Light-emitting element, light-emitting device

Abstract

The light-emitting element (2) of the present invention sequentially includes an anode (4), a hole transport layer (6), a light-emitting layer (8) containing quantum dots (16), and a cathode (12). The hole transport layer (6) includes an n+-type semiconductor layer (24); and a p+-type semiconductor layer (26) that is adjacent to the n+-type semiconductor layer (24) and is disposed on the light-emitting layer (8) side with respect to the n+-type semiconductor layer (24).

Description

Technical Field

[0001] The present invention relates to a light-emitting element including quantum dots in a light-emitting layer, and a light-emitting device including the light-emitting element. Background Art

[0002] Compared with conductive inorganic substances such as metals and semiconductors, the carrier mobility of conductive organic substances is extremely low. In addition, at the connection interface between the conductive organic substance and the conductive inorganic substance, an electrochemical reaction occurs by energization. Therefore, it is required to use a conductive inorganic substance in the hole transport layer.

[0003] In Patent Document 1, a configuration using p-type GaN quantum dots in the hole transport layer is disclosed.

[0004] In Patent Document 2, a configuration using a p-type NiO thin film in the hole transport layer is disclosed.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Laid-Open Gazette "Tokukai 2005-268384" (published on September 29, 2005)

[0008] Patent Document 2: Japanese Patent Laid-Open Gazette "Tokukai 2012-23388" (published on February 2, 2012) Summary of the Invention

[0009] Technical Problem to be Solved by the Invention

[0010] However, in the configurations disclosed in Patent Documents 1 and 2, there is a mismatch in the ionization potential between the anode and the light-emitting layer, that is, the energy level of the highest occupied molecular orbital (HOMO). Such an energy level mismatch has a problem of hindering hole injection into the light-emitting layer.

[0011] The present invention has been made in view of the above problems, and an object thereof is to realize a light-emitting element capable of improving the hole injection efficiency into the light-emitting layer and a light-emitting device including the light-emitting element.

[0012] Technical Solution for Solving the Technical Problem

[0013] To solve the above problems, a light-emitting element according to one aspect of the present invention includes: an anode; a cathode; a light-emitting layer disposed between the anode and the cathode and including quantum dots; and a hole transport layer disposed between the light-emitting layer and the anode, the hole transport layer including: an n+-type semiconductor layer; and a p+-type semiconductor layer adjacent to the n+-type semiconductor layer and disposed on the light-emitting layer side with respect to the n+-type semiconductor layer.

[0014] Advantageous Effects

[0015] With the above configuration, a light-emitting element capable of improving the hole injection efficiency into the light-emitting layer can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic cross-sectional view of a light-emitting device according to Embodiment 1 of the present disclosure.

[0017] Figure 2 is a band diagram showing an example of the Fermi level or the band gap when each layer in the light-emitting element according to Embodiment 1 of the present disclosure is not stacked.

[0018] Figure 3 is a band diagram showing an example of the Fermi level or the band gap when each layer of the light-emitting element according to Embodiment 1 of the present disclosure is stacked.

[0019] Figure 4 is a band diagram of a light-emitting element according to a comparative method.

[0020] Figure 5 (a) of is a band diagram of each layer when a driving voltage is applied to the light-emitting element of Embodiment 1 of the present disclosure, Figure 5 (b) of is an enlarged band diagram near the depletion layer.

[0021] Figure 6 is a schematic cross-sectional view of a modified example of the light-emitting device according to Embodiment 1 of the present disclosure.

[0022] Figure 7 is a schematic cross-sectional view of another modified example of the light-emitting device according to Embodiment 1 of the present disclosure.

[0023] Figure 8 is a schematic cross-sectional view of a light-emitting device according to Embodiment 2 of the present invention.

[0024] Figure 9 is an enlarged view of a band diagram showing only the vicinity of the ionization potential near the connection interface between the hole transport layer and the light-emitting layer of the light-emitting element of Embodiment 1 of the present invention.

[0025] Figure 10 is an enlarged view of a band diagram showing only the vicinity of the ionization potential near the connection interface between the hole transport layer and the light-emitting layer of the light-emitting element of Embodiment 2 of the present invention.

[0026] Figure 11 is a schematic cross-sectional view of a modified example of the light-emitting device according to Embodiment 2 of the present disclosure.

[0027] Figure 12 is a schematic cross-sectional view of another modified example of the light-emitting device according to Embodiment 2 of the present disclosure. Detailed Embodiments

[0028] [Embodiment 1]

[0029] In this specification, when designating the group of elements by Roman numerals, the group is designated based on the nomenclature of the old CAS system. In addition, when designating the group of elements by Arabic numerals, the group is designated based on the nomenclature of the elements of the current IUPAC system. In this specification, when designating by connecting numerical ranges with " ", the designated numerical range is the range that is greater than or equal to the left end and less than the right end.

[0030] (Configuration of the Light-Emitting Device)

[0031] Figure 1 is a schematic cross-sectional view of the light-emitting device 1 according to this embodiment.

[0032] As shown in Figure 1 , the light-emitting device 1 according to this embodiment includes a light-emitting element 2 and an array substrate 3. The light-emitting device 1 has a structure in which the respective layers of the light-emitting element 2 are stacked on the array substrate 3, and a TFT (Thin Film Transistor) (not shown) is formed on the array substrate 3. In addition, in this specification, the direction from the light-emitting element 2 of the light-emitting device 1 to the array substrate 3 is described as "downward", and the direction from the array substrate 3 of the light-emitting device 1 to the light-emitting element 2 is described as "upward".

[0033] In the light-emitting element 2, a hole transport layer 6, a light-emitting layer 8, a hole transport layer 10, and a cathode 12 are sequentially provided on the anode 4 from the lower layer. The anode 4 of the light-emitting element 2 formed on the upper layer of the array substrate 3 is electrically connected to the TFT of the array substrate 3. In the light-emitting element of other embodiments, it may also be a light-emitting element in which a cathode is provided on the upper layer of the array substrate, and an electron transport layer, a light-emitting layer, a hole transport layer, and an anode are sequentially provided on the cathode.

[0034] The anode 4 and the cathode 12 include a conductive material and are electrically connected to the hole transport layer 6 and the electron transport layer 10, respectively.

[0035] Either the anode 4 or the cathode 12 is a transparent electrode. As the transparent electrode, for example, ITO, IZO, ZnO, AZO, or BZO, etc. can also be used and formed by a sputtering method or the like. In addition, either the anode 4 or the cathode 12 may contain a metal material. As the metal material, Al, Cu, Au, or Ag, etc. with a high reflectance of visible light is preferred.

[0036] The light-emitting layer 8 is a layer containing a plurality of quantum dots (semiconductor nanoparticles) 16. The light-emitting layer 8 may also be a layer in which a plurality of light-emitting layers are stacked. Here, the quantum dots 16 in the light-emitting layer 8 are as shown in Figure 1The arrangement shown does not need to be regular, and the quantum dots 16 can also be included in the light-emitting layer 8 in a disordered manner. The light-emitting layer 8 can be formed into a film from a dispersion liquid in which the quantum dots 16 are dispersed in a solvent such as hexane or toluene by a spin coating method or an inkjet method. A dispersion material such as thiol or amine can also be mixed into the dispersion liquid. The film thickness of the light-emitting layer 8 is preferably 5 nm to 50 nm.

[0037] The quantum dots 16 are light-emitting materials that have a valence band energy level and a conduction band energy level and emit light through the recombination of holes in the valence band energy level and electrons in the conduction band energy level. The light emission from the quantum dots 16 has a narrow spectrum due to the quantum confinement effect, and thus light emission with a relatively deep chromaticity can be obtained.

[0038] In the present embodiment, the quantum dots 16 have a core / shell structure, which has a core 18 and a shell 20 that is the outer shell of the core 18. The core 18 is a semiconductor material particle that contains a band gap within the band gap of the shell 20. The core 18 can contain a II-IV group type semiconductor material or a III-V group type semiconductor material. The shell 20 contains a II-IV group type semiconductor material.

[0039] For example, the quantum dots 16 can have CdSe in the core and ZnS in the shell. In addition, the quantum dots 16 can be appropriately selected from the materials used in this field. For example, they can also have a core / shell structure such as CdSe / CdS, InP / ZnS, ZnSe / ZnS, or CIGS / ZnS.

[0040] The particle size of the quantum dots 16 is about 3 to 15 nm. The wavelength of the light emission from the quantum dots 16 can be controlled by the particle size of the core 18. Therefore, by controlling the particle size of the core 18, the wavelength of the light emitted by the light-emitting device 1 can be controlled. In addition, the light-emitting layer 8 can also have a ligand that is coordinately bonded to the shell 20 of the quantum dots 16.

[0041] The electron transport layer 10 is a layer that transports electrons from the cathode 12 to the light-emitting layer 8. The electron transport layer 10 can also have a function of hindering hole transport. The electron transport layer 10 can contain, for example, ZnO, TiO2, Ta2O3, or SrTiO3, etc., and can also be formed into a film by a sputtering method. The film thickness of the electron transport layer 10 can adopt a conventionally known film thickness, and is preferably 10 to 100 nm.

[0042] The hole transport layer 6 is a layer that transports holes from the anode 4 to the light-emitting layer 8. In the present embodiment, the hole transport layer 6 sequentially includes an n+-type semiconductor layer 24, a p+-type semiconductor layer 26, and a p-type semiconductor layer 28 from the lower layer. In a light-emitting element of other embodiments, it may also be a light-emitting element in which a cathode is provided on the upper layer of the array substrate, and the hole transport layer on the light-emitting layer sequentially includes a p-type semiconductor layer, a p+-type semiconductor layer, and an n+-type semiconductor layer from the lower layer. The n+-type semiconductor layer 24 and the p+-type semiconductor layer 26 are connected to each other, and the p+-type semiconductor layer 26 and the p-type semiconductor layer 28 are connected to each other.

[0043] In the present specification, a "p-type" semiconductor refers to a semiconductor in positive semiconductors with a conductivity lower than that of metals. A "p+-type" semiconductor refers to a semiconductor in positive semiconductors with the same conductivity as metals. Similarly, an "n-type" semiconductor refers to a semiconductor in negative semiconductors with a conductivity lower than that of metals, and an "n+-type" semiconductor refers to a semiconductor in negative semiconductors with the same conductivity as metals. In addition, an "i-type" semiconductor refers to an intrinsic semiconductor.

[0044] The n+-type semiconductor layer 24 contains a first II-VI group semiconductor as a base material. The first II-VI group semiconductor may contain at least one or more selected from the group consisting of ZnS, ZnSe, CdS, CdSe, CdTe, ZnTe, ZnCdSe, ZnCdS, ZnCdTe, ZnSeS, CdSeS, ZnTeS, ZnTeSe, CdTeS, and CdTeSe.

[0045] The n+-type semiconductor layer 24 further contains a first dopant selected from group 13 elements and group 17 elements, whereby the conductivity type and carrier concentration of the n+-type semiconductor layer 24 can be controlled. The first dopant may contain at least one or more selected from group 13 elements such as Al, In, Ga, etc. and group 15 elements such as Cl, Br, I, etc. The addition amount of the first dopant is preferably 1.00E+17 [cm -3 to 1.00E+23 [cm -3 , more preferably 1.00E+18 [cm -3 to 1.00E+19 [cm -3 .

[0046] Alternatively, in the first II-VI semiconductor in the n+-type semiconductor layer 24, the II-group element is in excess with respect to the stoichiometry (stoichiometric composition), whereby the conductivity type and carrier concentration of the n+-type semiconductor layer 24 can be controlled. As an example, the first II-VI semiconductor contains Cd and a VI-group element, and the content ratio of Cd with respect to the above VI-group element is larger than the stoichiometric state. Such a first II-VI semiconductor may contain at least one selected from the group consisting of CdS, CdSe, CdTe, ZnCdSe, ZnCdS, ZnCdTe, CdSeS, CdTeS, and CdTeSe. The difference between the concentration of the II-group element and the concentration of the VI-group element is preferably 1.00E+17 [cm -3 to 1.00E+23 [cm -3 , more preferably 1.00E+18 [cm -3 to 1.00E+19 [cm -3 .

[0047] Alternatively, the n+-type semiconductor layer 24 contains a first dopant, and the II-group element is in excess in the first II-VI semiconductor of the n+-type semiconductor layer 24, whereby the conductivity type and carrier concentration of the n+-type semiconductor layer 24 can be controlled.

[0048] The thickness of the n+-type semiconductor layer 24 is such that tunneling effect is not caused and is such that a quantum well can be formed. The thickness of the n+-type semiconductor layer 24 is preferably 5 nm to 50 nm, more preferably 5 nm to 10 nm.

[0049] The n-type semiconductor layer 24 is formed, for example, by a sputtering method using a material pre-doped with an n-type impurity as a target on the anode 4 or on the p+-semiconductor 26. In addition, the n+-type semiconductor layer 24 can also be formed, for example, by coating an n-type semiconductor material made into nanoparticles. In addition, the n+-type semiconductor layer 24 can also be formed by doping an n-type impurity and performing the above sputtering method. Not limited thereto, the n+-type semiconductor layer 24 can be formed by any method.

[0050] The p+-type semiconductor layer 26 contains a second II-VI semiconductor as a base material. The second II-VI semiconductor may contain at least one or more selected from the group consisting of ZnS, ZnSe, CdS, CdSe, CdTe, ZnTe, ZnCdSe, ZnCdS, ZnCdTe, ZnSeS, CdSeS, ZnTeS, ZnTeSe, CdTeS, and CdTeSe. The second II-VI semiconductor of the p+-type semiconductor layer 26 is preferably a semiconductor composed of the same elemental combination as the first II-VI semiconductor of the n+-type semiconductor layer 24. For example, when the first II-VI semiconductor of the n+-type semiconductor layer 24 is ZnS, the second II-VI semiconductor of the p+-type semiconductor layer 26 is also ZnS. In addition, when the first II-VI semiconductor of the n+-type semiconductor layer 24 is ZnCdS, the second II-VI semiconductor of the P+-type semiconductor layer 26 is also ZnCdS.

[0051] The p+-type semiconductor layer 26 further contains a second dopant selected from Group 1 elements, Group Ⅺ elements, and Group 15 elements, whereby the conductivity type and carrier concentration of the p+-type semiconductor layer 26 can be controlled. The second dopant may contain one or more selected from Group 15 elements such as N and P, transition metals with an electron configuration of 4s1 such as Cu and Ag, and alkali metals such as Li and Na. The addition amount of the second dopant is preferably 1.00E+17 [cm -3 to 1.00E+23 [cm -3 , more preferably 1.00E+18 [cm -3 to 1.00E+19 [cm -3 . The addition amount of the second dopant is preferably on the same order as the addition amount of the first dopant.

[0052] The thickness of the P+-type semiconductor layer 26 is such that a tunneling effect does not occur, preferably 5 nm to 50 nm, more preferably 4.5 nm to 10 nm. Moreover, the thickness of the p+-type semiconductor layer 26 is preferably on the same order as the thickness of the n+-type semiconductor layer 24. Specifically, it is preferably 80% to 125% of the thickness of the n+-type semiconductor layer 24, more preferably 90% to 100%.

[0053] The p+-type semiconductor layer 26 is formed, for example, by a sputtering method using a material pre-doped with a p-type impurity as a target, on the n+-type semiconductor layer 24 or on the p-type semiconductor layer 28. Alternatively, the p+-type semiconductor layer 26 can be formed, for example, by coating a p-type semiconductor material in the form of nanoparticles. Additionally, the p+-type semiconductor layer 26 can also be formed by doping with a p-type impurity and then performing the above-mentioned sputtering method. Not limited thereto, the p+-type semiconductor layer 26 can be formed by any method. Further, in a light-emitting element of other embodiments, the p-type semiconductor layer 28 can be omitted, and the P+-type semiconductor layer 26 can be formed by film formation on the n+-type semiconductor layer 24 or on the light-emitting layer 8.

[0054] Between the p+-type semiconductor layer 26 and the n+-type semiconductor layer 24, a thin insulating layer through which electrons or holes can tunnel, such as a passivation film, can be formed. Additionally, in a light-emitting element of other embodiments, a thin insulating layer through which electrons or holes can tunnel, such as a passivation film, can also be formed between the p+-type semiconductor layer 26 and the p-type semiconductor layer 28 or the light-emitting layer 8. In this specification, "adjacent" includes both a configuration of direct connection and a configuration of connection with a tunneling-capable thin layer interposed therebetween.

[0055] The p-type semiconductor layer 28 contains a third II-VI group semiconductor as a base material. The third II-VI group semiconductor can include at least one or more selected from the group consisting of ZnS, ZnSe, CdS, CdSe, CdTe, ZnTe, ZnCdSe, ZnCdS, ZnCdTe, ZnSeS, CdSeS, ZnTeS, ZnTeSe, CdTeS, and CdTeSe. The third II-VI group semiconductor of the p-type semiconductor layer 28 is preferably a semiconductor composed of the same elemental combination as the second II-VI group semiconductor of the p+-type semiconductor layer 26.

[0056] The p-type semiconductor layer 28 further includes a third dopant selected from group 1 elements, group 11 elements, and group 15 elements, whereby the conductivity type and carrier concentration of the p-type semiconductor layer 28 can be controlled. The third dopant can contain one or more selected from group 15 elements such as N and P, transition metals with an electron configuration of 4s1 such as Cu and Ag, and alkali metals such as Li and Na. The third dopant preferably contains the same elements as the second dopant. The concentration of the third dopant in the p-type semiconductor layer 28 relative to the third II-VI group semiconductor is lower than the concentration of the second dopant in the p+-type semiconductor layer 26 relative to the second II-VI group semiconductor. As a result, the carrier concentration of the p-type semiconductor layer 28 is lower than the carrier concentration of the p+-type semiconductor layer 26. The addition amount of the third dopant is preferably 1.00E+18 [cm -3 to 1.00E+20 [cm -3 , more preferably 1.00E+18 [cm -3~1.00E+19[cm -3 。

[0057] The thickness of the p-type semiconductor layer 28 is preferably thinner than the thicknesses of the n+-type semiconductor layer 24 and the p+-type semiconductor layer 26 and is at a level that does not cause a tunneling effect. Specifically, it is preferably 5 nm to 20 nm, more preferably 5 nm to 8 nm. In addition, in order to suppress an increase in resistance, the overall thickness of the hole transport layer 6 is preferably 100 nm or less, more preferably 75 nm or less.

[0058] The p-type semiconductor layer 28 can also be formed by various methods in the same manner as the p+-type semiconductor layer 26. The method for forming the p-type semiconductor layer 28 can be the same as or different from the method for forming the p+-type semiconductor layer 26.

[0059] Herein, the II-IV group semiconductor material contained in the shell 20 is used as the fourth II-IV group semiconductor material. At this time, the first to third II-IV group semiconductors can be composed of the same element combination as the fourth II-IV group semiconductor or can have a group II element belonging to a lower period in the periodic table than the group II element contained in the fourth II-IV group semiconductor. The second II-IV group semiconductor of the p+-type semiconductor layer 26 is preferably composed of the same element combination as the fourth II-IV group semiconductor. On the other hand, the first II-IV group semiconductor of the n+-type semiconductor layer 24 preferably has a group II element belonging to a lower period in the periodic table than the group II element contained in the fourth II-IV group semiconductor. For example, when the shell 20 contains Zn, the n+-type semiconductor layer 24 preferably contains Cd which is lower than Zn.

[0060] As described above, (i) the second II-VI semiconductor of the p+-type semiconductor layer 26 is preferably composed of the same elemental combination as the first II-VI semiconductor of the n+-type semiconductor layer 24, and (ii) the third II-VI semiconductor of the p-type semiconductor layer 28 is preferably composed of the same elemental combination as the second II-VI semiconductor of the p+-type semiconductor layer 26. Therefore, the first to fourth II-IV type semiconductors are preferably any one of the following three combinations. In the first combination, the first to third II-IV type semiconductors are composed of the same elemental combination as the fourth II-VI semiconductor. In the second combination, the first to third II-IV type semiconductors are composed of the same elemental combination as each other, and have a Group II element belonging to a lower period in the periodic table compared to the Group II element contained in the fourth II-IV type semiconductor. In the third combination, the first II-IV type semiconductor has a Group II element belonging to a lower period in the periodic table compared to the Group II element contained in the fourth II-IV type semiconductor, and the second to third II-IV type semiconductors are composed of the same elemental combination as the fourth II-VI semiconductor.

[0061] (Energy bands of the light-emitting element)

[0062] Next, with reference to Figure 2 the energy bands in each layer of the light-emitting element 2 of the present embodiment will be described.

[0063] Figure 2 FIG. is a band diagram showing an example of the Fermi level or band gap of each layer of the light-emitting element 2 according to the present embodiment before the layers are stacked.

[0064] In addition, in the band diagrams in this specification, the energy levels based on the vacuum level of each layer are shown. Further, in the band diagrams in this specification, the Fermi level or band gap of the components corresponding to the attached component numbers are shown. For the anode 4 and the cathode 12, the Fermi levels are shown, and for the hole transport layer 6, the light-emitting layer 8, and the electron transport layer 10, the band gaps from the electron affinity to the ionization potential are shown. Here, regarding the hole transport layer 6, it is divided into the n+-type semiconductor layer 24, the p+-type semiconductor layer 26, and the p-type semiconductor layer 28, and the respective band gaps are shown, and the respective Fermi levels 24f, 26f, and 28f are shown. Further, for the light-emitting layer 8, it is divided into the core 18 and the shell 20, and the respective band gaps are shown.

[0065] In the present embodiment, for example, when the n+-type semiconductor layer 24, p+-type semiconductor layer 26, and p-type semiconductor layer 28 of the hole transport layer 6 all contain ZnS as the base material, the ionization potential of each of the layers 24, 26, and 28 of the hole transport layer 6 is 5.2 eV, and the electron affinity is 3.2 eV. Further, in the present embodiment, for example, when the electron transport layer 10 contains ZnO, the ionization potential of the electron transport layer 10 is 7.0 eV, and the electron affinity of the electron transport layer 10 is 3.8 eV. Further, in the present embodiment, for example, when the shell 20 contains ZnS, the ionization potential in the shell 20 is 5.2 eV, and the electron affinity is 3.2 eV.

[0066] Here, Examples 1 to 10 in Table 1 show examples of combinations of materials for each layer in the present embodiment. Further, the columns of "ionization potential" and "electron affinity" in Table 1 are shown in units of eV with all of their energy levels being the vacuum level as the reference. Further, in Table 1, the values in the state where each layer is not stacked are described.

[0067] [Table 1]

[0068]

[0069] In Table 1, the columns of "material", "ionization potential", and "electron affinity" under the "base material" column of the "hole transport layer" show the material serving as the base material contained in the n+-type semiconductor layer 24, p+-type semiconductor layer 26, and p-type semiconductor layer 28 of the hole transport layer 6 in each example, and the ionization potential and electron affinity of the material. The columns of "material" and "concentration" under the "n+-type semiconductor layer" column of the "dopant" of the "hole transport layer" respectively represent the material of the first dopant of the n+-type semiconductor layer 24 in each example and the concentration of the first dopant doped into the base material of the n+-type semiconductor layer 24. Similarly, the columns of "material" and "concentration" under the "p+-type semiconductor layer" column of the "dopant" of the "hole transport layer" respectively represent the material of the second dopant of the p+-type semiconductor layer 26 in each example and the concentration of the second dopant doped into the base material of the p+-type semiconductor layer 26. Similarly, the columns of "material" and "concentration" under the "p-type semiconductor layer" column of the "dopant" of the "hole transport layer" respectively represent the material of the third dopant of the p-type semiconductor layer 28 in each example and the concentration of the third dopant doped into the base material of the p-type semiconductor layer 28. The columns of "material", "ionization potential", and "electron affinity" under the "shell" column of the "quantum dot" represent the material of the shell 20 covering the core 18 of the quantum dot 16 in each example, the ionization potential of the material, and the electron affinity.

[0070] In addition, in Embodiments 1 to 10 shown in Table 1, the materials included as the base materials in the n+-type semiconductor layer 24, p+-type semiconductor layer 26, and p-type semiconductor layer 28 are the same as the material of the shell 20, but the scope of the present invention is not limited thereto. The materials included as the base materials in the n+-type semiconductor layer 24, p+-type semiconductor layer 26, and p-type semiconductor layer 28 may be different from the material of the shell 20 or may be different from each other.

[0071] Figure 3 It is an energy band diagram showing an example of the Fermi level or energy band gap when each layer of the light-emitting element 2 of the present embodiment is stacked.

[0072] In the present embodiment, in the light-emitting element 2 in which each layer is stacked, the Fermi level or band gap of the anode 4, light-emitting layer 8, electron transport layer 10, and cathode 12 hardly changes from the respective energy levels or band gaps in the single state. However, in the hole transport layer 6 in the light-emitting element 2 in which each layer is stacked, the Fermi level and band gap change due to adjacency. In the hole transport layer 6, the n+-type semiconductor layer 24 and the p+-type semiconductor layer 26 are adjacent to each other in a pn connection, and the p+-type semiconductor layer 26 and the p-type semiconductor layer 28 are adjacent to each other. Due to the above adjacency, as Figure 3 shown, the electron affinity and ionization potential of each of the n+-type semiconductor layer 24, p+-type semiconductor layer 26, and p-type semiconductor layer 28 change. At the same time, a depletion layer 30 is generated across the n+-type semiconductor layer 24 and the p+-type semiconductor layer 26, and a depletion layer 32 is generated across the p+-type semiconductor layer 26 and the p-type semiconductor layer 28.

[0073] Specifically, due to the above adjacency, electrons diffuse in large quantities from the n+-type semiconductor layer 24 to the p+-type semiconductor layer 26, and holes diffuse in large quantities from the p+-type semiconductor layer 26 to the n+-type semiconductor layer 24. In addition, electrons diffuse from the p-type semiconductor layer 28 to the p+-type semiconductor layer 26, and holes diffuse from the p+-type semiconductor layer 26 to the p-type semiconductor layer 28. These diffusions continue until a thermal equilibrium state is reached in which the Fermi levels 24f, 26f, and 28f of the n+-type semiconductor layer 24, p+-type semiconductor layer 26, and p-type semiconductor layer 28 are in agreement with each other.

[0074] The carrier densities of both the n+-type semiconductor layer 24 alone and the p+-type semiconductor layer 26 alone are very large. Therefore, the adjacency of the n+-type semiconductor layer 24 and the p+-type semiconductor layer 26 causes significant changes in both the electron affinity and ionization potential of the n+-type semiconductor layer 24 and the p+-type semiconductor layer 26.

[0075] Specifically, the electron affinity and ionization potential of the n+-type semiconductor layer 24 change significantly from the interface between the n+-type semiconductor layer 24 and the p+-type semiconductor layer 26 to the interface between the n+-type semiconductor layer 24 and the anode 4. Similarly, the electron affinity and ionization potential of the p+-type semiconductor layer 26 change significantly from the interface between the n+-type semiconductor layer 24 and the p+-type semiconductor layer 26 to the interface between the p+-type semiconductor layer 26 and the p-type semiconductor layer 28.

[0076] The carrier density of the p-type semiconductor layer 28 alone is very small compared to the carrier density of the p+-type semiconductor layer 26 alone. Therefore, the adjacency of the p+-type semiconductor layer 26 and the p-type semiconductor layer 28 changes the respective electron affinities and ionization potentials of the p+-type semiconductor layer 26 and the p-type semiconductor layer 28, causing a more significant change in the p+-type semiconductor layer 26 than in the p-type semiconductor layer 28.

[0077] Specifically, the electron affinity and ionization potential of the p+-type semiconductor layer 26 change significantly from the interface between the p+-type semiconductor layer 26 and the p-type semiconductor layer 28 toward the interface between the n+-type semiconductor layer 24 and the p+-type semiconductor layer 26. In contrast, the electron affinity and ionization potential of the p-type semiconductor layer 28 change only slightly near the interface between the p+-type semiconductor layer 26 and the p-type semiconductor layer 28.

[0078] Table 2 is a table showing the amounts of change in the energy levels of the Fermi levels 24f and 26f based on the above-mentioned diffusion, and the ionization potential and electron affinity in the thermally balanced state, for the n+-type semiconductor layer 24 and the p+-type semiconductor layer 26 in the light-emitting element 2 of the present embodiment. In addition, the units of the values in Table 2 are all eV, and each example in Table 2 corresponds to each example in Table 1.

[0079] [Table 2]

[0080]

[0081] As shown in Table 2, in any example, the ionization potential and electron affinity of the n+-type semiconductor layer 24 after stacking are greater than those of the P+-type semiconductor layer 26 after stacking, compared to before stacking.

[0082] (Effect of the light-emitting element)

[0083] Comparison Figure 4 The energy band diagram of the light-emitting element 102 of the comparative method shown is compared with Figure 3 , Figure 5 The energy band diagram of the light-emitting element 2 of the present embodiment shown to illustrate the effect of the light-emitting element 2 of the present embodiment.

[0084] Figure 4The light-emitting element 102 of the comparison method shown differs from the Figure 3 configuration of the light-emitting element 2 of the present embodiment shown only in that it includes a hole transport layer 106 of the comparison method instead of the hole transport layer 6 of the present embodiment. The hole transport layer 106 of the comparison method is a single layer of a p-type semiconductor layer containing a metal oxide semiconductor (NiO in a stoichiometric state), has an ionization potential of 5.6 eV, and an electron affinity of 2.1 eV. Therefore, except for the hole transport layer 106, the energy levels of the respective layers of the light-emitting element 102 of the comparison method can be regarded as being the same as those of the monomers before laminating the respective layers of the light-emitting element 2 of the present embodiment.

[0085] When a potential difference is generated between the anode 4 and the cathode 12 of the light-emitting element related to the comparison method, holes are injected from the anode 4 side into the hole transport layer 106, and electrons are injected from the cathode 12 side into the electron transport layer 10. Thereafter, the holes injected into the hole transport layer 106 and the electrons injected into the electron transport layer 10 reach the core 18 via the shell 20 of the quantum dots 16 in the light-emitting layer 8. In the core 18, excitons are generated by the recombination of holes and electrons.

[0086] Here, when the electron affinity of the hole transport layer 106 is greater than the electron affinity of the shell 20, as shown by the arrow E1 in Figure 4 , the electrons further transmitted to the hole transport layer 106 via the shell 20 are blocked. As a result, the concentration of electrons remaining in the light-emitting layer 8 becomes higher, and the luminous efficiency is improved.

[0087] However, in the comparison method, the difference between the Fermi level of the anode 4 and the ionization potential of the hole transport layer 106 is large. Therefore, in the figure, as shown by the arrow H1, the barrier for hole injection from the anode 4 to the hole transport layer 106 becomes relatively large.

[0088] Furthermore, in the comparison method, the ionization potential of the hole transport layer 106 is greater than the ionization potential of the shell 20. Therefore, the concentration of holes in the hole transport layer 106 is relatively low. Therefore, in the light-emitting element of the comparison method, in Figure 4 , the hole injection efficiency from the hole transport layer 106 to the shell 20 shown by the arrow H2 is not improved.

[0089] Therefore, in the light-emitting element 102 of the comparison method, due to the above-described hole injection barrier, the injection efficiency of holes into the light-emitting layer 8 is reduced. As a result, the carrier balance in the light-emitting layer 8 deteriorates, and the non-luminous process in the light-emitting layer 8 increases. Therefore, the external quantum efficiency of the entire light-emitting element 102 deteriorates.

[0090] If only the efficiency of hole injection is improved, the material of the hole transport layer 106 can be a material with a small band gap. However, if the band gap of the hole transport layer 106 is simply reduced, it is difficult for the hole transport layer 106 to block the electron transport from the light-emitting layer 8 to the anode 4, and thus the external quantum efficiency of the light-emitting element 102 may not be improved sometimes.

[0091] Moreover, if the band gap of the hole transport layer 106 is simply reduced, only a limited improvement in the hole injection efficiency can be achieved. This is because the room for improvement in the hole transport efficiency from the anode 4 to the light-emitting layer 8 is restricted by the difference in ionization energies between the anode 4 and the light-emitting layer 8. The larger the difference in ionization potentials between the layers from the anode 4 to the light-emitting layer 8, the larger the sum of such differences, and the lower the hole transport efficiency from the anode 4 to the light-emitting layer 8. The anode 4 and the light-emitting layer 8 have very different ionization energies.

[0092] In the light-emitting element 2 of the present embodiment, hole transport from the anode 4 to the light-emitting layer 8 is not performed. Instead, in the light-emitting element 2 of the present embodiment, as Figure 2 shown, a combination of electron transport from the p+-type semiconductor layer 26 of the hole transport layer 6 to the anode 4 and hole transport from the p+-type semiconductor layer 26 of the hole transport layer 6 to the light-emitting layer 8 is performed. Hereinafter, this will be described in detail.

[0093] Figure 5 The energy band diagrams of each layer when a driving voltage is applied to the light-emitting element 2 according to the present embodiment are shown on the left, and the energy band diagrams near the depletion layer 30 and the depletion layer 32 are shown on the right. In the light-emitting element 2 according to the present embodiment, similar to the light-emitting element 102 according to the comparative mode, hole and electron transport occur, and excitons are generated in the light-emitting layer 8. However, hole injection from the hole transport layer 6 to the shell 20 is caused by the resonant tunneling effect generated in the hole transport layer 6. A positive voltage is applied to the anode 4 and a negative voltage is applied to the cathode 12 for the driving voltage of the light-emitting element 2. Such a driving voltage is a reverse bias with respect to the adjacency of the n+-type semiconductor layer 24 and the p+-type semiconductor layer 26, and a forward bias with respect to the adjacency of the p+-type semiconductor layer 26 and the p-type semiconductor layer 28.

[0094] In the present embodiment, as Figure 3 shown, through the pn junction of the n+-type semiconductor layer 24 and the p+-type semiconductor layer 26, the electron affinity of the n+-type semiconductor layer 24 is reduced, and the electron affinity of the p+-type semiconductor layer 26 is increased. As Figure 5 (a) of shows, during the application of the driving voltage, the electron affinity of the n+-type semiconductor layer 24 is further reduced, and the difference between the electron affinity of the n+-type semiconductor layer 24 and the electron affinity of the p+-type semiconductor layer 26 is very large. Therefore, through Figure 5The electron transfer efficiency from the p+-type semiconductor layer 26 to the n+-type semiconductor layer 24 shown by the arrow E3 in (a) is reduced due to the level mismatch of the electron affinity. In addition, since the carriers in the p+-type semiconductor layer 26 and the p-type semiconductor layer 28 are holes, the electron transfer from the shell 20 shown by the arrow E4 in (a) through the p-type semiconductor layer 28 and the p+-type semiconductor layer 26 must overcome the potential barrier at the interface, so it is difficult. Therefore, the hole transport layer 6 maintains the function of blocking the electron transfer from the light-emitting layer 8 to the anode 4. Figure 5 The electron transfer from the shell 20 shown by the arrow E4 in (a) through the p-type semiconductor layer 28 and the p+-type semiconductor layer 26 must overcome the potential barrier at the interface, so it is difficult. Therefore, the hole transport layer 6 maintains the function of blocking the electron transfer from the light-emitting layer 8 to the anode 4.

[0095] In the present embodiment, as Figure 3 shown, by the pn junction of the n+-type semiconductor layer 24 and the p+-type semiconductor layer 26, the electron affinity of the n+-type semiconductor layer 24 is reduced, and the ionization potential of the p+-type semiconductor layer 26 is increased. As a result, the energy level difference between the electron affinity of the n+-type semiconductor layer 24 and the ionization potential of the p+-type semiconductor layer 26 after lamination is reduced compared with that before lamination. As Figure 5 shown in (a), during the application of the driving voltage, the electron affinity of the n+-type semiconductor layer 24 is further reduced. As a result, the energy level difference between the electron affinity of the n+-type semiconductor layer 24 and the ionization potential of the p+-type semiconductor layer 26 is reversed, and the conduction band level of the n+-type semiconductor layer 24 and the valence band level of the p+-type semiconductor layer 26 are staggered. The depletion layer 30 becomes thin enough to cause the tunneling effect. Through this staggering and this tunneling effect, it is easy to generate Figure 5 the electron extraction represented by the arrow E5 in (a) and (b). Figure 5 The arrows E5 in (a) and (b) represent the extraction of electrons in the valence state level of the p+-type semiconductor layer 26 being pulled out to the conduction band level of the n+-type semiconductor layer 24 through the tunneling depletion layer 30. As a result of this extraction, holes are generated in the p+-type semiconductor layer 26.

[0096] In the present embodiment, as Figure 5 shown in (a) and (b), the depletion layer 32 across the p+-type semiconductor layer 26 and the p-type semiconductor layer 28 is not eliminated even during the application of the driving voltage. As a result, only the hole injection from the p+-type semiconductor layer 26 to the p-type semiconductor layer 28 shown by the arrow H3 in (a) and (b) is difficult. Figure 5 shown in (a) and (b), the depletion layer 32 across the p+-type semiconductor layer 26 and the p-type semiconductor layer 28 is not eliminated even during the application of the driving voltage. As a result, only the hole injection from the p+-type semiconductor layer 26 to the p-type semiconductor layer 28 shown by the arrow H3 in (a) and (b) is difficult.

[0097] On the other hand, the depletion layers 30 and 32 are thin enough to cause tunneling effects, and as described above, the thickness of the n+-type semiconductor layer 24 is such that quantum wells can be formed. Thus, a resonant tunneling effect can be generated between the n+-type semiconductor layer 24 and the p-type semiconductor layer 28. Moreover, during the application of a driving voltage, the valence band energy level of the p-type semiconductor layer 28 is staggered with the conduction band energy level of the n+-type semiconductor layer 24, similarly to the valence band energy level of the p+-type semiconductor layer 26. Therefore, through the resonant tunneling effect, electrons are easily pulled out from the valence band energy level of the p-type semiconductor layer 28 shown by the arrow E6 in (a) and (b) of Figure 5 to the conduction band energy level of the n+-type semiconductor layer 24. As a result of this pulling out, holes are generated in the p-type semiconductor layer 28.

[0098] In addition, the ionization potential of the p-type semiconductor layer 28 and the ionization potential of the shell 20 are substantially the same. Therefore, as shown by the arrow H4 in (a) of Figure 5 , holes are also easily injected from the p-type semiconductor layer 28 into the shell 20.

[0099] In the present embodiment, as shown by the arrow E7 in (a) of Figure 5 , electrons are transmitted from the n+-type semiconductor layer 24 to the anode 4. Since this transmission is the transmission of electrons from an n+-type semiconductor to a metal, it is easy.

[0100] As described above, Figure 5 the electron transmission shown by the arrow E7 in (a) of Figure 5 the pulling out of electrons shown by the arrows E6 in (a) and (b) of Figure 5 , and the hole injection shown by the arrow H4 in (a) of

[0101] are all very efficient. Therefore, the electron transmission efficiency from the p+-type semiconductor layer 26 of the hole transport layer 6 to the anode 4 and the hole transport efficiency from the p+-type semiconductor layer 26 of the hole transport layer 6 to the light-emitting layer 8 are also very high. In addition, the hole transport layer 6 maintains the function of blocking the electron transmission from the light-emitting layer 8 to the anode 4.

[0102] In the present embodiment, in any one of the embodiments, the materials contained as the base materials of the n+-type semiconductor layer 24, the p+-type semiconductor layer 26, and the p-type semiconductor layer 28 of the hole transport layer 6 are the same materials as those of the shell 20. However, the material of the n+-type semiconductor layer 24 is preferably a II-IV group semiconductor material having a group II element belonging to a period lower in the periodic table than the group II element contained in the material of the shell 20. According to this configuration, the II-IV group semiconductor as the n+-type semiconductor layer 24 contains an element having a larger ionic radius than the material of the shell 20. Therefore, in the n-type semiconductor layer 24, the binding of the valence electron orbits is relatively weak, and the energy at the top of the valence band, that is, the ionization potential becomes smaller. As a result, the valence band energy levels of the p+-type semiconductor layer 26 and the p-type semiconductor layer 28 are more staggered, and the pulling out of electrons represented by the arrows E5 and E6 in (a) and (b) of Figure 5 is more likely to occur at the conduction band energy level of the n+-type semiconductor layer 24.

[0103] (Modification example)

[0104] The light-emitting device 1 according to the present embodiment can be variously changed and improved.

[0105] The n+-type semiconductor layer 24 may contain a first metal oxide semiconductor in place of the first II-VI group semiconductor. The first metal oxide semiconductor may contain an oxide of any element in Group IIA, Group VIB, and Group VIIIB. That is, the first metal oxide semiconductor may contain an oxide of any element in Groups 6, 8 to 10, and 12. For example, the first metal oxide semiconductor may be MgO, Cr2O3, or NiO.

[0106] The first metal oxide semiconductor has an oxygen atom deficiency relative to the stoichiometric state, thereby controlling the conductivity type and carrier concentration of the n+-type semiconductor layer 24. The oxygen deficiency amount is preferably 1.00E+17 [cm -3 to 1.00E+23 [cm -3 , and more preferably 1.00E+18 [cm -3 to 1.00E+19 [cm -3 relative to the metal element.

[0107] The p+-type semiconductor layer 26 may include a second metal oxide semiconductor instead of the second II-VI group semiconductor. The second metal oxide semiconductor includes an oxide of any one element in Group IIA, Group VIB, and Group VIIIB. That is, the second metal oxide semiconductor contains an oxide of any one element in Group 6, Groups 8 to 10, and Group 12. For example, the second metal oxide semiconductor may be MgO, Cr2O3, NiO, or the like. In addition, the second metal oxide semiconductor may also include the same metal oxide semiconductor composed of the same combination of elements as the metal oxide semiconductor included in the first metal oxide semiconductor.

[0108] The second metal oxide semiconductor has an excess of oxygen atoms relative to the stoichiometric state, thereby controlling the conductivity type and carrier concentration of the p+-type semiconductor layer 26. The excess amount of oxygen is preferably 1.00E+17 [cm -3 to 1.00E+23 [cm -3 , more preferably 1.00E+18 [cm -3 to 1.00E+19 [cm -3 .

[0109] Figure 6 and Figure 7 are schematic cross-sectional views of a modification of the light-emitting device 1 according to the present embodiment. As Figure 6 shown, the light-emitting element 2 of the present embodiment may not include the p-type semiconductor layer 28. Alternatively, as Figure 7 shown, the light-emitting element 2 of the present embodiment may include an i-type semiconductor layer 38 including a third II-VI group semiconductor instead of the p-type semiconductor layer 28. However, the light-emitting element 2 preferably includes the p-type semiconductor layer 28. The reason is that, compared with the configuration in which the p+-type semiconductor layer 26 is in contact with the case 20, in the configuration in which the p-type semiconductor layer 28 is in contact with the case 20, the difference in ionization energy near the connection interface between the hole transport layer 6 and the case 20 is smaller. Another reason is that the resistance of the p-type semiconductor layer 28 is smaller than that of the i-type semiconductor layer 38, that is, the hole transport efficiency of the p-type semiconductor layer 28 is higher than that of the i-type semiconductor layer 38.

[0110] [Embodiment 2]

[0111] Figure 8 is a schematic cross-sectional view of the light-emitting device 1 according to the present embodiment. The light-emitting device 1 of the present embodiment has the same configuration as the light-emitting device 1 of the previous embodiment, except that a non-conductive layer 22 is provided between the hole transport layer 6 and the light-emitting layer 8.

[0112] The non-conductive layer 22 contains a non-conductor, which refers to an object that hardly has carriers and significantly lacks conductivity. Non-conductors are usually also referred to as insulators or dielectrics. Specifically, for example, the non-conductive layer 22 includes at least one selected from the group consisting of Al2O3, SiN, SiO2, SiON, and Cr2O3. The non-conductive layer 22 is in contact with both the hole transport layer 6 and the light-emitting layer 8.

[0113] In the light-emitting element 2 according to the present embodiment, similar to the light-emitting element 2 according to the previous embodiment, holes and electrons are transported, and excitons are generated in the light-emitting layer 8. However, for the hole injection from the hole transport layer 6 to the shell 20, due to the tunneling effect generated in the non-conductive layer 22, holes are generated by tunneling through the non-conductive layer 22.

[0114] Comparison Figure 9 The energy band diagram of the light-emitting element 2 according to the previous embodiment shown in Figure 10 and the energy band diagram of the light-emitting element 2 according to the present embodiment shown in Figure 9 and Figure 10 are enlarged views that only extract the vicinity of the ionization potential from the p-type semiconductor layer 28 of the hole transport layer 6 to the shell 20 in the energy band diagrams of the light-emitting elements 2 according to the previous embodiment and the present embodiment, respectively.

[0115] In the previous embodiment, the hole transport layer 6 and the light-emitting layer 8 are in direct contact. Here, the contact between the hole transport layer 6 and the light-emitting layer 8 is a contact between semiconductors. In addition, in the light-emitting element 2 of the present embodiment, like a general inorganic semiconductor light-emitting element, epitaxial growth is not used to fabricate the stacked structure. Therefore, in the present embodiment, it is difficult to avoid the generation of energy levels at the surfaces and interfaces of the respective layers of the light-emitting element 2. Therefore, interface energy levels are formed at the interface between the hole transport layer 6 and the shell 20.

[0116] Therefore, as Figure 9 shown, a carrier trap CT is formed at the interface between the hole transport layer 6 and the shell 20. If holes transported from the anode 4 are trapped in the carrier trap CT, the concentration of holes transported to the light-emitting layer 8 may decrease, and the carrier balance in the light-emitting layer 8 may deteriorate.

[0117] On the other hand, in the embodiment, as Figure 10 shown, a non-conductive layer 22 is formed between the hole transport layer 6 and the light-emitting layer 8. The contact between the hole transport layer 6 and the non-conductive layer 22 and the contact between the non-conductive layer 22 and the light-emitting layer 8 both become contacts between a semiconductor and a non-conductor.

[0118] Therefore, in the present embodiment, at the interface between the hole transport layer 6 and the non-conductor layer 22 and at the interface between the non-conductor layer 22 and the light-emitting layer 8, the interface energy level can be deactivated, and thus the generation of carrier traps CT can be reduced. Therefore, the situation where holes transported from the anode 4 are trapped by the carrier trap CT is reduced, and thus the carrier balance in the light-emitting layer 8 is further improved.

[0119] In the present embodiment, from the viewpoint of more reliably forming the non-conductor layer 22 and reducing the carrier traps in the non-conductor layer 22, the film thickness of the non-conductor layer 22 is preferably 1 nm or more. Further, in the present embodiment, in order to sufficiently obtain the tunneling effect of holes in the non-conductor layer 22, the film thickness of the non-conductor layer 22 is preferably 5 nm or less.

[0120] (Modification example)

[0121] Figure 11 and Figure 12 is a schematic cross-sectional view of a modification example of the light-emitting device 1 according to the present embodiment.

[0122] The light-emitting device 1 according to the present embodiment can be variously changed and improved in the same manner as the light-emitting device 1 according to the above-described Embodiment 1. For example, as Figure 11 shown, the light-emitting element 2 of the present embodiment may also include the non-conductor layer 22 and may not include the p-type semiconductor layer 28. Or, as Figure 12 shown, the light-emitting element 2 of the present embodiment may also include the non-conductor layer 22 and may include an i-type semiconductor layer 38 containing a third II-VI group semiconductor instead of the p-type semiconductor layer 28.

[0123] [Summary]

[0124] The light-emitting element according to Mode 1 of the present invention includes: an anode; a cathode; a light-emitting layer disposed between the anode and the cathode and containing quantum dots; and a hole transport layer disposed between the light-emitting layer and the anode, the hole transport layer including: an n+-type semiconductor layer; and a p+-type semiconductor layer adjacent to the n+-type semiconductor layer and disposed on the light-emitting layer side with respect to the n+-type semiconductor layer.

[0125] The light-emitting element according to Mode 2 of the present invention is the light-emitting element according to the above-described Mode 1, and the n+-type semiconductor layer may contain a first II-VI group semiconductor and a first dopant selected from Group 13 elements and Group 17 elements.

[0126] The light-emitting element related to Mode 3 of the present invention is the light-emitting element related to Mode 2 above, or the first II-VI semiconductor may contain at least one or more selected from the group consisting of ZnS, ZnSe, CdS, CdSe, CdTe, ZnTe, ZnCdSe, ZnCdS, ZnCdTe, ZnSeS, CdSeS, ZnTeS, ZnTeSe, CdTeS, and CdTeSe.

[0127] The light-emitting element related to Mode 4 of the present invention is the light-emitting element related to Mode 2 or 3 above, or the first dopant may contain at least one or more selected from Al, In, Ga, Cl, Br, and I.

[0128] The light-emitting element related to Mode 5 of the present invention is the light-emitting element related to any one of Modes 1 to 4 above, or the n+-type semiconductor layer may contain a first II-VI semiconductor, and the II-group element is in excess relative to the stoichiometric state in the first II-VI semiconductor.

[0129] The light-emitting element related to Mode 6 of the present invention is the light-emitting element related to Mode 5 above, or the first II-VI semiconductor may contain Cd and a VI-group element, and the content ratio of Cd is large relative to the VI-group element.

[0130] The light-emitting element related to Mode 7 of the present invention is the light-emitting element related to Mode 6 above, or the first II-VI semiconductor may contain at least one or more selected from the group consisting of CdS, CdSe, CdTe, ZnCdSe, ZnCdS, ZnCdTe, CdSeS, CdTeS, and CdTeSe.

[0131] The light-emitting element related to Mode 8 of the present invention is the light-emitting element related to Mode 1 above, or the n+-type semiconductor layer and the p+-type semiconductor layer may include the same metal oxide semiconductor composed of the same element combination. The metal oxide semiconductor contained in the n+-type semiconductor layer has an oxygen atom deficiency relative to the stoichiometric state, and the metal oxide semiconductor contained in the p+-type semiconductor layer has an oxygen atom excess relative to the stoichiometric state.

[0132] The light-emitting element related to Mode 9 of the present invention is the light-emitting element related to any one of Modes 1 to 8 above, or the p+-type semiconductor layer may contain a second II-VI semiconductor and a second dopant selected from Group 1 elements, Group 11 elements, and Group 15 elements.

[0133] The light-emitting element according to Mode 10 of the present invention is the light-emitting element according to any one of Modes 2 to 7 above, or the p+-type semiconductor layer may include: a second II-VI semiconductor; and a second dopant containing a selected element from Group 1 elements, Group 11 elements, and Group 15 elements, and the first II-VI semiconductor and the second II-VI semiconductor are semiconductors composed of the same element combination as each other.

[0134] The light-emitting element according to Mode 11 of the present invention is the light-emitting element according to Mode 9 or 10 above, or the second II-VI semiconductor may contain at least one or more selected from the group consisting of ZnS, ZnSe, CdS, CdSe, CdTe, ZnTe, ZnCdSe, ZnCdS, ZnCdTe, ZnSeS, CdSeS, ZnTeS, ZnTeSe, CdTeS, and CdTeSe.

[0135] The light-emitting element according to Mode 12 of the present invention is the light-emitting element according to any one of Modes 9 to 11 above, or the second dopant may contain at least one or more selected from N, P, Cu, Ag, Li, and Na.

[0136] The light-emitting element according to Mode 13 of the present invention is the light-emitting element according to any one of Modes 9 to 12 above, or the hole transport layer may include an i-type semiconductor layer that is adjacent to the p+-type semiconductor layer and is disposed on the light-emitting layer side with respect to the p+-type semiconductor layer, and the i-type semiconductor layer includes a third II-VI semiconductor composed of the same element combination as the second II-VI semiconductor.

[0137] The light-emitting element according to Mode 14 of the present invention is the light-emitting element according to any one of Modes 9 to 12 above, or the hole transport layer may include a p-type semiconductor layer that is adjacent to the p+-type semiconductor layer and is disposed on the light-emitting layer side with respect to the p+-type semiconductor layer, and the p-type semiconductor layer includes: a third II-VI semiconductor composed of the same element combination as the second II-VI semiconductor; and a third dopant selected from Group 1 elements, Group 11 elements, and Group 15 elements, and the concentration of the third dopant in the p-type semiconductor layer with respect to the third II-VI semiconductor is lower than the concentration of the second dopant in the p+-type semiconductor layer with respect to the second II-VI semiconductor.

[0138] The light-emitting element according to Mode 15 of the present invention is the light-emitting element according to Mode 13 above, or the thickness of the i-type semiconductor layer may be thinner than the thickness of the p+-type semiconductor layer.

[0139] The light-emitting element according to Mode 16 of the present invention is the light-emitting element according to Mode 14 described above, or the thickness of the p-type semiconductor layer may be thinner than the thickness of the p+-type semiconductor layer.

[0140] The light-emitting element according to Mode 17 of the present invention is the light-emitting element according to any one of Modes 9 to 16 described above, or the quantum dots may include: a core and a shell covering the core, and the shell contains a fourth II-VI semiconductor composed of the same elemental combination as the second II-VI semiconductor.

[0141] The light-emitting element according to Mode 18 of the present invention is the light-emitting element according to any one of Modes 2 to 4 described above, or in the n+-type semiconductor layer, the addition amount of the first dopant is 1.00E+17 [cm -3 to 1.00E+23 [cm -3 .

[0142] The light-emitting element according to Mode 19 of the present invention is the light-emitting element according to any one of Modes 9 to 17 described above, or in the p+-type semiconductor layer, the addition amount of the second dopant is 1.00E+17 [cm -3 to 1.00E+23 [cm -3 .

[0143] The light-emitting element according to Mode 20 of the present invention is the light-emitting element according to any one of Modes 9 to 17 described above, or the quantum dots may include a core and a shell covering the core, the shell contains a fourth II-VI semiconductor selected from II-VI semiconductors, and the II group element contained in the first II-VI semiconductor is included in a period lower than the II group element contained in the fourth II-VI semiconductor.

[0144] The light-emitting element according to Mode 21 of the present invention is the light-emitting element according to Mode 14 or 16 described above, or the third dopant contains the same element as the second dopant.

[0145] The light-emitting device according to Mode 22 of the present invention is configured to include the light-emitting element according to any one of Modes 1 to 21 described above.

[0146] The present disclosure is not limited to the above-described embodiments, and various changes can be made within the scope shown in the claims. Embodiments obtained by appropriately combining the technical solutions separately disclosed for different embodiments are also included in the technical scope of the present disclosure. Moreover, new technical features can be formed by combining the technical methods separately disclosed in each embodiment.

[0147] Description of Reference Numerals

[0148] 1 Light-emitting device

[0149] 2, 102 Light-emitting element

[0150] 4 Anode

[0151] 6, 106 Hole transport layer

[0152] 8 Light-emitting layer

[0153] 10 Electron transport layer

[0154] 12 Cathode

[0155] 16 Quantum dot

[0156] 18 Core

[0157] 20 Shell

[0158] 22 Non-conductor layer

[0159] 24 n+-type semiconductor layer

[0160] 26 p+-type semiconductor layer

[0161] 28 p-type semiconductor layer

[0162] 38 i-type semiconductor layer

Claims

1. A light-emitting element, characterized in that, Comprising: An anode; A cathode; A light-emitting layer disposed between the anode and the cathode and containing quantum dots; and A hole transport layer disposed between the light-emitting layer and the anode, The hole transport layer includes: An n+-type semiconductor layer; and A p+-type semiconductor layer adjacent to the n+-type semiconductor layer and disposed on the light-emitting layer side with respect to the n+-type semiconductor layer.

2. The light-emitting element according to claim 1, wherein The n+-type semiconductor layer contains a first II-VI semiconductor and a first dopant selected from group 13 elements and group 17 elements.

3. The light-emitting element according to claim 2, characterized in that, The first II-VI semiconductor contains one or more selected from the group consisting of ZnS, ZnSe, CdS, CdSe, CdTe, ZnTe, ZnCdSe, ZnCdS, ZnCdTe, ZnSeS, CdSeS, ZnTeS, ZnTeSe, CdTeS, CdTeSe.

4. The light-emitting element according to claim 2, wherein, The first dopant contains one or more selected from Al, In, Ga, Cl, Br, I.

5. The light-emitting element according to claim 1, wherein The n+-type semiconductor layer contains a first II-VI semiconductor, In the first II-VI semiconductor with respect to the stoichiometric state, the group II element is in excess.

6. The light-emitting element according to claim 5, wherein The first II-VI semiconductor contains Cd and a group VI element, The content ratio of Cd is large with respect to the group VI element.

7. The light-emitting element according to claim 6, wherein The first II-VI semiconductor contains one or more selected from the group consisting of CdS, CdSe, CdTe, ZnCdSe, ZnCdS, ZnCdTe, CdSeS, CdTeS, CdTeSe.

8. The light-emitting element according to claim 1, wherein The n+-type semiconductor layer and the p+-type semiconductor layer include the same metal oxide semiconductor composed of the same element combination, In the metal oxide semiconductor contained in the n+-type semiconductor layer with respect to the stoichiometric state, the oxygen atoms are insufficient; In the metal oxide semiconductor contained in the p+-type semiconductor layer with respect to the stoichiometric state, the oxygen atoms are in excess.

9. The light-emitting element according to claim 1, characterized in that, The p+-type semiconductor layer contains a second II-VI semiconductor and a second dopant selected from group 1 elements, group 11 elements, and group 15 elements. 10.The light-emitting element according to claim 2, wherein The p+-type semiconductor layer includes: A second II-VI semiconductor; and A second dopant containing one or more selected from group 1 elements, group 11 elements, and group 15 elements, The first II-VI semiconductor and the second II-VI semiconductor are semiconductors composed of the same element combination as each other.

11. The light-emitting element according to claim 9, wherein The second II-VI semiconductor contains one or more selected from the group consisting of ZnS, ZnSe, CdS, CdSe, CdTe, ZnTe, ZnCdSe, ZnCdS, ZnCdTe, ZnSeS, CdSeS, ZnTeS, ZnTeSe, CdTeS, CdTeSe.

12. The light-emitting element according to claim 9, wherein, The second dopant contains one or more of N, P, Cu, Ag, Li, and Na.

13. The light-emitting element according to claim 9, wherein the hole transport layer includes an i-type semiconductor layer that is adjacent to the p+-type semiconductor layer and is disposed on the light-emitting layer side with respect to the p+-type semiconductor layer, the i-type semiconductor layer includes a third II-VI semiconductor composed of the same elemental combination as the second II-VI semiconductor.

14. The light-emitting element according to claim 9, wherein the hole transport layer includes a p-type semiconductor layer that is adjacent to the p+-type semiconductor layer and is disposed on the light-emitting layer side with respect to the p+-type semiconductor layer, the p-type semiconductor layer includes: a third II-VI semiconductor composed of the same elemental combination as the second II-VI semiconductor; and a third dopant selected from Group 1 elements, Group 11 elements, and Group 15 elements, the concentration of the third dopant in the p-type semiconductor layer with respect to the third II-VI semiconductor is lower than the concentration of the second dopant in the p+-type semiconductor layer with respect to the second II-VI semiconductor.

15. The light-emitting element according to claim 13, wherein the thickness of the i-type semiconductor layer is thinner than the thickness of the p+-type semiconductor layer.

16. The light-emitting element according to claim 14, wherein the thickness of the p-type semiconductor layer is thinner than the thickness of the p+-type semiconductor layer.

17. The light-emitting element according to claim 9, wherein the quantum dot includes: a core and a shell covering the core, the shell includes a fourth II-VI semiconductor composed of the same elemental combination as the second II-VI semiconductor.

18. The light-emitting element according to claim 2, characterized in that, In the n+-type semiconductor layer, the addition amount of the first dopant is 1.00E+17 [cm -3 to 1.00E+23 [cm -3 .

19. The light-emitting element according to claim 9, wherein In the p+-type semiconductor layer, the addition amount of the second dopant is 1.00E+17 [cm -3 to 1.00E+23 [cm -3 .

20. The light-emitting element according to claim 2, wherein the quantum dot includes a core and a shell covering the core, the shell contains a fourth II-VI semiconductor selected from II-VI semiconductors, the Group II element included in the first II-VI semiconductor is included in a period lower than the Group II element included in the fourth II-VI semiconductor.

21. The light-emitting element according to claim 14, characterized in that, The third dopant contains the same elements as the second dopant.

22. A light-emitting device, characterized in that, A light-emitting element according to any one of claims 1 to 21.

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