Patent Publication Number: US-2023141485-A1

Title: Device transfer substrate, device transfer structure, and display apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2021-0154288, filed on Nov. 10, 2021, in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Field 
     The disclosure relates to a device transfer substrate for arranging devices, a device transfer structure, and a display apparatus, and more particularly, to a device transfer substrate for arranging devices capable of achieving a high transfer yield, a device transfer structure including the device transfer substrate, and a display apparatus manufactured using the device transfer substrate. 
     2. Description of Related Art 
     Light emitting diodes (LEDs), which consume low power and are eco-friendly, have increased in industrial demand and have been applied as display pixels, as well as used as pixels of display apparatuses, as well as used as backlights of lighting devices or liquid crystal displays (LCDs) Recently, micro-LED display apparatuses using a micro-LED chip as a pixel have been developed. In manufacturing display apparatuses using micro-LED chips, a pick and place method has been used as a method of transferring the micro-LEDs, but with this method, productivity decreases as the size of the micro-LEDs decreases and the size of displays increases. 
     SUMMARY 
     Provided are device transfer substrates for arranging devices to transfer a plurality of light emitting devices with high yield. 
     Provided are device transfer structures in which a plurality of light emitting devices are transferred and arranged using a device transfer substrate for arranging devices. 
     Provided are display apparatuses manufactured using a plurality of light emitting devices arranged in a device transfer structure. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of embodiments of the disclosure. 
     In accordance with an aspect of the disclosure, a device transfer substrate includes a plurality of recesses, wherein each of the plurality of recesses includes a first region having a shape of a first figure; a second region having a shape of a second figure; and an overlapping region on which a portion of the first region partially overlaps a portion of the second region, and wherein a maximum width of the overlapping region in a direction intersecting with a straight line passing through a center of the first figure and a center of the second figure is less than a diameter or a diagonal length of the first figure and less than a diameter or a diagonal length of the second figure. 
     An area of the overlapping region may be greater than 0 and less than or equal to ½ of an area of the first figure. 
     A distance between the center of the first figure and the center of the second figure may be greater than or equal to ½ of the diameter or the diagonal length of the first figure, and may be less than a sum of ½ of the diameter or the diagonal length of the first figure and ½ of the diameter or the diagonal length of the second figure. 
     A distance between the center of the first figure and the center of the second figure may be greater than or equal to ⅔ of the diameter or the diagonal length of the first figure and may be less than a sum of ½ of the diameter or the diagonal length of the first figure and ½ of the diameter or the diagonal length of the second figure. 
     A difference between the diameter or the diagonal length of the first figure and the diameter or the diagonal length of the second figure may be less than or equal to about 20% of the diameter or the diagonal length of the first figure. 
     The first figure and the second figure may have a circular or polygonal shape. 
     Both the first figure and the second figure may have a quadrangular shape, and the first region and the second region may be disposed such that a periphery of a vertex of the first figure overlaps a periphery of a vertex of the second figure or such that the periphery of the vertex of the first figure overlaps a periphery of one side of the second figure. 
     Both the first figure and the second figure may have a trapezoidal shape, and the first region and the second region may be disposed such that a periphery of a vertex of a shorter side of the first figure overlaps a periphery of a vertex of a shorter side of the second figure or such that a periphery of a vertex of a longer side of the first figure overlaps a periphery of a vertex of a longer side of the second figure. 
     Each of the plurality of recesses may further include a third region having a shape of a third figure, and the third region may be disposed to partially overlap the second region and is further disposed not to overlap the first region. 
     The device transfer substrate may further include a barrier surrounding a boundary of each of the plurality of recesses. 
     The first region, the second region, and the overlapping region of one recess may be surrounded by the barrier so that the first region and the second region are connected to each other based on the overlapping region in the one recess. 
     In accordance with an aspect of the disclosure, a device transfer structure includes a device transfer substrate comprising a plurality of recesses; and a light emitting device disposed in each of the plurality of recesses, wherein each of the plurality of recesses includes a first region having a shape of a first figure; a second region having a shape of a second figure; and an overlapping region on which a portion of the first region partially overlaps a portion of the second region, wherein the light emitting device disposed in each of the plurality of recesses is disposed in any one of the first region and the second region, and wherein a maximum width of the overlapping region in a direction intersecting with a straight line passing through a center of the first figure and a center of the second figure is less than a diameter or a diagonal length of the first figure and less than a diameter or a diagonal length of the second figure so that the light emitting device disposed in each of the plurality of recesses does not pass through the overlapping region. 
     An area of the overlapping region may be greater than 0 and less than or equal to ½ of an area of the first figure. 
     A distance between the center of the first figure and the center of the second figure may be greater than or equal to ½ of the diameter or the diagonal length of the first figure, and may be less than a sum of ½ of the diameter or the diagonal length of the first figure and ½ of the diameter or the diagonal length of the second figure. 
     A distance between the center of the first figure and the center of the second figure may be greater than or equal to ⅔ of the diameter or the diagonal length of the first figure and may be less than a sum of ½ of the diameter or the diagonal length of the first figure and ½ of the diameter or the diagonal length of the second figure. 
     A difference between the diameter or the diagonal length of the first figure and the diameter or the diagonal length of the second figure may be less than or equal to about 20 % of the diameter or the diagonal length of the first figure. 
     The diameter or the diagonal length of the first figure may be greater than a diameter or a diagonal length of the light emitting device, and a difference between the diameter or the diagonal length of the first figure and the diameter or the diagonal length of the light emitting device may be less than or equal to 20% of the diameter or the diagonal length of the light emitting device. 
     A difference between the diameter or the diagonal length of the first figure and a diameter or a diagonal length of the light emitting device may be less than or equal to 5 µm. 
     An area of the overlapping region may be less than an area of the light emitting device. 
     A size of the light emitting device may be in a range of 5 µm to 100 µm. 
     Each of the plurality of recesses of the device transfer substrate may further include a third region having a shape of a third figure, wherein the third region is disposed to partially overlap the second region and not to overlap the first region, and wherein the light emitting device is disposed only within the second region or within at least one of the first region and the third region. 
     Each of the plurality of recesses may further include a first electrode pair including a first driving electrode and a second driving electrode disposed in the first region; and a second electrode pair including a third driving electrode and a fourth driving electrode disposed in the second region, and the light emitting device may be electrically connected to any one of the first electrode pair and the second electrode pair. 
     The device transfer substrate may further include a barrier surrounding a boundary of each of the plurality of recesses. 
     The first region, the second region, and the overlapping region of one recess may be surrounded by the barrier so that the first region and the second region are connected based on the overlapping region in the one recess. 
     In accordance with an aspect of the disclosure, a display apparatus includes a display substrate including a plurality of sub-pixels arranged two dimensionally and a driving circuit; and a plurality of light emitting devices disposed on the display substrate, wherein each of the plurality of sub-pixels includes a first region and a second region partially overlapping each other on the display substrate, and wherein the plurality of light emitting devices are irregularly disposed in any one of the first region and the second region of the plurality of sub-pixels. 
     The display apparatus may further include a first electrode pair including a first driving electrode and a second driving electrode disposed in the first region; and a second electrode pair including a third driving electrode and a fourth driving electrode disposed in the second region, wherein, when the light emitting device is disposed in the first region, the light emitting device is electrically connected to the first electrode pair and not electrically connected to the second electrode pair, and wherein, when the light emitting device is disposed in the second region, the light emitting device is electrically connected to the second electrode pair and not electrically connected to the first electrode pair. 
     The display apparatus may further include a wavelength conversion layer configured to convert a wavelength of light emitted from the plurality of light emitting devices. 
     The wavelength conversion layer may include a first wavelength conversion layer configured to convert the light emitted from the plurality of light emitting devices into light having a first wavelength band; and a second wavelength conversion layer configured to convert the light emitted from the plurality of light emitting devices into light having a second wavelength band that is different from the first wavelength band. 
     The display apparatus may further include a color filter layer include a first filter disposed to face the first wavelength conversion layer and configured to transmit light having the first wavelength band; and a second color filter layer disposed to face the second wavelength conversion layer and configured to transmit light having the second wavelength band. 
     In accordance with an aspect of the disclosure, a device transfer substrate may include a plurality of recesses, each of the plurality of recesses including a first end having a first width, a second end having a second width, and a middle portion between the first end and the second end, the middle portion having a middle width, wherein the middle width is less than the first width and the middle width is less than the second width. 
     The first end may have a shape of a first figure and the second end may have a shape of a second figure, and the first figure and the second figure may partially overlap to form the middle portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    is a perspective view schematically illustrating a device transfer structure according to an embodiment; 
         FIG.  2    is a cross-sectional view schematically illustrating a structure of a light emitting device; 
         FIG.  3    is an enlarged schematic plan view of a partial region of the device transfer structure illustrated in  FIG.  1   ; 
         FIG.  4    is a plan view illustrating in detail a shape of a recess provided in a device transfer substrate of the device transfer structure illustrated in  FIG.  1   ; 
         FIGS.  5  and  6    are partial cross-sectional views schematically illustrating the device transfer structure illustrated in  FIG.  1   ; 
         FIG.  7    is a perspective view illustrating a method of arranging a light emitting device using a fluidic self-assembly method; 
         FIG.  8    schematically shows a scanning process of arranging a light emitting device through physical contact by a rod or a blade; 
         FIGS.  9 A and  9 B  are plan views illustrating a shape of a recess of a device transfer substrate according to an embodiment; 
         FIGS.  10 A and  10 B  are plan views illustrating a shape of a recess of a device transfer substrate according to an embodiment; 
         FIGS.  11 A to  11 D  are plan views illustrating a shape of a recess of a device transfer substrate according to an embodiment; 
         FIGS.  12 A to  12 D  are plan views illustrating a shape of a recess of a device transfer substrate according to an embodiment; 
         FIGS.  13 A to  13 C  are plan views illustrating a shape of a recess of a device transfer substrate according to an embodiment; 
         FIGS.  14 A to  14 C  are plan views illustrating a shape of a recess of a device transfer substrate and a shape of a light emitting device according to an embodiment; 
         FIG.  15    is a cross-sectional view schematically illustrating a process of transferring a light emitting device arranged on a device transfer substrate onto a display substrate of a display apparatus; 
         FIGS.  16 A to  16 C  are plan views illustrating various arrangements of electrode pairs that may be electrically connected to a light emitting device transferred on a display substrate; 
         FIG.  17    is a cross-sectional view schematically illustrating an arrangement of electrode pairs on a device transfer structure according to an embodiment; 
         FIG.  18    is a plan view illustrating an arrangement of a plurality of light emitting devices on a display substrate of a display apparatus according to an embodiment; 
         FIG.  19    is a cross-sectional view schematically illustrating a structure of a display apparatus according to an embodiment; 
         FIG.  20    is a cross-sectional view schematically illustrating a structure of a display apparatus according to an embodiment; 
         FIG.  21    is a schematic block diagram of an electronic device according to an embodiment; 
         FIG.  22    illustrates an example in which a display apparatus according to embodiments is applied to a mobile device; 
         FIG.  23    illustrates an example in which a display apparatus according to embodiments is applied to a vehicle display apparatus; 
         FIG.  24    illustrates an example in which a display apparatus according to embodiments is applied to augmented reality glasses or virtual reality glasses; 
         FIG.  25    illustrates an example in which a display apparatus according to embodiments is applied to a signage; and 
         FIG.  26    illustrates an example in which a display apparatus according to embodiments is applied to a wearable display. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, embodiments are merely described below, by referring to the figures, to explain aspects. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
     Hereinafter, a device transfer substrate for arranging devices, a device transfer structure, and a display apparatus will be described in detail with reference to the accompanying drawings. In the following drawings, like reference numerals refer to like components, and the size of each component in the drawings may be exaggerated for clarity and convenience of description. Embodiments described herein are merely examples, and various modifications may be made from these embodiments. 
     When it is described that a certain component is “above” or “on” another component, the certain component may be directly above another component, or a third component may be interposed therebetween. The singular expressions include plural expressions unless the context clearly dictates otherwise. When a part “includes” a component, it may indicate that the part does not exclude another component but may further include another component, unless otherwise stated. 
     The use of the terms “a” and “an” and “the” and similar referents may cover both the singular and the plural. The steps constituting a method may be performed in any suitable order unless there is a clear statement that the steps in the method should be performed in the order described, without being limited to the described order. 
     In addition, terms such as “unit” or “module,” disclosed in the specification indicate a unit for processing at least one function or operation, and this may be implemented by hardware, software, or a combination thereof. 
     The connecting lines, or connectors illustrated in the various figures presented are intended to represent example functional relationships and/or physical or logical couplings between the various elements. It should be noted that many alternative or additional functional relationships, physical connections or logical connections may be present in a practical device. 
     In addition, the use of all examples and example terms is merely for describing technical ideas in detail, and the scope of the disclosure is not limited by these terms unless limited by claims. 
       FIG.  1    is a perspective view schematically illustrating a device transfer structure  100  according to an example embodiment. Referring to  FIG.  1   , the device transfer structure  100  may include a device transfer substrate  110  for arranging devices, the device arrangement having a plurality of recesses  115 , and light emitting devices  120  respectively disposed in the recesses  115 . 
       FIG.  2    is a cross-sectional view schematically illustrating a structure of the light emitting device  120 . Referring to  FIG.  2   , the light emitting device  120  may include a first semiconductor layer  121 , a light emitting layer  122  disposed on an upper surface of the first semiconductor layer  121 , a second semiconductor layer  123  disposed on an upper surface of the light emitting layer  122 , an insulating layer  124  disposed on an upper surface of the second semiconductor layer  123 , a first device electrode  125  disposed on an upper surface of the insulating layer  124  and electrically connected to the second semiconductor layer  123 , and a second device electrode  126  disposed on an upper surface of the insulating layer  124  and electrically connected to the first semiconductor layer  121 . 
     The first semiconductor layer  121  and the second semiconductor layer  123  may include, for example, a group III-V or group II-VI compound semiconductor. The first semiconductor layer  121  and the second semiconductor layer  123  may provide electrons and holes to the light emitting layer  122 . To this end, the first semiconductor layer  121  and the second semiconductor layer  123  may be electrically doped in opposite types. For example, the first semiconductor layer  121  may be doped n-type and the second semiconductor layer  123  may be doped p-type, or the first semiconductor layer  121  may be doped p-type and the second semiconductor layer  123  may be doped n-type. 
     The light emitting layer  122  has a quantum well structure in which quantum wells are disposed between barriers. As electrons and holes provided from the first semiconductor layer  121  and the second semiconductor layer  123  are recombined in the quantum well in the light emitting layer  122 , light may be generated. A wavelength of light generated by the light emitting layer  122  may be determined according to an energy band gap of a material forming the quantum well in the light emitting layer  122 . The light emitting layer  122  may have only one quantum well or may have a multi-quantum well (MQW) structure in which a plurality of quantum wells and a plurality of barriers are alternately disposed. A thickness of the light emitting layer  122  or the number of quantum wells in the light emitting layer  122  may be appropriately selected considering a driving voltage and luminous efficiency of the light emitting device. 
     In order to easily arrange the light emitting device  120  in a fluidic self-assembly or dry self-assembly method to be described later, both the first device electrode  125  and the second device electrode  126  may be disposed on one surface (e.g., on the same surface) of the light emitting device  120 . For example, the insulating layer  124  may be formed on the upper surface of the second semiconductor layer  123 , and the first device electrode  125  and the second device electrode  126  may be disposed on the upper surface of the insulating layer  124 . In order to electrically connect the second device electrode  126  to the first semiconductor layer  121 , the light emitting device  120  may further include a via hole passing through the second semiconductor layer  123  and the light emitting layer  122 . The insulating layer  124  may extend to surround a sidewall of the via hole. In other words, a portion of the second semiconductor layer  123  and a portion of the light emitting layer  122 , exposed by the via hole, may be covered with the insulating layer  124 . The second device electrode  126  may extend from the upper surface of the insulating layer  124  to the upper surface of the first semiconductor layer  121  exposed through the via hole to contact the first semiconductor layer  121  through the via hole. The first device electrode  125  may be configured to pass through the insulating layer  124  and contact the second semiconductor layer  123 . Also, a portion of the first device electrode  125  may further extend in a lateral direction from the upper surface of the insulating layer  124 . 
     The light emitting device  120  may have a small size on a micro-scale. For example, the size of the light emitting device  120  may be in the range of 5 µm to 100 µm. Alternatively, the size of the light emitting device  120  may be in the range of 20 µm to 50 µm or in the range of 5 µm to 20 µm. Here, the size may be defined as a diameter of the light emitting device  120 , a width W of a longer side, or a square root of an area. In addition, the diameter or the width W of the longer side of the light emitting device  120  may be greater than a thickness T of the light emitting device  120 . For example, a ratio of the diameter or the width W of the longer side of the light emitting device  120  to the thickness T of the light emitting device  120  may be 1 or greater, or 5 or greater. 
     Referring back to  FIG.  1   , the device transfer substrate  110  is to arrange the light emitting devices  120  by a fluidic or dry self-assembly method, and the recesses  115 , in which the light emitting devices are disposed, may be provided on the upper surface of the device transfer substrate  110 . As illustrated in  FIG.  1   , the recesses  115  may be arranged in a two-dimensional array form in the upper surface of the device transfer substrate  110 , and the light emitting devices may be arranged in the recesses  115 , respectively. 
       FIG.  3    is an enlarged schematic plan view of a partial region of the device transfer structure  100  illustrated in  FIG.  1   . Referring to  FIG.  3   , each of the recesses  115  may include a first region  115   a  (e.g., a first end) and a second region  115   b  (e.g., a second end) in which the light emitting device  120  may be disposed. The light emitting device  120  may be positioned in only one of the first region  115   a  and the second region  115   b  of each recess  115 . In other words, a total of two light emitting devices  120  may not be received in any one of the recesses  115 . To this end, the first region  115   a  and the second region  115   b  may partially overlap each other. 
     In order for the first device electrode  125  and the second device electrode  126  of the light emitting device  120  to be easily bonded to the corresponding electrodes on a display substrate in the manufacturing process of the display apparatus, the first device electrode  125  and the second device electrode  126  may have a symmetrical shape. The first device electrode  125  may be disposed at the center of the light emitting device  120 . The first device electrode  125  may have a circular shape. However, the disclosure is not limited thereto, and the first device electrode  125  may have a quadrangle or other polygonal shape. The second device electrode  126  may be disposed at an edge of the light emitting device  120 . The second device electrode  126  may have a symmetrical shape with respect to the first device electrode  125 . For example, the second device electrode  126  may be disposed at two vertex regions facing each other in a diagonal direction. 
       FIG.  4    is a plan view illustrating in detail a shape of the recess  115  provided in the device transfer substrate  110  of the device transfer structure  100  illustrated in  FIG.  1   . Referring to  FIG.  4   , each of the recesses  115  has a first region  115   a  having a shape of a first figure, a second region  115   b  having a shape of a second figure, and an overlapping region  116  (e.g., a middle portion) formed as a portion of the first region  115   a  spatially overlaps a portion of the second region  115   b . In one recess  115 , the first region  115   a  and the second region  115   b  may be connected to each other based on the overlapping region  116 . Accordingly, the first region  115   a , the second region  115   b , and the overlapping region  116  are divided for convenience of description, and may actually form an internal space of one recess  115  together. 
     The first figure and the second figure may have the same size and shape, but are not limited thereto. Although the first figure and the second figure are illustrated as square in  FIG.  4   , the disclosure is not limited thereto. The first figure and the second figure may have a shape similar to a horizontal cross-sectional shape of the light emitting device  120 , but are not limited thereto. The first figure and the second figure may have a shape and size in which the light emitting device  120  may be stably positioned in the first region  115   a  or the second region  115   b . For example, the first figure and the second figure may have a circle shape or various polygonal shapes such as a rectangle, a square, a trapezoid, and a hexagon. In addition, the horizontal cross-section of the light emitting device  120  may also have a circle shape or various polygonal shapes, such as a rectangle, a square, a trapezoid, and a hexagon. 
     According to an embodiment, an area of each of the first figure and the second figure may be greater than an area of the cross-section of the light emitting device  120  so that the light emitting device  120  may be received in the first region  115   a  or the second region  115   b . For example, a diameter or a diagonal length of each of the first figure and the second figure may be greater than a diameter or diagonal length of the light emitting device  120 , and in particular, a difference between the diameter or diagonal length of each of the first figure and the second figure and the diameter or diagonal length of the light emitting device  120  may be less than or equal to about 20 % of the diameter or diagonal length of the light emitting device  120 . Alternatively, a difference between the diameter or diagonal length of each of the first figure and the second figure and the diameter or diagonal length of the light emitting device  120  may be greater than 0 µm and less than or equal to about 5 µm. Also, the sizes of the first figure and the second figure may be the same or different within a certain range. For example, a difference between the diameter or diagonal length of the first figure and the diameter or diagonal length of the second figure may be less than or equal to about 20% of the diameter or diagonal length of the first figure. 
     When the light emitting device  120  first enters the first region  115   a , an additional light emitting device  120  cannot enter the second region  115   b , and vice versa. To this end, a portion of the first region  115   a  and a portion of the second region  115   b  may spatially overlap each other. In addition, when both the first region  115   a  and the second region  115   b  are empty, the light emitting device  120  may enter only any one of the first region  115   a  and the second region  115   b  and cannot enter only the overlapping region. To this end, an area of the overlapping region  116  may be greater than 0 and less than the area of the light emitting device  120 . 
     In addition, a maximum width W1 of the overlapping region  116  (e.g., a middle width) in a direction intersecting with a straight line passing through a center C 1  of the first figure and a center C 2  of the second figure may be greater than 0 and may be less than a maximum width, a diameter, or a diagonal length W2 of the first region  115   a  (e.g., a first width) and the second region  115   b  (e.g., a second width). Accordingly, each of the recesses  115  may have a concave shape in a middle portion thereof. Accordingly, once the light emitting device  120  is positioned in the first region  115   a  or the second region  115   b , the light emitting device  120  cannot move to another region through the overlapping region  116  in the recess  115 . For example, when the light emitting device  120  is first positioned in the first region  115   a , the light emitting device  120  cannot then move to the second region  115   b  through the overlapping region  116  in the recess  115 , and when the light emitting device  120  is first positioned in the second region  115   b , the light emitting device  120  cannot then move to the first region  115   a  through the overlapping region  116  in the recess  115 . 
     In addition, if the degree of spatial overlap between the first region  115   a  and the second region  115   b  is too large, that is, if the center C 1  of the first figure and the center C 2  of the second figure are too close, it may be difficult to install driving electrodes of the display substrate to be described below not to overlap each other. Therefore, the distance d between the center C 1  of the first figure and the center C 2  of the second figure may be sufficiently large. For example, the distance d between the center C 1  of the first figure and the center C 2  of the second figure may be greater than or equal to ½ of the diameter or diagonal length W2 of the first figure, and may be less than the sum of ½ of the diameter or diagonal length of the first figure and ½ of the diameter or diagonal length of the second figure. Alternatively, the distance between the center C 1  of the first figure and the center C 2  of the second figure may be greater than or equal to ⅔ of the diameter or diagonal length of the first figure and may be less than the sum of ½ of the diameter or diagonal length of the first figure and ½ of the diameter or diagonal length of the second figure. Also, the area of the overlapping region  116  may be greater than 0 and less than or equal to ½ of the area of the first figure or less than or equal to ½ of the area of the second figure. 
       FIGS.  5  and  6    are partial cross-sectional views schematically illustrating the device transfer structure  100  illustrated in  FIG.  1   . In particular,  FIG.  5    is a cross-sectional view taken along line A-A′ of  FIG.  1   , and  FIG.  6    is a cross-sectional view taken along line B-B′ of  FIG.  1   . Referring to  FIGS.  5  and  6   , the device transfer substrate  110  may include a barrier  111  surrounding a boundary of each recess  115 . The first region  115   a , the second region  115   b , and the overlapping region  116  of one recess  115  may be surrounded by the barrier  111  so that the first region  115   a , the second region  115   b , and the overlapping region  116  of one recess  115  may be connected to each other based on the overlapping region  116  within the barrier  111 . A bottom surface  112  of each of the recesses  115  may extend along the first region  115   a , the second region  115   b , and the overlapping region  116 , and may have a smooth surface with little or no curvature. 
     In addition, referring to  FIG.  5   , a maximum width, a diameter, or a diagonal length W3 of the first region  115   a  and the second region  115   b  in a direction intersecting with a straight line passing through the center C 1  of the first figure and the center C 2  of the second figure may be slightly greater than a width W4 of the light emitting device  120 . For example, the maximum width, diameter, or diagonal length W3 of the first region  115   a  and the second region  115   b  in the direction intersecting with the straight line passing through the center C 1  of the first figure and the center C 2  of the second figure may be greater by about 20% than the width W4 of the light emitting device  120 . Alternatively, a difference between the maximum width, diameter, or diagonal length W3 of each of the first region  115   a  and the second region  115   b  in the direction intersecting with the straight line passing through the center C 1  of the first figure and the center C 2  of the second figure and the diameter of the diagonal length W4 of the light emitting device  120  may be greater than 0 µm and less than or equal to about 5 µm. Accordingly, the light emitting device  120  received in the recess  115  may move only within a limited range within the recess  115 , in particular, within the first region  115   a  or the second region  115   b . 
     Referring to  FIG.  6   , the light emitting device  120  may be disposed in only any one of the first region  115   a  and the second region  115   b , and the other one of the first region  115   a  or the second region  115   b , in which the light emitting device  120  is not disposed, may be empty. As illustrated in  FIG.  4   , because the width of the overlapping region  116  at the center in a direction passing through the center C 1  of the first figure and the center C 2  of the second figure is narrower than the width of the first region  115   a  and the second region  115   b , once the light emitting device  120  enters one of the first region  115   a  and the second region  115   b , the light emitting device  120  cannot then move to the other one of the second region  115   b  and the first region  115   a  and may move only within a limited range within the first region  115   a  or the second region  115   b . 
     In the recess  115  of the device transfer substrate, for example, the light emitting device  120  may be arranged by a fluidic self-assembly method or a dry self-assembly method.  FIG.  7    is a perspective view illustrating a method of arranging the light emitting device  120  using a fluidic self-assembly method. Referring to  FIG.  7   , the light emitting devices  120  may be provided on the upper surface of the device transfer substrate  110  having the recesses  115 , which are two-dimensionally arranged. The light emitting devices  120  may be directly scattered onto the device transfer substrate  110  after a liquid is supplied to the recesses  115  of the device transfer substrate  110  or may be included in a suspension and supplied onto the device transfer substrate  110 . 
     The light emitting devices  120  supplied on the device transfer substrate  110  pass by or over the recess  115  in the device transfer substrate  110  by external stimulus such as any one or more of ultrasonic waves, vibrations, magnetic fields, fluid flow, and physical contact according to a transfer method. For example,  FIG.  8    schematically shows a scanning process for arranging the light emitting device  120  through physical contact by a rod or a blade  10 . While the light emitting devices  120  pass by or over the recess  115 , the light emitting devices  120  are caught by a capillary force by a liquid L in the recess  115  and positioned in the recess  115  as the liquid L is evaporated, or blocked by the edge of the recess  115  to settle inside the recess  115 . 
     As described above, one recess  115  of the device transfer substrate according to the embodiment has two regions for accommodating the light emitting device  120 , that is, the first region  115   a  and the second region  115   b . The light emitting device  120  may settle in the first region  115   a  or the second region  115   b  with a high probability according to the fluidic self-assembly method or the dry self-assembly method. Therefore, compared to a case in which one recess includes one accommodation region having a size similar to that of the light emitting device  120 , transfer yield when arranging the light emitting device  120  on the device transfer substrate  110  may be improved. In addition, because only one light emitting device  120  enters one recess  115 , the amount of use of the light emitting device  120  may be reduced to almost half, compared to a case in which two light emitting devices are redundantly disposed in one cell of a display apparatus. 
       FIGS.  9 A and  9 B  are plan views illustrating a shape of the recess  115  of the device transfer substrate according to an embodiment. In the example of the recess  115  illustrated in  FIG.  4   , both the first figure of the first region  115   a  and the second figure of the second region  115   b  are square, and the first region  115   a  and the second region  115   b  are disposed such that the periphery of one vertex of the first figure and the periphery of one vertex of the second figure overlap each other. However, the recess  115  may have various other shapes and arrangements. For example, referring to  FIGS.  9 A and  9 B , both the first figure of the first region  115   a  and the second figure of the second region  115   b  may be square and the first region  115   a  and the second region  115   b  may be disposed such that the periphery of one vertex of the first figure and the periphery of one side of the second figure overlap each other. In other words, the first region  115   a  and the second region  115   b  may be disposed such that one of the first figure and the second figure is in a state of being rotated relative to the other. 
       FIGS.  10 A and  10 B  are plan views illustrating a shape of the recess  115  of the device transfer substrate according to an embodiment. Referring to  FIGS.  10 A and  10 B , both the first figure of the first region  115   a  and the second figure of the second region  115   b  may be circular. In this case, the cross-section of the light emitting device  120  may also be circular. The second device electrode  126  of the light emitting device  120  may be arranged in a ring shape along the edge of the upper surface of the light emitting device  120 . 
       FIGS.  11 A to  11 D  are plan views illustrating a shape of the recess  115  of the device transfer substrate  110  according to an embodiment. Referring to  FIGS.  11 A to  11 D , both the first figure of the first region  115   a  and the second figure of the second region  115   b  may have a trapezoidal shape. In this case, the cross-section of the light emitting device  120  may also have a trapezoidal shape. The second device electrode  126  of the light emitting device  120  may be disposed at one vertex region of a longer side of the trapezoidal shape, and the first device electrode  125  may be disposed at one vertex region of a shorter side of the trapezoidal shape. Also, the first device electrode  125  and the second device electrode  126  may be disposed in a trapezoidal diagonal direction. Accordingly, when the light emitting device  120  has a trapezoidal shape, the first device electrode  125  and the second device electrode  126  may not be symmetrically disposed. 
     As shown in  FIGS.  11 A and  11 B , the first region  115   a  and the second region  115   b  may be arranged such that the periphery of one vertex of the shorter side of the first figure and the periphery of one vertex of the shorter side of the second figure overlap each other. In particular, the first region  115   a  and the second region  115   b  may be disposed such that the periphery of the vertex, among the two vertices of the shorter side, corresponding to the position of the vertex of the first device electrode  125  of the light emitting device  120  overlap each other. Then, no matter which of the first region  115   a  and the second region  115   b  the light emitting device  120  is disposed in, the first device electrode  125  of the light emitting device  120  may always be positioned in the overlapping region  116  of the first region  115   a  and the second region  115   b . 
     Alternatively, as illustrated in  FIGS.  11 C and  11 D , the first region  115   a  and the second region  115   b  may be disposed such that the periphery of one vertex of the longer side of the first figure and the periphery of one vertex of the longer side of the second figure overlap each other. In particular, the first region  115   a  and the second region  115   b  may be disposed such that the periphery of the vertex, among the two vertices of the longer side, corresponding to the position of the vertex of the second device electrode  126  of the light emitting device  120  overlap each other. Then, no matter which of the first region  115   a  and the second region  115   b  the light emitting device  120  is disposed in, the second device electrode  126  of the light emitting device  120  may always be positioned in the overlapping region  116  of the first region  115   a  and the second region  115   b . 
       FIGS.  12 A to  12 D  are plan views illustrating a shape of the recess  115  of the device transfer substrate  110  according to an embodiment. So far, it has been described that one recess  115  has two regions which overlap each other, but the disclosure is not limited thereto and one recess  115  may have three or more regions which overlap each other. Referring to  FIGS.  12 A to  12 D , one recess  115  may include a first region  115   a  having a shape of a first figure, a second region  115   b  having a shape of a second figure, and a third region  115   c  having a shape of a third figure. For example, the first to third figures may each have a square shape, and the light emitting device  120  may also have a square shape. The first region  115   a  and the second region  115   b  may spatially partially overlap each other, and the second region  115   b  and the third region  115   c  may spatially partially overlap each other. However, the first region  115   a  and the third region  115   c  may not overlap each other. 
     In addition, as illustrated in  FIGS.  12 A and  12 B , the first region  115   a  to the third region  115   c  may be disposed such that the periphery of a vertex of the first figure and the periphery of one vertex of the second figure overlap each other and the periphery of the opposite vertex of the second figure and the periphery of a vertex of the third figure overlap each other. Alternatively, as illustrated in  FIGS.  12 C and  12 D , the first region  115   a  to the third region  115   c  may be disposed such that the periphery of a side of the first figure and the periphery of one vertex of the second figure overlap each other and the periphery of the opposite vertex of the second figure and the periphery of a side of the third figure overlap each other. Also, the first figure and the third figure may be in a shape rotated relative to each other. 
     When one recess  115  has three or more regions which overlap each other, the light emitting device  120  may be disposed in at least one of the first region  115   a  to the third region  115   c . As shown in  FIGS.  12 A and  12 C , when the light emitting device  120  is disposed in the second region  115   b  in the middle, the light emitting device  120  is not disposed in the first and third regions  115   a  and  115   c . As shown in  FIGS.  12 B and  12 D , when the light emitting device  120  is disposed in the first region  115   a , the light emitting device  120  may not be disposed in the second region  115   b  but may be further disposed in the third region  115   c . In addition, when the light emitting device  120  is disposed in the third region  115   c , the light emitting device  120  may not be disposed in the second region  115   b  but may be disposed in the first region  115   a . In other words, the light emitting device  120  may be disposed only in the second region  115   b  or may be disposed in at least one of the first region  115   a  and the third region  115   c . Accordingly, when the recess  115  includes n regions and each of the n regions overlaps with another adjacent region (n is a natural number greater than 2), 1 to n-1 light emitting devices  120  may be disposed in one recess  115 . 
       FIGS.  13 A to  13 C  are plan views illustrating a shape of the recess  115  of the device transfer substrate according to an embodiment. Referring to  FIGS.  13 A to  13 C , the first to third figures of the first to third regions  115   a ,  115   b , and  115   c  may be circles. Even in this case, descriptions given above with reference to  FIGS.  12 A to  12 D  may be applied as they are. As shown in  FIGS.  13 A and  13 B , the centers of the first to third figures may be positioned on a straight line. However, the disclosure is not necessarily limited thereto. For example, as illustrated in  FIG.  13 C , an angle θ between a line segment connecting the center of the first figure to the center of the second figure and a line segment connecting the center of the second figure to the center of the third figure may be in a range from 90 degrees to 180 degrees. 
       FIGS.  14 A to  14 C  are plan views illustrating a shape of the recess  115  of the device transfer substrate  110  and a shape of the light emitting device  120  according to an embodiment. In the embodiments described above, the shape of the light emitting device  120  is similar to the shape of the figures of the respective regions of the recess  115 , but is not necessarily limited thereto. For example, the first to third figures of the first to third regions  115   a ,  115   b , and  115   c  may have a square shape, and the light emitting device  120  may have a circular shape. The shape of the recess  115  and the shape of the light emitting device  120  may be a combination of other shapes not illustrated in  FIGS.  14 A to  14 C . The first to third figures may have any shape and size in which the light emitting device  120  may be stably positioned in each of the first to third regions  115   a ,  115   b , and  115   c . 
     The light emitting devices  120  arranged on the device transfer substrate  110  may be transferred onto a display substrate of the display apparatus to manufacture the display apparatus. In this case, the device transfer substrate  110  may be a transfer substrate for transferring the light emitting devices  120  onto the display substrate of the display apparatus.  FIG.  15    is a cross-sectional view schematically illustrating a process of transferring the light emitting device  120  arranged on the device transfer substrate  110  onto a display substrate  210 . 
     Referring to  FIG.  15   , the display substrate  210  may include a plurality of first electrode pairs  211  respectively disposed in regions on the display substrate  210  corresponding to the first regions  115   a  of the recesses  115  and a plurality of second electrode pairs  212  respectively disposed in regions on the display substrate  210  corresponding to the second regions  115   b  of the recesses  115 . Each of the first electrode pairs  211  may include a first driving electrode  211   a  and a second driving electrode  211   b , and each of the second electrode pairs  212  may include a third driving electrode  212   a  and a fourth driving electrode  212   b . When the light emitting devices  120  arranged in the recesses  115  of the device transfer substrate  110  are transferred to the display substrate  210 , it is not known in advance in which of the first region  115   a  and the second region  115   b  the light emitting device  120  is positioned, and thus, the first electrode pair  211  and the second electrode pair  212  may be provided at a position on the display substrate  210  corresponding to the first region  115   a  and a position on the display substrate  210  corresponding to the second region  115   b , respectively. 
     The light emitting device  120  may be electrically connected to any one of the first electrode pair  211  and the second electrode pair  212 . For example, the light emitting device  120  disposed in the first region  115   a  is electrically connected to the first electrode pair  211  and may not be electrically connected to the second electrode pair  212 . Also, the light emitting device  120  disposed in the second region  115   b  may not be electrically connected to the first electrode pair  211  but may be electrically connected to the second electrode pair  212 . In other words, the light emitting device  120  may be electrically connected to only any one of the first electrode pair  211  and the second electrode pair  212  in the region on the display substrate  210  corresponding to one recess  115  and may not be electrically connected to the other one of the first electrode pair  211  and the second electrode pair  212 . 
     The display substrate  210  may further include a driving circuit including a plurality of thin film transistors (TFTs) for independently controlling the light emitting devices  120 . For example, the thin film transistors may be disposed below the first electrode pair  211  and the second electrode pair  212  in the display substrate  210 , and the thin film transistors may be electrically connected to the first and second electrode pairs  211  and  212  through wirings. In particular, a driving circuit may be configured to apply the same driving signal simultaneously to the first electrode pair  211  and the second electrode pair  212  respectively disposed in regions corresponding to one recess  115  on the display substrate  210 . Then, the light emitting device  120  disposed in each of the recesses  115  may operate as if the light emitting device  120  is at the same position or at the same sub-pixel on the display substrate  210  no matter in which of the first region  115   a  and the second region  115   b  the light emitting device  120  is positioned. 
     The device transfer substrate  110  may be disposed such that the first and second device electrodes  125  and  126  of the light emitting device  120  face the display substrate  210 . In addition, the device transfer substrate  110  may press the display substrate  210  such that the first device electrode  125  of the light emitting device  120  comes into contact with the first driving electrode  211   a  or the third driving electrode  212   a  and the second device electrode  126  comes into contact with the second driving electrode  211   b  or the fourth driving electrode  212   b . Thereafter, the first device electrode  125  may be bonded to the first driving electrode  211   a  or the third driving electrode  212   a  and the second device electrode  126  to the second driving electrode  211   b  or the fourth driving electrode  212   b , through a bonding material such as a solder bump. In this manner, when the light emitting device  120  is completely fixed to the display substrate  210 , the device transfer substrate may be detached from the light emitting device  120 . 
     According to the embodiment described above, the light emitting devices  120  may be transferred onto the device transfer substrate  110  or the display substrate  210  with a high yield, while using a relatively small amount of the light emitting devices  120 . Accordingly, manufacturing costs for a display apparatus including a very large number of light emitting devices  120  may be reduced. 
       FIGS.  16 A to  16 C  are plan views illustrating various arrangements of electrode pairs that may be electrically connected to the light emitting device  120  transferred on the display substrate  210 . 
     Referring to  FIG.  16 A , when the light emitting device  120  has a square shape and the first and second shapes of the first and second regions  115   a  and  115   b   of the recess  115  have a square shape, the first driving electrode  211   a  and the third driving electrode  212   a  may be disposed at positions corresponding to the center of the first figure and the center of the second figure on the display substrate  210 , respectively. In addition, the second driving electrode  211   b  may be disposed at positions respectively corresponding to the three vertices of the first figure that are not positioned in the overlapping region, on the display substrate  210 , the fourth driving electrode  212   b  may be disposed at positions respectively corresponding to the three vertices of the second figure that are not positioned in the overlapping region, on the display substrate  210 . 
     A first wiring  211   c  and a third wiring  212   c  may be connected to the first driving electrode  211   a  and the third driving electrode  212   a , respectively. The first wiring  211   c  may extend between two adjacent second driving electrodes  211   b  on the display substrate  210  or extend below the display substrate  210  through a via hole, and the third wiring  212   c  may extend between two adjacent fourth driving electrodes  212   b  on the display substrate  210  or extend below the display substrate  210  through a via hole. Also, a second wiring  211   d  and a fourth wiring  212   d  may be connected to the second driving electrode  211   b  and the fourth driving electrode  212   b , respectively. The second wiring  211   d  may extend in an outward direction of the first figure from the display substrate  210  or extend below the display substrate  210  through a via hole, and the fourth wiring  212   d  may extend in an outward direction of the second figure from the display substrate  210  or extend below the display substrate  210  through a via hole. According to this electrode arrangement method, first to fourth driving electrodes  211   a ,  211   b ,  212   a , and  212   b  may be disposed apart from each other without a possibility of a short-circuit. 
     Referring to  FIG.  16 B , when the light emitting device  120  has a circular shape and the first and second figures of the first and second regions  115   a  and  115   b  of the recess  115  have a circular shape, the first driving electrode  211   a  and the third driving electrode  212   a  may be disposed at positions corresponding to the center of the first figure and the center of the second figure, respectively. In addition, two or more second driving electrodes  211   b  are disposed at positions corresponding to the edge portion of the first figure that are not positioned in the overlapping region, on the display substrate  210  and two or more fourth driving electrodes  212   b  may be disposed at positions corresponding to the edge portion of the second figure that are not positioned in the overlapping region, on the display substrate  210 . 
     Referring to  FIG.  16 C , the light emitting device  120  has a trapezoidal shape, the first and second figures of the first and second regions  115   a  and  115   b  of the recess  115  have a trapezoidal shape, and the first region  115   a  and the second region  115   b  may be disposed such that the periphery of the vertex corresponding to the position of the first device electrode  125  of the light emitting device  120 , among two vertices of the shorter side of the first and second figures, overlap each other. In this case, the first driving electrode  211   a  may be disposed at a position corresponding to the overlapping region  116  on the display substrate  210 , and the second driving electrode  211   b  and the fourth driving electrode  212   b  may be disposed at positions corresponding to two vertices of the longer side of the first and second figures in a diagonal direction of the overlapping region  116  on the display substrate  210 . In this configuration, the first electrode pair  211  and the second electrode pair  212  may share one first driving electrode  211   a . In other words, the first electrode pair  211  may include the first driving electrode  211   a  and the second driving electrode  211   b , and the second electrode pair  212  may include the first driving electrode  211   a  and the fourth driving electrode  212   b . 
     In addition, a display apparatus may be manufactured by directly disposing driving electrodes on the device transfer structure  100  illustrated in  FIG.  1    without transferring the light emitting device  120  to a separate display substrate  210 . In this case, the device transfer substrate  110  may have both a role of arranging the light emitting devices  120  and a role of a display substrate of the display apparatus.  FIG.  17    is a cross-sectional view schematically illustrating the arrangement of electrode pairs on the device transfer structure  100  according to an embodiment. Referring to  FIG.  17   , an insulating layer  216  may be formed on the device transfer substrate  110  on which the light emitting devices  120  are arranged. In addition, a plurality of first electrode pairs  211  and a plurality of second electrode pairs  212  may be formed on the insulating layer  216 . Because it is not known in advance in which of a first region  115   a  and a second region  115   b  the light emitting device  120  is positioned, the first electrode pair  211  and the second electrode pair  212  may be formed at a position corresponding to the first region  115   a  on the device transfer substrate  110  and a position corresponding to the second region  115   b  on the device transfer substrate  110 , respectively. 
     The first electrode pair  211  may include the first driving electrode  211   a  and the second driving electrode  211   b , and the second electrode pair  212  may include a third driving electrode  212   a  and a fourth driving electrode  212   b . To be electrically connected to the light emitting device  120 , the first to fourth driving electrodes  211   a ,  211   b ,  212   a , and  212   b  may extend into the insulating layer  216 . Then, any one of the first electrode pair  211  and the second electrode pair  212  in one recess  115  is electrically connected to the light emitting device  120 , and the other is not electrically connected to any of the light emitting devices. 
     A driving circuit including TFTs for independently controlling the light emitting devices  120  may be further included in the device transfer substrate  110 . Accordingly, the device transfer substrate  110  may serve as a display substrate of the display apparatus. The first to fourth driving electrodes  211   a ,  211   b ,  212   a , and  212   b  may be connected to the driving circuit inside the device transfer substrate  110  through via holes passing through the insulating layer  216 . Also, the arrangement of the driving electrodes illustrated in  FIGS.  16 A to  16 C  may be applied to the embodiment illustrated in  FIG.  17   . 
       FIG.  18    is a plan view illustrating an arrangement of the light emitting devices  120  on the display substrate  210  of a display apparatus  200  according to an embodiment. Referring to  FIG.  18   , the display apparatus  200  may include the display substrate  210  including a plurality of two-dimensionally arranged pixels  200 P and light emitting devices  120  disposed on the display substrate  210 . Each pixel  200 P may include three sub-pixels  200 R,  200 G, and  200 B disposed adjacent to each other. Accordingly, the display substrate  210  may include a plurality of sub-pixels  200 R,  200 G, and  200 B that are two-dimensionally arranged on the display substrate  210 . The sub-pixels  200 R,  200 G, and  200 B may emit red light, green light, and blue light, respectively. 
     Each of the sub-pixels  200 R,  200 G, and  200 B may include a first region  200   a  and a second region  200   b  that partially overlap each other on the display substrate  210 . The first region  200   a  and the second region  200   b  of the sub-pixels  200 R,  200 G, and  200 B may respectively correspond to the first region  115   a  and the second region  115   b  of the recess  115  of the device transfer substrate  110 . As illustrated in  FIG.  18   , the plurality of light emitting devices  120  may be irregularly arranged in any one of the first region  200   a  and the second region  200   b  of the sub-pixels  200 R,  200 G, and  200 B. 
     As described above with reference to  FIGS.  15  and  17   , the display apparatus  200  may further include a first electrode pair  211  including a first driving electrode  211   a  and a second driving electrode  211   b  disposed in the first region  200   a  and a second electrode pair  212  including a third driving electrode  212   a  and a fourth driving electrode  212   b  disposed in the second region  200   b . The light emitting device  120  disposed in the first region  200   a  may be electrically connected to the first electrode pair  211  but may not be electrically connected to the second electrode pair  212 , and the light emitting device  120  disposed in the second region  200   b  may not be electrically connected to the first electrode pair  211  but may be electrically connected to the second electrode pair  212 . 
       FIG.  19    is a cross-sectional view schematically illustrating a structure of a display apparatus  200  according to an embodiment. Referring to  FIG.  19   , the display apparatus  200  may include the display substrate  210 , the light emitting devices  120  mounted on the display substrate  210 , and a wavelength conversion layer  220  disposed on the light emitting devices  120 . In addition, the display apparatus  200  may further include an upper substrate  230  disposed on the wavelength conversion layer  220 . The wavelength conversion layer  220  may include a first wavelength conversion layer  220 R converting light emitted from the light emitting device  120  into light having a first wavelength band, a second wavelength conversion layer  220 G converting the light emitted from the light emitting device  120  into light having a second wavelength band different from the first wavelength band, and a third wavelength conversion layer  220 B converting the light emitted from the light emitting device  120  into light having a third wavelength band that is different from the first and second wavelength bands. For example, the light having the first wavelength band may be red light, the light having the second wavelength band may be green light, and the light having the third wavelength band may be blue light. The first wavelength conversion layer  220 R, the second wavelength conversion layer  220 G, and the third wavelength conversion layer  220 B may be apart from each other with a partition  221  therebetween and may face corresponding semiconductor light emitting devices  120 , respectively. 
     When the light emitting device  120  emits blue light, the third wavelength conversion layer  220 B may include a resin that transmits blue light. The second wavelength conversion layer  220 G may convert blue light emitted from the light emitting device  120  to emit green light. The second wavelength conversion layer  220 G may include quantum dots or phosphor excited by blue light to emit green light. The first wavelength conversion layer  220 R may change blue light emitted from the light emitting device  120  into red light to be emitted. The first wavelength conversion layer  220 R may include quantum dots or phosphor excited by blue light to emit red light. 
     The quantum dots included in the first wavelength conversion layer  220 R or the second wavelength conversion layer  220 G may have a core-shell structure having a core portion and a shell portion or may have a particle structure without a shell. The core-shell structure may include a single shell structure or a multi-shell structure, e.g., a double-shell structure. The quantum dots may include a group II-VI series semiconductor, a group III-V series semiconductor, a group IV-VI series semiconductor, a group IV series semiconductor, and/or graphene quantum dots. The quantum dots may include, for example, Cd, Se, Zn, S, and/or InP, and each quantum dot may have a diameter of tens of nm or less, for example, a diameter of about 10 nm or less. The quantum dots included in the first wavelength conversion layer  220 R and the second wavelength conversion layer  220 G may have different sizes. 
       FIG.  20    is a cross-sectional view schematically illustrating a structure of a display apparatus  300  according to an embodiment. Referring to  FIG.  20   , the display apparatus  300  may further include a capping layer  250  on the wavelength conversion layer  220  and a color filter layer  240  on the capping layer  250 . The capping layer  250  and the color filter layer  240  may be disposed between the wavelength conversion layer  220  and the upper substrate  230  of the display apparatus  200  illustrated in  FIG.  19   . The color filter layer  240  includes a first filter  240 R, a second filter  240 G, and a third filter  240 B apart from each other with a black matrix  241  therebetween. The first filter  240 R, the second filter  240 G, and the third filter  240 B face the first wavelength conversion layer  220 R, the second wavelength conversion layer  220 G, and the third wavelength conversion layer  220 B, respectively. The first filter  240 R, the second filter  240 G, and the third filter  240 B transmit red light, green light, and blue light, respectively, and absorb light of other colors. When the color filter layer  240  is provided, light other than red light emitted without wavelength conversion from the first wavelength conversion layer  220 R or light other than green light emitted without wavelength conversion from the second wavelength conversion layer  220 G may be removed by the first filter  240 R and the second filter  240 G, respectively, thereby increasing color purity of the display apparatus  300 . 
     The display apparatuses described above may be applied to various electronic devices having a screen display function.  FIG.  21    is a schematic block diagram of an electronic device  8201  according to an embodiment. Referring to  FIG.  21   , the electronic device  8201  may be provided in a network environment  8200 . In the network environment  8200 , the electronic device  8201  may communicate with another electronic device  8202  through a first network  8298  (a short-range wireless communication network, etc.), or may communicate with another electronic device  8204  and/or a server  8208  through a second network  8299  (a long-range wireless communication network, etc.). The electronic device  8201  may communicate with the electronic device  8204  through the server  8208 . The electronic device  8201  may include a processor  8220 , a memory  8230 , an input device  8250 , an audio output device  8255 , a display apparatus  8260 , an audio module  8270 , a sensor module  8276 , an interface  8277 , a haptic module  8279 , a camera module  8280 , a power management module  8288 , a battery  8289 , a communication module  8290 , a subscriber identification module  8296 , and/or an antenna module  8297 . Some of these components of the electronic device  8201  may be omitted or other components may be added to the electronic device  8201 . Some of these components may be implemented as one integrated circuit. For example, the sensor module  8276  (a fingerprint sensor, an iris sensor, an illuminance sensor, etc.) may be included in the display apparatus  8260  (display, etc.). 
     The processor  8220  may execute software (a program  8240 , etc.) to control one or a plurality of other components (hardware, software components, etc.) among electronic devices  8201  connected to the processor  8220  and perform various data processing or operations. As part of the data processing or operations, the processor  8220  may load instructions and/or data received from other components (the sensor module  8276 , the communication module  8290 , etc.) into a volatile memory  8232 , process instructions and/or data stored in the volatile memory  8232 , and store result data in a nonvolatile memory  8234 . The nonvolatile memory  8234  may include an internal memory  8236  mounted in the electronic device  8201  and a detachable external memory  8238 . The processor  8220  may include a main processor  8221  (a central processing unit, an application processor, etc.) and an auxiliary processor  8223  (a graphics processing unit, an image signal processor, a sensor hub processor, a communication processor, etc.) that may be operated independently or together with the main processor  8221 . The auxiliary processor  8223  may use less power than the main processor  8221  and may perform specialized functions. 
     The auxiliary processor  8223  may control functions and/or states related to some (the display apparatus  8260 , the sensor module  8276 , the communication module  8290 , etc.) of the components of the electronic device  8201  in place of the main processor  8221  while the main processor  8221  is inactive (a sleep state) or together with the main processor  8221  while the main processor  8221  is active (an application executed state). The auxiliary processor  8223  (an image signal processor, a communication processor, etc.) may be implemented as part of other functionally related components (the camera module  8280 , the communication module  8290 , etc.). 
     The memory  2230  may store various data required by the components (the processor  8220 , the sensor module  8276 , etc.) of the electronic device  8201 . The data may include, for example, software (the program  8240 , etc.) and input data and/or output data for commands related thereto. The memory  8230  may include the volatile memory  8232  and/or the nonvolatile memory  8234 . 
     The program  8240  may be stored as software in the memory  8230  and may include an operating system  8242 , middleware  8244 , and/or an application  8246 . 
     The input device  8250  may receive commands and/or data to be used by components (the processor  8220 , etc. of the electronic device  8201 ) from the outside (a user, etc.) of the electronic device  8201 . The input device  8250  may include a remote controller, a microphone, a mouse, a keyboard, and/or a digital pen (such as a stylus pen). 
     The audio output device  8255  may output an audio signal to the outside of the electronic device  8201 . The audio output device  8255  may include a speaker and/or a receiver. The speaker may be used for general purposes such as multimedia playback or recording playback, and the receiver may be used to receive incoming calls. The receiver may be combined as part of the speaker or may be implemented as an independent separate device. 
     The display apparatus  8260  may visually provide information to the outside of the electronic device  8201 . The display apparatus  8260  may include a display, a hologram device, or a projector, and a control circuit for controlling a corresponding device. The display apparatus  8260  may include the driving circuit, the light emitting device, a side reflective structure, a lower reflective structure, etc. The display apparatus  8260  may further include touch circuitry configured to detect a touch and/or a sensor circuit (a pressure sensor, etc.) configured to measure the strength of a force generated by the touch. 
     The audio module  8270  may convert sound into an electrical signal, or conversely, may convert an electrical signal into sound. The audio module  8270  may acquire sound through the input device  8250  and output sound through a speaker and/or a headphone of another electronic device (the electronic device  8202 , etc.) connected to the audio output device  8255  and/or the electronic device  8201  directly or wirelessly. 
     The sensor module  8276  may detect an operating state (power, temperature, etc.) of the electronic device  8201  or an external environmental state (a user state, etc.), and generate an electrical signal and/or data value corresponding to the detected state. The sensor module  8276  may include a gesture sensor, a gyro sensor, an atmospheric pressure sensor, a magnetic sensor, an acceleration sensor, a grip sensor, a proximity sensor, a color sensor, an infrared (IR) sensor, a biometric sensor, a temperature sensor, a humidity sensor, and/or an illuminance sensor. 
     The interface  8277  may support one or more designated protocols that may be used for the electronic device  8201  to be connected to another electronic device (e.g., the electronic device  8202 ) directly or wirelessly. The interface  8277  may include a high definition multimedia interface (HDMI), a universal serial bus (USB) interface, an SD card interface, and/or an audio interface. 
     A connection terminal  8278  may include a connector through which the electronic device  8201  may be physically connected to another electronic device (such as the electronic device  8202 ). The connection terminal  8278  may include an HDMI connector, a USB connector, an SD card connector, and/or an audio connector (such as a headphone connector). 
     The haptic module  8279  may convert an electrical signal into a mechanical stimulus (vibration, movement, etc.) or an electrical stimulus that a user may perceive through a tactile or motor sense. The haptic module  8279  may include a motor, a piezoelectric element, and/or an electrical stimulation device. 
     The camera module  8280  may capture a still image and video. The camera module  8280  may include a lens assembly including one or more lenses, image sensors, image signal processors, and/or flashes. The lens assembly included in the camera module  8280  may collect light emitted from a subject to be imaged. 
     The power management module  8288  may manage power supplied to the electronic device  8201 . The power management module  8288  may be implemented as part of a power management integrated circuit (PMIC). 
     The battery  8289  may supply power to components of the electronic device  8201 . The battery  8289  may include a non-rechargeable primary cell, a rechargeable secondary cell, and/or a fuel cell. 
     The communication module  8290  may establish a direct (wired) communication channel and/or a wireless communication channel between the electronic device  8201  and other electronic devices (the electronic device  8202 , the electronic device  8204 , the server  8208 , etc.) and support communication through the established communication channel. The communication module  8290  may include one or more communication processors operating independently of the processor  8220  (an application processor, etc.) and supporting direct communication and/or wireless communication. The communication module  8290  may include a wireless communication module  8292  (a cellular communication module, a short-range wireless communication module, a global navigation satellite system (GNSS) communication module, etc.) and/or a wired communication module  8294  (a local area network (LAN) communication module, a power line communication module, etc.). Among these communication modules, a corresponding communication module may communicate with another electronic device through the first network  8298  (a short-range communication network such as Bluetooth, WiFi Direct, or infrared Data Association (IrDA) or the second network  8299  (a telecommunication network such as a cellular network, the Internet, or a computer network (LAN), WAN, etc.). These various types of communication modules may be integrated into one component (a single chip, etc.) or may be implemented as a plurality of components (multiple chips) separate from each other. The wireless communication module  8292  may verify and authenticate the electronic device  8201  in the communication network such as the first network  8298  and/or the second network  8299  using subscriber information (an international mobile subscriber identifier (IMSI), etc.) stored in the subscriber identification module  8296 . 
     The antenna module  8297  may transmit signals and/or power to the outside (such as other electronic devices) or receive signals and/or power from the outside. The antenna may include a radiator including a conductive pattern formed on a board (a printed circuit board (PCB), etc.). The antenna module  8297  may include one or a plurality of antennas. When a plurality of antennas are included, an antenna suitable for a communication method used in a communication network such as the first network  8298  and/or the second network  8299  may be selected from among the plurality of antennas by the communication module  8290 . Signals and/or power may be transmitted or received between the communication module  8290  and other electronic devices through the selected antenna. A component (an RFIC, etc.) other than the antenna may be included as part of the antenna module  8297 . 
     Some of the components may be connected to each other through communication methods (a bus, a general purpose input and output (BPIO), a serial peripheral interface (SPI), a mobile industry processor interface (MIPI)) and exchange signals (commands, data, etc.) with each other. 
     The command or data may be transmitted or received between the electronic device  8201  and the electronic device  8204  through the server  8208  connected to the second network  8299 . The other electronic devices  8202  and  8204  may be the same or different types of devices as the electronic device  8201 . All or some of the operations executed by the electronic device  8201  may be executed by one or more of the other electronic devices  8202 ,  8204 , and  8208 . For example, when the electronic device  8201  needs to perform a function or service, the electronic device  8201  may request one or more other electronic devices to perform a portion or the entirety of the function or the service, instead of executing the function or service by itself. Upon receiving the request, one or more other electronic devices may execute an additional function or service related to the request, and transmit a result of the execution to the electronic device  8201 . To this end, cloud computing, distributed computing, and/or client-server computing technology may be used. 
       FIG.  22    illustrates an example in which a display apparatus according to embodiments is applied to a mobile device  9100 . The mobile device  9100  may include a display apparatus  9110 , and the display apparatus  9110  may include the driving circuit, the light emitting device, the side reflective structure, the lower reflective structure, and the like described above. The display apparatus  9110  may have a foldable structure, for example, a multi-foldable structure. 
       FIG.  23    illustrates an example in which the display apparatus according to embodiments is applied to a vehicle display apparatus. The display apparatus may be a head-up display apparatus  9200  for a vehicle and may include a display  9210  provided in a region of a vehicle and a light path changing member  9220  for changing a path of light so that a driver may see an image generated by the display  9210 . 
       FIG.  24    illustrates an example in which the display apparatus according to embodiments is applied to augmented reality (AR) glasses  9300  or virtual reality glasses. The AR glasses  9300  may include a projection system  9310  forming an image and an element  9320  guiding the image from the projection system  9310  to a user’s eye. The projection system  9310  may include the driving circuit, the light emitting device, the side reflective structure, the lower reflective structure, and the like described above. 
       FIG.  25    illustrates an example in which the display apparatus according to embodiments is applied to a signage  9400 . The signage  9400  may be used for outdoor advertisements using a digital information display and may control advertisement content and the like through a communication network. The signage  9400  may be implemented, for example, through the electronic device described above with reference to  FIG.  21   . 
       FIG.  26    illustrates an example in which the display apparatus according to embodiments is applied to a wearable display  9500 . The wearable display  9500  may include the driving circuit, the light emitting device, the side reflective structure, the lower reflective structure, and the like described above and may be implemented through the electronic device described above with reference to  FIG.  21   . 
     The display apparatus according to an example embodiment may be applied to various products such as a rollable TV, a stretchable display, etc. 
     It should be understood that embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. While one or more embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims.