Patent Publication Number: US-11653528-B2

Title: Light emitting device and display apparatus including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Korean Patent Application No. 10-2020-0026796, filed on Mar. 3, 2020, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     Example embodiments of the present disclosure relate to a light emitting device and a display apparatus including the light emitting device, and more particularly to, an organic light emitting device having high color purity without using a color filter and an organic light emitting display apparatus. 
     2. Description of Related Art 
     An organic light emitting device (OLED) is a display apparatus that forms an image via light emission according to a combination of holes supplied from an anode and electrons supplied from a cathode in an organic emission layer. The OLED has excellent display characteristics such as a wide viewing angle, a fast response speed, a thin thickness, a low manufacturing cost, and a high contrast. 
     Further, the OLED may emit a desired color according to selection of an appropriate material as a material of the organic emission layer. According to this principle, it may be possible to manufacture a color display apparatus by using the OLED. For example, an organic emission layer of a blue pixel may include an organic material that generates blue light, an organic emission layer of a green pixel may include an organic material that generates green light, and an organic emission layer of a red pixel may include an organic material that generates red light. Also, a white OLED may be manufactured by arranging a plurality of organic materials which respectively generate blue light, green light, and red light in one organic emission layer or by arranging pairs of two or more types of organic materials in a complementary relationship with each other. 
     SUMMARY 
     One or more example embodiments provide a light emitting device and a display apparatus having high color purity without using a color filter by using a planarization layer including a micro cavity having a phase modulation surface and a light absorber. 
     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 the example embodiments of the disclosure. 
     According to an aspect of an example embodiment, there is provide a light emitting device including a reflective layer including a phase modulation surface, a planarization layer disposed on the reflective layer, a first electrode disposed on the planarization layer, an organic emission layer disposed on the first electrode and configured to emit visible light that includes light of a first wavelength and light of a second wavelength that is shorter than the first wavelength, and a second electrode disposed on the organic emission layer, wherein the reflective layer and the second electrode form a micro cavity configured to resonate the light of the first wavelength, and wherein the planarization layer includes a light absorber configured to absorb the light of the second wavelength. 
     The phase modulating surface of the reflective layer may include a plurality of protrusions that are periodically two-dimensionally formed, and a resonance wavelength of the micro cavity may be determined based on a width or a diameter of each of the plurality of protrusions, a height of each of the plurality of protrusions, and distances between the plurality of protrusions. 
     When the first wavelength is λ, the width or the diameter of each of the plurality of protrusions, the height of each of the plurality of protrusions, and the distances between the plurality of protrusions may be set such that an optical length of the micro cavity is equal to nλ/2, where n is a natural number. 
     The phase modulating surface of the reflective layer may further include a plurality of recesses that are periodically two-dimensionally formed. 
     The plurality of recesses may be configured to absorb the light of the second wavelength. 
     The plurality of protrusions and the plurality of recesses may contact the planarization layer. 
     Each of the plurality of protrusions and each of the plurality of recesses may have a cylindrical shape or a polygonal column shape. 
     A dimension of each of the plurality of protrusions and a dimension of each of the plurality of recesses may be less than a wavelength of the visible light. 
     A diameter of each of the plurality of recesses may be less than or equal to 250 nm. 
     A difference between a diameter of each of the plurality of protrusions and the diameter of each of the plurality of recesses may be less than or equal to 100 nm. 
     A height of each of the plurality of protrusions and a depth of each of the plurality of recesses may be less than or equal to 100 nm. 
     The first electrode may be a transparent electrode, and the second electrode may be a semi-transmissive electrode configured to reflect a portion of light and transmit a remaining portion of the light. 
     The second electrode may include a reflective metal, and a thickness of the second electrode may be 10 nm to 20 nm. 
     The planarization layer may include a material that is transparent to the visible light, and a plurality of light absorbers may be dispersed in the planarization layer. 
     The visible light may be white light, the light of the first wavelength may include red light or green light, and the light of the second wavelength may include blue light. 
     The organic emission layer may include a hole injection layer disposed on the first electrode, an organic emission material layer disposed on the hole injection layer, and an electron injection layer disposed on the organic emission material layer. 
     According to another aspect of an example embodiment, there is provide a display apparatus including a first pixel configured to emit light of a first wavelength, and a second pixel configured to emit light of a second wavelength different from the first wavelength, the first pixel including a reflective layer including a phase modulation surface, a planarization layer disposed on the reflective layer, a first electrode disposed on the planarization layer, an organic emission layer disposed on the first electrode and configured to emit visible light that includes the light of the first wavelength and the light of the second wavelength that is shorter than the first wavelength, and a second electrode disposed on the organic emission layer, wherein the reflective layer and the second electrode form a micro cavity configured to resonate the light of the first wavelength, and wherein the planarization layer includes a light absorber configured to absorb the light of the second wavelength. 
     The phase modulating surface of the reflective layer may include a plurality of protrusions that are periodically two-dimensionally formed, and a resonance wavelength of the micro cavity may be determined by a width or a diameter of each of the plurality of protrusions, a height of each of the plurality of protrusions, and distances between the plurality of protrusions. 
     When the first wavelength is λ, a width or a diameter of each of the plurality of protrusions, a height of each of the plurality of protrusions, and distances between the plurality of protrusions may be set such that an optical length of the micro cavity is equal to nλ/2, where n is a natural number. 
     The phase modulating surface of the reflective layer may further include a plurality of recesses that are periodically two-dimensionally formed. 
     The plurality of recesses may be configured to absorb the light of the second wavelength. 
     The plurality of protrusions and the plurality of recesses may contact the planarization layer. 
     A dimension of each of the plurality of protrusions and a dimension of each of the plurality of recesses may be less than a wavelength of the visible light. 
     The second pixel may include a reflective layer including a flat surface, a planarization layer disposed on the reflective layer of the second pixel, a first electrode disposed on the planarization layer of the second pixel, an organic emission layer disposed on the first electrode of the second pixel and configured to emit the visible light that includes the light of the first wavelength and the light of the second wavelength, and a second electrode disposed on the organic emission layer of the second pixel, wherein the reflective layer of the second pixel and the second electrode of the second pixel form a micro cavity configured to resonate the light of the second wavelength. 
     The planarization layer of the second pixel may not include the light absorber configured to absorb the light of the second wavelength. 
     The planarization layer of the second pixel may include the light absorber configured to absorb the light of the second wavelength. 
     The reflective layer of the first pixel and the reflective layer of the second pixel may extend continuously. 
     The planarization layer of the first pixel and the planarization layer of the second pixel may extend continuously. 
     A physical thickness of the first pixel and a physical thickness of the second pixel may be same. 
     The visible light may be white light, the light of the first wavelength may include red light or green light, and the light of the second wavelength may include blue light. 
     The display apparatus may further include a third pixel configured to emit light of a third wavelength different from the first wavelength and the second wavelength, respectively, the third pixel may include a reflective layer including a phase modulation surface, a planarization layer disposed on the reflective layer of the third pixel, a first electrode disposed on the planarization layer of the third pixel, an organic emission layer disposed on the first electrode of the third pixel and configured to emit the visible light that includes the light of the first wavelength, the light of the second wavelength, and the light of the third wavelength, and a second electrode disposed on the organic emission layer of the third pixel, wherein the reflective layer of the third pixel and the second electrode of the third pixel form a micro cavity configured to resonate the light of the third wavelength. 
     The planarization layer of the third pixel may include the light absorber configured to absorb the light of the second wavelength that is shorter than the third wavelength. 
     The light absorber of the first pixel and the light absorber of the third pixel may include different materials. 
     A physical thickness of the first pixel, a physical thickness of the second pixel, and a physical thickness of the third pixel may be same. 
     The visible light may be white light, the light of the first wavelength may include red light, the light of the second wavelength may include blue light, and the light of the third wavelength may include green light. 
     According to an aspect of an example embodiment, there is provide a light emitting device including a reflective layer including a phase modulation surface, the phase modulation surface including a plurality of protrusions and a plurality of recesses, a planarization layer disposed on the reflective layer, a first electrode disposed on the planarization layer, an organic emission layer disposed on the first electrode and configured to emit visible light that includes light of a first wavelength and light of a second wavelength that is shorter than the first wavelength, and a second electrode disposed on the organic emission layer, wherein the reflective layer and the second electrode form a micro cavity configured to resonate the light of the first wavelength, and wherein the planarization layer includes a light absorber configured to absorb the light of the second wavelength. 
     A resonance wavelength of the micro cavity may be determined based on a width or a diameter of each of the plurality of protrusions, a height of each of the plurality of protrusions, and distances between the plurality of protrusions, and the plurality of recesses may be configured to absorb the light of the second wavelength 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects, features, and advantages of example 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 cross-sectional view schematically showing a structure of a light emitting device according to an example embodiment; 
         FIG.  2    is a cross-sectional view showing in more detail an example structure of an organic emission layer illustrated in  FIG.  1   ; 
         FIG.  3    is a cross-sectional view showing in more detail another example structure of an organic emission layer illustrated in  FIG.  1   ; 
         FIG.  4    is a perspective view schematically showing an example structure of a reflective layer illustrated in  FIG.  1   ; 
         FIG.  5    is a perspective view schematically showing another example structure of a reflective layer illustrated in  FIG.  1   ; 
         FIG.  6    is a graph showing an example of the absorption characteristics of a planarization layer including a light absorber; 
         FIG.  7    is a cross-sectional view showing a structure of a light emitting device according to a first related example; 
         FIG.  8    is a cross-sectional view showing a structure of a light emitting device according to a second related example; 
         FIG.  9    is a cross-sectional view showing a structure of a light emitting device according to a third related example; 
         FIG.  10    is a graph showing comparisons of spectrums of light emitted from the light emitting devices according to the first to third related examples and the example embodiment; 
         FIG.  11    shows comparisons of color coordinates of the light emitted from the light emitting devices according to the first to third related examples and the example embodiment; 
         FIG.  12    is a cross-sectional view schematically showing a structure of a light emitting device according to another example embodiment; 
         FIG.  13    is a perspective view schematically showing an example structure of a reflective layer illustrated in  FIG.  12   ; 
         FIG.  14    is a plan view schematically showing an example structure of the reflective layer illustrated in  FIG.  12   ; 
         FIG.  15 A  schematically shows light of a short wavelength flowing into a recess formed in a reflective layer; 
         FIG.  15 B  schematically shows light of a long wavelength blocked in the reflective layer in which the recess is formed; 
         FIG.  16    schematically shows light resonating in a light emitting device according to the example embodiment; 
         FIG.  17    is a plan view schematically showing another example structure of the reflective layer shown in  FIG.  12   ; 
         FIG.  18    is a perspective view schematically showing another example structure of the reflective layer shown in  FIG.  12   ; 
         FIG.  19    is a cross-sectional view schematically showing a structure of a display apparatus according to an example embodiment; 
         FIG.  20    is a cross-sectional view schematically showing a structure of a display apparatus according to another embodiment; 
         FIG.  21    is a cross-sectional view schematically showing a structure of a display apparatus according to another example embodiment; 
         FIG.  22    is a cross-sectional view schematically showing a structure of a display apparatus according to another example embodiment; and 
         FIG.  23    is a cross-sectional view schematically showing a structure of a display apparatus according to another example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to example embodiments of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the example embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the example 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. For example, the expression, “at least one of a, b, and c,” should be understood as including only a, only b, only c, both a and b, both a and c, both b and c, or all of a, b, and c. 
     Hereinafter, with reference to the accompanying drawings, a light emitting device and a display apparatus including the light emitting device will be described in detail. Like reference numerals refer to like elements throughout, and in the drawings, sizes of elements may be exaggerated for clarity and convenience of explanation. The example embodiments described below are merely exemplary, and various modifications may be possible from the example embodiments. 
     In a layer structure described below, an expression “above” or “on” may include not only “immediately on in a contact manner” but also “on in a non-contact manner”. An expression used in the singular encompasses the expression of the plural, unless it has a clearly different meaning in the context. It will be further understood that the terms “comprises” and/or “comprising” used herein specify the presence of stated features or elements, but do not preclude the presence or addition of one or more other features or elements. 
     The use of “the” and other demonstratives similar thereto may correspond to both a singular form and a plural form. Unless the order of operations of a method according to the present disclosure is explicitly mentioned or described otherwise, the operations may be performed in a proper order. The present disclosure is not limited to the order the operations are mentioned. 
     The term used in the example embodiments such as “unit” or “module” indicates a unit for processing at least one function or operation, and may be implemented in hardware or software, or in a combination of hardware and software. 
     The connecting lines, or connectors shown in the various figures presented are intended to represent 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. 
     The use of any and all examples, or language provided herein, is intended merely to better illuminate the disclosure and does not pose a limitation on the scope of the disclosure unless otherwise claimed. 
       FIG.  1    is a cross-sectional view schematically showing a structure of a light emitting device  100  according to an example embodiment. Referring to  FIG.  1   , the light emitting device  100  according to an example embodiment may include a reflective layer  110  having a phase modulation surface, a transparent planarization layer  120  disposed on the reflective layer  110 , a first electrode  131  disposed on the planarization layer  120 , an organic emission layer  140  disposed on the first electrode  131 , and a second electrode  132  disposed on the organic emission layer  140 . The light emitting device  100  may further include a transparent passivation layer  150  disposed on the second electrode  132  to protect the second electrode  132 . 
     The light emitting device  100  may be an organic light emitting diode (OLED). For example,  FIG.  2    is a cross-sectional view showing an example structure of the organic emission layer  140  illustrated in  FIG.  1    in more detail. Referring to  FIG.  2   , the organic emission layer  140  may include a hole injection layer  142  disposed on the planarization layer  120 , an organic emission material layer  141  disposed on the hole injection layer  142 , and an electron injection layer  143  disposed on the organic emission material layer  141 . In this structure, holes provided through the hole injection layer  142  and electrons provided through the electron injection layer  143  may be combined in the organic emission material layer  141  to generate light. A wavelength of the generated light may be determined according to an energy band gap of a light emitting material of the organic emission material layer  141 . 
     In addition, the organic emission layer  140  may further include a hole transfer layer  144  disposed between the hole injection layer  142  and the organic emission material layer  141  in order to further facilitate the transport of holes. In addition, the organic emission layer  140  may further include an electron transfer layer  145  disposed between the electron injection layer  143  and the organic emission material layer  141  in order to further facilitate the transport of electrons. In addition, the organic emission layer  140  may include various additional layers as necessary. For example, the organic emission layer  140  may further include an electron block layer between the hole transfer layer  144  and the organic emission material layer  141 , and may also further include a hole block layer between the organic emission material layer  141  and the electron transfer layer  145 . 
     The organic emission material layer  141  may be configured to emit visible light. For example, the organic emission material layer  141  may be configured to emit light in a wavelength band among a wavelength band of red light, a wavelength band of green light, and a wavelength band of blue light. However, embodiments are not limited thereto. For example, the organic emission material layer  141  may be configured to emit white visible light including all of red light, green light, and blue light. 
     For example,  FIG.  3    is a cross-sectional view showing another example structure of the organic emission layer  140  illustrated in  FIG.  1    in more detail. Referring to  FIG.  3   , the organic emission material layer  141  may include a first organic emission material layer  141   a  that emits red light, a second organic emission material layer  141   b  that emits green light, and a third organic emission material layer  141   c  that emits blue light. Further, an exciton blocking layer  146  may be disposed between the first organic emission material layer  141   a  and the second organic emission material layer  141   b  and between the second organic emission material layer  141   b  and the third organic emission material layer  141   c . Then, the organic emission layer  140  may emit white light. However, the structure of the organic emission layer  140  that emits white light is not limited thereto. For example, the organic emission layer  140  may include two organic emission material layers in complementary relation to each other. 
     The first electrode  131  disposed on the lower surface of the organic emission layer  140  may serve as an anode that provides holes. The second electrode  132  disposed on the upper surface of the organic emission layer  140  may serve as a cathode that provides electrons. To this end, the first electrode  131  may include a material having a relatively high work function, and the second electrode  132  may include a material having a relatively low work function. 
     In addition, the first electrode  131  may be a transparent electrode having a property of transmitting light, for example, visible light. For example, the first electrode  131  may include transparent conductive oxide, such as indium tin oxide (ITO), indium zinc oxide (IZO), or aluminum zinc oxide (AZO). 
     The second electrode  132  may be a semi-transmissive electrode that reflects a portion of light and transmits the remaining portion of light. To this end, the second electrode  132  may include a very thin reflective metal. For example, the second electrode  132  may be a mixed layer of silver (Ag) and magnesium (Mg) or a mixed layer of aluminum (Al) and lithium (Li). The entire thickness of the second electrode  132  may be about 10 nm to about 20 nm. Because the thickness of the second electrode  132  is very thin, a portion of light may pass through the reflective metal. 
     The reflective layer  110  may be configured to reflect light generated from the organic emission layer  140  and transmitted through the first electrode  131 . To this end, the reflective layer  110  may include silver (Ag), gold (Au), aluminum (Al), or an alloy including silver (Ag), gold (Au), and aluminum (Al). However, the reflective layer  110  is not limited thereto, and may include other reflective materials. 
     The reflective layer  110  may serves to configure a micro cavity L together with the second electrode  132 . For example, the micro cavity L may be formed between the reflective layer  110  and the second electrode  132  of the light emitting device  100 . For example, light generated from the organic emission layer  140  may reciprocate and resonate between the reflective layer  110  and the second electrode  132 , and then light corresponding to the resonance wavelength of the micro cavity L may be emitted to the outside through the second electrode  132 . 
     The resonance wavelength of the micro cavity L formed between the reflective layer  110  and the second electrode  132  may be determined by the optical length of the micro cavity L. For example, when the resonance wavelength of the micro cavity L is λ, the optical length of the micro cavity L may be nλ/2, where n is a natural number. The optical length of the micro cavity L may be determined as the sum of the optical thickness of layers forming the micro cavity L between the reflective layer  110  and the second electrode  132 , a phase delay by the second electrode  132 , and a phase shift, for example, a phase delay by the reflective layer  110 . Here, the optical thickness of the layers forming the micro cavity L between the reflective layer  110  and the second electrode  132  is not a simple physical thickness, but is the thickness considering the refractive index of materials of the layers forming the micro cavity L. For example, the optical thickness of the layers forming the micro cavity L may be the sum of the optical thickness of the planarization layer  120 , the optical thickness of the first electrode  131 , and the optical thickness of the organic emission layer  140 . 
     According to the example embodiment, the optical length of or the resonance wavelength of the micro cavity L may be adjusted by adjusting only the phase shift by the reflective layer  110  while fixing the optical thickness of the layers forming the micro cavity L and the phase delay by the second electrode  132 . In order to control the phase shift by the reflective layer  110 , a phase modulation surface may be formed on the reflective surface of the reflective layer  110  in contact with the planarization layer  120 . The phase modulation surface may include very small patterns in the nanoscale. For example, the phase modulation surface of the reflective layer  110  may have a meta structure in which nano patterns having a size smaller than the wavelength of visible light are periodically disposed. 
     Referring back to  FIG.  1   , the reflective layer  110  may include a base  111  and the phase modulation surface formed on an upper surface  114  of the base  111 . The phase modulation surface of the reflective layer  110  may include a plurality of protrusions  112  periodically formed on the upper surface  114  of the base  111 . The plurality of protrusions  112  may have a post shape protruding from the upper surface  114  of the base  111 . For example, the plurality of protrusions  112  may have a cylindrical shape. The plurality of protrusions  112  may be integrally formed with the base  111 . The reflective layer  110  may be disposed such that the plurality of protrusions  112  is in contact with the planarization layer  120 . 
     When each of the protrusions  112  is, for example, a cylinder, the optical characteristics of the phase modulation surface, for example, the phase delay of reflected light may be determined by a diameter W of each of the protrusions  112 , a height H each of the protrusions  112  and a pitch or period P of the plurality of protrusions  112 . When each of the protrusions  112  is a polygonal column, the optical characteristics of the phase modulation surface may be determined by a maximum width W of each of the protrusions  112 , the height H of each of the protrusions  112 , and the pitch or the period P of the plurality of protrusions  112 . 
     The diameter W, the height H, and the period P of the protrusions  112  may be constant with respect to the entire region of the phase modulation surface. For example, the diameter W of the protrusion  112  may be from about 30 nm to about 250 nm, the height H of the protrusion  112  may be from about 0 nm to about 150 nm, and the period P of the plurality of protrusions  112  may be from about 100 nm to about 300 nm. 
     When the size of each of the protrusions  112  of the phase modulation surface is smaller than the resonance wavelength as described above, a plurality of nano-light resonance structures may be formed while incident light resonates in the periphery of the protrusions  112 . In particular, in the incident light, an electric field component may not penetrate into a space between the protrusions  112 , and only a magnetic field component may resonate in the periphery of the protrusions  112 . Accordingly, the plurality of nano-light resonant structures formed in the space between the protrusions  112  may be a cylinder type magnetic resonator in which the magnetic field component of the incident light resonates in the periphery of the protrusions  112 . As a result, a phase shift greater than a simple phase shift due to an effective optical distance (H×n) determined by the product of the height H of the protrusions  112  and a refractive index n of the protrusions  112  may occur on the phase modulation surface of the reflective layer  110 . 
     Accordingly, the resonance wavelength of the micro cavity L may be determined by the diameter W of each of the protrusions  112  of the phase modulation surface, the height H of each of the protrusions  112  and the period P of the plurality of protrusions  112 . For example, when the resonance wavelength of the micro cavity L is λ, the diameter W of each of the protrusions  112  of the phase modulation surface, the height H of each of the protrusions  112  and the period P of the plurality of protrusions  112  of the phase modulation surface may be selected such that the optical length of the micro cavity L satisfies nλ/2, where n is a natural number. Then, the resonance wavelength of the micro cavity L in the light emitting device  100  may more easily match with the emitting wavelength or emitting color of the light emitting device  100 . For example, when the light emitting device  100  is a red light emitting device, the diameter W of each of the protrusions  112  of the phase modulation surface, the height H of each of the protrusions  112  and the period P of the plurality of protrusions  112  of the phase modulation surface may be selected such that the resonance wavelength of the micro cavity L corresponds to a red wavelength band. As described above, it may be possible to determine the emitting wavelength of the light emitting device  100  only by the structure of the phase modulation surface of the reflective layer  110 . 
     In order to prevent the micro cavity L from having a polarization dependency, the plurality of protrusions  112  may be regularly and periodically arranged to have a 4-fold symmetry characteristic. When the micro cavity L has the polarization dependency, only light of a specific polarization component may resonate, which may deteriorate the light emitting efficiency of the light emitting device  100 . For example,  FIG.  4    is a perspective view schematically showing an example structure of the reflective layer  110  illustrated in  FIG.  1   , and  FIG.  5    is a perspective view schematically showing another example structure of the reflective layer  110  illustrated in  FIG.  1   . Referring to  FIG.  4   , the plurality of protrusions  112  having a cylindrical shape on the upper surface  114  of the base  111  may be regularly arranged two-dimensionally. In addition, referring to  FIG.  5   , the plurality of protrusions  112  having a square column shape may be regularly arranged two-dimensionally on the upper surface  114  of the base  111 . In  FIGS.  4  and  5   , although the protrusion  112  has the cylindrical shape and the square column shape, the shape of the protrusion  112  is not necessarily limited thereto. For example, the protrusion  112  may have an elliptical column or a polygonal column shape of a pentagonal shape or more. 
     In addition, in  FIGS.  4  and  5   , the plurality of protrusions  112  is arranged in a regular two-dimensional array pattern. In this case, intervals between the two adjacent protrusions  112  in the entire region of a phase modulation surface may be constant. However, if the plurality of protrusions  112  has a 4-fold symmetry characteristic, the plurality of protrusions  112  may be arranged in any other type of array. For example, the plurality of protrusions  112  may be arranged irregularly. In this case, the micro cavity L may not have a polarization dependency. Meanwhile, in another example embodiment, the arrangement of the plurality of protrusions  112  may be designed differently from the 4-fold symmetry such that the light emitting device  100  intentionally emits only light of a specific polarization component. For example, the plurality of protrusions  112  may be arranged in a one-dimensional array pattern. 
     The planarization layer  120  may be disposed on the reflective layer  110  having the phase modulation surface including the plurality of protrusions  112  to provide a flat surface. The lower surface of the planarization layer  120  may have a shape complementary to the phase modulation surface of the reflective layer  110 , and the upper surface thereof has a flat shape. Therefore, the first electrode  131  disposed on the upper surface of the planarization layer  120  may have a flat lower surface. Then, the first electrode  131  may apply a uniform electric field to the organic emission layer  140 . The planarization layer  120  may include a material transparent to visible light. In addition, the planarization layer  120  may include an insulating material to prevent current from flowing from the first electrode  131  to the reflective layer  110 . For example, the planarization layer  120  may include metal oxide such as silicon dioxide (SiO 2 ), silicon nitride (SiNx), aluminum oxide (Al 2 O 3 ), or hafnium dioxide (HfO 2 ), metal nitride, or a transparent polymer compound. 
     Meanwhile, when considering the physical thickness of the organic emission layer  140 , the optical length of the micro cavity L may be selected to mainly use a second resonance. In other words, the optical length of the micro cavity L may be selected to be the same as the emitting wavelength λ of the light emitting device  100 , where n=2 in nλ/2. In this case, a portion of light having a wavelength shorter than the emitting wavelength of the light emitting device  100  may generate a third resonance, where n=3, and may be emitted from the light emitting device  100 . For example, when the light emitting device  100  is configured to emit red light, the optical length of the micro cavity L may be selected as 630 nm. In this case, part of light having a wavelength of 420 nm may generate the third resonance and may be emitted from the light emitting device  100 . Then, since blue light is emitted from the light emitting device  100  together with red light, the color purity of light emitted from the light emitting device  100  may be reduced. 
     According to the example embodiment, in order to suppress the light having the wavelength shorter than the emitting wavelength of the light emitting device  100  from being emitted from the light emitting device  100 , the planarization layer  120  may include a light absorber  121  that absorbs light in a wavelength band shorter than the emitting wavelength of the light emitting device  100 . The light absorber  121  may be selected, for example, to absorb light in a wavelength band that causes the third resonance within the micro cavity L of the light emitting device  100 . Then, the light in the wavelength band causing the second resonance in the micro cavity L may not be absorbed by the light absorber  121  but may be emitted from the light emitting device  100 . Meanwhile, the light in the wavelength band causing the third resonance in the micro cavity L may be absorbed by the light absorber  121  in the planarization layer  120  in a process of repeatedly passing through the planarization layer  120 . 
     In  FIG.  1   , a plurality of light absorbers  121  is uniformly dispersed inside the planarization layer  120 . In the planarization layer  120 , only the material of the light absorber  121  may be mixed and dispersed alone, but embodiments are not limited thereto. For example, the material of the light absorber  121  and an organic binder may be mixed and dissolved in an organic solvent, and then the organic solvent may be applied on the reflective layer  110  and cured by light or heat, and thus the planarization layer  120  may be formed. 
     For example,  FIG.  6    is a graph showing an example of the absorption characteristics of the planarization layer  120  including the light absorber  121 . In  FIG.  6   , a material that absorbs blue light is used as the light absorber  121 , and a change in the absorption characteristics of the planarization layer  120  is measured while changing the concentration of the material of the light absorber  121  dissolved in an organic solvent. In the graph of  FIG.  6   , the concentration represents the concentration of the material of the light absorber  121  before curing the organic solvent, and an absorbance is measured after curing the organic solvent to form the planarization layer  120 . Referring to the graph of  FIG.  6   , it may be seen that the planarization layer  120  has an absorption peak near a wavelength of about 450 nm and the absorbance increases as the material of the light absorber  121  increases. 
       FIG.  7    is a cross-sectional view showing the structure of a light emitting device  10  according to a first related example. Referring to  FIG.  7   , the light emitting device  10  according to the first related example may include a reflective layer  11 , a planarization layer  12 , a first electrode  13 , an organic emission layer  14 , a second electrode  15  and a passivation layer  16 . Compared to the light emitting device  100  according to the example embodiment, the light emitting device  10  is different in that the reflective layer  11  of the light emitting device  10  does not have a phase modulation surface and the planarization layer  12  does not include a light absorber. 
     In addition,  FIG.  8    is a cross-sectional view showing the structure of a light emitting device  20  according to a second related example. Referring to  FIG.  8   , the light emitting device  20  according to the second related example may include a reflective layer  21  having a phase modulation surface  21   a , a planarization layer  22 , a first electrode  23 , an organic emission layer  24 , a second electrode  25  and a passivation layer  26 . Compared with the light emitting device  100  according to the example embodiment, the light emitting device  20  is different in that the planarization layer  22  of the light emitting device  20  does not include a light absorber. 
     In addition,  FIG.  9    is a cross-sectional view showing the structure of a light emitting device  30  according to a third related example. Referring to  FIG.  9   , the light emitting device  30  according to the third related example may include a reflective layer  31 , a planarization layer  32  including a light absorber  32   a , a first electrode  33 , an organic emission layer  34 , a second electrode  35  and a passivation layer  36 . Compared to the light emitting device  100  according to the example embodiment, the light emitting device  30  is different in that the reflective layer  31  of the light emitting device  30  does not have a phase modulation surface. 
       FIG.  10    is a graph showing comparisons of spectrums of light emitted from the light emitting devices  10 ,  20 ,  30 , and  100  according to the first to third related examples and the example embodiment. All of the light emitting devices  10 ,  20 ,  30 , and  100  according to the first to third related examples and the example embodiment select optical lengths of micro cavities such that a second resonance occurs in a wavelength band of red light. The graph of  FIG.  10    illustrates that the intensity of blue light emitted from the light emitting device  10  according to the first related example is the greatest. In addition, the intensity of blue light emitted from the light emitting devices  20  and  30  according to the second and third related examples are similar to each other. In the light emitting device  100  according to the example embodiment, the emission of blue light is greatly reduced. 
     In addition,  FIG.  11    shows comparisons of color coordinates of light emitted from the light emitting devices  10 ,  20 ,  30 , and  100  according to the first to third related examples and the example embodiment. The color coordinates shown in  FIG.  11    are CIE 1934 color coordinates.  FIG.  11    illustrates that light emitted from the light emitting device  100  according to the example embodiment is closest to pure red light. Then, the color purity of the emitted light deteriorates as the color of the emitted light is gradually closer to blue light in the order of the third related example, the second related example, and the first related example. 
     As described above, according to the example embodiment, the light emitting device  100  including a micro cavity may more easily match a resonance wavelength of the micro-cavity to the emitting wavelength of the light emitting device  100  by appropriately configuring a phase modulation surface. In addition, because the planarization layer  120  disposed on the phase modulation surface includes a light absorber that absorbs light that is not a target light emitting wavelength component, for example, light of another wavelength component that causes a third resonance in the micro cavity, the light emitting device  100  may emit only light of the target emitting wavelength component and suppress light of the remaining wavelength components. Therefore, the light emitting device  100  may achieve higher color purity. 
       FIG.  12    is a cross-sectional view schematically showing a structure of a light emitting device  200  according to another example embodiment. Referring to  FIG.  12   , the light emitting device  200  according to another example embodiment may include a reflective layer  210  including a phase modulation surface, a planarization layer  220  disposed on the reflective layer  210  and including a light absorber  221 , a first electrode  231  disposed on the planarization layer  220 , an organic emission layer  240  disposed on the first electrode  231 , and a second electrode  232  disposed on the organic emission layer  240 . In addition, the light emitting device  200  may further include a transparent passivation layer  250  disposed on the second electrode  232 . Compared with the light emitting device  100  shown in  FIG.  1   , the structure of the phase modulation surface formed on the reflective layer  210  of the light emitting device  200  shown in  FIG.  12    is different from the structure of a phase modulation surface of the light emitting device  100  shown in  FIG.  1   . The remaining configuration of the light emitting device  200  illustrated in  FIG.  12    is the same as that of the light emitting device  100  illustrated in  FIG.  1   , and thus descriptions thereof will be omitted. 
       FIG.  13    is a perspective view schematically showing an example structure of the reflective layer  210  illustrated in  FIG.  12   , and  FIG.  14    is a plan view schematically showing an example structure of the reflective layer  210  illustrated in  FIG.  12   . Referring to  FIGS.  12  to  14   , the phase modulation surface may include a plurality of protrusions  212  and a plurality of recesses  213  periodically disposed on an upper surface  214  of a base  211  facing the first electrode  231 . The reflective layer  210  may be disposed such that the plurality of protrusions  212  and the plurality of recesses  213  are in contact with the planarization layer  220 . 
     Each of the protrusions  212  protruding from the upper surface  214  of the base  211  and each of the recesses  213  recessed from the upper surface  214  of the base  211  may have dimensions smaller than the wavelength of visible light. As shown in  FIGS.  13  and  14   , the protrusions  212  and the recesses  213  may be formed to be spaced apart, and an area occupied by the upper surface  214  may be greater than an area occupied by the plurality of protrusions  212  or the plurality of recesses  213 . In addition, the area occupied by each of the protrusions  212  may be greater than or equal to the area occupied by each of the recesses  213 . 
     The plurality of protrusions  212  may be periodically arranged with a predetermined pitch P 1  on the upper surface  214  of the base  211 .  FIG.  14    shows an example of the protrusions  212  periodically arranged in the shape of a square array. However, this is merely an example, and in addition, the plurality of protrusions  212  may be arranged in an array of various other shapes such as a regular triangle, a regular hexagon, etc. Each of the protrusions  212  may have, for example, a diameter W 1  of approximately 300 nm or less. However, each of the protrusions  212  is not necessarily limited thereto. For example, each of the protrusions  212  may have the diameter W 1  of approximately 30 nm to 250 nm. Further, each of the protrusions  212  may have, for example, a height H 1  of approximately 100 nm or less. However, these numerical values are only examples. 
     As described above, the plurality of protrusions  212  may serve to adjust the optical length of the micro cavity L to resonate light corresponding to the emitting wavelength of the light emitting device  200 . For example, when the resonance wavelength of the micro cavity L is λ, the diameter W 1  and the height H 1  of each of the protrusions  212  of the phase modulation surface and the pitch P 1  of the protrusions  212  may be selected such that the optical length of the micro cavity L satisfies nλ/2, where n is a natural number. 
     The plurality of recesses  213  may be formed at a predetermined depth H 2  on the upper surface  214  of the base  211 . The plurality of recesses  213  may be periodically two-dimensionally arranged with a predetermined pitch P 2  between the plurality of protrusions  212 .  FIGS.  13  and  14    show examples of each of the recesses  213  disposed between the two adjacent protrusions  212 . Each of the recesses  213  may be formed in a cylindrical shape. Each of the recesses  213  may have, for example, a diameter W 2  of approximately 250 nm or less. More specifically, for example, each of the recesses  213  may have a diameter W 2  of approximately 80 nm to 250 nm, but is not limited thereto. Further, each of the recesses  213  may have, for example, a depth H 2  of approximately 100 nm or less but this is merely an example. In addition, a difference between the diameter W 1  of each of the protrusions  212  and the diameter W 2  of each of the recesses  213  may be, for example, approximately 100 nm or less, but is not limited thereto. 
     The plurality of the recesses  213  may serve to absorb light of a wavelength of which resonance is not desired within the micro cavity L.  FIG.  15 A  schematically shows light of a short wavelength flowing into the recess  213  formed in the reflective layer  210 , and  FIG.  15 B  schematically shows light of a long wavelength blocked in the reflective layer  210  in which the recess  213  is formed. As shown in  FIG.  15 A , the light of the short wavelength flows into and is absorbed in the nano-sized recess  213  formed in the upper surface  214  of the base  211 , whereas, as shown in  FIG.  15 B , the light of the long wavelength does not flow into the recess  213  and is reflected from the upper surface  214  of the base  211 . 
     The wavelength of the light absorbed into the recess  213  formed in the reflective layer  210  may vary according to the size of the recess  213 . For example, when the protrusions  212  are not considered, the recess  213  having a diameter of approximately 190 nm formed on the surface of the flat reflective layer  210  including silver (Ag) may absorb blue light of a wavelength of 450 nm, and the recess  213  having a diameter of approximately 244 nm may absorb green light of a wavelength of 550 nm. 
     As described above, in the light emitting device  200  configured to emit red light, when the optical length of the micro cavity L is selected as 630 nm, a portion of light of a wavelength of 420 nm may cause a third resonance to be emitted from the light emitting device  200 . Then, because blue light is emitted from the light emitting device  200  together with red light, the color purity of light emitted from the light emitting device  200  may be reduced. In the example embodiment, light of a wavelength of which resonance is not desired may be absorbed by the light absorber  221  in the planarization layer  220 . In addition, the light of the wavelength of which resonance is not desired may be additionally absorbed by the recess  213  by forming the plurality of nano-sized recesses  213  along with the plurality of protrusions  212  on the phase modulation surface of the reflective layer  210 . Therefore, the color purity of the light emitting device  200  may be further improved. 
       FIG.  16    schematically shows light resonating in the light emitting device  200  according to the example embodiment. In  FIG.  16   , a red light emitting device is illustrated as the light emitting device  200  as an example, and for convenience, only the reflective layer  210  and the second electrode  232  constituting the micro cavity L are illustrated. Referring to  FIG.  16   , in the micro cavity L, a red light R may not flow into the recess  213  formed in the surface of the reflective layer  210  but may be reflected from the surface of the reflective layer  210 . However, it may be seen that a blue light B having a wavelength shorter than the red light R flows into and is absorbed in the recess  213  formed in the surface of the reflective layer  210 . As described above, each of the recesses  213  may have, for example, a diameter of approximately 250 nm or less. Accordingly, in the micro cavity L, only the red light R may resonate and be emitted outside the light emitting device  200 . 
     According to an example embodiment, the light emitting device  200  may be a green light emitting device. In general, in a case where the surface of a reflective layer has a flat structure, when a second resonance of a green light occurs in a micro cavity, a third resonance of an ultraviolet light occurs, which does not affect a display apparatus in a visible light region. However, when the reflective layer  210  having the phase modulation surface is used, there is a possibility that a third resonance of the blue light B occurs in the micro cavity L due to the phase modulation. In addition, because the optical length varies according to the refractive index and thickness of the planarization layer  220 , the resonance wavelength may change. Accordingly, blue light B of an undesired short wavelength in the green light emitting device may be emitted. Therefore, even when the light emitting device  200  is the green light emitting device, the undesired emission of the blue light B may be further suppressed by forming the plurality of recesses  213  in the surface of the reflective layer  210  and dispersing the light absorber  221  in the planarization layer  220 . 
     As described above, by forming the plurality of recesses  213  in the phase modulation surface of the reflective layer  210  and dispersing the light absorber  221  in the planarization layer  220 , light having a long wavelength of which resonance is desired, for example, red light or green light, may resonate and be emitted, and light of a short wavelength, for example, blue light of which resonance is not desired may be absorbed, and thus color purity may be further improved. 
       FIG.  17    is a plan view schematically showing another example structure of the reflective layer  210  shown in  FIG.  12   . In the example embodiment shown in  FIGS.  13  and  14   , the protrusions  212  are periodically arranged in a square array, and each of the recesses  213  may be formed between the two adjacent protrusions  212 . In the reflective layer  210  shown in  FIG.  17   , the protrusions  212  protruding from the upper surface  214  of the base  211  may be periodically arranged in the square array, and the recesses  213  may be arranged between the two protrusions  212  arranged adjacent to each other in a diagonal direction on the upper surface  214  of the base  211  at a predetermined depth. In other words, each of the recesses  213  may be disposed in the center of a unit array of a square shape including the four adjacent protrusions  212 . However, this is merely an example, and the protrusions  212  and the recesses  213  may be arranged in various other shapes. 
     In addition,  FIG.  18    is a perspective view schematically showing another example structure of the reflective layer  210  shown in  FIG.  12   . In the example embodiment shown in  FIGS.  13  and  14   , the protrusions  212  have a cylindrical shape and the recesses  213  are formed in a cylindrical shape. In the metal reflective layer  210  shown in  FIG.  18   , the protrusions  212  have a square column shape. In this case, the maximum width of the protrusion  212  may correspond to the diameter. In addition, the recesses  213  may be formed in the cylindrical shape between the two adjacent protrusions  212 . However, this is merely an example, and each of the protrusions  212  may have a variety of other polyprism shapes, such as a triangular column or a pentagonal column. In addition, each of the recesses  213  may also be formed in various other shape. 
     The above-described light emitting devices  100  and  200  may be applied to a plurality of pixels of a display apparatus.  FIG.  19    is a cross-sectional view schematically showing a structure of a display apparatus  1000  according to an example embodiment. Referring to  FIG.  19   , the display apparatus  1000  may include a plurality of pixels that emit light of different colors. Here, the plurality of pixels may include a red pixel  1100 , a green pixel  1200 , and a blue pixel  1300  disposed adjacent to each other on the same plane of a substrate. For example, only one unit pixel including the red pixel  1100 , the green pixel  1200 , and the blue pixel is illustrated for convenience. 
     The red pixel  1100  may have the same structure as the light emitting device  100  illustrated in  FIG.  1   . The red pixel  1100  may include a first reflective layer  1110  including a first phase modulation surface, a first planarization layer  1120  disposed on the first reflective layer  1110 , a first electrode  1131  disposed on the first planarization layer  1120 , an organic emission layer  1140  disposed on the first electrode  1131 , and a second electrode  1132  disposed on the organic emission layer  1140 . The red pixel  1100  may further include a transparent passivation layer  1150  disposed on the second electrode  1132 . The first reflective layer  1110  may include a plurality of first protrusions  1112  formed to protrude on an upper surface  1114  of a base  1111 . The first reflective layer  1110  may form a first micro cavity that resonates the red light R together with the second electrode  1132 . Also, the first planarization layer  1120  may include a light absorber  1121  that absorbs blue light B. 
     The green pixel  1200  may have the same structure as the light emitting device  100  shown in  FIG.  1   . The green pixel  1200  may include a second reflective layer  1210  including a second phase modulation surface, a second planarization layer  1220  disposed on the second reflective layer  1210 , the first electrode  1131  disposed on the second planarization layer  1220 , the organic emission layer  1140  disposed on the first electrode  1131 , the second electrode  1132  disposed on the organic emission layer  1140 , and the passivation layer  1150  disposed on the second electrode  1132 . The second reflective layer  1210  may include a plurality of second protrusions  1212  formed to protrude over an upper surface  1214  of a base  1211 . The second reflective layer  1210  may form a second micro cavity that resonates the green light G together with the second electrode  1132 . In the case of the green pixel  1200 , the second planarization layer  1220  may not include a light absorber. 
     In addition, the blue pixel  1300  may include a third reflective layer  1310 , a third planarization layer  1320  disposed on the third reflective layer  1310 , a first electrode  1131  disposed on the third planarization layer  1320 , the organic emission layer  1140  disposed on the first electrode  1131 , the second electrode  1132  disposed on the organic emission layer  1140 , and the passivation layer  1150  disposed on the second electrode  1132 . The upper surface of the third reflective layer  1310  in the blue pixel  1300  may include a flat reflective surface. Also, the third planarization layer  1320  may not include a light absorber. 
     The third reflective layer  1310  may form a third micro cavity that resonates blue light B together with the second electrode  1132 . The third micro cavity may have a resonance wavelength of the blue light B by adjusting structural and optical characteristics of the layers disposed between the third reflective layer  1310  and the second electrode  1132 . Here, the upper surface of the third reflective layer  1310  may be formed at the same height as the upper surfaces of the first protrusions  1112  of the first phase modulation surface and the second protrusions  1212  of the second phase modulation surface. The third reflective layer  1310  may have a third phase modulation surface having a resonance wavelength of the blue light B. In this case, the third phase modulation surface may include a plurality of protrusions that protrude at a predetermined height on the upper surface of the third reflective layer  1310 . 
     In the display apparatus  1000  according to the example embodiment having the above structure, the first reflective layer  1110 , the second reflective layer  1210 , and the third reflective layer  1310  of the red pixel  1100 , the green pixel  1200 , and the blue pixel  1300  adjacent to each other may continuously extend. Also, the first planarization layer  1120 , the second planarization layer  1220 , and the third planarization layer  1320  may also continuously extend to each other. Also, the first electrodes  1131  of the red pixel  1100 , the green pixel  1200 , and the blue pixel  1300  may integrally extend. For example, the first electrode  1131  may be a common electrode. For independent driving of the red pixel  1100 , the green pixel  1200 , and the blue pixel disposed adjacent to each other, the organic emission layers  1140  and the second electrodes  1132  of the red pixel  1100 , the green pixel  1200 , and the blue pixel  1300  may be separated from each other. For example, the second electrode  1132  may be a pixel electrode. In addition, the red pixel  1100 , the green pixel  1200 , and the blue pixel  1300  may include the same organic emission layer  1140 . In this case, the organic emission layer  1140  may be configured to emit white light. 
     In the red pixel  1100 , in the white light generated in the organic emission layer  1140 , the red light R may reciprocate and resonate between the first reflective layer  1110  and the second electrode  1132 , and then may be emitted to the outside through the second electrode  1132 . At this time, in the white light generated in the organic emission layer  1140 , the blue light B may be absorbed by the light absorber  1121  in the first planarization layer  1120 , and thus the red light R with improved color purity may be emitted in the red pixel  1100 . 
     In the green pixel  1200 , in the white light generated from the organic emission layer  1140 , the green light G may reciprocate and resonate between the second reflective layer  1210  and the second electrode  1132  and then may be emitted to the outside through the second electrode  1132 . In addition, in the blue pixel  1300 , in the white light generated in the organic emission layer  1140 , the blue light B may reciprocate and resonate between the third reflective layer  1310  and the second electrode  1132 , and then may be emitted to the outside through the second electrode  1132 . 
     According to the example embodiment, the red pixel  1100  and the green pixel  1200  may respectively include the plurality of first protrusions  1112  and the plurality of second protrusions  1212  that have the first phase modulation surface and the second phase modulation surface having the sizes smaller than the wavelength of incident light and periodically disposed, and may more easily induce resonance of a desired wavelength by adjusting the sizes and pitches of the first protrusions  1112  and the second protrusions  1212 . Accordingly, in order to adjust the optical length of a micro cavity of each of the red pixel  1100 , the green pixel  1200 , and the blue pixel  1300 , the physical thickness of each of the red pixel  1100 , the green pixel  1200 , and the blue pixel  1300  may not need to be individually adjusted, and only the first phase modulation surface of the red pixel  1100  and the second phase modulation surface of the green pixel  1200  may be individually configured. Then, the physical thicknesses of the red pixel  1100 , the green pixel  1200 , and the blue pixel  1300  may all be the same. In addition, the upper surfaces of the first protrusions  1112  and the second protrusions  1212  in the red pixel  1100  and the green pixel  1200  may be formed to have the same height as the upper surfaces of the third reflective layer  1310  in the blue pixel  1300 . Thus, the display apparatus  1000  may be manufactured more easily. In addition, the light absorber  1121  in the first planarization layer  1120  of the red pixel  1100  may absorb the blue light B, and thus the color purity of the red light R emitted from the red pixel  1100  may be improved. 
       FIG.  20    is a cross-sectional view schematically showing a structure of a display apparatus  2000  according to another example embodiment. In the case of the display apparatus  2000  illustrated in  FIG.  20   , the second planarization layer  1220  of the green pixel  1200  may further include the light absorber  1121  that absorbs the blue light B. Then, the color purity of the green light G emitted from the green pixel  1200  may be improved. Here, the light absorber  1121  disposed on the first planarization layer  1120  of the red pixel  1200  and the light absorber  1121  disposed on the second planarization layer  1220  of the green pixel  1200  may include the same material or different materials. For example, the light absorber  1121  disposed on the first planarization layer  1120  of the red pixel  1200  may be selected as a material that does not absorb the red light R, and the light absorber  1121  disposed on the second planarization layer  1220  of the green pixel  1200  may be selected as a material that does not absorb the green light G. 
     In addition,  FIG.  21    is a cross-sectional view schematically showing a structure of a display apparatus  3000  according to another example embodiment. In the display apparatus  3000  illustrated in  FIG.  21   , a planarization layer of all pixels may include the light absorber  1121  that absorbs the blue light B. In other words, the light absorbers  1121  of the same material that absorbs the blue light B may be dispersed in the first planarization layer  1120  of the red pixel  1100 , the second planarization layer  1220  of the green pixel  1200 , and the third planarization layer  1320  of the blue pixel  1300 . Then, the first planarization layer  1120 , the second planarization layer  1220 , and the third planarization layer  1320  of the red pixel  1100 , the green pixel  1200 , and the blue pixel  1300  may be formed more simply in a single process. 
     As illustrated in  FIG.  21   , the distance between the upper surface of the third reflective layer  1310  and the lower surface of the first electrode  1131  may be the shortest in the blue pixel  1300 . In the red pixel  1100 , the distance between the upper surface  1114  of the base  1111  of the first reflective layer  1110  and the lower surface of the first electrode  1131  may be the longest. Therefore, in the third planarization layer  1320  of the blue pixel  1300 , because a path through which the blue light B passes is the shortest, the loss of the blue light B due to the light absorber  1121  in the third planarization layer  1320  may be relatively small. In addition, in the first planarization layer  1120  of the red pixel  1100 , because a path through which the blue light B passes is the longest, the blue light B may be sufficiently absorbed by the light absorber  1121  in the first planarization layer  1120 . 
       FIG.  22    is a cross-sectional view schematically showing a structure of a display apparatus  4000  according to another example embodiment. Referring to  FIG.  22   , the first reflective layer  1110  of the red pixel  1100  of the display apparatus  4000  may further include a plurality of first recesses  1113  that absorb the blue light B. The second reflective layer  1210  of the green pixel  1200  may include only the second protrusion  1212 . Accordingly, the first recess  1113  together with the light absorber  1121  in the red pixel  1100  may absorb the blue light B, and thus the color purity of the red light R emitted from the red pixel  1100  may be improved. 
     In addition,  FIG.  23    is a cross-sectional view schematically showing a structure of a display apparatus  5000  according to another example embodiment. Referring to  FIG.  23   , the first reflective layer  1110  of the red pixel  1100  of the display apparatus  5000  may further include the plurality of first recesses  1113  that absorb the blue light B, and the second reflective layer  1210  of the green pixel  1200  may further include a plurality of second recesses  1213  that absorb the blue light B. 
     In  FIGS.  22  and  23   , only the red pixel  1100  includes the light absorber  1121 , but is not limited thereto. For example, as in the example embodiment illustrated in  FIG.  20   , in the example embodiments of  FIGS.  22  and  23   , the red pixel  1100  and the green pixel  1200  may include the light absorber  1121 . Also, as in the example embodiment illustrated in  FIG.  21   , in the example embodiments of  FIGS.  22  and  23   , the red pixel  1100 , the green pixel  1200 , and the blue pixel  1300  may all include the light absorber  1121 . 
     It should be understood that example embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each example embodiment should typically be considered as available for other similar features or aspects in other embodiments. 
     While example 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.