraction grating structure is composed of SiO ₂ . [14] The laser element according to any one of [6] to [13], wherein the DFB diffraction grating structure is provided between the organic layer and the transparent electrode. [15] The laser element according to any one of [1] to [14], which does not contain a triplet quencher. [Effects of the invention]

According to the present invention, a laser element with a low laser oscillation threshold can be realized.

Hereinafter, the content of the present invention will be described in detail. The description of the constituent elements described below may be based on typical embodiments and specific examples of the present invention, but the present invention is not limited to such embodiments and specific examples. In addition, the numerical range indicated by "～" in this specification means the range which includes the numerical value described before and after "～" as the lower limit and the upper limit. In addition, when it is referred to as a "main component" in this specification, it means the component with the largest content among its constituent components. In addition, the isotopic types of hydrogen atoms present in the molecule of the compound used in the present invention are not particularly limited. For example, all hydrogen atoms in the molecule may be ¹ H, or some or all of the ^{hydrogen atoms may be 2} H (deuterium D).

＜Laser components＞ The laser element of the present invention is characterized by having a two-dimensional DFB (distributed feedback) diffraction grating structure (distributed feedback diffraction grating structure) with at least two linear convex portions arranged in different arranging directions. Hereinafter, a configuration example of the DFB diffraction grating structure and the laser element of the laser element of the present invention will be described.

[DFB diffraction grating structure] The DFB diffraction grating structure used in the present invention is provided with at least two types of linear protrusion arrangements with different arrangement directions. Here, the “linear convex portion” is a line segment of the convex portion, and two or more linear convex portions are arranged at intervals from each other in a direction orthogonal to the extending direction of the linear convex portion. Therefore, the "arrangement direction" corresponds to the direction orthogonal to the extending direction of the linear convex portions. In the DFB diffraction grating structure used in the present invention, there are at least two groups including such linear convex portions arranged at intervals, and the alignment directions of the linear convex portions of these groups are different from each other. In the DFB diffraction grating structure used in the present invention, it is preferable that there are 2 to 6 groups of linear convex portions whose arrangement directions are different from each other, and it is more preferable that there are 2 to 4 groups. For example, there may be two groups of linear convex parts arranged in different directions to form a concentric rectangular DFB diffraction grating structure, and there may be three groups of linear convex parts arranged in different directions from each other to form a concentric hexagonal DFB diffraction grating structure. For the diffraction grating structure, there may also be a DFB diffraction grating structure in which 4 groups of linear convex portions arranged in different directions are formed to form a concentric octagonal shape. It is preferable that the linear convex portions constituting each group include periodically arranged regions. Here, “periodical” means that the linear protrusions are arranged at substantially constant intervals. In this specification, the interval Λ between the outer peripheries of adjacent linear protrusions or adjacent rectangular rings is referred to as “grating period”. The DFB diffraction grating structure used in the present invention is preferably formed concentrically. The "concentric shape" in the present invention refers to a first grating convex portion that is annular in plan view (a shape that is approximately a similar shape cut out from the ring one week smaller than the ring) and that is in a plan view with the first grating convex portion A shape in which the second grating convex parts to the n-th grating convex parts of substantially similar shapes are arranged in such a way that the centers overlap. Here, the second grating convex portion to the n-th grating convex portion (n is an integer of 3 or more) are also approximately similar shapes to each other, and the ring of the first grating convex portion is the smallest, and the larger the number of n, the larger the ring. n can be selected from, for example, a range of 3 or more, a range of 10 or more, a range of 50 or more, a range of 100 or more, a range of 200 or more, a range of 500 or more, and a range of 1000 or more. In addition, n can be selected from a range of less than 2000, a range of less than 800, a range of less than 400, and a range of less than 150. In addition, the ring here may not be a complete ring, for example, it may be partially missing, or the ring may be connected to each other by adjacent grating protrusions. In addition, the width of the ring may be narrower or thicker than the area that occupies more than half of the area. In addition, the center of the ring where the first grating convex portion to the n-th grating convex portion overlap represents the center of gravity of the ring. For example, in the case of a ring having rotational symmetry, it is the center of rotational symmetry. Here, in the DFB diffraction grating structure, it is possible to have a ring-shaped convex portion in a region that includes the center of the ring on the inner side of the first grating convex portion. It is preferable that the ring-shaped convex part has a shape substantially similar to the ring of the first grating convex part in a plan view. Polygonal rings formed concentrically are preferred. In this case, a part of the polygonal ring may include a curved portion. For example, the part (corner) where the sides constituting the polygon intersect may be formed in a curved shape. In addition, the polygonal ring may not include the curved portion. In addition, the polygonal ring may be partially missing, for example, it may be missing corners or half-cut edges. In the polygonal ring, the inner angles of the ring can all be the same, but they can also be different. The polygonal ring can be a regular polygon. As an example of a polygonal shape, a rectangular shape, a hexagonal shape, an octagonal shape, etc. can be given. In a preferred aspect of the present invention, the DFB diffraction grating structure is formed in a concentric rectangular shape. The "rectangle" of the concentric rectangular shape means a quadrangular shape. In other words, it is only necessary to have a shape surrounded by 4 straight lines. Specific examples of "rectangular" include squares, rectangles, rhombuses, parallelograms, etc., squares and rectangles are preferable, and squares are more preferable. For example, in the concentric square shape shown in FIG. 1, the arrangement direction between the arrangement of adjacent sides (adjacent linear convex portions) of the rectangular ring shape is formed in different directions between the X direction and the Y direction. By having such a concentric two-dimensional DFB diffraction grating structure in the laser element of the present invention, it can be inferred that optical feedback occurs in each arrangement direction to effectively form an inverted distribution, and extremely low laser oscillation can be achieved. Threshold.

In the DFB diffraction grating structure used in the present invention, _{each linear convex is selected with Λ=λ/2n eff} (λ: wavelength of light that causes Bragg reflection, n _eff : effective average refractive index of the diffraction grating) as an index. The grating period Λ of the arrangement of the part. The height h of each linear convex portion is preferably less than 75 nm, more preferably 20 to 70 nm. Here, the grating period Λ of the arrangement of the linear convex portions may be the same or different between the arrangements, but it is preferable that they are substantially the same. The width w and the height h of each linear convex portion may be the same as or different from each other in each arrangement, but it is preferable that they are substantially the same. In addition, the width w and the height h of the linear convex portions may be the same as or different from each other between the arrays, but they are preferably substantially the same.

As a constituent material of the DFB diffraction grating structure (each grating convex portion and annular convex portion), a material that can be used as a DFB diffraction grating or a material that has already been used can be mentioned. It is preferable to use SiO _2.

[Examples of laser components] The laser element of the present invention can be a light-excited laser element that performs laser oscillation by irradiating excitation light to the active layer, or it can be generated by the recombination of holes and electrons that are injected into the active layer The energy of the current excitation type laser element (semiconductor laser element) for laser oscillation. The light-excited laser element has at least a DFB diffraction grating structure and a structure with an active layer formed on the substrate. In addition, the current-excited laser element has at least an anode and a cathode (a pair of electrodes), a DFB diffraction grating structure and a structure formed with an active layer between the anode and the cathode, and a voltage is applied between the pair of electrodes. Laser oscillation is performed by energizing the active layer. In each laser element, the DFB diffraction grating structure has a concentric shape.

The active layer is a layer that induces emission by the incidence of light after receiving energy to generate excitons and form an inverted distribution. Here, in a current-excited laser element, it is preferable that the excitons generated in the active layer due to current excitation do not substantially disappear (disappear due to collisions between excitons). Specifically, the loss caused by the disappearance of excitons is preferably less than 10%, more preferably less than 5%, further preferably less than 1%, still more preferably less than 0.1%, particularly preferably less than 0.01%, and most preferably 0%. Furthermore, in the current-excited laser element, it is preferable that the polaron absorption loss is not substantially exhibited at the laser oscillation wavelength, that is, there is no substantial overlap between the polaron absorption spectrum and the emission spectrum. For better. Specifically, the loss caused by polaron absorption is preferably less than 10%, more preferably less than 5%, further preferably less than 1%, still more preferably less than 0.1%, particularly preferably less than 0.01%, most preferably Is 0%. Furthermore, it is preferable that the oscillation wavelength of the laser element and the absorption wavelength region in the excited state and the absorption wavelength region of radical cations or radical anions do not substantially overlap. The loss caused by absorption in the excited state is preferably less than 10%, more preferably less than 5%, still more preferably less than 1%, still more preferably less than 0.1%, particularly preferably less than 0.01%, and most preferably 0 %. Furthermore, it is preferable that the laser element of the present invention does not contain a triplet quencher.

In the laser device of the present invention, the active layer is preferably an organic layer containing an organic compound, and more preferably an organic layer made of an organic compound. In addition, the active layer may constitute a light-emitting part together with other layers. Here, the light-emitting portion has a laminated structure including an active layer and other layers laminated on the active layer. For example, in a current-excited laser element, the entire light-emitting portion is arranged between the anode and the cathode. The other layer constituting the light-emitting part is preferably an organic layer containing an organic compound, but an inorganic layer may be included in addition to the organic layer. Here, the organic layer may be made of only organic compounds, or may be a layer including organic compounds and inorganic substances. Among them, when it is a layer including an organic compound and an inorganic substance, an organic compound-based main component (a component of 60% by weight or more) is preferred. In addition, in this specification, each organic layer constituting the light-emitting part may be individually referred to as an "organic layer". In addition, when the organic layer is continuously laminated (in the case where the inorganic layer is not interposed and laminated), there is The entire layered structure of the organic layer is also referred to as the "organic layer". In addition, the organic layer (active layer) having only the active layer as the organic layer is sometimes referred to as the "organic layer as a unit", and the organic layer when the active layer and other organic layers are successively laminated are sometimes referred to as the organic layer (active layer). The entire layered structure of the layers is called "organic layer as a whole".

It is preferable to form an organic layer directly on the DFB diffraction grating structure. In this way, the Bragg reflected light can be directly introduced into the organic layer in the DFB diffraction grating structure, thereby contributing to the induced emission in the active layer. It is preferable that the refractive index of the organic layer directly formed on the DFB diffraction grating structure is different from the refractive index of the DFB diffraction grating structure. The organic layer directly formed on the DFB diffraction grating structure may be an active layer, or may be an organic layer disposed between the DFB diffraction grating structure and the active layer. In this case, the organic layer between the DFB diffraction grating structure and the active layer may have a single-layer structure or a multilayer structure. The organic layer directly formed on the DFB diffraction grating structure (as an integral organic layer) preferably contains an organic compound having at least one stilbene unit, including 4,4'-bis[(N-carbazole)styryl] Biphenyl (BSBCz) is better, including 4,4'-bis[(N-carbazole)styryl]biphenyl (BSBCz) and 4,4'-bis(N-carbazole)-1,1 '-Biphenyl (CBP) is further preferred. In addition, it is also preferable that the organic layer directly formed on the DFB diffraction grating structure (as an integral organic layer) contains an organic compound having at least one tea unit. The organic compound with at least one stilbene unit and the organic compound with at least one stilbene unit easily form an inverted distribution and can effectively induce induced emission. Therefore, it is preferable that these compounds are contained in the active layer. In addition, the laser element including BSBCz and CBP in the organic layer is characterized by showing a PL quantum yield of almost 100%, a short PL lifetime of about 1 ns, a large radiation attenuation constant (Kr), and a low ASE threshold.

The thickness of the organic layer directly formed on the DFB diffraction grating structure is preferably 80-350 nm, more preferably 100-300 nm, and still more preferably 150-250 nm. Here, when the organic layer is successively laminated on the organic layer directly formed on the DFB diffraction grating structure, the thickness of the entire laminated structure of the organic layer, that is, the thickness of the organic layer as a whole, is within the above-mentioned thickness range Inside. For example, when the layer farthest from the DFB diffraction grating structure in the light-emitting portion is an inorganic layer and the other layers are organic layers, the thickness obtained by subtracting the thickness of the inorganic layer from the thickness of the light-emitting portion is set to fall within the above-mentioned thickness range.

In addition, it is preferable that the DFB diffraction grating structure is arranged between the electrode and the organic layer. For example, the DFB diffraction grating structure can be arranged between the cathode and the organic layer, between the anode and the organic layer, or on both. In this case, it is preferable that the electrode with the DFB diffraction grating structure sandwiched between the organic layer and the organic layer is a transparent electrode. In addition, it is preferable that the DFB diffraction grating structure is formed directly on the electrode.

Examples of other layers constituting the light-emitting portion include a hole transport layer, a hole injection layer, an electron blocking layer, a hole blocking layer, an electron injection layer, an electron transport layer, an exciton blocking layer, and the like. The hole transport layer may be a hole injection transport layer with a hole injection function, and the electron transport layer may be an electron injection transport layer with an electron injection function. Fig. 2 shows an example of the structure of a specific current-excited laser element. In FIG. 2, 1 is a substrate, 2 is a cathode, 3 is a DFB diffraction grating structure, 4 is an electron injection layer, 5 is an active layer, 6 is a hole injection layer, and 7 is an anode. Here, as an example of the laser element shown in FIG. 2, the hole injection layer 6 is a metal oxide layer such as molybdenum oxide, and the electron injection layer 4 and the active layer 5 are organic layers. In addition, an organic layer made of HAT-CN or the like may be inserted between the metal oxide layer and the anode 7. In addition, the organic layer between the metal oxide layer and the DFB diffraction grating structure 3 may have a single-layer structure or a multi-layer structure of three or more layers in addition to the two-layer structure shown in FIG. 2. In the current-excited current-excited laser element, the laser light generated in the active layer can be taken out through the anode to the outside, can be taken out through the cathode to the outside, and can also be taken out through the anode and cathode to the outside. In addition, the laser light generated in the active layer can be taken out from the end surface of the light-emitting part to the outside. Hereinafter, each member and each layer of the current-excited laser element will be described. In addition, the description of the substrate and the active layer is also applicable to the light-excited laser element and the active layer. For the description of DFB diffraction grating structure, please refer to [DFB diffraction grating structure].

(Substrate) The current excitation type laser element of the present invention is preferably supported by the substrate. As the substrate, when the current-excited laser element has a structure in which the laser light is taken out from the substrate side, a substrate that is translucent to the laser light is used, and a transparent substrate made of glass, transparent plastic, quartz, etc. is preferably used. On the other hand, when the current-excited laser element has a structure in which the laser light is taken out from the side opposite to the substrate, the substrate is not particularly limited. In addition to the above-mentioned transparent substrate, a substrate made of silicon, paper, or cloth can also be used. .

(Anode) As the anode in the current-excited laser element, it is preferable to use metals, alloys, conductive compounds, and mixtures thereof with a large work function (4 eV or more) as electrode materials. Specific examples of such electrode materials include metals such as Al and Au, and conductive transparent materials such as _{CuI, indium tin oxide (ITO), SnO 2, ZnO, and TiN.} In addition, a material capable of producing a transparent conductive film with an amorphous substance, such as _{IDIXO (In 2} O _{3 -ZnO), can be used.} The anode can be formed by forming a film of these electrode materials by methods such as vapor deposition or sputtering. In addition, a pattern of a desired shape can be formed on the formed thin film by photolithography as an anode, or when the pattern accuracy is not required (about 100 μm or more), the electrode material can be vapor deposited or sputtered. A pattern is formed through a mask of the desired shape. Alternatively, when a coatable material such as an organic conductive compound is used, a wet film forming method such as a printing method and a coating method can also be used. Among them, when the current-excited laser element is a structure in which the laser light is taken out through the anode, the anode needs to be translucent to the laser light. The transmittance of the laser light is preferably greater than 1%, and it is better if the transmittance of the laser light is greater than 10%. Better. Specifically, it is preferable to use the above-mentioned conductive transparent material for the anode, or use a thin film formed of a metal or alloy with a thickness of 10 to 100 nm for the anode. The sheet resistivity of the anode is preferably 100Ω/□ or less. Moreover, the film thickness depends on the material, and is usually selected in the range of 10-1000 nm, preferably in the range of 10-200 nm.

(Cathode) On the other hand, as the cathode, a metal (called an electron injecting metal), alloy, conductive compound, and a mixture thereof having a smaller work function than the material used for the anode is used as an electrode material. Specific examples of such electrode materials include sodium, sodium-potassium alloy, magnesium, lithium, magnesium/copper mixture, magnesium/silver mixture, magnesium/aluminum mixture, magnesium/indium mixture, aluminum/alumina (Al ₂ O ₃ ) mixtures, indium, lithium/aluminum mixtures, rare earth metals, etc. Among them, from the standpoint of electron injectability and durability against oxidation, etc., it is preferable to use an electron injecting metal and a metal having a larger and stable work function value than the electron injecting metal, that is, the second metal For example, magnesium/silver mixture, magnesium/aluminum mixture, magnesium/indium mixture, aluminum/alumina (Al ₂ O ₃ ) mixture, lithium/aluminum mixture, aluminum, etc. The cathode can be formed by forming a film of these electrode materials by methods such as vapor deposition or sputtering. Among them, when the current-excited laser element is a structure that takes out the laser light through the cathode, the cathode needs to be transparent to the laser light. The transmittance of the laser light is preferably greater than 1%, and the structure is greater than 10%. Better. Specifically, it is preferable to use a thin film with a thickness of 10-100 nm formed of the above-mentioned electrode material for the cathode, or to use a conductive transparent material such as ITO exemplified in the above item (anode) for the cathode. The sheet resistivity of the cathode is preferably 100Ω/□ or less, and the film thickness is usually selected in the range of 10nm-5μm, preferably in the range of 50-200nm.

(Active layer) The active layer is a layer that generates excitons by recombination of holes and electrons separately injected from the anode and the cathode, and forms an inverted distribution, and then induces emission by light incidence. The active layer preferably contains an organic compound, and is preferably made of an organic compound. Furthermore, it is preferable that the active layer contains an organic compound as the luminescent material for laser. As the luminescent material for lasers, any known ones can be used, and organic compounds having at least one stilbene unit and organic compounds having at least one stilbene unit are preferred. As a specific example of the organic compound having at least one stilbene unit, BSBCz can be cited. In addition, in order to exhibit high luminous efficiency, it is important to efficiently convert the energy supplied to the active layer into excited singlet energy and move it to the luminescent material, and to confine the singlet excitons generated in the luminescent material in the luminescent material . Therefore, it is preferable that the active layer and the light-emitting material contain the host material together. As the host material, an organic compound having the lowest excited singlet energy level value higher than that of the light-emitting material can be used. As a result, the excited singlet energy generated in the host material can be easily transferred to the luminescent material, and the singlet excitons generated in the luminescent material can be enclosed in the molecules of the luminescent material, and its luminous efficiency can be fully exhibited . However, even if the singlet excitons cannot be sufficiently confined, high luminous efficiency can sometimes be obtained. Therefore, as long as it is a host material capable of realizing high luminous efficiency, it can be used in the present invention without particular limitation. The host material can be appropriately selected according to the luminescent material. For example, when BSBCz is used as the luminescent material, CBP can be preferably used as the host material. When the host material is used, the amount of the luminescent material for laser contained in the active layer is preferably 0.1% by weight or more, more preferably 1% by weight or more, more preferably 50% by weight or less, and 20% by weight or less More preferably, 10% by weight or less is even more preferable. As the host material in the active layer, an organic compound that has hole transport energy and electron transport energy and prevents the long wavelength of light emission, and has a high glass transition temperature is preferable. The thickness of the active layer is preferably 5 to 500 nm, and more preferably 50 to 300 nm.

(Injection layer) The injection layer refers to a layer provided between the electrode and the active layer in order to reduce the driving voltage or increase the luminescence brightness. It has a hole injection layer and an electron injection layer, and may exist between the anode and the active layer or the hole transport layer, and Between the cathode and the active layer or electron transport layer. The injection layer can be set as required. The hole injection material and the electron injection material can use well-known organic hole injection materials or well-known organic electron injection materials, metal oxides such as molybdenum oxide can also be used as the hole injection material, and alkali metals such as Cs can also be used. Organic materials are used as electron injection materials.

(Barrier layer) The barrier layer is a layer capable of blocking the diffusion of charges (electrons or holes) and/or excitons existing in the active layer to the outside of the active layer. The electron blocking layer can be arranged between the active layer and the hole transport layer to block electrons from passing through the active layer toward the hole transport layer. Similarly, the hole blocking layer can be arranged between the active layer and the electron transport layer to block the holes from passing through the active layer toward the electron transport layer. The barrier layer can also be used to block the diffusion of excitons to the outside of the active layer. That is, the electron blocking layer and the hole blocking layer can individually function as exciton blocking layers. The electron blocking layer or exciton blocking layer mentioned in this specification is used to include a layer having the functions of an electron blocking layer and an exciton blocking layer.

(Hole blocking layer) The hole blocking layer functions as an electron transport layer in a broad sense. The hole blocking layer has the function of transporting electrons and blocking holes from reaching the electron transport layer, thereby increasing the probability of recombination of electrons and holes in the active layer. As the material of the hole blocking layer, the material of the electron transport layer described later can be used as necessary.

(Electron blocking layer) The electron barrier layer has the function of transmitting holes in a broad sense. The electron blocking layer has the function of transporting holes and blocking electrons from reaching the hole transport layer, thereby increasing the probability of recombination of electrons and holes in the active layer.

(Exciton blocking layer) The exciton blocking layer refers to a layer used to block the excitons generated by the recombination of holes and electrons in the active layer from diffusing to the charge transport layer. By inserting this layer, the excitons can be efficiently enclosed in the active layer Among them, the luminous efficiency of the element can be improved. The exciton blocking layer can be inserted into either of the anode side and the cathode side adjacent to the active layer, or can be inserted into both at the same time. That is, when there is an exciton blocking layer on the anode side, this layer can be inserted between the hole transport layer and the active layer adjacent to the active layer, and when inserted on the cathode side, it can be inserted between the active layer and the cathode. This layer is inserted adjacent to the active layer. In addition, a hole injection layer or an electron blocking layer may be provided between the anode and the exciton blocking layer adjacent to the anode side of the active layer, and the exciton blocking layer adjacent to the cathode side of the active layer There may be an electron injection layer, an electron transport layer, a hole blocking layer, etc. in between. When the barrier layer is configured, it is preferable that at least one of the excited singlet energy and the excited triplet energy of the material used as the barrier layer is higher than the excited singlet energy and the excited triplet energy of the luminescent material.

(Hole transport layer) The hole transport layer can be made of a hole transport material that has the function of transmitting holes, and the hole transport layer can be provided with a single layer or multiple layers. As the hole transport material, it has any one of hole injection or transport, and electron barrier properties, and may be either organic or inorganic. Examples of well-known hole transport materials that can be used include triazole derivatives, oxadiazole derivatives, imidazole derivatives, carbazole derivatives, indolocarbazole derivatives, and polyarylalkane derivatives. , Pyrazoline derivatives and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, azole derivatives, styrylanthracene derivatives, fluorenone derivatives , Hydrazone derivatives, stilbene derivatives, silazane derivatives, aniline copolymers and conductive polymer oligomers, especially thiophene oligomers, etc., using porphyrin compounds, aromatic tertiary amine compounds and styrene Amine compounds are preferred, and aromatic tertiary amine compounds are more preferred.

(Electron Transport Layer) The electron transport layer can be made of a material that has the function of transporting electrons, and the electron transport layer can be provided with a single layer or multiple layers. As an electron transport material (sometimes also used as a hole blocking material), it only needs to have the function of transporting electrons injected from the cathode to the active layer. As the electron transport layer that can be used, for example, nitro substituted quinone derivatives, dibenzoquinone derivatives, thiopyran dioxide derivatives, carbodiimides, fluorenylidene methane derivatives, anthradimethane And anthrone derivatives, oxadiazole derivatives, etc. In addition, among the above-mentioned oxadiazole derivatives, a thiadiazole derivative obtained by substituting a sulfur atom on the oxygen atom of the oxadiazole ring, and a quinoline derivative having a quinoline ring known as an electron withdrawing group It can also be used as an electron transport material. Furthermore, it is also possible to use a polymer material in which these materials are introduced into the polymer chain or the materials are used as the main chain of the polymer.

The film forming method of each layer constituting the laser elements is not particularly limited, and it can be produced by any one of a dry process and a wet process.

In the current-excited laser element shown above, if a current above the threshold current density flows between the anode and the cathode, holes and electrons are injected into the active layer to generate excitons. After the inversion distribution is formed, the Induced emission and induced emission light is radiated from the active layer. The light radiated from the active layer undergoes Bragg reflection by the DFB diffraction grating structure, so that the light of specific wavelengths intensifies each other, and also propagates in the horizontal direction to the main surface of the substrate and returns to the active layer, causing induced emission in the active layer. The repetition of such optical feedback causes laser oscillation in a single vertical mode. At this time, in the laser element of the present invention, the DFB diffraction grating structure has at least two kinds of linear convex arrangements with different arrangement directions. Therefore, the optical feedback is caused in each arrangement direction to effectively form the inversion distribution, and it is effective. The light enhancement caused by Bragg reflection, and the light effectively returns to the active layer. As a result, the laser oscillation threshold can be greatly reduced, and good laser oscillation characteristics can be obtained. [Example]

Hereinafter, the features of the present invention will be further described in detail with examples. The materials, processing contents, processing procedures, etc. shown below can be appropriately changed as long as they do not depart from the gist of the present invention. Therefore, the scope of the present invention should not be limitedly interpreted by the specific examples shown below. In addition, the measurement of the emission spectrum during pulse driving was performed using a multi-channel spectrometer (manufactured by Hamamatsu Photonics KK: PMA-50), and the measurement of the element characteristics during pulse driving used an amplifier (NF Corporation: HSA4101) and a photomultiplier tube (manufactured by Hamamatsu Photonics KK). Made by Photonics KK: C9525-02). In addition, electron beam lithography (manufactured by JEOL Ltd.: JBX-5500SC system) was used to form diffraction gratings, and the film thickness was measured using a profiler (manufactured by Bruker: DektakXT), and SEM photographs were used for shooting Scanning electron microscope (manufactured by Hitachi High-Tech Corporation: SU8000) was performed.

(Embodiment 1) Manufacturing of a laser element with a DFB diffraction grating structure with a concentric square shape FIG. 3 shows the manufacturing steps of the laser element performed in this embodiment. Here, as the diffraction grating structure, the DFB diffraction grating structure of the concentric square shape shown in FIG. 1 is formed. The grating period Λ of the linear convex portions constituting the concentric square shape is set to 280 nm, the width w is set to 140 nm, and the height h is set to 60 nm. First, as shown in FIG. 3(a), a glass substrate on which a cathode made of indium tin oxide (ITO) with a thickness of 30 nm is formed is prepared. Then, as shown in FIG. 3(b), in the central area (10×10 mm) of the ITO, silicon oxide (SiO ₂ ) was formed into a film with a _{thickness of 60 nm by a sputtering method to form an SiO 2} film. Then, as shown in FIG. 3(c), _{four concentric square patterns are formed on the SiO 2} film using electron beam lithography and dry etching, thereby forming a DFB diffraction grating structure. The patterning of the SiO ₂ film is performed as follows. First, _{hexamethyldisilazane (HMDS) was spin-coated on the surface of the SiO 2} film and annealed at 120° C. for 120 seconds to perform HMDS treatment. Next, spin-coated resist solution (manufactured by Zeon Corporation: ZEP520A-7) was baked to form a resist layer with a thickness of 70 nm. The resist layer was irradiated with an electron beam line by an electron beam lithography device, and processed with a developer (manufactured by Zeon Corporation: ZED-N50) to obtain a resist mask with a pattern corresponding to the DFB diffraction grating structure. _{Then, plasma etching was performed using CHF 3} from the resist mask, and _{SiO 2} was etched in the area where the mask was not formed until the ITO surface was exposed. Then, _{plasma etching is performed with O 2} to remove the resist mask, thereby forming the concentric square-shaped DFB diffraction grating structure shown in FIG. 1. Next, as shown in FIG. 3(d), on the DFB diffraction grating structure, the thin films and anodes constituting the light-emitting part were laminated ^{by a vacuum vapor deposition method at a vacuum degree of 1.5×10 -4 Pa.} First, cesium (Cs) and CBP were vapor deposited from different vapor deposition sources on the DFB diffraction grating structure to form a layer with a thickness of 50 nm. At this time, the concentration of cesium was set to 20% by weight. Then, BSBCz and CBP were vapor-deposited from different vapor deposition sources together to form a 160 nm thick layer to form an active layer. At this time, the concentration of BSBCz was set to 6 wt%. Next, molybdenum trioxide (MoO ₃ ) was formed to a thickness of 10 nm, and aluminum (Al) was vapor-deposited to a thickness of 100 nm to form an anode, thereby fabricating a laser element.

(Comparative example 1) Manufacturing of laser elements without DFB diffraction grating structure Except that the DFB diffraction grating structure was not formed, a light-emitting part was directly formed on ITO, and an Al anode was formed on the light-emitting part, and a laser element was manufactured in the same manner as in Example 1, except that the light-emitting part was formed directly on the ITO.

(Comparative Examples 2-7) Manufacturing of laser elements with other DFB diffraction grating structures The laser element was manufactured in the same manner as in Example 1, except that the top-view shape of the DFB diffraction grating structure was changed to the shape shown in the SEM photographs of FIGS. 4(a) to (f). FIG. 4(g) is an SEM photograph of the DFB diffraction grating structure formed in Example 1. FIG.

FIG. 5 shows the current density-voltage characteristics when a DC voltage is applied to each laser element of Example 1 and Comparative Example 1. FIG. When the ^{external quantum efficiency is measured in the range of 100-150 Acm -2} , the laser element of Example 1 shows a higher external quantum efficiency than the laser element of Comparative Example 1. 6 shows the emission spectra when pulse voltages are applied to the laser element of Example 1 at various current densities, and FIG. 7 shows the results of plotting the emission peak intensity with respect to the current density. The pulse voltage used here has a pulse width of 400ns and a pulse frequency of 1kHz. As shown in FIG. 6, by applying a pulse voltage, a sharp peak derived from laser oscillation was observed in the laser element of Example 1. In addition, the laser oscillation threshold obtained from Fig. 7 is 20 Acm ^-1 , which is an extremely low value. Fig. 8 shows the results of measuring the angular dependence of the luminous intensity by driving the laser element of Example 1 with ^{110 Acm -2 exceeding the threshold.} The horizontal axis in the graph of FIG. 8 represents the measurement angle of the luminous intensity, which is set to 90° when measured from the normal direction to the substrate surface, and set to 0° or 180 when measured from the horizontal direction relative to the substrate surface. ° Those. As shown in FIG. 8, in the laser element of Example 1, the luminous intensity was the highest in the direction normal to the substrate surface, and the directivity of the luminescence was confirmed.

In addition, for each laser element of Comparative Examples 2 to 7, the laser oscillation threshold J _{th was} obtained in the same manner as in Example 1, and the emission wavelength λ _DFB and the half-width FWHM at the threshold J _{th were measured.} Table 1 shows these measurement results.

【Table 1】 Example No DFB diffraction grating structure Oscillation frequency λ _DFB (nm) Oscillation threshold J _th (Acm ^-2 ) FWHM (nm) Comparative example 2 (a) One-dimensional DFB 476.0 284 0.45 Comparative example 3 (b) Alternately have a mixed dimension DFB of the first area and the second area with different grating periods 480.3 600 0.20 Comparative example 4 (c) Two-dimensional DFB of the convex part of the square shape 475.4 490 0.48 Comparative example 5 (d) Two-dimensional DFB of square shape recess 477.0 455 0.43 Comparative example 6 (e) Circular two-dimensional DFB 474.9 298 0.53 Comparative example 7 (f) A circular hybrid two-dimensional DFB with alternating first and second regions with different grating periods 473.9 98 0.44 Example 1 (g) Two-dimensional DFB of concentric square shape 474.0 20 0.50

As shown in Table 1, compared with the laser oscillation threshold J _th of Comparative Examples 2-7, the laser oscillation threshold J _th of the laser element of Example 1 is much lower. It can be seen that by setting the DFB diffraction grating structure to have at least two linear convex arrangements with different alignment directions, the laser oscillation threshold can be effectively reduced, and the laser oscillation threshold can be effectively reduced, and the operation can be carried out at a relatively low current density. Current excitation type organic laser element for laser oscillation. In addition, in the laser element of Example 1, a layer made of HAT-CN _{can be inserted between the Al anode and the MoO 3 layer.}

[產業上之可利用性][Chemical formula 1]

[Industrial availability]

The laser oscillation threshold of the laser element of the present invention is extremely low, and even when it is configured as a current-excited organic laser element, laser oscillation can be performed at a relatively low current density. Therefore, according to the present invention, a current-excited organic laser device with high practicality can also be realized. Therefore, the industrial applicability of the present invention is high.

1: substrate 2: cathode 3: DFB diffraction grating structure 4: Electron injection layer 5: Active layer 6: Hole injection layer 7: anode w: width Λ: grating period

FIG. 1 is a schematic plan view showing an example of a DFB diffraction grating structure equipped with the laser element of the present invention. Fig. 2 is a schematic cross-sectional view showing an example of the layer structure of the laser element of the present invention. 3(a)~(d) are schematic perspective views showing the manufacturing steps of the laser element performed in the first embodiment. Fig. 4 is an SEM photograph of the DFB diffraction grating structure of the laser element manufactured in Example 1 and the laser element manufactured in Comparative Examples 2-7. Fig. 5 shows the current during DC driving of the laser element with the DFB diffraction grating structure of the concentric square shape manufactured in Example 1 and the laser element without the DFB diffraction grating structure manufactured in Comparative Example 1 Graph of density-voltage characteristics. Fig. 6 shows the emission spectra of the laser element having the DFB diffraction grating structure with a concentric square shape manufactured in Example 1 when driven by pulses measured at various current densities. Fig. 7 is a two logarithmic graph plotting the emission peak intensity in Fig. 6 with the current density as the horizontal axis. 8 is a graph showing the angular dependence of the luminous intensity measured ^{at 110 Acm -2 for} the laser element with the DFB diffraction grating structure of the concentric square shape manufactured in Example 1.

w: width

Λ: grating period

Claims (15)

A laser element has a two-dimensional DFB diffraction grating structure with at least two linear convex portions arranged in different arranging directions. The laser element according to claim 1, wherein The aforementioned DFB diffraction grating structure has a concentric rectangular shape. The laser element according to claim 1, wherein The aforementioned DFB diffraction grating structure has a concentric square shape. The laser element according to claim 1, wherein The grating periods are the same between the two types of arrangement of linear convex portions. The laser element described in claim 1 has a pair of electrodes and performs laser oscillation by energization. The laser element according to claim 1, wherein An organic layer is directly formed on the aforementioned DFB diffraction grating structure. The laser element according to claim 6, wherein The aforementioned organic layer contains an organic compound having at least one stilbene unit. The laser element according to claim 6, wherein The aforementioned organic layer contains 4,4'-bis[(N-carbazole)styryl]biphenyl (BSBCz). The laser element according to claim 8, wherein The aforementioned organic layer contains 4,4'-bis[(N-carbazole)styryl]biphenyl (BSBCz) and 4,4'-bis(N-carbazole)-1,1'-biphenyl (CBP ). The laser element according to any one of claim 6 to claim 9, wherein The aforementioned organic layer contains a compound having at least one chlorophyll unit. The laser element according to any one of claim 6 to claim 9, wherein The aforementioned organic layer has a thickness of 80-350 nm. The laser element according to any one of claim 1 to claim 9, wherein The height of each linear convex portion constituting the aforementioned DFB diffraction grating structure is less than 75 nm. The laser element according to any one of claim 1 to claim 9, wherein the aforementioned DFB diffraction grating structure is composed of SiO ₂ . The laser element according to any one of claim 6 to claim 9, wherein The aforementioned DFB diffraction grating structure is arranged between the aforementioned organic layer and the transparent electrode. The laser element according to any one of claims 1 to 9, which does not contain a triplet quencher.

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