Light emitting element and method for manufacturing light emitting element

Abstract

A light-emitting element is provided, which has: a first active layer that emits light with a first wavelength by injecting current; a second active layer that emits light with a second wavelength different from the first wavelength by absorbing the light with the first wavelength; and a first reflector, where the reflectivity of the light with the first wavelength at the first reflector is greater than the reflectivity of the light with the second wavelength, wherein the first reflector is disposed at a position closer to an emission end than the first active layer and the second active layer, and light emitted by the first active layer or the second active layer is projected from the emission end to the outside.

Description

Technical Field

[0001] The present invention relates to a light emitting element and a method for manufacturing the light emitting element. Background Art

[0002] Patent document 1 discloses a technology for forming light-emitting elements emitting light of different wavelengths on the same wafer. In this technology, by repeatedly forming a mask on a portion other than a required portion and then forming an active layer for each wavelength, a plurality of light-emitting regions emitting light of different wavelengths can be formed adjacent to each other.

[0003] [Citation List]

[0004] [Patent Document]

[0005] PTL 1: Japanese Patent Application Publication No. 2009-70893 Summary of the invention

[0006] [Technical issues]

[0007] According to the method of growing an active layer multiple times on the same substrate as described in PTL 1, it is necessary to repeatedly perform a process for growing an active layer for each wavelength by placing the substrate in a crystal growth apparatus multiple times. In this case, the following problems may arise.

[0008] First, when growing the active layer, the growth surface needs to be cleaned at the atomic level. Since the cleanliness of the surface greatly affects the quality and yield of the active layer, multiple growths of the active layer may lead to degradation and / or instability in yield.

[0009] The growth process of the active layer accounts for a large proportion of the manufacturing cost of the light-emitting device. In the case of multiple growth of the active layer, for each growth step, processing time including mounting the substrate in a crystal growth device, raising the temperature required for crystal growth, etc. is required, which significantly increases the manufacturing cost.

[0010] As described above, in the method of growing the active layer multiple times, there may be a goal to improve the yield and stability while maintaining the quality of the active layer, and the manufacturing cost is further reduced. Therefore, the object of the present invention is to provide a light-emitting element that can be manufactured by a simpler process and a method for manufacturing the light-emitting element.

[0011] [Solution to the problem]

[0012] According to one aspect of the present invention, a light-emitting element is provided, which includes: a first active layer, which emits light with a first wavelength by injecting current; a second active layer, which emits light with a second wavelength different from the first wavelength by absorbing the light with the first wavelength; and a first reflector, in which the reflectivity of the light with the first wavelength is higher than the reflectivity of the light with the second wavelength, wherein the first reflector is disposed at a position closer to an emission end than the first active layer and the second active layer, and the light emitted by the first active layer or the second active layer is emitted from the emission end to the outside.

[0013] According to another aspect of the present invention, a method for manufacturing a light-emitting element is provided, the manufacturing method comprising: forming a second active layer that emits light having a second wavelength different from the first wavelength by absorbing light having a first wavelength; forming a first active layer that emits light having the first wavelength by injecting current; and forming a first reflector having a reflectivity of light having the first wavelength higher than a reflectivity of light having the second wavelength, wherein the first reflector is disposed at a position closer to an emission end than the first active layer and the second active layer, and light emitted by the first active layer or the second active layer is emitted from the emission end to the outside.

[0014] [Beneficial effects of the present invention]

[0015] According to the present invention, a light-emitting element that can be manufactured in a simple process and a method of manufacturing the light-emitting element can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] [ Figure 1 ]

[0017] Figure 1 is a sectional view schematically showing the structure of a light emitting device according to a first embodiment.

[0018] [ Figure 2 ]

[0019] Figure 2 is a sectional view schematically showing the structure of a light emitting device according to a second embodiment.

[0020] [ Figure 3A ]

[0021] Figure 3A is a cross-sectional view showing a model of a light emitting device used in the simulation in the second embodiment.

[0022] [ Figure 3B ]

[0023] Figure 3B is a cross-sectional view showing a model of a light emitting device used in the simulation in the second embodiment.

[0024] [ Figure 3C]

[0025] Figure 3C is a graph showing simulation results of the second embodiment.

[0026] [ Figure 4 ]

[0027] Figure 4 is a graph showing the reflectivity characteristics of the distributed Bragg reflector used in the simulation of the second embodiment.

[0028] [ Figure 5A ]

[0029] Figure 5A is a graph showing simulation results of emission ratio when the absorptivity of the green quantum well active layer is changed.

[0030] [ Figure 5B ]

[0031] Figure 5B is a graph showing simulation results of emission ratio when the absorptivity of the green quantum well active layer is changed.

[0032] [ Fig. 6A ]

[0033] Fig. 6A is a sectional view schematically showing the structure of a light emitting device according to a third embodiment.

[0034] [ Figure 6B ]

[0035] Figure 6B is a sectional view schematically showing the structure of a light emitting device according to a third embodiment.

[0036] [ Figure 6C ]

[0037] Figure 6C is a sectional view schematically showing the structure of a light emitting device according to a third embodiment.

[0038] [ Figure 7 ]

[0039] Figure 7 is a sectional view schematically showing the structure of a light emitting device according to a fourth embodiment.

[0040] [ Figure 8 ]

[0041] Figure 8 is a sectional view schematically showing the structure of a light emitting device according to a fifth embodiment.

[0042] [ Fig. 9 ]

[0043] Fig. 9 is a sectional view schematically showing the structure of a light emitting device according to a sixth embodiment.

[0044] [ Fig.10 ]

[0045] Fig.10 is a sectional view schematically showing the structure of a light emitting device according to a seventh embodiment.

[0046] [ Fig.11A ]

[0047] Fig.11A is a cross-sectional view schematically showing the structure of a transfer substrate according to a seventh embodiment.

[0048] [ Fig. 11B ]

[0049] Fig. 11B is a cross-sectional view schematically showing the structure of a transfer substrate according to a seventh embodiment. DETAILED DESCRIPTION

[0050] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the accompanying drawings, the same or corresponding elements are denoted by the same reference numerals, and the description thereof may be omitted or simplified.

[0051] [First embodiment]

[0052] Figure 1 FIG. 1 is a cross-sectional view schematically showing the structure of the light emitting device according to the present embodiment. Figure 1 As shown in the figure, the light emitting device of the present embodiment has a stacked structure in which a first semiconductor layer 101, a second active layer 102, a second semiconductor layer 103, a first active layer 104, a third semiconductor layer 105 and a first reflector 106 are sequentially arranged on a substrate 100. These layers may be formed by epitaxial growth. The light emitting element of the present embodiment includes a first electrode 107 disposed above the second semiconductor layer 103 and a second electrode 108 disposed above the third semiconductor layer 105.

[0053] When current is injected, the first active layer 104 emits light having a wavelength distribution with the first wavelength as the main peak. In this specification, "light having a wavelength distribution with the first wavelength as the main peak" may be simply referred to as "light of the first wavelength". When the second active layer 102 absorbs light of the first wavelength, the second active layer 102 emits light of a second wavelength different from the first wavelength by optical excitation. The light of the first wavelength may be, for example, blue light having a wavelength of about 450 nm. The light of the second wavelength may be, for example, green light having a wavelength of about 525 nm.

[0054] The first active layer 104 and the second active layer 102 may be formed of a single layer of material, or may be formed of a multi-quantum well structure in which multiple pairs of quantum well layers and barrier layers are alternately stacked. By appropriately setting the materials, compositions, thicknesses, logarithms, etc. of the active layer, quantum well layer, and barrier layer depending on the type of substrate and designing the active layer, quantum well layer, and barrier layer to have a desired band gap, a light-emitting element that emits light of a desired wavelength may be realized. For example, if the material of the substrate 100 is sapphire and the material of the active layer is InGaN, the central emission wavelength may be changed by changing the proportion of In. The greater the proportion of In, the longer the central emission wavelength becomes.

[0055] For example, the first semiconductor layer 101 is n-type or i-type, the second semiconductor layer 103 is n-type, and the third semiconductor layer 105 is p-type. In other words, the first active layer 104 is inserted between a semiconductor layer of a first conductivity type (n-type) and a semiconductor layer of a second conductivity type (p-type) opposite to the first conductivity type. The second active layer 102 is inserted between a first conductivity type or i-type semiconductor layer and a first conductivity type semiconductor layer. The conductivity type of the substrate 100 may be any one of n-type, p-type, and i-type.

[0056] Note that the i-type semiconductor layer in this specification refers to a non-doped (undoped) semiconductor layer. Non-doped layers may include those that are not intentionally doped with a dopant for controlling the conductivity type during the growth of the semiconductor layer and those that are doped with substantially the same amount of p-type and n-type dopants. The carrier concentration in the i-type semiconductor layer is preferably less than or equal to 1×10 16 cm -3 .

[0057] When each semiconductor layer is made of a Group III nitride semiconductor such as a GaN or AlGaN-based material, Si, Ge, etc. are used as an n-type dopant, and Mg, Zn, etc. are used as a p-type dopant. If each semiconductor layer is formed of an AlGaAs-based material that is a Group III-V semiconductor, Group II elements (Mg, Zn, etc.) are used as a p-type dopant, Group VI elements (Se, etc.) are used as an n-type dopant, and Group IV elements (C, Si, etc.) are used as a p-type dopant or an n-type dopant.

[0058] In the light emitting element of the present embodiment, the emission end from which light is emitted to the outside is the opposite side to the substrate 100, that is, Figure 1 The first reflector 106 is disposed on the emission end side of the light emitting element. In other words, the upper surface of the first reflector 106 corresponds to the emission end of the light emitting element. The first reflector 106 is designed so that the reflectivity of the light of the first wavelength is higher than the reflectivity of the light of the second wavelength.

[0059] The first reflector 106 is, for example, a distributed Bragg reflector. Hereinafter, a distributed Bragg reflector is referred to as a DBR (distributed Bragg reflector). A DBR is a reflector having a structure in which two thin films having different refractive indices are alternately and periodically formed to have an optical film thickness of a quarter wavelength. The first reflector 106 may be a plurality of semiconductor layers formed by epitaxial growth, or may be a plurality of dielectric layers. Of these two types of structures, a structure using a plurality of dielectric layers is preferred because the refractive index difference between the two thin films can be increased, and a high reflectivity can be achieved using a small logarithm.

[0060] Different potentials are applied to the first electrode 107 and the second electrode 108 so that current can be injected into the first active layer 104. If current is injected into the first active layer 104, the first active layer 104 emits light of the first wavelength. Of the light of the first wavelength emitted from the first active layer 104, the component emitted downward directly enters the second active layer 102. A portion of the light of the first wavelength emitted from the first active layer 104 that is emitted upward is reflected by the first reflector 106 and enters the second active layer 102. Here, since the reflectivity of the first reflector 106 is designed to be high relative to the light of the first wavelength, the light of the first wavelength transmitted through the first reflector 106 is small. Therefore, most of the light of the first wavelength is incident on the second active layer 102.

[0061] The second active layer 102 absorbs the light of the first wavelength and emits the light of the second wavelength by optical excitation. A portion of the light of the second wavelength is reflected by the first reflector 106 and returns to the substrate 100 side. However, since the reflectivity of the first reflector 106 with respect to the light of the second wavelength is designed to be lower than the reflectivity of the light of the first wavelength, most of the light of the second wavelength passes through the first reflector 106 and is reflected in the vertical direction ( Figure 1 The light emitting element of the present embodiment can selectively emit light of the second wavelength to the outside.

[0062] By using the first active layer 104, the second active layer 102 and the first reflector 106, the light emitting device of the present embodiment can convert the light of the first wavelength into the light of the second wavelength and selectively emit light to the outside. By arranging the first reflector 106, the above-mentioned effect can be obtained in a state where the first active layer 104 and the second active layer 102 are stacked in the thickness direction. Therefore, it is not necessary to perform patterning between the formation of the first active layer 104 and the second active layer 102. Therefore, according to the present embodiment, a light emitting device capable of forming multiple active layers with a simple process is provided.

[0063] The light-emitting element of this embodiment is used, for example, in the pixels of a display device. By manufacturing the light-emitting element of this embodiment with a size of tens of microns to hundreds of microns and arranging it into multiple rows and columns, a display surface of a display device can be formed. This display device using inorganic compound semiconductor LEDs (light-emitting diodes) is sometimes referred to as a μLED display. μLED displays are superior to liquid crystal displays and organic LED displays in terms of life, brightness, etc. Below, the effect obtained when the light-emitting device of this embodiment is used in a μLED display will be described.

[0064] An example of a method for manufacturing a μLED display is a method of installing light-emitting elements manufactured for individual colors such as blue, green, and red on a substrate of the display. In this method, since a large number of light-emitting elements need to be installed, there is a problem of making the installation cost high. Therefore, in order to reduce the installation cost, it is preferred to form light-emitting elements of multiple colors on the same wafer so that multiple light-emitting elements can be installed together.

[0065] In order to form a plurality of light-emitting elements on the same wafer, it is necessary to form a plurality of active layers with different emission wavelengths on the same wafer. In the method of forming a mask during the formation of a plurality of active layers described in PTL1, the manufacturing process becomes complicated and the manufacturing cost increases. The reasons are as follows. In the manufacturing process of a light-emitting device using a compound semiconductor, a semiconductor layer such as an active layer is formed by epitaxial growth. In the process flow of forming a mask during the formation of a plurality of active layers, the epitaxial growth of each layer cannot be performed at one time, and the epitaxial growth process must be performed multiple times. The epitaxial growth process includes time-consuming processes such as mounting a substrate in a crystal growth device and raising the temperature to the growth temperature. If the epitaxial growth process is performed multiple times, the number of processes increases in proportion to the number of processes, so that the manufacturing cost increases.

[0066] In contrast, the light-emitting device of the present embodiment has a structure in which wavelength conversion can be performed in a state where the first active layer 104 and the second active layer 102 are stacked in the thickness direction. Therefore, patterning is not required between the formation of the first active layer 104 and the second active layer 102. Therefore, even if two colors of light-emitting elements are formed on the same wafer, two active layers can be continuously formed by epitaxial growth. Therefore, in manufacturing a μLED display using the light-emitting element of the present embodiment, multiple active layers can be formed by a simple process, so that costs can be reduced.

[0067] In addition, by continuously forming two active layers by epitaxial growth, surface contamination caused by removal from a crystal growth device, etc. is reduced. Therefore, in the manufacture of the light-emitting device of this embodiment, the cleanliness of the growth surface is maintained, so that the effects of improving the yield, stabilizing the manufacturing process, and improving the quality of the active layer can be obtained.

[0068] The reasons why the light-emitting element of the present embodiment can be appropriately used as a pixel of a μLED display and its effects have been described above. The same is true for the other embodiments described later. However, the application of the light-emitting element of the present embodiment and other embodiments is not limited thereto, and can be applied to applications other than display devices such as lighting devices.

[0069] In this embodiment, the transmitting end corresponds to Figure 1 The emitting end is located on the upper side (the side opposite to the substrate 100) in the substrate 100, but the emitting end may be on the substrate 100 side. In the case where the emitting end is on the substrate 100 side, it is preferable to design a structure or a material so that the light absorption rate in the substrate 100 is low. As an example of a specific design, a material having a low absorption rate with respect to the wavelength of light to be emitted may be used for the substrate 100, or the thickness of the substrate 100 may be sufficiently reduced.

[0070] Although in the present embodiment, the first active layer 104 is disposed closer to the emission end than the second active layer 102, the stacking order of the first active layer 104 and the second active layer 102 may be reversed. If the order of the first active layer 104 and the second active layer 102 is changed, the positions of the first electrode 107 and the second electrode 108 need to be appropriately changed so that current is injected into the first active layer 104.

[0071] However, if Figure 1 As shown in , the first active layer 104 is preferably disposed closer to the emission end than the second active layer 102. In other words, the second active layer 102 is preferably disposed between the first active layer 104 and the substrate 100. In this configuration, compared with the case where the first active layer 104 and the second active layer 102 are arranged opposite to each other, there are advantages in that the contact hole in which the first electrode 107 for current injection is arranged can be made shallower and the etching amount can be reduced.

[0072] Preferably, the semiconductor layer between the first active layer 104 or the second active layer 102 and the substrate 100 is not doped with a p-type dopant. If the semiconductor layer is doped with a p-type dopant, the crystal quality of the semiconductor layer may be degraded. If the active layer is grown on the semiconductor layer, the quality of the active layer may be degraded due to the poor crystal quality of the semiconductor layer. In particular, if the active layer is made of a GaN-based material, the quality of the active layer has a great influence on the light emission characteristics. Therefore, the light emission characteristics can be improved by not doping the p-type dopant under the active layer.

[0073] More specifically, the first semiconductor layer 101 and the second active layer 102 are n-type or i-type without p-type doping, and the second semiconductor layer 103 is n-type without p-type doping. Therefore, in both the first active layer 104 and the second active layer 102, the degradation of the active layer quality due to the p-type dopant can be reduced, and the light emitting characteristics are improved.

[0074] [Second embodiment]

[0075] The light emitting element of this embodiment is different from the light emitting element of the first embodiment in that a second reflecting mirror 201 is further provided. Figure 2 1 is a cross-sectional view schematically showing the structure of the light emitting device according to the present embodiment. The first semiconductor layer 101 includes a second reflector 201. The second reflector 201 is arranged on a side opposite to the first reflector 106 relative to the first active layer 104 and the second active layer 102. Similar to the first reflector 106, the second reflector 201 is designed so that the reflectivity with respect to the light of the first wavelength is higher than the reflectivity with respect to the light of the second wavelength.

[0076] The second reflector 201 is, for example, a DBR. In this case, the second reflector 201 may be a DBR in which two types of semiconductor layers having different refractive indices are alternately stacked. Examples of two different types of semiconductor layers constituting the DBR include AlGaN and InGaN.

[0077] The light having the first wavelength emitted from the first active layer 104 is Figure 2 The light with the first wavelength emitted downward from the first active layer 104 is emitted in both the upward and downward directions. A portion of the light with the first wavelength emitted downward from the first active layer 104 is absorbed by the second active layer 102. At this time, the second active layer 102 emits light of the second wavelength by optical excitation. Another portion of the light of the first wavelength emitted downward is transmitted without being absorbed by the second active layer 102. The light with the first wavelength transmitted through the second active layer 102 is reflected by the second reflector 201 and re-enters the second active layer 102 to excite the light with the second wavelength. On the other hand, as described in the first embodiment, the light with the first wavelength emitted upward from the first active layer 104 is reflected by the first reflector 106, enters the second active layer 102, and excites the light with the second wavelength.

[0078] As described above, in the present embodiment, the second reflector 201 is arranged on the side opposite to the first reflector 106 with respect to the first active layer 104 and the second active layer 102. According to this configuration, since the light of the first wavelength emitted downward from the first active layer 104 and transmitted through the second active layer 102 can be returned to the second active layer 102 again, the conversion efficiency from the light of the first wavelength to the light of the second wavelength can be improved. Therefore, the light emission efficiency of the light of the second wavelength is improved. In addition, the leakage of the light of the first wavelength can be reduced.

[0079] Here, it is preferred that the first reflector 106 and the second reflector 201 are designed to have a film thickness of each layer to form a resonator for the first wavelength. More specifically, the film thickness of each layer can be designed so that the reciprocal of the length of light propagating between the first reflector 106 and the second reflector 201 is an integer multiple of half the first wavelength. Due to the above design, the conversion efficiency from the light of the first wavelength to the light of the second wavelength can be further improved.

[0080] The effects of this embodiment will be described in more detail with reference to simulation results in the case where the first reflector 106 and the second reflector 201 form a resonator. Figure 3A and Figure 3B Describes the layer structure of the simulation model of the light emitting element.

[0081] Figure 3A FIG. 2 shows a cross-sectional view of a light emitting element 300a as a model for simulation of a structure corresponding to the present embodiment. The light emitting element 300a has GaN / AlInN semiconductor DBRs 301 (10 pairs), a 1λ resonator 310 made of GaN, and a SiO 2 / SiN dielectric DBR 306 (6 pairs) are sequentially arranged in a stacked structure on the GaN substrate 100. The 1λ resonator 310 includes a blue quantum well active layer 304 (light emission wavelength is 450nm) and a green quantum well active layer 302 (light emission wavelength is 525nm). The 1λ resonator 310 is configured to have an optical film thickness of 1λ (1 wavelength) including the layer thickness of these two active layers. The wavelength of each DBR and 1λ resonator 310 is designed to be 450nm, which is the same as the emission wavelength of the blue quantum well active layer 304. When light with a wavelength of 450nm is transmitted from one surface to another, the absorption rate of light with a wavelength of 450nm in the green quantum well active layer 302 is designed to be 5.8%. This design can be achieved by adjusting the number of quantum wells.

[0082] on the other hand, Figure 3B A cross-sectional view of a light emitting element 300b is shown as a model for simulation of a comparative example with respect to the present embodiment. The light emitting element 300b is a configuration in which SiO is excluded from the configuration of the light emitting element 300a.2 / SiN dielectric DBR 306 and does not constitute a resonator.

[0083] Figure 3C is a graph showing simulation results of the absorption rate in the green quantum well active layer 302 when light is incident in a direction perpendicular to the stacked surface of the semiconductor layers. Figure 3C , the vertical axis represents the absorptivity in the green quantum well active layer 302, and the horizontal axis represents the wavelength of the incident light. Figure 3C The light emitting element 300a (ie, having SiO 2 In the simulation of the comparative example using the model of the light emitting element 300b, the absorptivity for light having a wavelength of 450nm was 0.044.

[0084] Figure 4 The SiO 2 Graphs showing the reflectivity characteristics of GaN / SiN dielectric DBR 306 and the reflectivity characteristics of GaN / AlInN semiconductor DBR 301. Figure 4 , the vertical axis represents reflectivity, and the horizontal axis represents the wavelength of incident light. Figure 4 The solid line indicates SiO 2 The dotted line indicates the reflectivity characteristic of the GaN / AlInN semiconductor DBR 301. 2 In the GaN / AlInN dielectric DBR 306, the reflectivity at a wavelength of 450 nm is 0.96, which indicates a high value. On the other hand, the reflectivity at a wavelength of 525 nm is 0.4 or less, which indicates a low value. Regarding the GaN / AlInN semiconductor DBR 301, a similar trend is observed, although not as high as that of the SiO 2 / SiN dielectric DBR 306 is significant. Through optical simulation, it is obtained Figure 4 reflectivity characteristics.

[0085] As will be understood from the above description, by providing SiO 2 / SiN dielectric DBR 306, the absorption rate of light with a wavelength of 450nm in the green quantum well active layer 302 becomes about 10 times larger. Therefore, it is found that by configuring the resonator structure with two reflectors, the absorption efficiency of light with a first wavelength (450nm) can be improved and the emission efficiency of light with a second wavelength (525nm) can be improved. In addition, due to the SiO 2 The SiN / SiN dielectric DBR 306 has high reflectivity at the first wavelength and low reflectivity at the second wavelength, so light leakage at the first wavelength can be reduced.

[0086] In this manner, by only providing a DBR without processing the active layer, the absorption efficiency of light of the first wavelength can be improved, and through a simple process, the emission efficiency of light of the second wavelength can be improved.

[0087] The emission intensity of the second wavelength of light can depend on the SiO 2 The dielectric DBR 306 is formed in the upper layer. That is, by forming SiO at a desired position in the wafer surface, the dielectric DBR 306 is changed. 2 / SiN dielectric DBR 306, can be used without SiO 2 When the semiconductor layer below the SiN dielectric DBR 306 is processed, a position for selectively emitting light of the second wavelength is provided. Therefore, the portion for selectively emitting light of the second wavelength can be formed by a simple process.

[0088] The above simulation is based on the premise that light propagates in a direction perpendicular to the stacked surface. However, even for light propagating in an oblique direction, although a difference in the resonance wavelength occurs, a similar effect can be obtained.

[0089] Figure 5A and Figure 5B 3 is a graph showing the simulation results of the emission ratio when the light absorption rate of the green quantum well active layer 302 is changed. The structure and characteristics of the light emitting element used in this simulation are similar to those of FIG. 3A to FIG. 3C and Figure 4 The structure and features shown in are the same.

[0090] Figure 5A and Figure 5B The horizontal axis indicates the absorption rate when light having a wavelength of 450 nm is transmitted from one surface to another surface in the green quantum well active layer 302. The vertical axis represents the ratio of light emission upward from each active layer of the blue quantum well active layer 304 or the green quantum well active layer 302. Figure 5A and Figure 5B , the solid line indicates the emission ratio from the green quantum well active layer 302 , and the dotted line indicates the emission ratio from the blue quantum well active layer 304 .

[0091] In the simulation, the amount of light emitted from the blue quantum well active layer 304 is set to 1. If blue light is absorbed by the green quantum well active layer, the light is 100% converted into green light.

[0092] Figure 5A : is a graph showing a case where a light emitting element is used in a state where the ratio of the amount of light of green and blue is 1:1. Figure 5B : is a graph showing the case where the light emitting element is used in a state where the ratio of the amount of light of green to that of blue is 1:3. That is, Figure 5BShows the ratio Figure 5A In the case shown, the value of the emission ratio of the amount of green light is three times greater.

[0093] like Figure 5A As shown in , if the light emitting device of this embodiment is used in a state where the brightness ratio of green to blue is 1:1, the absorption rate of the green quantum well active layer 302 is preferably adjusted to about 35%.

[0094] An example of adjusting the insufficient green emission ratio may be a method of adjusting the emission ratio by adjusting the amount of current injected into each pixel. For example, in the case of the present embodiment, the green light emission ratio may be increased by increasing the amount of current injected into the green pixel to be greater than the amount of current injected into the blue pixel. In addition, the light emission ratio of each pixel may be adjusted by changing the reflectivity of the DBR. For example, by configuring the SiO 2 / SiN dielectric DBR 306 to reduce the reflectivity of the wavelength corresponding to green, the green emission ratio can be increased.

[0095] In the case where the light emitting device of the present embodiment is used in a device such as a display device or a lighting device that performs adjustment in consideration of user visibility, the brightness of the light emitting devices can be distinguished from each other in consideration of the difference in visibility between green and blue. Figure 5B As shown in FIG, the green-blue light quantity ratio is 1:3, and the above light quantity ratio is achieved by setting the absorptivity of the green quantum well active layer 302 to 3% or more and 7% or less (if the allowable deviation is about ±30%). In addition, the above light quantity ratio is more appropriately achieved by setting it to 4% or more and 6% or less (if the allowable deviation is about ±10%).

[0096] The above example is merely an example of a method of using the light emitting element of the present embodiment. Since the design of the absorptivity of the green quantum well active layer 302 can be changed as needed depending on the reflectivity of the reflector, the conversion efficiency of the light excited from the excitation light, the brightness ratio of each color, the degree of reduction of the color mixing ratio, etc., a design different from the above example can be performed. For example, if the wavelength dependence of the reflectivity of the reflector is different from that used in this simulation, Figure 4 If the reflectivity at 525 nm, which is the wavelength of green light, is reduced by changing the design of the dielectric DBR to increase the emission ratio of green light, the range of the appropriate absorbance is changed to a range lower than the above value.

[0097] In this embodiment, if two different wavelengths of light (for example, blue and green) are generated, the light emission amount itself is changed, rather than removing a portion of the light such as a filter. For example, in this embodiment, by introducing a resonator structure for light having a green wavelength, the absorption efficiency can be increased by about ten times. Therefore, a light-emitting element capable of more efficient light emission is provided.

[0098] [Third embodiment]

[0099] The light emitting device of the present embodiment includes the light emitting device according to the first embodiment or the second embodiment, and is configured to be capable of emitting light of two wavelengths different from each other from two light emitting regions formed on the same wafer. Fig. 6A is a sectional view schematically showing a first configuration example of the light emitting device according to the present embodiment.

[0100] like Fig. 6A As shown in the figure, in a plan view from a direction perpendicular to the substrate 100, the light emitting element of the present embodiment includes a first region 501 and a second region 502. The first region 501 mainly emits light of a first wavelength to the outside. The second region 502 mainly emits light of a second wavelength to the outside. The first region 501 and the second region 502 are formed on the same wafer. The first reflector 106 is disposed on the third semiconductor layer 105 of the second region 502. The first reflector 106 is not disposed on the third semiconductor layer 105 in the first region 501.

[0101] The structure of the second region 502 is similar to that of the first embodiment. Figure 1 The structure of the first active layer 104 is the same as that of the first active layer 104. That is, the second region 502 is provided with a first reflector 106 having a high reflectivity for light of the first wavelength. When current is injected into the first active layer 104 through the first electrode 107 and the second electrode 108, the first active layer 104 emits light of the first wavelength. The second active layer 102 is excited by the light of the first wavelength, and the second active layer 102 emits light of the second wavelength. In addition, the first reflector 106 has a high reflectivity with respect to the light of the first wavelength. Therefore, the light of the second wavelength is mainly emitted from the second region 502.

[0102] Near the first region 501, the third electrode 503 is disposed on the third semiconductor layer 105 as an electrode for injecting current into the first active layer 104 of the first region 501. When current is injected into the first active layer 104 through the first electrode 107 and the third electrode 503, the first active layer 104 of the first region 501 emits light of a first wavelength. The first electrode 107 is a common electrode for supplying current to the first active layer 104 of the first region 501 and the first active layer 104 of the second region 502. On the other hand, the second electrode 108 and the third electrode 503 are independently provided. Therefore, the light emitting element of the present embodiment has a structure that can independently supply current to the first active layer 104 of the first region 501 and the first active layer 104 of the second region 502. Therefore, the first region 501 and the second region 502 can independently emit light of different wavelengths.

[0103] Another configuration example of the light emitting element according to the present embodiment will be described. Figure 6B 2 is a cross-sectional view schematically showing a second configuration example of the light emitting element according to the present embodiment. In this configuration example, similar to the second embodiment, the first semiconductor layer 101 includes a second reflector 201. The second reflector 201 is designed to have a high reflectivity at least for light of the first wavelength.

[0104] With such a configuration, the light emission efficiency of the light of the second wavelength in the second region 502 is improved for the same reason as described in the second embodiment. In addition, in the first region 501, the light of the first wavelength emitted downward from the first active layer 104 is reflected by the second reflector 201 and returned upward. Therefore, in the first region 501, the light emission efficiency of the light of the first wavelength is also improved. As described above, in this configuration example, in addition to the effects similar to those of the first configuration example, the light emission efficiency can be further improved.

[0105] It should be noted that the second reflector 201 can be designed to have a high reflectivity with respect to the light of the second wavelength. In this case, in the second region 502, the light of the second wavelength emitted downward from the second active layer 102 is also reflected by the second reflector 201 and returned upward. This further improves the light emission efficiency of the light of the second wavelength in the second region 502.

[0106] Still another configuration example of the light emitting element according to the present embodiment will be described. Figure 6C 501 is a cross-sectional view schematically showing a third configuration example of the light emitting device according to the present embodiment. This configuration example is one of the configurations for reducing the component of the second wavelength included in the light emitted from the first region 501.

[0107] In this configuration example, the third reflector 504 is disposed on the third semiconductor layer 105 of the first region 501. The reflectivity of the third reflector 504 with respect to the light of the second wavelength is higher than the reflectivity of the third reflector 504 with respect to the light of the first wavelength. The other configurations are the same as the first configuration example. When current is injected from the first electrode 107 and the third electrode 503 into the first active layer 104 of the first region 501, the first active layer 104 emits light of the first wavelength. When the light of the first wavelength is absorbed by the second active layer 102, the second active layer 102 emits light of the second wavelength. Since the light of the second wavelength is reflected by the third reflector 504, the component of the second wavelength included in the light emitted from the first region 501 is reduced. Therefore, the proportion of the first wavelength included in the light emitted from the first region 501 increases, while the proportion of the second wavelength decreases, thereby allowing the color mixing between the light of the first wavelength and the light of the second wavelength to be reduced.

[0108] As described above, according to the first configuration example to the third configuration example of the present embodiment, the first region 501 and the second region 502 emitting light of different wavelengths can be formed on the same wafer. In this configuration, the structure for changing the wavelength of the emitted light is the first reflector 106 disposed on the third semiconductor layer 105. Therefore, by forming the first reflector 106 at a desired position in the wafer surface, the first region 501 and the second region 502 emitting light of different wavelengths can be formed without performing any processing on the semiconductor layer below the first reflector 106. Therefore, a light-emitting element capable of independently emitting two wavelengths of light can be formed using a simple process.

[0109] [Fourth embodiment]

[0110] The light emitting element of this embodiment is obtained by modifying the number of light emitting regions of the third embodiment from two to three. That is, the light emitting element of this embodiment is configured to emit three different wavelengths of light from three light emitting regions formed on the same wafer. Figure 7 is a cross-sectional view schematically showing a configuration example of a light emitting element according to the present embodiment.

[0111] In addition to the second configuration example of the third embodiment ( Figure 6B ) of the element structure, the light emitting element of this embodiment mainly includes a third region 601 that emits light of a third wavelength to the outside. In this embodiment, similar to the third configuration example ( Figure 6C ), the third reflector 504 is deployed on the third semiconductor layer 105 in the first region 501.

[0112] In the third region 601, the cross-sectional structure below the third semiconductor layer 105 is similar to the cross-sectional structures in the first region 501 and the second region 502. In the third region 601, the fourth semiconductor layer 604, the third active layer 602 and the fifth semiconductor layer 605 are sequentially arranged on the third semiconductor layer 105.

[0113] Near the third region 601, the fourth electrode 603 is disposed on the third semiconductor layer 105 as an electrode for injecting current into the first active layer 104 in the third region 601. When the current is injected into the first active layer 104 through the first electrode 107 and the fourth electrode 603, the first active layer 104 in the third region 601 emits light of the first wavelength. The light of the first wavelength excites the third active layer 602, and the third active layer 602 emits light of the third wavelength. The light of the third wavelength may be, for example, red light having a wavelength of about 630 nm.

[0114] According to the present embodiment, the first region 501, the second region 502, and the third region 601 emitting light of different wavelengths can be formed on the same wafer. In this structure, the structure for changing the wavelength of the emitted light is each layer disposed on the third semiconductor layer 105, that is, the first reflector 106, the third reflector 504, the fourth semiconductor layer 604, the third active layer 602, and the fifth semiconductor layer 605. Therefore, by forming these layers at desired positions in the wafer surface, the first region 501, the second region 502, and the third region 601 emitting light of different wavelengths can be formed without performing any processing on the semiconductor layer below the layer.

[0115] In this embodiment, light of the third wavelength is emitted by light excitation caused by light emission from the first active layer 104 of the third region 601. To achieve the above, the fourth semiconductor layer 604, the third active layer 602, and the fifth semiconductor layer 605 do not need to be electrically connected to the third semiconductor layer 105, and can be located at a predetermined position. Therefore, a light-emitting element capable of independently emitting three wavelengths of light can be formed using a simple process.

[0116] For example, by epitaxial growth, the fourth semiconductor layer 604, the third active layer 602, and the fifth semiconductor layer 605 may be formed on the third semiconductor layer 105. However, other methods may be used.

[0117] Examples of other methods mentioned above will be described below. Another transfer substrate on which the fifth semiconductor layer 605, the third active layer 602, and the fourth semiconductor layer 604 are sequentially formed from the substrate side is prepared in advance. The transfer substrate is bonded to the substrate 100 on which the semiconductor layer below the third semiconductor layer 105 is formed, and then only the transfer substrate is removed by wet etching or the like. In addition, by this method, the fourth semiconductor layer 604, the third active layer 602, and the fifth semiconductor layer 605 can be formed on the third semiconductor layer 105. If a p-type dopant is doped as described above, the crystal quality of the semiconductor layer may degrade. Therefore, the crystal quality of the layer formed by epitaxial growth on the semiconductor layer doped with the p-type dopant may degrade. In this method, it is not necessary to form a semiconductor layer on the p-type third semiconductor layer 105 by epitaxial growth. Therefore, the quality of the third active layer 602 can be improved, and the light emission characteristics can be improved.

[0118] Preferably, after the fourth semiconductor layer 604, the third active layer 602 and the fifth semiconductor layer 605 are bonded to determine the position of the third region 601, steps such as forming the first reflector 106 and the third reflector 504 to determine the first region 501 and the second region 502 are performed. Due to this order, substrate bonding can be performed on a flat substrate immediately after epitaxial growth, rather than on a substrate having roughness after the process. The above configuration allows a better state of the bonding surface and reduces the process difficulty. As a result, the yield is improved. In addition, based on the position of the third region 601 that has been formed, the position of the first region 501 and the second region 502 can be determined with high positional accuracy by photolithography. Therefore, compared with the case where the first region 501 and the second region 502 are predetermined, the alignment accuracy required for bonding can be reduced. In addition, as described above, compared with the method of installing a light-emitting element manufactured for each color on the substrate of a display device, multiple colors of elements can be arranged on the entire surface of the wafer by bonding at one time. Therefore, it is possible to achieve improved yield and reduced installation costs.

[0119] [Fifth embodiment]

[0120] Another specific design example and another manufacturing process example of the light emitting element having two light emitting areas described in the third embodiment will be described below as a fifth embodiment. Figure 8 1 is a cross-sectional view schematically showing the structure of the light emitting device according to the present embodiment. Figure 6C ) is similar in structure, so the detailed description of the structure can be omitted or simplified.

[0121] The light emitting device of the present embodiment is formed by sequentially epitaxially growing an i-type GaN layer 701, an i-type green quantum well active layer 702, an n-type GaN layer 703, an i-type blue quantum well active layer 704, and a p-type GaN layer 705 on a sapphire substrate 700. A buffer layer (not shown) is formed between the sapphire substrate 700 and the GaN layer 701.

[0122] The green quantum well active layer 702 includes an InGaN well layer and a GaN barrier layer. In the green quantum well active layer 702, the In composition of the InGaN well layer is about 20%, and in this case, the central emission wavelength is 525 nm.

[0123] The blue quantum well active layer 704 also includes an InGaN well layer and a GaN barrier layer. In the blue quantum well active layer 704, the In composition of the InGaN well layer is about 15%, and in this case, the central emission wavelength is 450 nm.

[0124] In a plan view from a direction perpendicular to the sapphire substrate 700, the light emitting device of the present embodiment includes a region 711 emitting blue light and a region 712 emitting green light. In the light emitting device, after forming the GaN layer 705, an isolation groove for isolating the regions 711 and 712 from each other is formed. The depth of the isolation groove is set so that the position of the bottom surface of the isolation groove is between the upper surface and the lower surface of the GaN layer 703. After forming the isolation groove, an n-electrode 707 for applying a common potential to each region is formed at the bottom of the isolation groove. P electrodes 708 and 713 for independently applying a potential to regions 712 and 711 are formed on the GaN layer 705. In addition, a reflector 706 that mainly reflects light of a blue wavelength and a reflector 714 that mainly reflects light of a green wavelength are formed in regions 712 and 711, respectively.

[0125] The reflector 706 includes six pairs of SiN and SiO 2 The film thickness of each layer is determined in consideration of the refractive index of each layer so that the optical film thickness is one quarter of the wavelength of blue light (450 nm). The reflector 714 includes six pairs of SiN and SiO 2 The thickness of each film is determined in consideration of the refractive index of each film so that the optical film thickness becomes a quarter of the wavelength of green light (525 nm).

[0126] According to the present embodiment, a light emitting element in which the region 711 emitting light of a blue wavelength and the region 712 emitting light of a green wavelength are formed on the same wafer can be manufactured using a simple process.

[0127] [Sixth embodiment]

[0128] Next, a light emitting device according to a sixth embodiment will be described. According to the sixth embodiment, a DBR corresponding to the second reflector 201 in the second configuration example of the third embodiment is added to the light emitting device according to the fifth embodiment. Fig. 9 is a cross-sectional view schematically showing the structure of a light emitting device according to the present embodiment. In the light emitting device of the present embodiment, an i-type GaN layer 801 includes an i-type DBR layer 802. The other structures are the same as those of the fifth embodiment, and thus description thereof will be omitted.

[0129] The DBR layer 802 has a stacked structure in which ten pairs of AlGaN layers and GaN layers are alternately stacked. The film thickness of each layer is determined in consideration of the refractive index of each layer so that the optical film thickness is one quarter of the wavelength of blue light (450 nm). The thickness of each layer, etc. is set so that the DBR layer 802 and the reflector 706 form a resonator for the blue wavelength.

[0130] With this configuration, in region 712, blue light (wavelength of 450 nm) resonates in the resonator. Therefore, the absorptivity of blue light in the green quantum well active layer 702 increases, and the emission efficiency of green light from the green quantum well active layer 702 improves. On the other hand, in region 711, of the light generated in the blue quantum well active layer 704, the light emitted toward the sapphire substrate 700 side is reflected by the DBR layer 802 and travels upward, so that the light emission efficiency of the blue light is improved.

[0131] Therefore, in addition to effects similar to those of the fifth embodiment, the light emission efficiency of blue light and green light is further improved as compared with that of the fifth embodiment.

[0132] [Seventh embodiment]

[0133] Next, a seventh embodiment is described. According to the seventh embodiment, the light emitting device according to the sixth embodiment is modified to emit three colors of light as in the fourth embodiment. Fig.10 7 is a cross-sectional view schematically showing the structure of the light emitting device according to the present embodiment. When viewed from a plane perpendicular to the sapphire substrate 700, the light emitting device of the present embodiment further includes a region 901 emitting red light. The other structures are the same as those of the sixth embodiment, so description thereof will be omitted.

[0134] In the region 901, an AlInP cladding layer 904, an AlGaInP active layer 902, and an AlInP cladding layer 905 are sequentially formed on the GaN layer 705. The central emission wavelength of the AlGaInP active layer 902 is adjusted to 630 nm.

[0135] A p-electrode 903 for applying a potential to the region 901 is formed on the GaN layer 705 of the region 901. When current is injected into the blue quantum well active layer 704 through the n-electrode 707 and the p-electrode 903, the blue quantum well active layer 704 emits blue light. The AlGaInP active layer 902 is excited by the blue light, and the AlGaInP active layer 902 emits red light. Therefore, red light is emitted from the region 901.

[0136] refer to Fig.11A and Fig. 11B , an outline of the method of manufacturing the light emitting device of this embodiment will be described. Fig.11A and Fig. 11B is a cross-sectional view schematically showing the structure of a transfer substrate according to the present embodiment.

[0137] like Fig.11A As shown in FIG. 7 , an AlInP capping layer 905, an AlGaInP active layer 902, and an AlInP capping layer 904 are sequentially epitaxially grown on a GaAs substrate 910 different from the sapphire substrate 700. Next, as shown in FIG. Fig. 11B As shown in FIG. 1 , patterning is performed by etching the AlInP cap layer 904, the AlGaInP active layer 902, and the AlInP cap layer 905 to leave only a portion corresponding to the light emitting region. Thereafter, by spin coating on Fig. 11B A polyimide layer (not shown) is formed on the upper surface of the substrate. Through these processes, a transfer substrate for transfer by bonding is completed.

[0138] Then, in the case of having Fig.10 The GaN layer 705 of the sapphire substrate 700 and the AlInP capping layer 904 of the transfer substrate are heated in a state where they are aligned facing each other. Therefore, the GaN layer 705 and the AlInP capping layer 904 are bonded to each other via the polyimide layer. Then, the GaAs substrate 910 is removed by wet etching. Therefore, the AlInP capping layer 904, the AlGaInP active layer 902, and the AlInP capping layer 905 are transferred onto the GaN layer 705. Then, similar to the fifth embodiment, the separation groove 906 is formed, the reflectors 706 and 714 are formed, and the process is completed. Fig.10 The light emitting device shown in FIG.

[0139] According to this embodiment, a light emitting element in which the region 711 for emitting light of a blue wavelength, the region 712 for emitting light of a green wavelength, and the region 901 for emitting light of a red wavelength are formed on the same wafer can be manufactured using a simple process.

[0140] [Modified Example]

[0141] The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, an example in which a part of the configuration of any embodiment is added to another embodiment or an example in which a part of the configuration of another embodiment is replaced is also included in the embodiments of the present invention.

[0142] The above-mentioned embodiments are merely examples of implementation modes for carrying out the present invention, and the technical scope of the present invention should not be interpreted as being limited thereto. That is, the present invention can be implemented in various forms without departing from its technical ideas or its main features.

[0143] Priority is claimed on Japanese Patent Application No. 2019-139551 filed on Jul. 30, 2019, the entire contents of which are incorporated herein by reference.

[0144] [Reference Symbol List]

[0145] 101 First semiconductor layer

[0146] 102 Second active layer

[0147] 103 Second semiconductor layer

[0148] 104 First active layer

[0149] 105 Third semiconductor layer

[0150] 106 First Reflector

Claims

1. A light emitting element, comprising: a first active layer, the first active layer emitting light having a first wavelength by injecting current; a second active layer that emits light having a second wavelength different from the first wavelength by absorbing light having the first wavelength; a first reflector in which a reflectivity of light having a first wavelength is higher than a reflectivity of light having a second wavelength; as well as a third reflecting mirror in which the reflectivity of the light having the second wavelength is higher than the reflectivity of the light having the first wavelength, The first reflector is disposed at a position closer to the emission end than the first active layer and the second active layer, and the light emitted by the first active layer or the second active layer is emitted from the emission end to the outside. Wherein, in the plan view, the light emitting element further includes a first region and a second region, wherein the first active layer and the second active layer are disposed in each of the first region and the second region, wherein, in plan view, the first reflector is disposed in the second region, and the first reflector is not disposed in the first region, wherein, in plan view, the third reflector is disposed in the first region, wherein, in the first region, the emission amount of light having the first wavelength is greater than the emission amount of light having the second wavelength, and In the second region, the emission amount of the light having the second wavelength is greater than the emission amount of the light having the first wavelength.

2. The light-emitting element according to claim 1, wherein The first active layer is disposed closer to the emission end than the second active layer.

3. The light emitting element according to claim 1 or 2, further comprising a second reflector, wherein the reflectivity of the light having the first wavelength in the second reflector is higher than the reflectivity of the light having the second wavelength, in, The second reflecting mirror is disposed on a side opposite to the first reflecting mirror with respect to the first active layer and the second active layer.

4. The light-emitting element according to claim 3, wherein The first mirror and the second mirror constitute a resonator for light having a first wavelength.

5. The light emitting element according to claim 4, wherein An absorptivity of light having the first wavelength in the second active layer is greater than or equal to 3% and less than or equal to 7%.

6. The light emitting element according to claim 4, wherein An absorptivity of light having the first wavelength in the second active layer is greater than or equal to 4% and less than or equal to 6%.

7. The light-emitting element according to claim 1 or 2, wherein: The first active layer is interposed between a first conductivity type semiconductor layer and a second conductivity type semiconductor layer opposite to the first conductivity type.

8. The light-emitting element according to claim 7, wherein The second active layer is interposed between the first conductivity type or i-type semiconductor layer and the first conductivity type semiconductor layer.

9. The light-emitting element according to claim 1 or 2, further comprising a substrate, in, A first active layer, a second active layer, and a first reflector are stacked on a substrate, and Wherein, the p-type dopant is not doped in the semiconductor layer disposed between the substrate and the first active layer or the second active layer disposed farther from the substrate.

10. The light emitting element according to claim 1 or 2, further comprising, in a plan view, a third region that emits light having a third wavelength different from the first wavelength and the second wavelength, in, In the third region, the emission amount of light having the third wavelength is greater than the emission amount of light having the first wavelength and the emission amount of light having the second wavelength.

11. The light emitting element according to claim 10, further comprising a third active layer emitting light having a third wavelength in the third region, in, The third active layer is disposed at a position closer to the emission end than the first active layer.

12. The light emitting element according to claim 10, wherein The light having the first wavelength is blue light, the light having the second wavelength is green light, and the light having the third wavelength is red light.

13. The light-emitting element according to claim 1 or 2, wherein: The first reflector is a distributed Bragg reflector including a plurality of dielectric layers having different refractive indices.

14. The light emitting element according to claim 1, wherein The light having the first wavelength is blue light.

15. The light emitting element according to claim 14, wherein The second wavelength of light is green light.

16. A method for manufacturing a light emitting element, comprising: forming a second active layer that emits light having a second wavelength different from the first wavelength by absorbing light having the first wavelength; forming a first active layer that emits light having a first wavelength by injecting current; forming a first reflector having a higher reflectivity for light having a first wavelength than for light having a second wavelength; as well as forming a third reflector having a reflectivity of light having the second wavelength higher than a reflectivity of light having the first wavelength, The first reflector is disposed at a position closer to the emission end than the first active layer and the second active layer, and the light emitted by the first active layer or the second active layer is emitted from the emission end to the outside. Wherein, in the plan view, the light emitting element further includes a first region and a second region, wherein the first active layer and the second active layer are disposed in each of the first region and the second region, wherein, in plan view, the first reflector is disposed in the second region, and the first reflector is not disposed in the first region, wherein, in plan view, the third reflector is disposed in the first region, wherein, in the first region, the emission amount of light having the first wavelength is greater than the emission amount of light having the second wavelength, and In the second region, the emission amount of the light having the second wavelength is greater than the emission amount of the light having the first wavelength.

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