Patent Publication Number: US-2023163234-A1

Title: Light emitting element and display device including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority to and benefits of Korean Patent Application No. 10-2021-0161846 under 35 U.S.C. § 119, filed on Nov. 23, 2021, in the Korean Intellectual Property Office (KIPO), the disclosure of which is incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The disclosure relates to a light emitting element and a display device including the same. 
     2. Description of the Related Art 
     The importance of display devices is increasing with the development of multimedia. Accordingly, various types of display devices, such as an organic light emitting display (OLED) device, a liquid crystal display (LCD) device, and the like are being used. 
     A device which displays an image of the display device includes a display panel such as an organic light emitting display panel or a liquid crystal display panel. Among the above, the light emitting display panel may include a light emitting element, and for example, a light emitting diode (LED) includes an organic light emitting diode (OLED) using an organic material as a light emitting material, an inorganic light emitting diode using an inorganic material as a light emitting material, and the like. 
     SUMMARY 
     Aspects of the disclosure provide a light emitting element capable of preventing or suppressing injection of holes from a central portion of a light emitting element core into a damaged surface area of the light emitting element core by a band bending effect between the central portion of the light emitting element core and the damaged surface area of the light emitting element core by including a second p-type semiconductor layer disposed between a first p-type semiconductor layer doped with a p-type dopant and an element active layer and having a doping concentration of the p-type dopant lower than a defect density of the damaged surface area of the light emitting element core. 
     Aspects of the disclosure also provide a light emitting element capable of preventing or suppressing injection of holes from a central portion of a light emitting element core into a damaged surface area of the light emitting element core by a band bending effect between the central portion of the light emitting element core and the damaged surface area of the light emitting element core by including a semiconductor layer disposed between a first p-type semiconductor layer doped with a p-type dopant and an element active layer and not doped with the p-type dopant. 
     Aspects of the disclosure also provide a display device capable of having improved light emitting efficiency by including the light emitting element. 
     However, aspects of the disclosure are not restricted to those set forth herein. The above and other aspects of the disclosure will become more apparent to one of ordinary skill in the art to which the disclosure pertains by referencing the detailed description of the disclosure given below. 
     According to the embodiments of the disclosure, a light emitting element may include a light emitting element core including a first area and a second area surrounding the first area. The light emitting element core may include a first semiconductor layer doped with a first conductivity-type dopant, a second semiconductor layer disposed on the first semiconductor layer, the second semiconductor layer doped with a second conductivity-type dopant different from the first conductivity-type dopant, an element active layer disposed between the first semiconductor layer and the second semiconductor layer; and a third semiconductor layer disposed between the element active layer and the second semiconductor layer, the third semiconductor layer doped with the second conductivity-type dopant. The second area of the light emitting element core may be located on an outer circumference of the light emitting element core, the second area of the light emitting element including an outer surface of the light emitting element core, and a doping concentration of the second conductivity-type dopant of the third semiconductor layer may be lower than a defect density of the second area of the light emitting element core. 
     The doping concentration of the second conductivity-type dopant of the third semiconductor layer may be about 10 18 /cm 3  or less. 
     The first semiconductor layer may be an n-type semiconductor layer, and the second semiconductor layer and the third semiconductor layer may each be a p-type semiconductor layer. 
     A light emitting element may further include an electron blocking layer disposed between the element active layer and the third semiconductor layer. The electron blocking layer may have a single-layer structure. 
     A light emitting element may further include an electron blocking layer disposed between the element active layer and the third semiconductor layer, 
     wherein a thickness of the electron blocking layer may be about 5 nm or less. 
     A light emitting element may further include an electron blocking layer disposed between the element active layer and the third semiconductor layer. The electron blocking layer may include aluminum (Al), and a composition of the aluminum in the electron blocking layer may be about 15% or less. 
     The doping concentration of the second conductivity-type dopant of the third semiconductor layer may be lower than a doping concentration of the second conductivity-type dopant of the second semiconductor layer. 
     A thickness of the third semiconductor layer may be greater than a thickness of the second semiconductor layer. 
     A light emitting element may further include an electron blocking layer disposed between the element active layer and the third semiconductor layer. A thickness of the electron blocking layer may be smaller than the thickness of the third semiconductor layer. 
     The light emitting element core may extend in a first direction, the first semiconductor layer, the element active layer, the third semiconductor layer, and the second semiconductor layer mat be sequentially disposed in the first direction, and a width of the light emitting element core may be about 10 μm or less. 
     According to an embodiment of the disclosure, a light emitting element may include a first semiconductor layer doped with a first conductivity-type dopant, a second semiconductor layer disposed on the first semiconductor layer, the second semiconductor layer doped with a second conductivity-type dopant different from the first conductivity-type dopant, an element active layer disposed between the first semiconductor layer and the second semiconductor layer, and a third semiconductor layer disposed between the element active layer and the second semiconductor layer. The third semiconductor layer may be not doped with a conductivity-type dopant. 
     The first semiconductor layer may be an n-type semiconductor layer, and the second semiconductor layer may be a p-type semiconductor layer. 
     The light emitting element may further include an electron blocking layer disposed between the element active layer and the third semiconductor layer. The electron blocking layer may have a single-layer structure. 
     The light emitting element may further include an electron blocking layer disposed between the element active layer and the third semiconductor layer. A thickness of the electron blocking layer may be about 5 nm or less. 
     The light emitting element may further include an electron blocking layer disposed between the element active layer and the third semiconductor layer. The electron blocking layer may include aluminum (Al), and a composition of the aluminum in the electron blocking layer may be about 15% or less. 
     A thickness of the third semiconductor layer may be greater than a thickness of the second semiconductor layer. 
     The light emitting element may further include an electron blocking layer disposed between the element active layer and the third semiconductor layer. A thickness of the electron blocking layer may be smaller than the thickness of the third semiconductor layer. 
     According to an embodiment of the disclosure, a display device may include a first electrode and a second electrode disposed on a substrate and spaced apart from each other, and a light emitting element disposed between the first electrode and the second electrode. The light emitting element may include a light emitting element core including a first area and a second area surrounding the first area. The light emitting element core may include a first semiconductor layer doped with a first conductivity-type dopant, a second semiconductor layer disposed on the first semiconductor layer, the second semiconductor layer doped with a second conductivity-type dopant different from the first conductivity-type dopant, an element active layer disposed between the first semiconductor layer and the second semiconductor layer; and a third semiconductor layer disposed between the element active layer and the second semiconductor layer, the third semiconductor layer doped with the second conductivity-type dopant. The second area of the light emitting element core may be located on an outer circumference of the light emitting element core, the second area of the light emitting element including an outer surface of the light emitting element core, and a doping concentration of the second conductivity-type dopant of the third semiconductor layer may be lower than a defect density of the second area of the light emitting element core. 
     The doping concentration of the second conductivity-type dopant of the third semiconductor layer may be about 10 18 /cm 3  or less. 
     According to an embodiment of the disclosure, a display device may include a first electrode and a second electrode disposed on a substrate and spaced apart from each other, and a light emitting element disposed between the first electrode and the second electrode. The light emitting element may include a first semiconductor layer doped with a first conductivity-type dopant, a second semiconductor layer disposed on the first semiconductor layer, the second semiconductor layer doped with a second conductivity-type dopant different from the first conductivity-type dopant, an element active layer disposed between the first semiconductor layer and the second semiconductor layer; and a third semiconductor layer disposed between the element active layer and the second semiconductor layer. The third semiconductor layer may be not doped with a conductivity-type dopant. 
     The light emitting element according to an embodiment may include a second p-type semiconductor layer disposed between a first p-type semiconductor layer doped with a p-type dopant and an element active layer. A doping concentration of the p-type dopant of the second p-type semiconductor layer may be lower than a defect density of a damaged surface area of a light emitting element core. Accordingly, it is possible to prevent or suppress injection of holes from a central portion of the light emitting element core into the damaged surface area of the light emitting element core by a band bending effect between the central portion of the light emitting element core and the damaged surface area of the light emitting element core. 
     The light emitting element according to an embodiment of the disclosure may include a semiconductor layer disposed between a p-type semiconductor layer doped with a p-type dopant and an element active layer that is not doped with the p-type dopant. Accordingly, it is possible to prevent or suppress injection of holes from a central portion of the light emitting element core into the damaged surface area of the light emitting element core by a band bending effect at an interface portion between the central portion of the light emitting element core and the damaged surface area of the light emitting element core. 
     Accordingly, non-radiative recombination in the damaged surface area of the light emitting element core may be reduced, so that light emitting efficiency of the light emitting element may be improved. 
     Since the display device according to an embodiment includes the light emitting element, light emitting efficiency per unit area may be improved. 
     However, the effects of the embodiments are not restricted to the one set forth herein. The above and other effects of the embodiments will become more apparent to one of daily skill in the art to which the embodiments pertain by referencing the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects and features of the disclosure will become more apparent by describing in detail embodiments thereof with reference to the attached drawings, in which: 
         FIG.  1    is a schematic perspective view of a light emitting element according to an embodiment; 
         FIG.  2    is a schematic cross-sectional view of the light emitting element illustrating an embodiment taken along line I-I′ of  FIG.  1   ; 
         FIG.  3    is a schematic enlarged cross-sectional view illustrating a light emitting element core according to an embodiment; 
         FIG.  4    is a schematic view for comparing a light emitting element core not including a third semiconductor layer and a light emitting element core including a third semiconductor layer; 
         FIG.  5    is a view illustrating a schematic band diagram of a light emitting element core taken along lines II-II′ and III-III′ of  FIG.  4   ; 
         FIG.  6    is a view illustrating recombination rate contour maps of areas B_R and B of  FIG.  4   ; 
         FIG.  7    is a graph comparing energy efficiencies according to light emitting element cores; 
         FIG.  8    is a schematic cross-sectional view of a light emitting element illustrating an embodiment taken along line I-I′ of  FIG.  1   ; 
         FIG.  9    is a plan view of a display device according to an embodiment; 
         FIG.  10    is a plan layout view illustrating a pixel of a display device according to an embodiment; 
         FIG.  11    is a schematic cross-sectional view illustrating an embodiment taken along line Q-Q′ of  FIG.  10   ; 
         FIG.  12    is a schematic enlarged cross-sectional view illustrating an embodiment of area P of  FIG.  11   ; and 
         FIG.  13    is a schematic enlarged cross-sectional view illustrating embodiment of area P of  FIG.  11   . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments are shown. This disclosure may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. 
     In the drawings, the sizes, thicknesses, ratios, and dimensions of the elements may be exaggerated for ease of description and for clarity. Like numbers refer to like elements throughout. 
     In the description, it will be understood that when an element (or region, layer, part, etc.) is referred to as being “on”, “connected to”, or “coupled to” another element, it can be directly on, connected to, or coupled to the other element, or one or more intervening elements may be present therebetween. In a similar sense, when an element (or region, layer, part, etc.) is described as “covering” another element, it can directly cover the other element, or one or more intervening elements may be present therebetween. 
     As used herein, the expressions used in the singular such as “a,” “an,” and “the,” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. For example, “A and/or B” may be understood to mean “A, B, or A and B.” The terms “and” and “or” may be used in the conjunctive or disjunctive sense and may be understood to be equivalent to “and/or”. 
     In the specification and the claims, the term “at least one of” is intended to include the meaning of “at least one selected from the group of” for the purpose of its meaning and interpretation. For example, “at least one of A and B” may be understood to mean “A, B, or A and B.” When preceding a list of elements, the term, “at least one of” modifies the entire list of elements and does not modify the individual elements of the list. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. Thus, a first element could be termed a second element without departing from the teachings of the disclosure. Similarly, a second element could be termed a first element, without departing from the scope of the disclosure. 
     Unless otherwise defined or implied herein, all terms (including technical and scientific terms) used have the same meaning as commonly understood by those skilled in the art to which this disclosure pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and should not be interpreted in an ideal or excessively formal sense unless clearly defined in the specification. 
       FIG.  1    is a schematic perspective view of a light emitting element according to an embodiment.  FIG.  2    is a schematic cross-sectional view of the light emitting element illustrating an embodiment taken along line I-I′ of  FIG.  1   .  FIG.  3    is a schematic enlarged cross-sectional view illustrating a light emitting element core according to an embodiment. 
     Referring to  FIGS.  1  to  3   , the light emitting element ED may be a particle type element, and may have a rod shape or a cylindrical shape having an aspect ratio. The light emitting element ED has a shape extending in one direction X, and a length of the light emitting element ED in the extending direction (or longitudinal direction X) may be greater than a diameter of the light emitting element ED, and the aspect ratio thereof may be 1.2:1 to 100:1, but is not limited thereto. For example, the light emitting element ED may have a shape such as a cylinder, a rod, a wire, a tube, and the like, may have a polygonal prism shape such as a cube, a rectangular parallelepiped, or a hexagonal prism, or may have a shape extending in one direction and having an outer surface partially inclined. Hereinafter, in the drawings for explaining the shape of the light emitting element ED, the terms of the one direction X, the extension direction X of the light emitting element ED, and the longitudinal direction X of the light emitting element ED may be interchangeably used. 
     The light emitting element ED may have a size of a nanometer scale (1 nm or more and less than 1 μm) to a micrometer scale (1 μm or more and less than 1 mm). In an embodiment, the light emitting element ED may have a size of a nanometer scale or have a size of a micrometer scale, in both the diameter and the length thereof. In other embodiments, the diameter of the light emitting element ED may have a size of a nanometer scale, while the length of the light emitting element ED may have a size of a micrometer scale. In embodiments, some light emitting elements ED may have a size of a nanometer scale in diameter and/or length, while other light emitting elements ED may have a size of a micrometer scale in diameter and/or length. 
     In an embodiment, the light emitting element ED may be an inorganic light emitting diode. The inorganic light emitting diode may include multiple semiconductor layers. For example, the inorganic light emitting diode may include a first conductivity-type (e.g., n-type) semiconductor layer, a second conductivity-type (e.g., p-type) semiconductor layer, and an active semiconductor layer interposed therebetween. The active semiconductor layer may receive holes and electrons from the first conductivity-type semiconductor layer and the second conductivity-type semiconductor layer, respectively, and the holes and the electrons reaching the active semiconductor layer may be combined with each other to emit light. The inorganic light emitting diode may be aligned between two electrodes in which polarities are formed in case that an electric field is formed in a specific direction between the two electrodes facing each other. 
     The light emitting element ED may include a light emitting element core  30  and an element insulating layer  38 . 
     The light emitting element core  30  may have a shape extending in one direction X. The light emitting element core  30  may have a rod or cylindrical shape. However, the light emitting element core  30  is not limited thereto and may have a polygonal prism shape such as a cube, a rectangular parallelepiped, or a hexagonal prism or may have a shape extending in one direction X and having an outer surface partially inclined. 
     The light emitting element core  30  according to an embodiment may include multiple semiconductor layers and an element electrode layer  37 . The multiple semiconductor layers of the light emitting element core  30  may include a first semiconductor layer  31 , a second semiconductor layer  32 , an element active layer  33 , a third semiconductor layer  34 , and an electron blocking layer  35 . The first semiconductor layer  31 , the element active layer  33 , the electron blocking layer  35 , the third semiconductor layer  34 , the second semiconductor layer  32 , and the element electrode layer  37  may be sequentially stacked each other along one direction X, which is a longitudinal direction of the light emitting element core  30 . 
     The light emitting element core  30  may include a first area A 1  and a second area A 2 . The first area A 1  of the light emitting element core  30  may be a central area in the multiple semiconductor layers of the light emitting element core  30 . The first area A 1  of the light emitting element core  30  may occupy most of the area of the light emitting element core  30 . The second area A 2  of the light emitting element core  30  may surround the first area A 1  of the light emitting element core  30 . The second area A 2  of the light emitting element core  30  may be a damaged surface area A 2  of the light emitting element core  30  including an outer circumference surface of the light emitting element core  30 . Hereinafter, for convenience of explanation in the specification, the second area A 2  of the light emitting element core  30  may also be referred to as a damaged surface area A 2  of the light emitting element core  30 . The first area A 1  and the second area A 2  of the light emitting element core  30  may be divided according to a relative size of a defect density without a physical interface. 
     The multiple semiconductor layers of the light emitting element core  30  may have a damaged surface area A 2  having a thickness from an outer surface of each semiconductor layer. The damaged surface area A 2  of the semiconductor layer of the light emitting element core  30  may be formed in an etching process of the multiple semiconductor layers during a manufacturing process of the light emitting element ED. For example, the light emitting element ED may be manufactured by forming multiple semiconductor layers on a target substrate by an epitaxial growth method, and then etching the semiconductor layers in a direction perpendicular to a top surface of the target substrate. The semiconductor layers grown on the target substrate may be smoothly grown without inter-crystal lattice defects depending on the growth conditions, but in a process of etching the semiconductor layers, a defect DFT may occur on an etched surface (e.g., an outer circumference surface) of the semiconductor layers. Accordingly, the light emitting element core  30  may include the damaged surface area A 2  of the light emitting element core  30  having a high defect density and the first area A 1  of the light emitting element core  30 . 
     The first semiconductor layer  31  may be doped with a first conductivity-type dopant. The first conductivity-type may be an n-type, and the first conductivity-type dopant may include Si, Ge, Sn, or the like. For example, the first semiconductor layer  31  may be an n-type semiconductor. In an embodiment in which the light emitting element ED emits light in a blue wavelength band, the first semiconductor layer  31  may include a semiconductor material having a chemical formula: Al x Ga y In 1-x-y N (0≤x≤1, 0≤y≤1, and 0≤x+y≤1). For example, the first semiconductor layer  31  may include any one semiconductor material of AlGaInN, GaN, AlGaN, InGaN, AlN, and InN doped with the first conductivity-type dopant, but is not limited thereto. In an embodiment, the first semiconductor layer  31  may be n-GaN doped with n-type Si. 
     The second semiconductor layer  32  may be disposed to be spaced apart from the first semiconductor layer  31  with the element active layer  33  interposed therebetween. The second semiconductor layer  32  may be doped with a second conductivity-type dopant. The second conductivity-type may be a p-type, and the second conductivity-type dopant may include Mg, Zn, Ca, Sr, Ba, or the like. For example, the second semiconductor layer  32  may be a p-type semiconductor. In an embodiment in which the light emitting element ED emits light in a blue wavelength band, the second semiconductor layer  32  may include a semiconductor material having a chemical formula: Al x Ga y In 1-x-y N (0≤x≤1, 0≤y≤1, and 0≤x+y≤1). For example, the second semiconductor layer  32  may include any one semiconductor material of AlGaInN, GaN, AlGaN, InGaN, AlN, and InN doped with the second conductivity-type dopant, but is not limited thereto. In an embodiment, the second semiconductor layer  32  may be p-GaN doped with p-type Mg. 
     It has been illustrated in drawings that the first semiconductor layer  31  and the second semiconductor layer  32  are configured as one layer, but the disclosure is not limited thereto. The first semiconductor layer  31  and the second semiconductor layer  32  may further include multiple layers, for example, a clad layer or a tensile strain barrier reducing (TSBR) layer, according to a material included in the element active layer  33 . 
     The element active layer  33  may be disposed between the first semiconductor layer  31  and the second semiconductor layer  32 . The element active layer  33  may include a material having a single or multiple quantum well structure. The element active layer  33  may emit light by a combination of electron-hole pairs according to an electrical signal applied through the first semiconductor layer  31  and the second semiconductor layer  32 . For example, in case that the element active layer  33  emits light in a blue wavelength band, the element active layer  33  may include a material such as AlGaN or AlGaInN, but is not limited thereto. 
     In embodiments, the element active layer  33  may have a structure in which semiconductor materials having large band gap energy and semiconductor materials having small band gap energy are alternately stacked each other, and may include other Group III to Group V semiconductor materials according to a wavelength band of emitted light. The light emitted by the element active layer  33  is not limited to the light in the blue wavelength band, and in some cases, the element active layer  33  may emit light in a red or green wavelength band. 
     The light emitted from the element active layer  33  may be emitted not only from both end surfaces in one direction X, which is a longitudinal direction of the light emitting element ED, but also from a side surface of the light emitting element ED. An emission direction of the light emitted from the element active layer  33  is not limited to one direction. 
     The electron blocking layer  35  may be disposed between the second semiconductor layer  32  and the element active layer  33 . The electron blocking layer  35  may serve to prevent electrons from being injected from the first semiconductor layer  31 . The electron blocking layer  35  may include a semiconductor material having a chemical formula of Al x Ga y In 1-x-y N (0≤x≤1, 0≤y≤1, and 0≤x+y≤1). For example, the electron blocking layer  35  may include any one semiconductor material of AlGaInN, AlGaN, and AlN, but is not limited thereto. 
     In an embodiment, the electron blocking layer  35  may have a single-layer structure. In embodiments, the electron blocking layer  35  may include aluminum (Al), and an aluminum composition of the electron blocking layer  35  may be 15% or less. In embodiments, a thickness d 3  of the electron blocking layer  35  may be about 5 nm or less. 
     The third semiconductor layer  34  may be disposed between the second semiconductor layer  32  and the electron blocking layer  35 . The third semiconductor layer  34  may be disposed between the element active layer  33  and the second semiconductor layer  32  to serve to prevent the holes of the second semiconductor layer  32  from leaking into the damaged surface area A 2  of the light emitting element core  30  to be described later. 
     In an embodiment, the third semiconductor layer  34  may be doped with a second conductivity-type dopant. The second conductivity-type may be a p-type, and the second conductivity-type dopant may include Mg, Zn, Ca, Sr, Ba, or the like. For example, the third semiconductor layer  34  may be a p-type semiconductor. In an embodiment, the third semiconductor layer  34  may be p-GaN doped with p-type Mg. 
     In an embodiment, a doping concentration of the second conductivity-type dopant doped in the third semiconductor layer  34  may be lower than that of the second conductivity-type dopant doped in the second semiconductor layer  32 . The doping concentration of the second conductivity-type dopant doped in the third semiconductor layer  34  may be lower than a defect density of the damaged surface area A 2  of the light emitting element core  30 . The doping concentration of the second conductivity-type dopant of the third semiconductor layer  34  may have a range of 10 18 /cm 3  or less. In an embodiment in which the second semiconductor layer  32  and the third semiconductor layer  34  are each doped with p-type Mg, an Mg doping concentration of the third semiconductor layer  34  may be lower than an Mg doping concentration of the second semiconductor layer  32 . The Mg doping concentration of the third semiconductor layer  34  may be lower than the defect density of the damaged surface area A 2  of the light emitting element core  30 , and may have a range of 10 18 /cm 3  or less. 
     In case that both ends of the light emitting element ED and the electrode are electrically connected to each other in order to apply an electric signal to the first semiconductor layer  31  and the second semiconductor layer  32 , the element electrode layer  37  may be disposed between the second semiconductor layer  32  and the electrode to serve to reduce resistance. The element electrode layer  37  may include at least one of aluminum (Al), titanium (Ti), indium (In), gold (Au), silver (Ag), indium tin oxide (ITO), indium zinc oxide (IZO), and indium tin-zinc oxide (ITZO). The element electrode layer  37  may also include a semiconductor material doped with an n-type or p-type dopant. 
     The element insulating layer  38  may be disposed to surround the side surface of the light emitting element core  30 . The element insulating layer  38  may be disposed to surround at least a side surface of the element active layer  33 , and may extend in one direction X in which the light emitting element core  30  extends. The element insulating layer  38  may function to protect the multiple semiconductor layers and the element active layer  33  of the light emitting element core  30 . Since the element insulating layer  38  includes a material having insulating properties, it is possible to prevent an electrical short-circuit that may occur in case that an electrode that transmits an electrical signal to the light emitting element ED and the element active layer  33  are in direction contact with each other. The element insulating layer  38  may protect each side surface of the multiple semiconductor layers as well as the element active layer  33 , and may thus prevent a decrease in light emitting efficiency of the light emitting element ED. 
     It has been illustrated in the drawings that the element insulating layer  38  extends in one direction X on the side surface of the light emitting element core  30  to completely cover from the side surface of the first semiconductor layer  31  to the side surface of the element electrode layer  37 , but the disclosure is not limited thereto. For example, the element insulating layer  38  may cover only the side surfaces of the element active layer  33  as well as some semiconductor layers, or may cover a partial area of the side surface of the element electrode layer  37 , but may expose other partial areas of the side surface of the element electrode layer  37 . It has been illustrated in the drawings that the element insulating layer  38  is formed as a single layer, but the disclosure is not limited thereto. For example, the element insulating layer  38  may have a structure in which multiple insulating layers including an insulating material are stacked each other. 
     In an embodiment, a diameter W of the light emitting element core  30  may be about 10 μm or less. In case that the diameter W of the light emitting element core  30  is about 10 μm or less, an area ratio of the outer circumference surface of the light emitting element core  30  may be relatively increased. Accordingly, in the light emitting element core  30 , a ratio of the damaged surface area A 2  of the light emitting element core  30  may be relatively rapidly increased. A surface defect DFT may occur in the light emitting element core  30 , and thus a relative ratio of the damaged surface area A 2  of the light emitting element core  30  having a high defect density may increase. 
     As described above, the surface defect DFT may occur in the process of etching the semiconductor layers during the manufacturing process of the light emitting element ED, and the surface defect DFT may include vacancy defects of gallium (Ga) or nitrogen (N) positioned on the outer surfaces of the multiple semiconductor layers. Due to the surface defect DFT, holes or electrons may leak from the first area A 1  of the light emitting element core  30  to the damaged surface area A 2  of the light emitting element core  30 , and non-radiative recombination may occur in the damaged surface area A 2  of the light emitting element core  30 . 
     In case that the diameter of the light emitting element ED decreases, a ratio of non-radiative recombination may increase as the ratio of the damaged surface area A 2  of the light emitting element core  30  is rapidly increased. Accordingly, holes of the second semiconductor layer  32  may leak into the damaged surface area A 2  of the light emitting element core  30 , and thus a ratio of holes that do not emit light in the element active layer  33  may increase, so that the light emitting efficiency of the light emitting element ED may be reduced. Therefore, there is a need to efficiently prevent the holes from leaking from the second semiconductor layer  32  overlapping the first area A 1  of the light emitting element core  30  to the damaged surface area A 2  of the light emitting element core  30 . 
     The light emitting element ED according to the disclosure may prevent holes from leaking from the first area A 1  of the second semiconductor layer  32  to the damaged surface area A 2  of the light emitting element core  30  by including the third semiconductor layer  34  disposed between the second semiconductor layer  32  and the element active layer  33  and doped with a second conductivity-type dopant having a doping concentration lower than the defect density of the damaged surface area A 2  of the light emitting element core  30  or a doping concentration having a range of 10′ 8 /cm 3  or less. A detailed description thereof will be provided later. 
     In an embodiment, a thickness d 2  of the third semiconductor layer  34  may be greater than a thickness d 1  of the second semiconductor layer  32 . The thickness d 2  of the third semiconductor layer  34  may be greater than a thickness d 3  of the electron blocking layer  35 . By forming the thickness d 2  of the third semiconductor layer  34  to be greater than the thickness d 1  of the second semiconductor layer  32  and the thickness d 3  of the electron blocking layer  35 , the third semiconductor layer  34  may effectively prevent the holes provided from the second semiconductor layer  32  from leaking into the damaged surface area A 2  of the light emitting element core  30  between the second semiconductor layer  32  and the element active layer  33 . 
       FIG.  4    is a schematic view for comparing a light emitting element core not including a third semiconductor layer and a light emitting element core including a third semiconductor layer.  FIG.  5    is a view illustrating a schematic band diagram of a light emitting element core taken along lines II-II′ and III-III′ of  FIG.  4   .  FIG.  6    is a view illustrating recombination rate contour maps of areas B_R and B of  FIG.  4   . 
     First, referring to  FIG.  4   , a light emitting element core  30 _R illustrated in (a- 1 ) of  FIG.  4    may be a light emitting element core in which the third semiconductor layer  34  is omitted, and the light emitting element core  30  illustrated in (b- 1 ) of  FIG.  4    may be a light emitting element core  30  according to the disclosure, which may be a light emitting element core in which the third semiconductor layer  34  is further disposed between the second semiconductor layer  32  and the electron blocking layer  35 . A vector map of hole currents in an area A_R of the light emitting element core  30 _R is illustrated on a right side of the light emitting element core  30 _R in (a- 1 ) of  FIG.  4   , and a vector map of hole currents in area A of the light emitting element core  30  is illustrated on a right side of the light emitting element core  30  in (b- 1 ) of  FIG.  4   . Purple to red in the vector map of the hole current may indicate an amount of the hole current. For example, purple may mean that a small amount of hole current flows, and red may mean that a large amount of hole current flows. 
     Referring to (a- 1 ) of  FIG.  4   , in case that a semiconductor layer having a lower doping concentration of the second conductivity-type dopant is not interposed between the second semiconductor layer  32  and the electron blocking layer  35 , it may be seen that a large amount of hole current flows in a damaged surface area A 2 _R of the second semiconductor layer  32 . It may be seen that holes provided from the first area A 1  of the second semiconductor layer  32  have a hole flow M 1  flowing from the first area A 1  of the second semiconductor layer  32  to the damaged surface area A 2 _R of the electron blocking layer  35 . 
     Referring to (b- 1 ) of  FIG.  4   , in case that the third semiconductor layer  34  having a doping concentration of the second conductivity-type dopant lower than the defect density of the damaged surface area A 2  of the light emitting element core  30  is interposed between the second semiconductor layer  32  and the electron blocking layer  35 , it may be seen that a small amount of hole current flows in the damaged surface area A 2  of the second semiconductor layer  32  and the damaged surface area A 2  of the third semiconductor layer  34 . It may be seen that the holes provided from the first area A 1  of the second semiconductor layer  32  have a hole flow M 2  flowing in a direction of the first area A 1  of the electron blocking layer  35  through the first area A 1  of the third semiconductor layer  34 . 
     For example, by disposing the third semiconductor layer  34  having the lower doping concentration of the second conductivity-type dopant between the second semiconductor layer  32  and the electron blocking layer  35 , the amount of holes provided from the second semiconductor layer  32  leaking into the damaged surface area A 2  of the second semiconductor layer  32  or the damaged surface area A 2  of the electron blocking layer  35  may be reduced. Accordingly, it may be seen that the holes are induced to flow from the first area A 1  of the second semiconductor layer  32  and the third semiconductor layer  34  to the first area A 1  of the electron blocking layer  35 . 
     Referring to  FIG.  5   , (a- 2 ) of  FIG.  5    illustrates a schematic band diagram of the first area A 1  and the damaged surface area A 2 _R of the second semiconductor layer  32  in the light emitting element core  30 _R illustrated in (a- 1 ) of  FIG.  4    in which the third semiconductor layer  34  is omitted, and (b- 2 ) of  FIG.  5    illustrates a schematic band diagram of the first area A 1  and the damaged surface area A 2  of the third semiconductor layer  34  in the light emitting element core  30  illustrated in (b- 1 ) of  FIG.  4    in which the third semiconductor layer  34  is included. In the schematic band diagrams, an x-axis represents a position, and a y-axis represents band energy. 
     Referring to (a- 2 ) and (b- 2 ) of  FIG.  5   , a band energy difference el between the first area A 1  and the damaged surface area A 2 _R of the second semiconductor layer  32  in the light emitting element core  30 _R with the third semiconductor layer  34  omitted may be smaller than a band energy difference e 2  between the first area A 1  and the damaged surface area A 2  of the third semiconductor layer  34  in the light emitting element core  30  including the third semiconductor layer  34 . 
     Specifically, in the damaged surface area A 2 _R of the second semiconductor layer  32  of the light emitting element core  30 _R with the third semiconductor layer  34  omitted, ionization of the second conductivity-type dopant may occur due to damage to the surface of the second semiconductor layer  32 , and a valence band bending effect in which the band energy difference el between the damaged surface area A 2 _R and the first area A 1  of the second semiconductor layer  32  is reduced may occur by the ionization of the second conductivity-type dopant in the damaged surface area AR_ 2  of the second semiconductor layer  32  as illustrated in (a- 2 ) of  FIG.  5   . Accordingly, holes h+ provided from the second semiconductor layer  32  may readily flow from the first area A 1  of the second semiconductor layer  32  to the damaged surface area A 2 _R of the second semiconductor layer  32 . 
     The light emitting element core  30  according to an embodiment may include the third semiconductor layer  34  disposed between the second semiconductor layer  32  and the element active layer  33  and the third semiconductor layer  34  may be doped with the second conductivity-type dopant having the doping concentration lower than the defect density of the damaged surface area A 2  of the light emitting element core  30  or the doping concentration having a range of 10 18 /cm 3  or less. As described above, in case that the third semiconductor layer  34  is doped with the second conductivity-type dopant having the doping concentration lower than the defect density of the damaged surface area A 2  of the light emitting element core  30  or the doping concentration about 10 18 /cm 3  or less, a density of an ionized second conductivity-type dopant between the first area A 1  of the third semiconductor layer  34  and the damaged surface area A 2  of the third semiconductor layer  34 , for example, an Mg ionized density difference may be large In case that a high concentration of ionized Mg is doped, the amount of holes h+ increases to alleviate band-bending caused by surface damage, but in case that the concentration of ionized Mg is lowered, the band-bending caused by surface damage may not be sufficiently alleviated. Accordingly, the band-bending or band energy difference e 2  may increase between the first area A 1  of the third semiconductor layer  34  and the damaged surface area A 2  of the third semiconductor layer  34  by the Mg ionized density difference between the first area A 1  that is the central portion of the third semiconductor layer  34  and the damaged surface area A 2  of the third semiconductor layer  34 . Therefore, it may be difficult for holes h+ provided from the second semiconductor layer  32  to flow from the first area A 1  of the third semiconductor layer  34  to the damaged surface area A 2  of the second semiconductor layer  32  or the third semiconductor layer  34 . For example, a band-bending effect may occur between the first area A 1  of the third semiconductor layer  34  and the damaged surface area A 2  of the third semiconductor layer  34 , such that it is possible to prevent holes h+ from being injected from the first area A 1  of the light emitting element core  30  into the damaged surface area A 2  of the light emitting element core  30 . 
     Referring to  FIG.  6   , (a- 3 ) of  FIG.  6    illustrates a recombination rate contour map of the first area A 1  and the damaged surface area A 2 _R of the electron blocking layer  35  in the light emitting element core  30 _R illustrated in (a- 1 ) of  FIG.  4    with the third semiconductor layer  34  omitted, and (b- 3 ) of  FIG.  6    illustrates a recombination rate contour map of the first area A 1  and the damaged surface area A 2  of the electron blocking layer  35  in the light emitting element core  30  illustrated in (b- 1 ) of  FIG.  4   . 
     Referring to (a- 3 ) and (b- 3 ) of  FIG.  6   , it may be seen that a recombination rate in the electron blocking layer  35  of the light emitting element core  30  including the third semiconductor layer  34  of (b- 3 ) is reduced compared to a recombination rate in the electron blocking layer  35  of the light emitting element core  30 _R with the third semiconductor layer  34  omitted as illustrated in (a- 3 ). For example, by further disposing the third semiconductor layer  34 , it may be seen that non-radiative recombination in the damaged surface area A 2  of the light emitting element core  30  is reduced, and accordingly, light emitting efficiency of the light emitting element ED may be improved. 
       FIG.  7    is a graph comparing energy efficiencies between light emitting element cores. 
       FIG.  7    is a graph illustrating an efficiency of the light emitting element ED according to a current density. An x-axis of  FIG.  7    may represent current density, and a y-axis thereof may represent efficiency of the light emitting element ED. #1 of  FIG.  7    may be a light emitting element ED including a light emitting element core that does not include the third semiconductor layer  34 , #2 of  FIG.  7    may be a light emitting element ED including a light emitting element core including an electron blocking layer  35  having an aluminum composition of 15% or less, and #3 of  FIG.  7    may be a light emitting element ED including a light emitting element core  30  including the electron blocking layer  35  having the aluminum composition of 15% or less and the third semiconductor layer  34 . 
     Referring to #1 of  FIG.  7   , it may be seen that the efficiency of the light emitting element ED that does not include the third semiconductor layer  34  decreases as the current density increases. Referring to #2 of  FIG.  7   , it may be seen that a decrease in the efficiency of the light emitting element ED including the light emitting element core including the electron blocking layer  35  having the aluminum composition of 15% or less is reduced as the current density increases, but a maximum efficiency of the light emitting element is reduced. Referring to #3 of  FIG.  7   , it may be seen that a decrease in efficiency of the light emitting element ED including the light emitting element core  30  including the electron blocking layer  35  having the aluminum composition of 15% or less and the third semiconductor layer  34  is reduced and the maximum efficiency of the light emitting element is increased compared to that of the light emitting element of #2 of  FIG.  7    as the current density increases. 
     Hereinafter, another embodiment of a light emitting element will be described. In the following embodiments, a description for the same configurations as those of the embodiment described above will be omitted or simplified and configurations different from those of the embodiment described above will be described. 
       FIG.  8    is a schematic cross-sectional view of a light emitting element illustrating an embodiment taken along line I-I′ of  FIG.  1   . 
     A light emitting element ED_ 1  according to the embodiment is different from the embodiment of  FIG.  2    in that it includes a light emitting element core  30 _ 1  including a third semiconductor layer  34 _ 1  undoped with a conductivity-type dopant. 
     Specifically, the third semiconductor layer  34 _ 1  may include an undoped semiconductor. The third semiconductor layer  34 _ 1  may include substantially the same material as the second semiconductor layer  32 , but may include a material that is not doped with a second conductivity-type dopant. 
     In the embodiment, as the third semiconductor layer  34 _ 1  includes substantially the same material as the second semiconductor layer  32 , but is not doped with the conductivity-type dopant, a band bending effect may occur at an interface between a first area A 1  of the third semiconductor layer  34 _ 1  and a damaged surface area A 2  of the third semiconductor layer  34 _ 1 . Accordingly, it is possible to prevent the holes provided from the second semiconductor layer  32  from leaking into the damaged surface area A 2 , and the holes provided from the second semiconductor layer  32  may be induced to flow in the first area A 1  of the light emitting element core  30  in which no defect has occurred. Accordingly, non-radiative recombination in the damaged surface area A 2  of the light emitting element core  30  may be reduced, so that light emitting efficiency of the light emitting element may be improved. 
       FIG.  9    is a plan view of a display device according to an embodiment. 
     Referring to  FIG.  9   , a display device  10  displays a moving image or a still image. The display device  10  may refer to all electronic devices that provide display screens. For example, televisions, laptop computers, monitors, billboards, Internet of Things (IoT), mobile phones, smartphones, tablet personal computers (PCs), electronic watches, smartwatches, watch phones, head mounted displays, mobile communication terminals, electronic organizers, electronic books, portable multimedia players (PMPs), navigation devices, game machines, digital cameras, camcorders, and the like, that provide display screens may be included in the display device  10 . 
     The display device  10  may include a display panel providing a display screen. Examples of the display panel may include an inorganic light emitting diode display panel, an organic light emitting display panel, a quantum dot light emitting display panel, a plasma display panel, a field emission display panel, and the like. Hereinafter, a case where the above-described light emitting element ED, specifically, the inorganic light emitting diode display panel is applied as an embodiment of the display panel will be described by way of example, but the disclosure is not limited thereto, and the same technical idea may be applied to other display panels if applicable. 
     Hereinafter, in the drawings of an embodiment for describing the display device  10 , a first direction DR 1 , a second direction DR 2 , and a third direction DR 3  are defined. The first direction DR 1  and the second direction DR 2  may be directions perpendicular to each other in one plane. The third direction DR 3  may be a direction perpendicular to the plane in which the first direction DR 1  and the second direction DR 2  are positioned. The third direction DR 3  is perpendicular to each of the first direction DR 1  and the second direction DR 2 . In embodiments for describing the display device  10 , the third direction DR 3  refers to a thickness direction of the display device  10 . 
     The display device  10  may have a rectangular shape including a long side and a short side in which the first direction DR 1  is longer than the second direction DR 2  in a plan view. A corner portion where the long side and the short side of the display device  10  meet in a plan view may be right-angled, but is not limited thereto, and may have a rounded curved shape. The shape of the display device  10  in a plan view is not limited to that described above, and may be other shapes such as a square shape, a quadrangular shape with rounded corners (vertices), other polygonal shapes, and a circular shape. 
     A display surface of the display device  10  may be disposed on one side in the third direction DR 3 , which is the thickness direction. In embodiments for describing the display device  10 , unless otherwise stated, “upper portion” refers to a display direction as a side in the third direction DR 3 , and “upper surface” refers to a surface facing one side in the third direction DR 3 . “Lower portion” refers to a direction opposite to the display direction as another side in the third direction DR 3 , and “lower surface” refers to a surface facing the other side in the third direction DR 3 . “left”, “right”, “upper”, and “lower” refer to directions in case that the display device  10  is viewed in a plan view. For example, “right side” refers to a side in the first direction DR 1 , “left side” refers to another side in the first direction DR 1 , “upper side” refers to a side in the second direction DR 2 , and “lower side” refers to another side in the second direction DR 2 . 
     The display device  10  may include a display area DPA and a non-display area NDA. The display area DPA may be an area in which a screen is displayed, and the non-display area NDA may be an area in which a screen is not displayed. 
     A shape of the display area DPA may follow the shape of the display device  10 . For example, the shape of the display area DPA may have a rectangular shape in a plan view, similar to the overall shape of the display device  10 . The display area DPA may occupy substantially the center of the display device  10 . 
     The display area DPA may include multiple pixels PX. The multiple pixels PX may be arranged in a matrix direction. A shape of each pixel PX may be a rectangular or square shape in a plan view. However, the disclosure is not limited thereto, and the shape of each pixel PX may be a rhombic shape in which each side is inclined with respect to one direction. Each pixel PX may be alternately arranged in a stripe type or a pentile® type. 
     The non-display area NDA may be disposed around the display area DPA. The non-display area NDA may completely or partially surround the display area DPA. In an embodiment, the display area DPA may have a rectangular shape, and the non-display area NDA may be disposed adjacent to four sides of the display area DPA. The non-display area NDA may constitute a bezel of the display device  10 . Wirings, circuit drivers, or a pad portion on which an external device is mounted, which are included in the display device  10 , may be disposed in the non-display area NDA. 
       FIG.  10    is a plan layout view illustrating a pixel of a display device according to an embodiment.  FIG.  11    is a schematic cross-sectional view illustrating an embodiment taken along line Q-Q′ of  FIG.  10   . 
     Referring to  FIG.  10   , each pixel PX of the display device  10  may include an emission area EMA and a non-emission area. The emission area EMA may be an area from which the light emitted from the light emitting element ED is emitted, and the non-emission area may be defined as an area where light emitted from the light emitting element ED does not reach and thus does not emit light. 
     The emission area EMA may include an area in which the light emitting elements ED are disposed and an area adjacent thereto. The emission area may further include an area in which the light emitted from the light emitting elements ED is reflected or refracted by other members and then emitted. 
     Each pixel PX may further include a sub-area SA disposed in the non-emission area. The light emitting elements ED may not be disposed in the sub-area SA. The sub-area SA may be disposed on an upper side of the emission area EMA in a plan view in a pixel PX. The sub-area SA may be disposed between emission areas EMA of pixels PXs neighboring each other in the second direction DR 2 . The sub-area SA may include an area in which an electrode layer  200  and a contact electrode  700  are electrically connected to each other through contact portions CT 1  and CT 2 . 
     The sub-area SA may include a separation portion ROP. The separation portion ROP of the sub-area SA may be an area in which a first electrode  210  and a second electrode  220  included in the electrode layer  200  included in each pixel PX adjacent to each other along the second direction DR 2  are separated from each other. 
     Referring to  FIGS.  10  and  11   , the display device  10  may include a substrate SUB, a circuit element layer disposed on the substrate SUB, and a light emitting element layer disposed on the circuit element layer. 
     The substrate SUB may be an insulating substrate. The substrate SUB may be made of an insulating material such as glass, quartz, or a polymer resin. The substrate SUB may be a rigid substrate, but may also be a flexible substrate that may be bent, folded, or rolled. 
     The circuit element layer may be disposed on the substrate SUB. The circuit element layer may include a lower metal layer  110 , a semiconductor layer  120 , a first conductive layer  130 , a second conductive layer  140 , a third conductive layer  150 , and multiple insulating films. 
     The lower metal layer  110  may be disposed on the substrate SUB. The lower metal layer  110  may include a light blocking pattern BML. The light blocking pattern BML, may be disposed below an active layer ACT of a transistor TR so as to cover at least a channel area of the active layer ACT of the transistor TR. However, the light blocking pattern BML is not limited thereto and may be omitted. 
     The lower metal layer  110  may include a material that blocks light. For example, the lower metal layer  110  may be formed of an opaque metal material that blocks transmission of the light. 
     A buffer layer  161  may be disposed on the lower metal layer  110 . The buffer layer  161  may be disposed to cover the entire surface of the substrate SUB on which the lower metal layer  110  is disposed. The buffer layer  161  may serve to protect multiple transistors from moisture permeating through the substrate SUB vulnerable to moisture permeation. 
     The semiconductor layer  120  may be disposed on the buffer layer  161 . The semiconductor layer  120  may include the active layer ACT of the transistor TR. The active layer ACT of the transistor TR may be disposed to overlap the light blocking pattern BML of the lower metal layer  110 , as described above. 
     The semiconductor layer  120  may include polycrystalline silicon, single crystal silicon, an oxide semiconductor, or the like. In an embodiment, in case that the semiconductor layer  120  includes the polycrystalline silicon, the polycrystalline silicon may be formed by crystallizing amorphous silicon. In case that the semiconductor layer  120  includes the polycrystalline silicon, the active layer ACT of the transistor TR may include multiple doped areas doped with impurities and a channel area between the multiple doped areas. In an embodiment, the semiconductor layer  120  may include an oxide semiconductor. The oxide semiconductor may be, for example, indium-tin oxide (ITO), indium-zinc oxide (IZO), indium-gallium oxide (IGO), indium-zinc-tin Oxide (IZTO), indium-gallium- zinc oxide (IGZO), indium-gallium-tin oxide (IGTO), indium-gallium-zinc-tin oxide (IGZTO), or the like. 
     A gate insulating film  162  may be disposed on the semiconductor layer  120 . The gate insulating layer  162  may function as a gate insulating film of the transistor. The gate insulating layer  162  may be formed as a multiple layer in which inorganic layers including an inorganic material, for example, silicon oxide (SiO x ), silicon nitride (SiN x ), or silicon oxynitride (SiO x N y ) are alternately stacked each other. 
     The first conductive layer  130  may be disposed on the gate insulating layer  162 . The first conductive layer  130  may include a gate electrode GE of the transistor TR. The gate electrode GE may be disposed to overlap the channel area of the active layer ACT in the third direction DR 3 , which is the thickness direction of the substrate SUB. 
     A first interlayer insulating film  163  may be disposed on the first conductive layer  130 . The first interlayer insulating film  163  may be disposed to cover the gate electrode GE. The first interlayer insulating film  163  may function as an insulating film between the first conductive layer  130  and other layers disposed on the first conductive layer  130 , and may protect the first conductive layer  130 . 
     The second conductive layer  140  may be disposed on the first interlayer insulating film  163 . The second conductive layer  140  may include a drain electrode SD 1  of the transistor TR and a source electrode SD 2  of the transistor TR. 
     The drain electrode SD 1  and the source electrode SD 2  of the transistor TR may be electrically connected to both end areas of the active layer ACT of the transistor TR through contact holes penetrating the first interlayer insulating film  163  and the gate insulating film  162 , respectively. The source electrode SD 2  of the transistor TR may be electrically connected to the light blocking pattern BML, of the lower metal layer  110  through another contact hole penetrating the first interlayer insulating film  163 , the gate insulating film  162 , and the buffer layer  161 . 
     A second interlayer insulating film  164  may be disposed on the second conductive layer  140 . The second interlayer insulating film  164  may be disposed to cover the drain electrode SD 1  of the transistor TR and the source electrode SD 2  of the transistor TR. The second interlayer insulating film  164  may function as an insulating film between the second conductive layer  140  and other layers disposed on the second conductive layer  140 , and may protect the second conductive layer  140 . 
     The third conductive layer  150  may be disposed on the second interlayer insulating film  164 . The third conductive layer  150  may include a first voltage line VL 1 , a second voltage line VL 2 , and a conductive pattern CDP. 
     The first voltage line VL 1  may overlap at least a portion of the drain electrode SD 1  of the transistor TR in the thickness direction of the substrate SUB. A high potential voltage (or a first source voltage) supplied to the transistor TR may be applied to the first voltage line VL 1 . 
     The second voltage line VL 2  may be electrically connected to the second electrode  220  through a second electrode contact hole CTS penetrating a via layer  166  and a passivation layer  165  to be described later. A low potential voltage (or a second power voltage) lower than the high potential voltage supplied to the first voltage line VL 1  may be applied to the second voltage line VL 2 . For example, the high potential voltage (or the first source voltage) supplied to the transistor TR may be applied to the first voltage line VL 1 , and the low potential voltage (or the second source voltage) lower than the high potential voltage supplied to the first voltage line VL 1  may be applied to the second voltage line VL 2 . 
     The conductive pattern CDP may be electrically connected to the source electrode SD 2  of the transistor TR. The conductive pattern CDP may be electrically connected to the source electrode SD 2  of the transistor TR through a contact hole penetrating the second interlayer insulating film  164 . The conductive pattern CDP may be electrically connected to the first electrode  210  through a first electrode contact hole CTD penetrating the via layer  166  and the passivation layer  165  to be described later. The transistor TR may transfer the first source voltage applied from the first voltage line VL 1  to the first electrode  210  through the conductive pattern CDP. 
     A passivation layer  165  may be disposed on the third conductive layer  150 . The passivation layer  165  may be disposed to cover the third conductive layer  150 . The passivation layer  165  may serve to protect the third conductive layer  150 . 
     Each of the buffer layer  161 , the gate insulating film  162 , the first interlayer insulating film  163 , the second interlayer insulating film  164 , and the passivation layer  165  may be formed of multiple inorganic layers alternately stacked each other. For example, each of the buffer layer  161 , the gate insulating film  162 , the first interlayer insulating film  163 , the second interlayer insulating film  164 , and the passivation layer  165  may be formed as a double layer in which inorganic layers including at least one of silicon oxide (SiO x ), silicon nitride (SiN x ), and silicon oxynitride (SiO x N y ) are stacked each other or multiple layers in which these layers are alternately stacked each other. However, the disclosure is not limited thereto, and each of the buffer layer  161 , the gate insulating film  162 , the first interlayer insulating film  163 , the second interlayer insulating film  164 , and the passivation layer  165  may also be formed as a single inorganic layer including the insulating material described above. 
     The via layer  166  may be disposed on the passivation layer  165 . The via layer  166  may include an organic insulating material, for example, an organic material such as polyimide (PI). The via layer  166  may perform a function of planarizing a surface. Accordingly, an upper surface (or surface) of the via layer  166  on which a light emitting element layer, which will be described later, is disposed, may have a generally flat surface regardless of a shape or presence of a pattern disposed on a lower side thereof. 
     The light emitting element layer may be disposed on the circuit element layer. The light emitting element layer may be disposed on the via layer  166 . The light emitting element layer may include a first bank  400 , an electrode layer  200 , a first insulating layer  510 , a second bank  600 , multiple light emitting elements ED, and a contact electrode  700 . 
     The first bank  400  may be disposed on the via layer  166  in the emission area EMA. The first bank  400  may be directly disposed on a surface of the via layer  166 . The first bank  400  may have a structure in which at least a portion thereof protrudes upward (e.g., toward one side in the third direction DR 3 ) with respect to the surface of the via layer  166 . The protruding portion of the first bank  400  may have inclined side surfaces. The first bank  400  may have the inclined side surfaces to serve to change a traveling direction of light emitted from the light emitting elements ED so that the light traveling toward the side surfaces of the first bank  400  may reflect to an upper direction (e.g., a display direction). 
     The first bank  400  may include a first sub-bank  410  and a second sub-bank  420  spaced apart from each other. The first sub-bank  410  and the second sub-bank  420  spaced apart from each other may provide a space in which the light emitting elements ED are disposed and also assist in the role of reflective partitions that change the traveling direction of the light emitted from the light emitting elements ED to the display direction. 
     It has been illustrated in the drawings that the side surfaces of the first bank  400  are inclined in a linear shape, but the disclosure is not limited thereto. For example, the side surfaces (or outer surfaces) of the first bank  400  may have a curved semicircular or semielliptical shape. In an embodiment, the first bank  400  may include an organic insulating material such as polyimide (PI), but is not limited thereto. 
     The electrode layer  200  may have a shape extending in one direction and may be disposed throughout the emission area EMA and the sub-area SA. The electrode layer  200  may transmit an electric signal applied from the circuit element layer to the light emitting element ED to emit light. The electrode layer  200  may be used to generate an electric field used in an alignment process of the multiple light emitting elements ED. 
     The electrode layer  200  may be disposed on the first bank  400  and the via layer  166  exposed by the first bank  400 . In the emission area EMA, the electrode layer  200  may be disposed on the first bank  400 , and in the non-emission area, the electrode layer  200  may be disposed on the via layer  166  exposed by the first bank  400 . 
     The electrode layer  200  may include a first electrode  210  and a second electrode  220 . The first electrode  210  and the second electrode  220  may be spaced apart from each other. 
     The first electrode  210  may be disposed on the left side of each pixel PX in a plan view. The first electrode  210  may have a shape extending in the second direction DR 2  in a plan view. The first electrode  210  may be disposed throughout the emission area EMA and the sub-area SA. The first electrode  210  may extend in the second direction DR 2  in a plan view, and may be separated from the first electrode  210  of the neighboring pixel PX in the second direction DR 2  in the separation portion ROP of the sub-area SA. 
     The second electrode  220  may be spaced apart from the first electrode  210  in the first direction DR 1 . The second electrode  220  may be disposed on the right side of each pixel PX in a plan view. The second electrode  220  may have a shape extending in the second direction DR 2  in a plan view. The second electrode  220  may be disposed to cross the emission area EMA and the sub-area SA. The second electrode  220  may extend in the second direction DR 2  in a plan view, and may be separated from the second electrode  220  of the neighboring pixel PX in the second direction DR 2  in the separation portion ROP of the sub-area SA. 
     Specifically, in the emission area EMA, the first electrode  210  may be disposed on the first sub-bank  410 , and the second electrode  220  may be disposed on the second sub-bank  420 . The first electrode  210  may extend outwardly from the first sub-bank  410  and may also be disposed on the via layer  166  exposed by the first sub-bank  410 . Similarly, the second electrode  220  may extend outwardly from the second sub-bank  420  and may also be disposed on the via layer  166  exposed by the second sub-bank  420 . The first electrode  210  and the second electrode  220  may be spaced apart from each other and may face each other in a spaced area between the first sub-bank  410  and the second sub-bank  420 . The via layer  166  may be exposed in an area where the first electrode  210  and the second electrode  220  are spaced apart from each other and face each other. 
     The first electrode  210  may be spaced apart from a first electrode  210  of another pixel PX adjacent in the second direction DR 2  with the separation portion ROP interposed therebetween in the sub-area SA. Similarly, the second electrode  220  may be spaced apart from a second electrode  220  of another pixel PX adjacent in the second direction DR 2  with the separation portion ROP interposed therebetween in the sub-area SA. Accordingly, the first electrode  210  and the second electrode  220  may expose the via layer  166  in the separation portion ROP of the sub-area SA. 
     The first electrode  210  may be electrically connected to the conductive pattern CDP of the circuit element layer through the first electrode contact hole CTD penetrating the via layer  166  and the passivation layer  165 . Specifically, the first electrode  210  may be in contact with an upper surface of the conductive pattern CDP exposed by the first electrode contact hole CTD. The first source voltage applied from the first voltage line VL 1  may be transferred to the first electrode  210  through the conductive pattern CDP. 
     The second electrode  220  may be electrically connected to the second voltage line VL 2  of the circuit element layer through the second electrode contact hole CTS penetrating the via layer  166  and the passivation layer  165 . Specifically, the second electrode  220  may be in contact with an upper surface of the second voltage line VL 2  exposed by the second electrode contact hole CTS. The second source voltage applied from the second voltage line VL 2  may be transferred to the second electrode  220 . 
     The electrode layer  200  may include a conductive material having high reflectivity. For example, the electrode layer  200  may include a metal such as silver (Ag), copper (Cu), aluminum (Al), or the like, or include an alloy including aluminum (Al), nickel (Ni), lanthanum (La), or the like, as the material having the high reflectivity. The electrode layer  200  may reflect the light emitted from the light emitting element ED so that the light traveling toward the side surfaces of the first bank  400  may reflect to an upper direction of each pixel PX. 
     However, the disclosure is not limited thereto, and the electrode layer  200  may include a transparent conductive material. For example, the electrode layer  200  may include a material such as ITO, IZO, or ITZO. In the embodiments, the electrode layer  200  may have a structure in which one or more layers made of the transparent conductive material and one or more layers made of the metal having the high reflectivity are stacked each other or may be formed as one layer including the transparent conductive material and the metal having the high reflectivity. For example, the electrode layer  200  may have a stacked structure such as ITO/Ag/ITO, ITO/Ag/IZO, or ITO/Ag/ITZO/IZO. 
     The first insulating layer  510  may be disposed on the via layer  166  on which the electrode layer  200  is formed. The first insulating layer  510  may protect the electrode layer  200  and may insulate the first electrode  210  and the second electrode  220  from each other. 
     The first insulating layer  510  may include an inorganic insulating material. For example, the first insulating layer  510  may include at least one of an inorganic insulating material such as silicon oxide (SiO x ), silicon nitride (SiN x ), silicon oxynitride (SiO x N y ), aluminum oxide (Al x O y ), and aluminum nitride (AlN). The first insulating layer  510  made of the inorganic material may have a surface shape reflecting a pattern shape of the electrode layer  200  disposed below. For example, the first insulating layer  510  may have a stepped structure according to the shape of the electrode layer  200  disposed below the first insulating layer  510 . Specifically, the first insulating layer  510  may include a stepped structure in which a portion of the upper surface thereof is recessed in an area where the first electrode  210  and the second electrode  220  are spaced apart from each other and face each other. Therefore, a height of the upper surface of the first insulating layer  510  disposed on an upper portion of the first electrode  210  and an upper portion of the second electrode  220  may be higher than a height of the upper surface of the first insulating layer  510  disposed on the via layer  166  in which the first electrode  210  and the second electrode  220  are not disposed. In the specification, a height of an upper surface of any layer may be relatively compared with a height measured from a flat reference surface (e.g., the upper surface of the via layer  166 ) without a lower stepped structure. 
     The first insulating layer  510  may include a first contact portion CT 1  exposing a portion of the upper surface of the first electrode  210  and a second contact portion CT 2  exposing a portion of the upper surface of the second electrode  220  in the sub-area SA. The first electrode  210  may be electrically connected to a first contact electrode  710  to be described later through the first contact portion CT 1  penetrating the first insulating layer  510  in the sub-area SA, and the second electrode  220  may be electrically connected to a second contact electrode  720  to be described later through the second contact portion CT 2  penetrating the first insulating layer  510  in the sub-area SA. 
     The second bank  600  may be disposed on the first insulating layer  510 . The second bank  600  may be disposed in a lattice pattern by including portions extending in the first direction DR 1  and the second direction DR 2  in a plan view. 
     The second bank  600  may be disposed across boundaries between the adjacent pixels PX to divide neighboring pixels PX, and may divide the emission area EMA and the sub-area SA. The second bank  600  may be formed to have a greater height than the first bank  400  to allow ink in which the multiple light emitting elements ED are dispersed to be sprayed into the emission area EMA without being mixed into the adjacent pixels PX in an inkjet printing process for aligning the light emitting elements ED of the process of manufacturing the display device  10 . 
     The multiple light emitting elements ED may be disposed in the emission area EMA. The multiple light emitting elements ED may not be disposed in the sub-area SA. 
     The multiple light emitting elements ED may be disposed on the first insulating layer  510  between the first sub-bank  410  and the second sub-bank  420 . The multiple light emitting elements ED may be disposed between the first electrode  210  and the second electrode  220  on the first insulating layer  510 . 
     The light emitting element ED may have a shape extending in one direction, and may be disposed so that both ends thereof are placed on the first electrode  210  and the second electrode  220 , respectively. For example, the multiple light emitting elements ED may be disposed so that one end of the light emitting element ED is placed on the first electrode  210  and another end of the light emitting element ED is placed on the second electrode  220 . 
     A length of each light emitting element ED (i.e., a length of the light emitting element ED in the first direction DR 1  in the drawing) may be smaller than the shortest distance between the first sub-bank  410  and the second sub-bank  420  spaced apart from each other in the first direction DR 1 . The length of each light emitting element ED may be greater than the shortest distance between the first electrode  210  and the second electrode  220  spaced apart from each other in the first direction DR 1 . As the distance between the first sub-bank  410  and the second sub-bank  420  in the first direction DR 1  is formed to be longer than the length of each light emitting element ED, and the distance between the first electrode  210  and the second electrode  220  in the first direction DR 1  is formed to be shorter than the length of each light emitting element ED, the multiple light emitting elements ED may be disposed so that both ends of the multiple light emitting elements ED are placed on the first electrode  210  and the second electrode  220  in the area between the first sub-bank  410  and the second sub-bank  420 , respectively. 
     The multiple light emitting elements ED may be spaced apart from each other along the second direction DR 2  in which the first electrode  210  and the second electrode  220  extend, and may be aligned substantially parallel to each other. 
     The second insulating layer  520  may be disposed on the light emitting element ED. The second insulating layer  520  may be disposed on a part of the light emitting element ED to expose both ends of the light emitting element ED. The second insulating layer  520  may be disposed to partially cover the outer surface of the light emitting element ED so as not to cover one end and the other end of the light emitting element ED. 
     A portion of the second insulating layer  520  disposed on the light emitting element ED may be disposed to extend in the second direction DR 2  on the first insulating layer  510  in a plan view to form a linear or island-shaped pattern in each pixel PX. The second insulating layer  520  may protect the light emitting element ED and may fix the light emitting element ED in the process of manufacturing the display device  10 . The second insulating layer  520  may be disposed to fill a spaced space between the light emitting element ED and the first insulating layer  510  on the lower side of the light emitting element ED. 
     The contact electrode  700  may be disposed on the second insulating layer  520 . The contact electrode  700  may be disposed on the first insulating layer  510  on which the light emitting element ED is disposed. The contact electrode  700  may include a first contact electrode  710  and a second contact electrode  720  spaced apart from each other. 
     The first contact electrode  710  may be disposed on the first electrode  210  in the emission area EMA. The first contact electrode  710  may have a shape extending in the second direction DR 2  on the first electrode  210 . The first contact electrode  710  may be in contact with each of the first electrode  210  and an end of the light emitting element ED. 
     The first contact electrode  710  may be in contact with the first electrode  210  exposed by the first contact portion CT 1  penetrating the first insulating layer  510  in the sub-area SA, and may be in contact with an end of the light emitting element ED in the emission area EMA. For example, the first contact electrode  710  may serve to electrically connect the first electrode  210  and an end of the light emitting element ED to each other. 
     The second contact electrode  720  may be disposed on the second electrode  220  in the emission area EMA. The second contact electrode  720  may have a shape extending in the second direction DR 2  on the second electrode  220 . The second contact electrode  720  may be in contact with each of the second electrode  220  and another end of the light emitting element ED. 
     The second contact electrode  720  may be in contact with the second electrode  220  exposed by the second contact portion CT 2  penetrating the first insulating layer  510  in the sub-area SA, and may be in contact with the other end of the light emitting element ED in the emission area EMA. For example, the second contact electrode  720  may serve to electrically connect the second electrode  220  and the other end of the light emitting element ED to each other. 
     The first contact electrode  710  and the second contact electrode  720  may be spaced apart from each other on the light emitting element ED. Specifically, the first contact electrode  710  and the second contact electrode  720  may be spaced apart from each other with the second insulating layer  520  interposed therebetween. The first contact electrode  710  and the second contact electrode  720  may be electrically insulated from each other. 
     The first contact electrode  710  and the second contact electrode  720  may include a same material. For example, each of the first contact electrode  710  and the second contact electrode  720  may include a conductive material. For example, the first contact electrode  710  and the second contact electrode  720  may include ITO, IZO, ITZO, aluminum (Al), or the like. For example, each of the first contact electrode  710  and the second contact electrode  720  may include a transparent conductive material. As each of the first contact electrode  710  and the second contact electrode  720  includes the transparent conductive material, the light emitted from the light emitting element ED may transmit through the first contact electrode  710  and the second contact electrode  720  to travel toward the first electrode  210  and the second electrode  220 , and may be reflected from surfaces of the first electrode  210  and the second electrode  220 . 
     The first contact electrode  710  and the second contact electrode  720  may include a same material and may be formed as a same layer. The first contact electrode  710  and the second contact electrode  720  may be simultaneously formed by a same process. 
     A third insulating layer  530  may be disposed on the contact electrode  700 . The third insulating layer  530  may cover the light emitting element layer disposed below. The third insulating layer  530  may cover the first bank  400 , the electrode layer  200 , the first insulating layer  510 , the multiple light emitting elements ED, and the contact electrode  700 . The third insulating layer  530  may be disposed on the second bank  600  to cover the second bank  600 . 
     The third insulating layer  530  may serve to protect the light emitting element layer disposed below from foreign substances such as moisture, oxygen or particles of dust. The third insulating layer  530  may serve to protect the first bank  400 , the electrode layer  200 , the first insulating layer  510 , the multiple light emitting elements ED, and the contact electrode  700 . 
       FIG.  12    is a schematic enlarged cross-sectional view illustrating an embodiment of area P of  FIG.  11   . 
     Referring to  FIG.  12   , the light emitting element ED may be disposed so that an extension direction of the light emitting element ED is parallel to a surface of the substrate SUB. The multiple semiconductor layers included in the light emitting element ED may be sequentially disposed along a direction parallel to the upper surface of the substrate SUB (or the upper surface of the via layer  166 ). For example, the first semiconductor layer  31 , the element active layer  33 , the electron blocking layer  35 , the third semiconductor layer  34 , and the second semiconductor layer  32  of the light emitting element ED may be sequentially disposed to be parallel to the upper surface of the substrate SUB. 
     Specifically, in the light emitting element ED, the first semiconductor layer  31 , the element active layer  33 , the electron blocking layer  35 , the third semiconductor layer  34 , the second semiconductor layer  32 , and the element electrode layer  37  may be sequentially formed on a cross-section crossing both ends of the light emitting element ED in a direction parallel to the upper surface of the substrate SUB. 
     The light emitting element ED may be disposed so that an end thereof is placed on the first electrode  210  and another end thereof is placed on the second electrode  220 . However, the disclosure is not limited thereto, and the light emitting element ED may also be disposed so that an end thereof is placed on the second electrode  220  and the other end thereof is placed on the first electrode  210 . 
     The second insulating layer  520  may be disposed on the light emitting element ED. The second insulating layer  520  may be disposed to surround an outer surface of the light emitting element ED. The second insulating layer  520  may be disposed on the element insulating layer  38  of the light emitting element ED and may surround an outer surface of the element insulating layer  38  of the light emitting element ED facing the display direction DR 3 . 
     In an area in which the light emitting element ED is disposed, the second insulating layer  520  may be disposed to surround the outer surface of the light emitting element ED (specifically, the element insulating layer  38  of the light emitting element ED), and in an area in which the light emitting element ED is not disposed, the second insulating layer  520  may be disposed on the first insulating layer  510  exposed by the light emitting element ED. 
     The first contact electrode  710  may be in contact with an end of the light emitting element ED exposed by the second insulating layer  520 . Specifically, the first contact electrode  710  may be disposed to surround an end surface of the light emitting element ED exposed by the second insulating layer  520 . The first contact electrode  710  may be in contact with the element insulating layer  38  and the element electrode layer  37  of the light emitting element ED. 
     The second contact electrode  720  may be in contact with another end of the light emitting element ED exposed by the second insulating layer  520 . Specifically, the second contact electrode  720  may be disposed to surround the other end surface of the light emitting element ED exposed by the second insulating layer  520 . The second contact electrode  720  may be in contact with the element insulating layer  38  and the first semiconductor layer  31  of the light emitting element ED. 
     The first contact electrode  710  and the second contact electrode  720  may be spaced apart from each other with the second insulating layer  520  interposed therebetween. The first contact electrode  710  and the second contact electrode  720  may expose at least a portion of the upper surface of the second insulating layer  520 . 
     The first contact electrode  710  and the second contact electrode  720  may be formed on a same layer and may include a same material. For example, the first contact electrode  710  and the second contact electrode  720  may be simultaneously formed by a mask process. Accordingly, since an additional mask process for forming the first contact electrode  710  and the second contact electrode  720  is not required, an efficiency of the process of manufacturing the display device  10  may be improved. 
       FIG.  13    is a schematic enlarged cross-sectional view illustrating an embodiment of area P of  FIG.  11   . 
     Referring to  FIG.  13   , a display device  10  according to the embodiment is different from the display device  10  according to the embodiment described above with reference to  FIG.  12    in that a contact electrode  700   1  includes a first contact electrode  710  and a second contact electrode  720 _ 1  formed on different layers and the light emitting element layer further includes a fourth insulating layer  540 . 
     Specifically, the contact electrode  700   1  may include a first contact electrode  710  and a second contact electrode  720 _ 1  formed on different layers. 
     The first contact electrode  710  may be disposed on the first electrode  210  and an end of the light emitting element ED. The first contact electrode  710  may extend from an end of the light emitting element ED toward the second insulating layer  520  to be also disposed on a sidewall of the second insulating layer  520  and an upper surface of the second insulating layer  520 . The first contact electrode  710  may be disposed on the upper surface of the second insulating layer  520 , but may expose at least a portion of the upper surface of the second insulating layer  520 . 
     The fourth insulating layer  540  may be disposed on the first contact electrode  710 . The fourth insulating layer  540  may be disposed to completely cover the first contact electrode  710 . The fourth insulating layer  540  may be disposed to completely cover a sidewall and the upper surface of the second insulating layer  520 , but may not be disposed on another sidewall of the second insulating layer  520 . An end of the fourth insulating layer  540  may be aligned with the other sidewall of the second insulating layer  520 . 
     The second contact electrode  720 _ 1  may be disposed on the second electrode  220  and another end of the light emitting element ED. The second contact electrode  720 _ 1  may extend from the other end of the light emitting element ED toward the second insulating layer  520  to be also disposed on the other sidewall of the second insulating layer  520  and an upper surface of the fourth insulating layer  540 . 
     The third insulating layer  530  may be disposed on the fourth insulating layer  540  and the second contact electrode  720 _ 1 . The third insulating layer  530  may be disposed on the fourth insulating layer  540  and the second contact electrode  720 _ 1  to cover the fourth insulating layer  540  and the second contact electrode  720 _ 1 . 
     In the embodiment, a manufacturing process of the display device  10  may be added by forming the first contact electrode  710  and the second contact electrode  720 _ 1  on the different layers and interposing the fourth insulating layer  540  between the first contact electrode  710  and the second contact electrode  720 _ 1 , such that the efficiency of the process of manufacturing the display device  10  may decrease, but reliability of the display device  10  may be improved. Specifically, a problem that the first contact electrode  710  and the second contact electrode  720 _ 1  are short-circuited in the process of manufacturing the display device  10  may be minimized by forming the first contact electrode  710  and the second contact electrode  720 _ 1  on the different layers and further disposing the fourth insulating layer  540  between the first contact electrode  710  and the second contact electrode  720 _ 1 . 
     Embodiments have been disclosed herein, and although terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. In some instances, as would be apparent by one of ordinary skill in the art, features, characteristics, and/or elements described in connection with an embodiment may be used singly or in combination with features, characteristics, and/or elements described in connection with other embodiments unless otherwise specifically indicated. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the disclosure as set forth in the claims.