Light-emitting element and method for manufacturing light-emitting element

Abstract

This light-emitting element comprises a hole transport layer, an electron transport layer, a light-emitting layer, a cathode, and an anode. The light-emitting layer is sandwiched between the hole transport layer and the electron transport layer. The anode and the cathode are electrically connected to the hole transport layer and the electron transport layer, respectively. Each of the hole transport layer, the electron transport layer, and the light-emitting layer includes a compound semiconductor represented by composition formula: InxAlyGazN. Here: x+y+z=1±0.05; 0<x<1; 0≤y<1; 0≤z<1; 0<z when y=0; and 0<y when z=0. At least one of the following relations are satisfied: (1) y in the hole transport layer and y in the electron transport layer are both larger than y in the light-emitting layer; and (2) z in the hole transport layer and z in the electron transport layer are both smaller than z in the light-emitting layer.

Description

Light-emitting device and method for manufacturing the same

[0001] One embodiment of the present invention relates to a light emitting device including a compound semiconductor and a method for manufacturing the same.

[0002] In recent years, inorganic light-emitting devices containing nitrides of Group 13 elements such as gallium nitride (GaN) and indium nitride (InN) as active layers have been widely used. Conventionally, such inorganic light-emitting devices have been fabricated using silicon substrates or sapphire substrates, but Patent Documents 1 to 3, for example, disclose that inorganic light-emitting devices can also be formed on glass substrates.

[0003] JP 2019-41113 A JP 2018-168029 A JP 2000-124140 A

[0004] An object of one embodiment of the present invention is to provide a light-emitting element having a novel structure and a method for manufacturing the same. Alternatively, an object of one embodiment of the present invention is to provide an inorganic light-emitting element having excellent luminous efficiency and reliability and a method for manufacturing the same.

[0005] One embodiment of the present invention is a light-emitting device. The light-emitting device includes a hole transport layer, an electron transport layer, a light-emitting layer, a cathode, and an anode. The light-emitting layer is sandwiched between the hole transport layer and the electron transport layer. The anode and cathode are electrically connected to the hole transport layer and the electron transport layer, respectively. The hole transport layer, the electron transport layer, and the light-emitting layer are all made of In. ｘ Al ｙ Ga ｚ The compound semiconductor includes a compound semiconductor represented by the composition formula of N, where x + y + z = 1 ± 0.05, 0 < x < 1, 0 ≦ y < 1, 0 ≦ z < 1, and when y = 0, 0 < z, and when z = 0, 0 < y. At least one of the following relationships is satisfied: (1) y in the hole transport layer and the electron transport layer is both larger than y in the light-emitting layer, and (2) z in the hole transport layer and the electron transport layer is both smaller than z in the light-emitting layer.

[0006] One embodiment of the present invention is a method for manufacturing a light-emitting device. This method includes forming a hole transport layer, an electron transport layer, and a light-emitting layer sandwiched between the hole transport layer and the electron transport layer by a sputtering method, and forming an anode and a cathode electrically connected to the hole transport layer and the electron transport layer, respectively. The hole transport layer, the electron transport layer, and the light-emitting layer are all made of In. ｘ Al ｙ Ga ｚ The compound semiconductor includes a compound semiconductor represented by the composition formula of N, where x + y + z = 1 ± 0.05, 0 < x < 1, 0 ≦ y < 1, 0 ≦ z < 1, and when y = 0, 0 < z, and when z = 0, 0 < y. At least one of the following relationships is satisfied: (1) y in the hole transport layer and the electron transport layer is both larger than y in the light-emitting layer, and (2) z in the hole transport layer and the electron transport layer is both smaller than z in the light-emitting layer.

[0007] One embodiment of the present invention is a display device. The display device includes a substrate and a plurality of pixels on the substrate. Each of the plurality of pixels has a light-emitting element. The light-emitting element includes a hole transport layer, an electron transport layer, a light-emitting layer, a cathode, and an anode. The light-emitting layer is sandwiched between the hole transport layer and the electron transport layer. The anode and cathode are electrically connected to the hole transport layer and the electron transport layer, respectively. The hole transport layer, the electron transport layer, and the light-emitting layer are all made of In. ｘ Al ｙ Ga ｚ The compound semiconductor includes a compound semiconductor represented by the composition formula of N, where x + y + z = 1 ± 0.05, 0 < x < 1, 0 ≦ y < 1, 0 ≦ z < 1, and when y = 0, 0 < z, and when z = 0, 0 < y. At least one of the following relationships is satisfied: (1) y in the hole transport layer and the electron transport layer is both larger than y in the light-emitting layer, and (2) z in the hole transport layer and the electron transport layer is both smaller than z in the light-emitting layer.

[0008] One embodiment of the present invention is a lighting device. The lighting device includes a substrate and a plurality of light sources on the substrate. Each of the plurality of light sources has a light-emitting element. The light-emitting element includes a hole transport layer, an electron transport layer, a light-emitting layer, a cathode, and an anode. The light-emitting layer is sandwiched between the hole transport layer and the electron transport layer. The anode and cathode are electrically connected to the hole transport layer and the electron transport layer, respectively. The hole transport layer, the electron transport layer, and the light-emitting layer are all made of In. ｘ Al ｙ Ga ｚ The compound semiconductor includes a compound semiconductor represented by the composition formula of N, where x + y + z = 1 ± 0.05, 0 < x < 1, 0 ≦ y < 1, 0 ≦ z < 1, and when y = 0, 0 < z, and when z = 0, 0 < y. At least one of the following relationships is satisfied: (1) y in the hole transport layer and the electron transport layer is both larger than y in the light-emitting layer, and (2) z in the hole transport layer and the electron transport layer is both smaller than z in the light-emitting layer.

[0009] 1 is a schematic end view of a light-emitting element according to an embodiment of the present invention; 2 is a schematic end view of a light-emitting element according to an embodiment of the present invention; 3 is a schematic end view of a light-emitting layer included in a light-emitting element according to an embodiment of the present invention; 4 is a schematic top view of a display device according to an embodiment of the present invention; 5 is a schematic end view of a display device according to an embodiment of the present invention; 6 is a schematic top view of a lighting device according to an embodiment of the present invention;

[0010] Hereinafter, various embodiments of the present invention will be described with reference to the drawings, etc. However, the present invention can be embodied in various forms without departing from the spirit of the present invention, and should not be construed as being limited to the description of the embodiments exemplified below.

[0011] In order to clarify the description, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual embodiment, but these are merely examples and do not limit the interpretation of the present invention. In this specification and each drawing, elements having the same function as those described in the previous drawings may be given the same reference numerals, and duplicated explanations may be omitted. This reference numeral is used to collectively represent multiple identical or similar structures, and when these are individually represented, a hyphen and a natural number are added after the reference numeral.

[0012] In this specification and claims, when expressing an aspect of placing another structure on top of a certain structure, the term "on top" is used, unless otherwise specified, to include both a case in which another structure is placed directly on top of a certain structure so as to be in contact with the certain structure, and a case in which another structure is placed above a certain structure via yet another structure.

[0013] In this specification and claims, the expression "a structure exposed from another structure" means a state in which a part of a structure is not covered by another structure, and includes a state in which the part not covered by another structure is covered by yet another structure. The state expressed by this expression also includes a state in which a structure is not in contact with another structure.

[0014] First Embodiment In this embodiment, a light emitting device according to one embodiment of the present invention will be described. This light emitting device is an inorganic light emitting device including a compound semiconductor containing a Group 13 element and a Group 15 element.

[0015] 1. Structure FIG. 1A shows a schematic end view of a light-emitting element 100 according to an embodiment of the present invention. As shown in FIG. 1A, the light-emitting element 100 is formed on a substrate 120 and includes an electron transport layer 104, a hole transport layer 108, and a light-emitting layer 106 sandwiched between the electron transport layer 104 and the hole transport layer 108. The light-emitting element 100 further includes a cathode 114 and an anode 112 electrically connected to the electron transport layer 104 and the hole transport layer 108, respectively. The light-emitting element 100 may further include a hole injection layer 110 between the anode 112 and the hole transport layer 108, or an electron injection layer 102 between the cathode 114 and the electron transport layer 104. The electron injection layer 102, the electron transport layer 104, the light-emitting layer 106, the hole transport layer 108, and the hole injection layer 110 may each have a single-layer structure or may include multiple layers. For example, the light-emitting layer 106 may have a so-called quantum well structure. The quantum well structure is a structure in which multiple layers with different band gaps and thicknesses of several nanometers are alternately stacked. By applying a potential difference equal to or greater than the light emission threshold voltage between the anode 112 and the cathode 114, holes and electrons are injected from the anode 112 and the cathode 114, respectively, and the holes and electrons recombine in the light-emitting layer 106, resulting in light emission.

[0016] 1A , the electron injection layer 102, the electron transport layer 104, the light-emitting layer 106, the hole transport layer 108, and the hole injection layer 110 are stacked in this order from the substrate 120 side, with a portion of the electron injection layer 102 exposed from the electron transport layer 104 and a cathode 114 provided on the exposed portion. However, the configuration of the light-emitting element 100 is not limited to this. For example, as shown in FIG. 1B , the hole injection layer 110, the hole transport layer 108, the light-emitting layer 106, the electron transport layer 104, the electron injection layer 102, and the cathode 114 may be stacked in this order from the anode 112 side provided on the substrate 120.

[0017] Each component will be described below.

[0018] (1) Substrate The substrate 120 is configured to support the light-emitting element 100 provided thereon. There are no particular restrictions on the material contained in the substrate 120, and it may be, for example, quartz, single-crystal silicon, single-crystal germanium, single-crystal sapphire, amorphous glass, or a polymer such as polyimide, polyamide, or polycarbonate. The substrate 120 may be thick enough to be flexible (e.g., 0.1 mm to 0.5 mm), or may be thicker (e.g., 0.5 mm to 2 mm).

[0019] When an amorphous glass substrate is used as the substrate 120, it is preferable to use a substrate with a high strain point and high surface flatness. For example, an alkali-free glass substrate with a strain point of 600°C or higher can be used as the substrate 120. In this case, the substrate 120 contains silicon dioxide, aluminum oxide, boron oxide, and alkaline earth metal oxides such as calcium oxide and barium oxide. The content of alkali metals such as sodium in the substrate 120 is preferably 0.1% or less. There are no restrictions on the size of the glass substrate. For example, a large rectangular amorphous glass substrate, also known as mother glass, can be used as the substrate 120. Specifically, a glass substrate measuring 2160 mm x 2460 mm, called an 8th generation mother glass, a glass substrate measuring 2400 mm x 2800 mm, called a 9th generation mother glass, a glass substrate measuring 2880 mm x 3130 mm, called a 10th generation mother glass, or even larger glass substrates may be used.

[0020] (2) Electron Injection Layer, Electron Transport Layer, Light Emitting Layer, Hole Transport Layer, and Hole Injection Layer The electron injection layer 102, electron transport layer 104, light emitting layer 106, hole transport layer 108, and hole injection layer 110 (hereinafter, these layers may be referred to as functional layers) all contain an indium-containing compound semiconductor. More specifically, these functional layers all contain In ｘ Al ｙ Ga ｚThe functional layer includes a compound semiconductor represented by the formula N. Here, x + y + z = 1 ± 0.05, 0 < x < 1, 0 ≦ y < 1, and 0 ≦ z < 1. Furthermore, when y = 0, 0 < z, and when z = 0, 0 < y. Considering stoichiometry, x + y + z is 1. However, the composition of a compound semiconductor does not necessarily match the stoichiometry, and measurement always contains errors. Therefore, the sum of x, y, and z is allowed up to 1 ± 0.05. Since 0 < x < 1, each functional layer contains In as well as nitrogen. Furthermore, when y = 0, 0 < z, and when z = 0, 0 < y, each functional layer contains In and nitrogen, as well as at least one of Al and Ga. The composition of each functional layer may be determined using, for example, secondary ion mass spectroscopy (SIMS), X-ray photoelectron spectroscopy (XPS), or energy dispersive spectroscopy (EDS). The electron injection layer 102 and the electron transport layer 104 may further include n-type dopants such as silicon or germanium. Similarly, the hole injection layer 110 and the hole transport layer 108 may include p-type dopants such as magnesium, zinc, cadmium, or beryllium.

[0021] Furthermore, in the functional layer, at least one of the following relationships (A) and (B) is satisfied: (A) y in the hole transport layer 108 and the electron transport layer 104 is greater than y in the light-emitting layer 106; (B) z in the hole transport layer 108 and the electron transport layer 104 is less than z in the light-emitting layer 106. Relationship (A) means that the hole transport layer 108 and the electron transport layer 104 both have a higher aluminum composition than the light-emitting layer 106. In contrast, relationship (B) means that the hole transport layer 108 and the electron transport layer 104 both have a lower gallium composition than the light-emitting layer 106. Note that the y in the hole transport layer 108 and the electron transport layer 104 may be the same, or one may be greater than the other. Similarly, the z in the hole transport layer 108 and the electron transport layer 104 may be the same, or one may be greater than the other.

[0022] By satisfying the relationships (A) and (B), it is possible to configure the light-emitting element 100 in which the band gaps of the hole transport layer 108 and the electron transport layer 104 are both larger than that of the light-emitting layer 106. This suppresses energy transfer from the light-emitting layer 106 to the hole transport layer 108 and / or the electron transport layer 104, allowing the light emitted from the light-emitting layer 106 to be extracted efficiently.

[0023] When the light-emitting element 100 includes a hole injection layer 110, the light-emitting element 100 is configured so that the following relationships (C) and (D) are further satisfied: (C) y in the hole injection layer is smaller than y in the hole transport layer and equal to or greater than y in the light-emitting layer; (D) z in the hole injection layer is greater than z in the hole transport layer and equal to or less than z in the light-emitting layer. Relationship (C) means that the aluminum composition of the hole injection layer 110 is smaller than that of the hole transport layer 108 and equal to or greater than that of the light-emitting layer 106. In contrast, relationship (D) means that the gallium composition of the hole injection layer 110 is greater than that of the hole transport layer 108 and equal to or less than that of the light-emitting layer 106. Therefore, the aluminum and / or gallium composition of the hole injection layer 110 and the light-emitting layer 106 may be the same.

[0024] By satisfying the relationships (C) and (D), the band gap of the hole injection layer 110 can be made smaller than that of the hole transport layer 108, and the light-emitting element 100 can be made larger than that of the light-emitting layer 106. This suppresses the energy transfer described above, and also suppresses an increase in the hole injection barrier from the anode 112 to the functional layer.

[0025] When the light-emitting element 100 includes an electron injection layer 102, the light-emitting element 100 is configured so that the following relationships (E) and (F) are further satisfied: (E) y in the electron injection layer is smaller than y in the electron transport layer and equal to or larger than y in the light-emitting layer; (F) z in the electron injection layer is larger than z in the electron transport layer and equal to or smaller than z in the light-emitting layer. Relationship (E) means that the aluminum composition of the electron injection layer 102 is smaller than that of the electron transport layer 104 and equal to or larger than that of the light-emitting layer 106. In contrast, relationship (F) means that the gallium composition of the electron injection layer 102 is larger than that of the electron transport layer 104 and equal to or smaller than that of the light-emitting layer 106. Therefore, the aluminum and / or gallium composition may be the same in the electron injection layer 102 and the light-emitting layer 106. Note that the y in the hole injection layer 110 and the electron injection layer 102 may be the same, or one may be larger than the other. Similarly, z in the hole injection layer 110 and the electron injection layer 102 may be the same, or one may be larger than the other.

[0026] By satisfying the relationships (E) and (F), it is possible to configure a light-emitting element 100 in which the band gap of the electron injection layer 102 is smaller than that of the electron transport layer 104 and is equal to or larger than that of the light-emitting layer 106. This makes it possible to suppress the above-mentioned energy transfer and also to suppress an increase in the electron injection barrier from the cathode 114 to the functional layer.

[0027] In addition, when at least one of the functional layers is composed of multiple layers, the composition of the compound semiconductor is determined so that the above relationships (A) to (F) are satisfied for the multiple layers included in each functional layer. For example, as shown in Figure 2, when the light-emitting layer 106 has an alternating stack (quantum well structure) of multiple layers with different band gaps (multiple low band gap layers 106-1 and multiple high band gap layers 106-2), the composition of the compound semiconductor is determined so that both the low band gap layer 106-1 and the high band gap layer 106-2 satisfy the above relationships (A) to (F). Furthermore, the light-emitting layer 106 is configured so that the layer in contact with the electron transport layer 104 and the layer in contact with the hole transport layer 108 are both high band gap layers 106-2.

[0028] As described above, the light-emitting layer 106 is also made of In ｘ Al ｙ Ga ｚ N. Therefore, in order to create a band gap difference between the low band gap layer 106-1 and the high band gap layer 106-2, the low band gap layer 106-1 and the high band gap layer 106-2 are configured such that the Al composition y in the high band gap layer 106-2 is larger than that in the low band gap layer 106-1, and z in the high band gap layer 106-2 is smaller than z in the low band gap layer 106-1.

[0029] Furthermore, the compound semiconductors contained in each functional layer are preferably selected so that their band gaps are 1.5 eV or more and 3.5 eV or less. This ensures that the lattice constants of the compound semiconductors contained in the functional layers fall within a certain range (e.g., 0.327 nm or more and 0.344 nm or less), reducing the lattice constant mismatch (difference) between the functional layers. As a result, high crystallinity can be achieved throughout the light-emitting device 100. This minimizes crystal defects, preventing shortened lifetimes and shifts in emitted light color due to crystal defects. Furthermore, when y is 0<y, i.e., when Al is present in all functional layers, the refractive index of each functional layer becomes relatively small, and the difference in refractive index between adjacent functional layers is reduced. This suppresses total reflection of light from the light-emitting layer 106 between adjacent functional layers, resulting in high extraction efficiency. This contributes to increased efficiency (current efficiency) of the light-emitting device 100.

[0030] (3) Modifications As one modification, the light emitting device 100 may be configured so that none of the functional layers contain gallium. That is, z may be 0 in each functional layer. In this case, the composition where y=0 is excluded, and 0<y<1. In other words, all of the functional layers contain In ｘ Al ｙThe light-emitting element 100 includes a compound semiconductor represented by a composition of N, where x + y = 1 ± 0.05, 0 < x < 1, and 0 < y < 1. Thus, each functional layer does not contain Ga, but contains indium, aluminum, and nitrogen. In this case, the compound semiconductor of each functional layer is selected so that the above relationship (A) is satisfied. Furthermore, when the light-emitting element 100 includes a hole injection layer 110 and an electron injection layer 102, the compound semiconductor of each functional layer is selected so that the above relationships (C) and (E) are satisfied, respectively.

[0031] Even in this modification, the compound semiconductor contained in each functional layer is preferably selected so that its band gap is 1.5 eV or more and 3.5 eV or less. This ensures that the lattice constant of the compound semiconductor contained in each functional layer falls within a certain range (e.g., 0.327 nm or more and 0.344 nm or less), reducing the difference in lattice constant between the functional layers and achieving high crystallinity throughout the light-emitting element 100. Furthermore, the refractive index of each functional layer is relatively small, and the difference in refractive index between adjacent functional layers is reduced. This suppresses total reflection of light obtained in the light-emitting layer 106 between adjacent functional layers, thereby achieving high extraction efficiency. This contributes to increasing the current efficiency of the light-emitting element 100.

[0032] (4) Other Configurations A. Buffer Layer The light-emitting element 100 may further include a buffer layer 126 on the substrate 120 ( FIGS. 1A and 1B ). In this case, the electron transport layer 104 or the hole transport layer 108 is located between the buffer layer 126 and the light-emitting layer 106. When the light-emitting element 100 has the structure shown in FIG. 1A , i.e., when the electron transport layer 104, the light-emitting layer 106, and the hole transport layer 108 are stacked in this order from the substrate 120 side, the buffer layer 126 is located between the substrate 120 and the electron transport layer 104. The buffer layer 126 may be in contact with the electron transport layer 104, and when the electron injection layer 102 is provided, the buffer layer 126 is provided so as to be in contact with the electron injection layer 102.

[0033] 1B , i.e., when the hole transport layer 108, the light-emitting layer 106, and the electron transport layer 104 are stacked in this order from the substrate 120 side, the buffer layer 126 is located between the substrate 120 and the hole transport layer 108. The buffer layer 126 may be in contact with the hole transport layer 108, and when the hole injection layer 110 is provided, the buffer layer 126 is provided so as to be in contact with the hole injection layer 110.

[0034] The buffer layer 126 is a film that contributes to promoting crystallization of the functional layers provided thereon, and also prevents deformation (warping) of the substrate 120 under the conditions during manufacturing of the light-emitting element 100 by improving adhesion between the functional layers and the substrate 120. Therefore, by using the buffer layer 126, it is possible to effectively suppress the occurrence of crystal defects in the functional layers of the light-emitting element 100.

[0035] Specifically, the buffer layer 126 may include an insulating or conductive material having a hexagonal close-packed structure, a face-centered cubic structure, or a structure equivalent thereto. Here, a hexagonal close-packed structure or a structure equivalent thereto includes a crystal structure in which the c-axis is not perpendicular to the a-axis and the b-axis. Therefore, in this structure, the buffer layer 126 is oriented in the (0001) direction, i.e., the c-axis direction, relative to the substrate 120. Furthermore, a buffer layer 126 having a face-centered cubic structure or a structure equivalent thereto is oriented in the (111) direction relative to the substrate 120. Therefore, the c-axis of the buffer layer 126 is oriented perpendicular or approximately perpendicular to the surface on which the buffer layer 126 is provided (the surface of the substrate 120 in the examples shown in FIGS. 1A and 1B ). Meanwhile, the compound semiconductors included in each functional layer of the light-emitting element 100 have a wurtzite structure and undergo crystal growth in the c-axis direction to minimize their surface energy. Therefore, by forming a functional layer containing a compound semiconductor on the buffer layer 126, crystal growth in the c-axis direction of the functional layer is promoted, and as a result, the crystallinity of each functional layer is improved.

[0036] Such a buffer layer 126 may include metal nitrides such as aluminum indium nitride, aluminum nitride, titanium nitride, and gallium nitride; metal oxides such as zinc oxide, lithium niobate (LiNbO), BiLaTiO, SrFeO, BiFeO, BaFeO, ZnFeO, and PMnN-PZT; silicon; germanium; or basic calcium phosphate (biological apatite). Using such materials allows for the formation of an insulating buffer layer 126. In particular, using aluminum indium nitride can reduce the lattice constant mismatch between the buffer layer 126 and the adjacent functional layer, thereby promoting more effective c-axis orientation of the functional layer. Alternatively, the buffer layer 126 may include metals such as titanium, aluminum, silver, nickel, copper, strontium, rhodium, palladium, iridium, platinum, and gold. When containing a metal, the buffer layer 126 is conductive and functions as wiring, and may therefore be used as wiring for supplying a potential to the anode 112. Alternatively, although not shown, the buffer layer 126 may be used as the anode 112 in contact with the hole injection layer 110 or the hole transport layer 108 .

[0037] The buffer layer 126 may be formed by CVD or sputtering. To more effectively crystallize the functional layer in the c-axis direction, the buffer layer 126 preferably has a highly flat surface. Specifically, the arithmetic mean roughness (Ra) of the surface of the buffer layer 126 is preferably smaller than 2.3 nm. Furthermore, the root-mean-square roughness (Rq) of the surface of the buffer layer 126 is preferably smaller than 2.9 nm. To achieve high surface flatness, the buffer layer 126 preferably has a thickness of 50 nm or less, and is formed with a thickness of, for example, 10 nm to 50 nm. The buffer layer 126 may also have a single-layer structure or a multilayer structure.

[0038] A. Overcoat and Undercoat An overcoat 122 may be disposed above the substrate 120, in contact with the substrate 120. An undercoat 124 may also be disposed below the substrate 120, in contact with the substrate 120. The overcoat 122 and undercoat 124 may be configured as a single film or a laminate of multiple films containing a silicon-containing inorganic compound such as silicon oxide or silicon nitride, or an aluminum-containing inorganic compound such as aluminum nitride or aluminum oxide. Providing the overcoat 122 and / or undercoat 124 can prevent the diffusion of impurities, such as alkali metal ions, contained in the substrate 120. Furthermore, the undercoat 124 and overcoat 122 suppress the desorption of impurities, such as water, from the substrate 120 under the conditions used during the manufacture of the light-emitting element 100, preventing impurities from being mixed into the functional layer and preventing warping of the substrate 120 due to differences in the thermal expansion coefficient between the substrate 120 and the functional layer or between the substrate 120 and the buffer layer 126. Therefore, a thermal expansion coefficient of 4.0×10 －６ / °C higher than 5.0 x 10 －６ It is preferable to configure the undercoat 124 and the overcoat 122 so that the temperature is less than 1 / °C.

[0039] C. Protective Film As an optional configuration, the light-emitting element 100 may include a protective film 130 that covers part of the functional layer, the cathode 114, and the anode 112. Examples of materials contained in the protective film 130 include silicon-containing inorganic compounds such as silicon nitride, silicon oxide, silicon nitride oxide, and silicon oxynitride, as well as polymers such as acrylic resin, epoxy resin, polyimide, and polyamide. For example, a laminate having a structure in which a polymer is sandwiched between two silicon-containing inorganic compounds may be used as the protective film 130. The protective film 130 has openings that expose part of the cathode 114 and the anode 112, and electrical connection to the light-emitting element can be made through these openings.

[0040] As described above, each functional layer included in the light emitting device 100 according to one embodiment of the present invention is made of In. ｘ Al ｙ Ga ｚThe light-emitting element 100 includes a compound semiconductor represented by the composition formula N, with certain restrictions imposed on x, y, and z between the functional layers. Furthermore, the light-emitting element 100 is configured so that the above-mentioned relationships (A) to (F) are appropriately satisfied, and the compound semiconductor can be selected so that the band gap of each functional layer is 1.5 eV or more and 3.5 eV or less. This reduces the difference in refractive index and lattice constant between the functional layers, resulting in high crystallinity throughout the light-emitting element 100 and high extraction efficiency. Therefore, by applying the embodiments of the present invention, it is possible to provide a light-emitting element with high reliability and high luminous efficiency.

[0041] 2. Manufacturing Method of Light-Emitting Device A manufacturing method of the light-emitting device 100 will be described below using the configuration shown in FIG. 1A as an example. The undercoat 124, overcoat 122, and buffer layer 126 can be formed using known materials and methods, and therefore detailed description thereof will be omitted. Briefly, the undercoat 124 and overcoat 122 may be formed on the substrate 120 using a sputtering method or a chemical vapor deposition (CVD) method as appropriate. The buffer layer 126 may be formed on the substrate 120 directly or via the overcoat 122 using a sputtering method, a CVD method, or an evaporation method. After forming the buffer layer 126, annealing may be performed to promote crystallization and increase the density of the buffer layer 126. The temperature at this time may be appropriately selected from the range of 500°C to 700°C, for example. The overcoat 122, undercoat 124, and buffer layer 126 are optional, and therefore, it is not necessary to form one or all of them.

[0042] (1) Formation of Functional Layer The functional layer is formed so that the light-emitting layer 106 is sandwiched between the hole transport layer 108 and the electron transport layer 104. When the light-emitting element 100 includes the electron injection layer 102 and the hole injection layer 110, the functional layer is formed so that the hole transport layer 108, the electron transport layer 104, and the light-emitting layer 106 are sandwiched between the electron injection layer 102 and the hole injection layer 110. Therefore, the electron injection layer 102, the electron transport layer 104, the light-emitting layer 106, the hole transport layer 108, and the hole injection layer 110 may be formed on the substrate 120 in this order, or the functional layers may be stacked in the reverse order.

[0043] Each functional layer constituting the light-emitting element 100 is formed by a sputtering method, which does not require high temperatures for epitaxial growth of compound semiconductors using a CVD method, and each functional layer can be formed at a temperature below the strain point of an amorphous glass substrate, for example.

[0044] A. When 0<y<1, 0<z<1 When the composition of the compound semiconductor contained in the functional layer satisfies 0<y and 0<z, i.e., when the functional layer contains aluminum, indium, and gallium, the functional layer can be formed by reactive co-sputtering using an aluminum (Al) target, an indium (In) target, or an aluminum-indium (AlIn) target, and a gallium nitride (GaN) target or a gallium (Ga) target, with nitrogen gas or the like as a reactive gas. Alternatively, the functional layer can be formed by reactive co-sputtering using an aluminum-indium (AlIn) target, and a gallium nitride (GaN) target or a gallium (Ga) target. When a gallium (Ga) target is used, the formed functional layer may be irradiated with nitrogen radicals. Alternatively, the functional layer may be formed by reactive co-sputtering using an indium nitride (InN) target or an aluminum-indium nitride (AlInN) target, and a gallium nitride (GaN) target. Alternatively, the functional layer may be formed by reactive sputtering of an aluminum-indium-gallium (AlInGa) target using nitrogen gas as the reactive gas. In this case, co-sputtering may be performed using an aluminum-indium (AlIn) target in addition. Alternatively, the functional layer may be formed by sputtering of an aluminum nitride-indium-gallium (AlInGaN) target using argon gas as the sputtering gas. Even in this case, co-sputtering may be performed using, for example, an aluminum nitride-indium (AlInN) target in addition. The aluminum-indium-gallium (AlInGaN) target may be formed, for example, by injecting molten aluminum and indium into the voids of a gallium nitride (GaN) target. Note that if the functional layer contains a dopant, a corresponding target containing the dopant may be used.

[0045] When using a target made of a single metal or a target made of a single metal nitride (i.e., an aluminum (Al) target, an indium (In) target, a gallium nitride (GaN) target, or an indium nitride (InN) target), the amount of material displaced from each target can be controlled by controlling the voltage between the target and the substrate 120, thereby controlling the composition of the functional layer. When using a target made of multiple metals or a target made of multiple metal nitrides (i.e., an aluminum-indium (AlIn) target, an aluminum-indium nitride-indium (AlInN) target, an aluminum-indium-gallium (AlInGa) target, or an aluminum-indium-gallium nitride (AlInGaN) target), the composition of each functional layer can be controlled by adjusting the composition of these targets.

[0046] (a) When 0<y<1, z=0 When the composition of the compound semiconductor contained in the functional layer satisfies 0<y<1 and z=0, i.e., when the functional layer contains aluminum and indium but not gallium, the functional layer can be formed by reactive co-sputtering using an aluminum (Al) target and an indium (In) target and nitrogen gas or the like as a reactive gas. Alternatively, the functional layer may be formed by reactive sputtering of an aluminum-indium (AlIn) target using nitrogen as a reactive gas, or by sputtering of an aluminum nitride-indium (AlInN) target using argon gas. As in the case of z≠0, when the functional layer contains a dopant, a corresponding target containing the dopant may be used. Furthermore, when a target made of a single metal or a target made of a single metal nitride is used, the composition of the functional layer can be controlled by controlling the voltage between the target and the substrate 120. When a target made of multiple metals or a target made of multiple metal nitrides is used, the composition of each functional layer can be controlled by adjusting the composition of these targets.

[0047] (c) When y = 0, 0 < z When the composition of the compound semiconductor contained in the functional layer satisfies y = 0 and 0 < z, i.e., when the functional layer contains indium and gallium but not aluminum, the functional layer can be formed by reactive co-sputtering using an indium (In) target or an indium nitride (InN) target and a gallium nitride (GaN) target, with nitrogen gas or the like as a reactive gas, or by co-sputtering using argon gas. As in the case of z ≠ 0, when the functional layer contains a dopant, a corresponding target containing the dopant can be used. Furthermore, the composition of the functional layer can be controlled by controlling the voltage between the target and the substrate 120.

[0048] (2) Anode and Cathode The anode 112 can be made of, for example, a metal such as palladium or gold, an alloy thereof, or a thin film of a conductive oxide that transmits visible light, such as indium-tin mixed oxide (ITO) or indium-zinc mixed oxide (IZO). The cathode 114 can be made of a metal such as aluminum, titanium, gold, silver, or indium, or an alloy thereof. Both the anode 112 and the cathode 114 can have a single-layer structure or can be a laminate of multiple films having different compositions. The anode 112 and the cathode 114 can be formed by applying a sputtering method, a vapor deposition method, or the like.

[0049] (3) Protective Film The protective film 130, which may have any configuration, may also be formed by, for example, a CVD method or a sputtering method. When the protective film 130 contains a polymer, it may be formed by an inkjet method, a spin coating method, a vapor deposition method, or the like. For example, a film containing a silicon-containing inorganic compound may be formed by a sputtering method or a CVD method, a film containing a polymer may be formed thereon by an inkjet method, a spin coating method, or a vapor deposition method, and a film containing a silicon-containing inorganic compound may be further formed thereon by a sputtering method or a CVD method. The opening may be formed by appropriately using photolithography.

[0050] As described above, each functional layer included in the light-emitting device 100 can be formed by sputtering. Therefore, epitaxial growth of compound semiconductors in the CVD method is not required, and therefore the high-temperature process required for epitaxial growth is not necessary. Therefore, not only single-crystal substrates such as single-crystal silicon substrates but also substrates containing amorphous glass can be used as the substrate 120. Furthermore, while indium tends to segregate in the CVD method, sputtering is a non-equilibrium process, which can suppress the segregation of specific elements. Therefore, the composition of the compound semiconductor in each functional layer is nearly uniform, which also contributes to the high crystallinity of the functional layer. Furthermore, depending on the composition of the compound semiconductor, functional layers can be formed without using a gallium nitride (GaN) target with a relatively high oxygen content. Therefore, functional layers with high purity and crystallinity can be formed, improving the reliability and performance of the light-emitting device 100.

[0051] Second Embodiment In this embodiment, a display device 200 including the light-emitting element 100 described in the first embodiment will be described. Descriptions of configurations that are the same as or similar to the configuration described in the first embodiment may be omitted.

[0052] FIG. 3 shows a schematic top view of a display device 200. The display device 200 includes a substrate 202. Various patterned thin films of insulators, conductors, and semiconductors are laminated on the substrate 202, thereby forming a plurality of pixels 204, drive circuits (scanning line drive circuit 206, signal line drive circuit 208), and various wirings (not shown) that electrically connect these. The plurality of pixels 204 are arranged in a matrix. A single region surrounding all of the pixels 204 is the display region, and the area outside the display region is called the peripheral region or frame region. A plurality of wirings extend from the drive circuit to one side of the substrate 202 and are exposed at the edge of the substrate 202 to form a plurality of terminals (not shown). The plurality of terminals are electrically connected to a connector 210 such as a flexible printed circuit (FPC) board, thereby supplying power and various signals to the drive circuit from an external circuit (not shown) via the connector 210. Instead of the signal line driver circuit 208 or together with the signal line driver circuit 208 , a driver IC 212 including an integrated circuit formed on a semiconductor substrate may be mounted on the substrate 202 or the connector 210 .

[0053] The plurality of pixels 204 are respectively connected to a scanning line driver circuit 206 and a signal line driver circuit 208. The scanning line driver circuit 206 and the signal line driver circuit 208 generate signals (video signals, gate signals, initialization signals, etc.) for displaying an image based on signals supplied from external circuits, and supply these signals together with power to the plurality of pixels 204. This controls the plurality of pixels 204, making it possible to display an image on the display area.

[0054] Each pixel 204 is formed with a pixel circuit connected to a scanning line drive circuit 206 and a signal line drive circuit 208, and is provided with a light-emitting element 100 electrically connected to the pixel circuit. The configuration of the pixel circuit can be determined arbitrarily, and the pixel circuit is formed by appropriately combining one or more transistors and one or more capacitive elements. The pixel circuit operates in response to a signal supplied from the drive circuit, thereby controlling the light-emitting element 100.

[0055] An example of a pixel 204 is shown in a schematic end view in FIG. 4 . While FIG. 4 illustrates a single transistor 220 as a pixel circuit, as described above, each pixel circuit may include multiple transistors and may further include one or more capacitors. The pixel circuit including the transistor 220 is provided directly on the substrate 202 or via an overcoat 214 of any configuration. The transistor 220 shown in FIG. 4 includes a gate electrode 222, a gate insulating film 224 on the gate electrode 222, a semiconductor film 226 on the gate insulating film 224, a first interlayer insulating film 228 and a second interlayer insulating film 240 on the semiconductor film 226, and a first terminal 232 and a second terminal 234 electrically connected to the semiconductor film 226 through openings provided in the first interlayer insulating film 228 and the second interlayer insulating film 240. The transistor 220 is a so-called bottom-gate transistor, but there is no limitation on the structure of the transistor 220. The transistor 220 may be a top-gate transistor or a transistor having a pair of gate electrodes above and below the semiconductor film 226.

[0056] A planarization film 242 can be provided on the second interlayer insulating film 240, and a pixel electrode 246 on the planarization film 242 is electrically connected to the second terminal 234 through an opening provided in the planarization film 242. A common electrode 248 to which a constant potential is supplied is provided on the planarization film 242. The display device 200 may further include a protective insulating film 250 that covers the ends of the pixel electrode 246 and the common electrode 248. These components can be formed by appropriately applying known materials and film formation methods, so detailed description thereof will be omitted.

[0057] A light-emitting element 100 is provided in each pixel 204. That is, each pixel 204 is formed by transferring a light-emitting element 100 formed on a substrate 120 to the pixel 204. Therefore, when the light-emitting element 100 has the structure shown in FIG. 1A , the cathode 114 and the anode 112 are electrically connected to the common electrode 248 and the pixel electrode 246, respectively, via bumps 252 that function as conductive adhesive. The bumps 252 are, for example, an alloy containing a metal such as silver or tin. Although not shown, the light-emitting element 100 may also include a buffer layer 126 on the electron injection layer 102.

[0058] As described in the first embodiment, in the light-emitting device 100, the difference in refractive index and lattice constant between the functional layers can be reduced due to the composition of the compound semiconductor contained in the functional layers. As a result, there are few lattice defects throughout the light-emitting device 100, and high crystallinity and extraction efficiency can be achieved. Therefore, by applying this embodiment, a display device that exhibits low power consumption and high reliability can be provided.

[0059] Third Embodiment In this embodiment, a lighting device 300 including the light-emitting element 100 described in the first embodiment will be described. Descriptions of configurations that are the same as or similar to the configurations described in the first and second embodiments may be omitted.

[0060] FIG. 5 is a schematic top view of an illumination device 300 according to an embodiment of the present invention. As shown in FIG. 5, the illumination device 300 includes a substrate 302 and one or more light sources 304 on the substrate 302. The light sources 304 may be arranged in any desired manner, such as in a matrix as shown in FIG. 5, or in a line or concentric circles (not shown). Alternatively, the light sources 304 may be arranged randomly. The shape of the substrate 302 is also arbitrary and may be determined appropriately taking into consideration the location where the illumination device 300 is installed and the design of the illumination device 300. For example, the planar shape of the substrate 302 may be circular, elliptical, or polygonal, including square and rectangular.

[0061] A driving circuit 306 connected to each light source 304 is provided on the substrate 302, and the driving circuit 306 is electrically connected to the light sources 304 by wiring (not shown). The driving circuit 306 is configured to receive a control command from a control device (not shown) via wire or wirelessly, and is configured to control the light sources 304 in accordance with the control command.

[0062] One or more of the light emitting elements 100 described in the first embodiment are disposed in each light source 304. For example, red, green, and blue light emitting elements 100 having different structures of the light emitting layer 106 may be disposed in each light source 304, or one or more light emitting elements 100 emitting the same light color may be disposed in each light source 304. By using red, green, and blue light emitting elements 100, it is possible to manufacture a lighting device that can provide light of various colors.

[0063] As described in the first embodiment, in the light-emitting device 100, the difference in refractive index and lattice constant between the functional layers can be reduced due to the composition of the compound semiconductor contained in the functional layers. As a result, there are few lattice defects throughout the light-emitting device 100, and high crystallinity and extraction efficiency can be achieved. Therefore, by applying this embodiment, it is possible to provide a lighting device that exhibits low power consumption and high reliability.

[0064] The above-described embodiments of the present invention can be combined as appropriate as long as they are not mutually inconsistent. Furthermore, even if a person skilled in the art appropriately adds or deletes components or modifies the design of a display device of each embodiment, or adds or omits processes or modifies conditions, such a display device is included in the scope of the present invention as long as it includes the gist of the present invention.

[0065] Even if there are other effects and advantages different from those brought about by the aspects of each of the above-mentioned embodiments, those that are clear from the description in this specification or that can be easily predicted by a person skilled in the art are naturally understood to be brought about by the present invention.

[0066] 100: Light-emitting element, 102: Electron injection layer, 104: Electron transport layer, 106: Light-emitting layer, 106-1: Low band gap layer, 106-2: High band gap layer, 108: Hole transport layer, 110: Hole injection layer, 112: Anode, 114: Cathode, 120: Substrate, 120: Target-substrate, 122: Overcoat, 124: Undercoat, 126: Buffer layer, 130: Protective film, 200: Display device, 202: Substrate, 204: Pixel, 206: Scanning line driving circuit, 2 08: signal line driving circuit, 210: connector, 212: driving IC, 214: overcoat, 220: transistor, 222: gate electrode, 224: gate insulating film, 226: semiconductor film, 228: first interlayer insulating film, 232: first terminal, 234: second terminal, 240: second interlayer insulating film, 242: planarizing film, 246: pixel electrode, 248: common electrode, 250: protective insulating film, 252: bump, 300: lighting device, 302: substrate, 304: light source, 306: driving circuit

Claims

1. A light-emitting device comprising: a hole transport layer; an electron transport layer; a light-emitting layer sandwiched between the hole transport layer and the electron transport layer; and an anode and a cathode electrically connected to the hole transport layer and the electron transport layer, respectively; wherein the hole transport layer, the electron transport layer, and the light-emitting layer are all made of In ｘ Al ｙ Ga ｚ N, wherein x+y+z=1±0.05, 0<x<1, 0≦y<1, 0≦z<1, and 0<z when y=0, and 0<y when z=0, and at least one of the following relationships is satisfied: (1) y in the hole transport layer and the electron transport layer is both larger than y in the light-emitting layer; and (2) z in the hole transport layer and the electron transport layer is both smaller than z in the light-emitting layer.

2. The light-emitting device according to claim 1, wherein the band gap of the compound semiconductor is 1.5 eV or more and 3.5 eV or less.

3. The light-emitting device according to claim 1, wherein the lattice constant of the compound semiconductor is 0.327 nm or more and 0.337 nm or less.

4. The light-emitting device according to claim 1, wherein the hole transport layer and the electron transport layer further comprise a p-type dopant and an n-type dopant, respectively.

5. The light-emitting device according to claim 1, wherein the light-emitting layer has a quantum well structure.

6. The light-emitting device according to claim 1, further comprising a hole injection layer located between the hole transport layer and the anode and containing the compound semiconductor, wherein at least one of the following relationships is satisfied: (3) y in the hole injection layer is smaller than y in the hole transport layer and is equal to or greater than y in the light-emitting layer; and (4) z in the hole injection layer is greater than z in the hole transport layer and is equal to or less than z in the light-emitting layer.

7. The light-emitting device according to claim 1, further comprising an electron injection layer located between the electron transport layer and the cathode and containing the compound semiconductor, wherein at least one of the following relationships is satisfied: (5) y in the electron injection layer is smaller than y in the electron transport layer and is equal to or larger than y in the light-emitting layer; and (6) z in the electron injection layer is larger than z in the electron transport layer and is equal to or smaller than z in the light-emitting layer.

8. The light-emitting device according to claim 1, wherein z=0 and 0<y<1.

9. The light-emitting device according to claim 8, wherein the lattice constant of the compound semiconductor is 0.327 nm or more and 0.344 nm or less.

10. The light-emitting device of claim 1, further comprising a buffer layer, wherein the electron transport layer or the hole transport layer is located between the buffer layer and the light-emitting layer, and the buffer layer comprises a material selected from aluminum indium nitride, aluminum nitride, aluminum oxide, gallium nitride, zinc oxide, silicon, germanium, titanium, aluminum, silver, nickel, and copper.

11. A method for manufacturing a semiconductor device comprising: forming a hole transport layer, an electron transport layer, and a light emitting layer sandwiched between the hole transport layer and the electron transport layer by a sputtering method; and forming an anode and a cathode electrically connected to the hole transport layer and the electron transport layer, respectively; wherein the hole transport layer, the electron transport layer, and the light emitting layer are all made of In. ｘ Al ｙ Ga ｚ N, wherein x+y+z=1±0.05, 0<x<1, 0≦y<1, 0≦z<1, and 0<z when y=0, and 0<y when z=0, and at least one of the following relationships is satisfied: (1) y in the hole transport layer and the electron transport layer is both larger than y in the light-emitting layer; and (2) z in the hole transport layer and the electron transport layer is both smaller than z in the light-emitting layer.

12. The manufacturing method according to claim 11, wherein the band gap of the compound semiconductor is 1.5 eV or more and 3.5 eV or less.

13. The manufacturing method according to claim 11, wherein the lattice constant of the compound semiconductor is 0.327 nm or more and 0.337 nm or less.

14. The method of claim 11, wherein the hole transport layer and the electron transport layer further comprise a p-type dopant and an n-type dopant, respectively.

15. The manufacturing method according to claim 11, wherein the light emitting layer has a quantum well structure.

16. The manufacturing method of claim 11, further comprising forming a hole injection layer containing the compound semiconductor by a sputtering method so as to be sandwiched between the anode and the hole transport layer, wherein at least one of the following relationships is satisfied: (3) y in the hole injection layer is smaller than y in the hole transport layer and is equal to or greater than y in the light-emitting layer; or (4) z in the hole injection layer is greater than z in the hole transport layer and is equal to or less than z in the light-emitting layer.

17. The manufacturing method according to claim 11, further comprising forming an electron injection layer containing the compound semiconductor by a sputtering method so as to be sandwiched between the cathode and the electron transport layer, wherein at least one of the following relationships is satisfied: (5) y in the electron injection layer is smaller than y in the electron transport layer and is equal to or larger than y in the light-emitting layer; (6) z in the electron injection layer is larger than z in the electron transport layer and is equal to or smaller than z in the light-emitting layer.

18. The method of claim 11, wherein z=0 and 0<y<1.

19. The manufacturing method according to claim 18, wherein the lattice constant of the compound semiconductor is 0.327 nm or more and 0.344 nm or less.

20. The method of claim 11, further comprising forming a buffer layer before forming the hole transport layer, the electron transport layer, and the light emitting layer, wherein the buffer layer comprises a material selected from aluminum indium nitride, aluminum nitride, aluminum oxide, gallium nitride, zinc oxide, silicon, germanium, titanium, aluminum, silver, nickel, and copper.

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