KR20080093558A - Nitride light emitting device - Google Patents

Nitride light emitting device Download PDF

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KR20080093558A
KR20080093558A KR1020070037416A KR20070037416A KR20080093558A KR 20080093558 A KR20080093558 A KR 20080093558A KR 1020070037416 A KR1020070037416 A KR 1020070037416A KR 20070037416 A KR20070037416 A KR 20070037416A KR 20080093558 A KR20080093558 A KR 20080093558A
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South Korea
Prior art keywords
photonic crystal
light emitting
emitting device
layer
period
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KR1020070037416A
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Korean (ko)
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김선경
장준호
조현경
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엘지이노텍 주식회사
엘지전자 주식회사
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Priority claimed from KR1020060041006A external-priority patent/KR100736623B1/en
Application filed by 엘지이노텍 주식회사, 엘지전자 주식회사 filed Critical 엘지이노텍 주식회사
Priority to KR1020070037416A priority Critical patent/KR20080093558A/en
Publication of KR20080093558A publication Critical patent/KR20080093558A/en

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Abstract

The present invention relates to a nitride-based light emitting device, and more particularly to a nitride-based light emitting device that can improve the luminous efficiency and reliability of the light emitting device. In the light emitting device, the present invention preferably comprises a photonic crystal layer including at least two or more photonic crystal structures having different periods on the same plane on the semiconductor layer.

Description

Nitride-based light emitting device

1 is a cross-sectional view showing an example of a structure for light extraction efficiency of a light emitting device.

FIG. 2 is a graph showing extraction efficiency with increasing refractive index of the hemisphere of FIG. 1.

3 is a cross-sectional view illustrating an embodiment of a horizontal light emitting device having a photonic crystal structure.

4 is a cross-sectional view showing an embodiment of a vertical light emitting device having a photonic crystal structure.

5 is a cross-sectional view showing an example of a vertical light emitting device structure for computer simulation.

6 is a cross-sectional view illustrating the absorption rate of the light emitting layer in the structure of FIG. 5.

7 is a diagram showing a radiation pattern when the light emitting layer is sufficiently far from the mirror.

8 is a graph illustrating the light extraction efficiency while changing the period of the photonic crystal.

9 is a graph showing a change in light extraction efficiency according to the size of the hole of the photonic crystal.

10 is a graph showing a change in light extraction efficiency according to the etching depth of the photonic crystal.

11 is a schematic diagram showing the principle of extracting light corresponding to the total reflection angle of the photonic crystal structure.

12 is a cross-sectional view illustrating a structure in which a photonic crystal is introduced into an upper layer portion of a horizontal light emitting device.

13 is a cross-sectional view showing a light emitting device structure formed on a substrate on which a pattern is formed.

14 is a cross-sectional view showing a light emitting device structure in which a photonic crystal and a patterned substrate are simultaneously introduced.

15 is a graph showing a change in light extraction efficiency according to a distance that light travels along a substrate on which a photonic crystal and a pattern are formed.

16 is a cross-sectional view showing an example of a light emitting element having a mixed period photonic crystal.

17 is a planar electron micrograph of the structure shown in FIG. 16.

18 is a cross-sectional electron micrograph of the structure shown in FIG. 16.

19A is a plan view illustrating an example of a mixing period photonic crystal.

19B is a cross-sectional view of FIG. 19A.

20 is a graph showing the light extraction efficiency of the structure in which the mixed period photonic crystal is introduced.

21 to 24 are cross-sectional views showing examples of the mixing cycle photonic crystal.

25 is a cross-sectional view showing an embodiment of a vertical light emitting device having a mixed period photonic crystal.

<Brief description of the main parts of the drawing>

100 semiconductor layer 110 n-type semiconductor layer

120: light emitting layer 130: p-type semiconductor layer

200: photonic crystal layer 210: first photonic crystal

220: second photonic crystal 300: reflective ohmic electrode

400: support layer 500: n-type electrode

The present invention relates to a nitride-based light emitting device, and more particularly to a nitride-based light emitting device that can improve the luminous efficiency and reliability of the light emitting device.

Light Emitting Diodes (LEDs) are well-known semiconductor light emitting devices that convert current into light.In 1962, red LEDs using GaAsP compound semiconductors were commercialized, along with GaP: N series green LEDs. It has been used as a light source for display images of electronic devices, including.

The wavelength of light emitted by such LEDs depends on the semiconductor material used to make the LEDs. This is because the wavelength of the emitted light depends on the band-gap of the semiconductor material, which represents the energy difference between valence band electrons and conduction band electrons.

Gallium nitride compound semiconductors (Gallium Nitride (GaN)) have high thermal stability and wide bandgap (0.8 to 6.2 eV), which has attracted much attention in the development of high-power electronic components including LEDs.

One reason for this is that GaN can be combined with other elements (indium (In), aluminum (Al), etc.) to produce semiconductor layers that emit green, blue and white light.

In this way, the emission wavelength can be adjusted to match the material's characteristics to specific device characteristics. For example, GaN can be used to create white LEDs that can replace incandescent and blue LEDs that are beneficial for optical recording.

Due to the advantages of these GaN-based materials, the GaN-based LED market is growing rapidly. Therefore, since commercial introduction in 1994, GaN-based optoelectronic device technology has rapidly developed.

The brightness or output of the LED using the GaN-based material as described above is large, the structure of the active layer, the light extraction efficiency to extract light to the outside, the size of the LED chip, the type and angle of the mold (mold) when assembling the lamp package , Fluorescent material and the like.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a nitride based light emitting device capable of improving light extraction efficiency by forming a vertical light emitting device structure having a photonic crystal.

As a first aspect for achieving the above technical problem, the present invention preferably comprises a photonic crystal layer including at least two or more photonic crystal structures having different periods on the same plane on a semiconductor layer in a light emitting device. .

The photonic crystal layer may be a pattern of a plurality of hole patterns or a plurality of protruding particles, and the hole pattern and the protruding particles may be mixed and used.

The period of the photonic crystal layer having the longest period of the photonic crystal layer may be 800 nm to 5000 nm, and in this case, the depth of the pattern forming the longest photonic crystal is preferably 300 nm to 3000 nm.

In addition, the period of the photonic crystal layer with the shortest period of the photonic crystal layer may be 50nm to 1000nm, the depth of the pattern that forms the shortest photonic crystal is preferably 50nm to 500nm.

On the other hand, when the period of the photonic crystal layer is a, the depth of the hole forming the photonic crystal of the photonic crystal layer is preferably 0.1a to 0.45a.

The semiconductor layer includes a p-type semiconductor layer; A light emitting layer on the p-type semiconductor layer; The light emitting layer may include an n-type semiconductor layer, and the photonic crystal layer may be formed on the n-type semiconductor layer.

In addition, a reflective ohmic electrode layer may be positioned on the other side of the semiconductor layer, and a support layer made of a semiconductor or a metal may be further included on the reflective ohmic electrode layer.

On the other hand, the photonic crystal layer, the first photonic crystal having a first period; It may be configured to include a second photonic crystal having a period longer than the first period.

In this case, the first photonic crystal or the second photonic crystal may have a plurality of hole patterns, and the second photonic crystal layer may be formed in a plurality of holes forming the first photonic crystal.

In addition, the second photonic crystal may be formed of a plurality of protruding particles.

As a second aspect for achieving the above technical problem, the present invention provides a light emitting device comprising a photonic crystal layer including a periodic photonic crystal structure on the same plane on a semiconductor layer and a light extraction structure having a random structure. It is preferable.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

While the invention allows for various modifications and variations, specific embodiments thereof are illustrated by way of example in the drawings and will be described in detail below. However, it is not intended to be exhaustive or to limit the invention to the precise forms disclosed, but rather the invention includes all modifications, equivalents, and alternatives consistent with the spirit of the invention as defined by the claims.

Like reference numerals denote like elements throughout the description of the drawings. In the drawings the dimensions of layers and regions are exaggerated for clarity. In addition, each embodiment described herein includes an embodiment of a complementary conductivity type.

When an element such as a layer, region or substrate is referred to as being on another component "on", it will be understood that it may be directly on another element or there may be an intermediate element in between. . If a part of a component, such as a surface, is expressed as 'inner', it will be understood that this means that it is farther from the outside of the device than other parts of the element.

Furthermore, relative terms such as "beneath" or "overlies" refer to the relationship of one layer or region to one layer or region and another layer or region with respect to the substrate or reference layer, as shown in the figures. Can be used to describe.

It will be understood that these terms are intended to include other directions of the device in addition to the direction depicted in the figures. Finally, the term 'directly' means that there is no element in between. As used herein, the term 'and / or' includes any and all combinations of one or more of the recorded related items.

Although the terms first, second, etc. may be used to describe various elements, components, regions, layers, and / or regions, such elements, components, regions, layers, and / or regions It will be understood that it should not be limited by these terms.

These terms are only used to distinguish one element, component, region, layer or region from another region, layer or region. Thus, the first region, layer or region discussed below may be referred to as the second region, layer or region.

Embodiments of the present invention will be described with reference to a gallium nitride (GaN) based light emitting device formed on a nonconductive substrate such as, for example, a sapphire (Al 2 O 3 ) based substrate. However, the present invention is not limited to this structure.

Embodiments of the invention may use other substrates, including conductive substrates. Thus, combinations of AlGaInP diodes on GaP substrates, GaN diodes on SiC substrates, SiC diodes on SiC substrates, SiC diodes on sapphire substrates, and / or GaN, SiC, AlN, ZnO and / or nitride based diodes on other substrates may be included. have. Moreover, the present invention is not limited to the use of the diode region. Other forms of active area may also be used in accordance with some embodiments of the present invention.

The extraction efficiency of the semiconductor light emitting device (LED) is determined by the difference in refractive index between the semiconductor light emitting layer in which light is generated and the medium (air or epoxy) that finally observes the light. Since the semiconductor medium typically has a high refractive index (n> 2), the light extraction efficiency is usually only a few%.

For example, in the case of a blue light emitting device based on gallium nitride (n = 2.4), assuming that an external material is epoxy (n = 1.4), light extraction efficiency through the upper portion of the light emitting device is only about 9%. The rest of the light is trapped by the total reflection process inside the device, and is lost by an absorbing layer such as a quantum well layer.

In order to improve the extraction efficiency of the semiconductor light emitting device, the structure must be modified to extract the light that undergoes total reflection. The simplest of these structural modifications is to overlay a hemisphere made of a material with high refractive index on the upper layer of the light emitting device.

Since the angle of incidence is the angle between the light and the plane of incidence, the angle of incidence is always perpendicular at each point of the hemisphere. The transmission between two media with different refractive indices is highest when the angle of incidence is perpendicular, and the total reflection angle no longer exists for all directions.

In fact, in the case of a semiconductor light emitting device, hemispheres made of epoxy are covered, which contributes not only to surface protection but also to improving extraction efficiency.

A further advantage of this effect is the introduction of a hemisphere 3 with a similar refractive index to the semiconductor between the epoxy layer 1 and the semiconductor element 2, as in FIG. In this case, as shown in FIG. 2, the extraction efficiency gradually increases as the refractive index of the additionally introduced hemisphere approaches the refractive index of the semiconductor.

This is because the critical angle between the semiconductor element and the additional introduced hemisphere is increased. As an example of a transparent material having no absorption in the visible light region, TiO 2 may be proposed. For example, assuming that a hemisphere made of this material is applied to a red light emitting device, it is theoretically possible to obtain an extraction efficiency improvement of about 3 times or more.

The introduction of hemispheres with high refractive indices is a simple and very effective method. However, in order to apply such a method, a transparent material having high refractive index and no absorption in the emission wavelength range of light must be found.

In addition, manufacturing a hemisphere with a size sufficient to cover the light emitting device, and attaching the hemisphere can be a challenge.

Another method of improving the external light extraction efficiency is to deform the side of the light emitting structure into an inverted pyramid shape. This is based on the principle that the light propagating sideways while being totally reflected in the light emitting device is reflected from the pyramid plane and comes out to the upper layer.

However, this method has a disadvantage in that the improvement effect decreases as the size of the device increases. This is due to the absorption loss inevitably accompanied by the light traveling sideways. Therefore, in order to obtain a high enhancement effect in the actual structure with absorption, it is important to go to the outside after a short path to light.

To this end, studies have been conducted to introduce a structure into the light emitting device that can alleviate the total reflection condition. Typically, a light emitting device structure is designed in the form of a resonator to drive output in a specific direction from the beginning, and a method of increasing a critical angle by arranging a hemispherical lens of several microns or more in an upper layer.

However, these methods have not been brought to practical use due to manufacturing difficulties. As another method, there is a method of increasing extraction efficiency through a scattering process by introducing a rough surface corresponding to the size of the wavelength of light to the light emitting device output unit.

In the method of forming the rough surface on the upper portion of the light emitting device, various chemical processes have been developed depending on the material of each light emitting device. When light meets a rough surface, some of the light may pass through even the incident angle corresponding to total reflection.

However, the transmission by one scattering is not so large, so the same scattering process must be repeated repeatedly in order to expect a high extraction effect. Therefore, when there is a constituent material having a high absorption in the light emitting device, the extraction efficiency improvement by the rough surface is not very effective.

In comparison, when a photonic crystal having a spatially periodic refractive index arrangement is introduced, the extraction efficiency can be improved relatively large. In addition, when the appropriate photonic crystal period is selected, the directivity of the light emitting device output can be adjusted. Since a meaningful viewing angle varies depending on the application field of the light emitting device, it is important to design a directionality suitable for each application.

Large-area photonic crystals can be used for holographic lithography, ultraviolet photolithography, nano-imprinted lithography, and the like.

Efforts to improve the light extraction efficiency of the light emitting device through the photonic crystal start from the study that the spontaneous emission rate can be controlled by using the photonic crystal.

Thereafter, it has been theoretically proved that the photonic crystal contributes to the extraction efficiency of the light emitting device by using the dispersion characteristic curve, and the process of the photonic crystal to the extraction efficiency can be summarized into two ways.

One is to extract light in the vertical direction by blocking the light movement in the planar direction by using the photonic band-gap effect. The other is a state density mode that is located outside the light cone in the dispersion curve. To combine and extract outside.

These two principles can be applied independently depending on the period of the photonic crystal. However, in order to define the optical band gap mirror effect or the state density of the dispersion curve well, it is possible to form a photonic crystal in a situation where a thin film having a thickness of about half wavelength has a high refractive index contrast up and down.

Furthermore, since the air hole of the photonic crystal penetrates the light emitting layer, it inevitably leads to a loss of the gain medium, and further reduction of the internal quantum efficiency due to surface non-emitting coupling is inevitable.

Since the optical bandgap mirror effect or the strong dispersion property is difficult to implement in a general light emitting device structure, it can be said to be applied only in a special case. In order to solve this problem, the photonic crystal should be fabricated only on the surface without including the active medium of the light emitting device.

In this case, strong dispersion characteristics cannot be utilized as in the case of introducing a photonic crystal into a thin film having a high refractive index contrast, but according to general diffraction theory, light corresponding to total reflection can be extracted to the outside in combination with a periodic structure.

At present, efforts have been actively made to improve the extraction efficiency by spatially separating the photonic crystal and the light emitting layer of the semiconductor layer without degrading the characteristics of the light emitting layer.

In the same way, there is an example in which the extraction efficiency is improved for the light emitting device structure adopting InGaAs quantum well, and the result of increasing the external light extraction efficiency by 1.5 times or more by using the photonic crystal formed on the glass substrate in the organic light emitting device has been reported. .

As mentioned above, a method of extracting light trapped by total reflection by introducing a periodic photonic crystal structure to the surface has been attempted. For example, it has been reported that the extraction efficiency is increased by forming a photonic crystal having a period of about 200 nm on the p-type GaN semiconductor surface.

In addition, there has been a study that reports a high extraction efficiency improvement effect using the optical band gap effect after fabricating the photonic crystal to the active medium region of the GaN series light emitting device, but the extraction efficiency is lowered as the input current increases . This is because, as pointed out above, when the photonic crystal is introduced by etching the light emitting layer, in particular, the current-voltage characteristic is degraded.

In summary, the principle of improving the external light extraction efficiency of the light emitting device is to reduce the total reflection condition by modifying the structure, to introduce a rough surface on the surface, and to form a photonic crystal in a thin film having a large refractive index contrast to the optical band. It can be summarized as a method using a gap effect, a method of separating the photonic crystal and the light emitting layer and extracting the light trapped by total reflection to the outside through a diffraction process.

Among these, considering the reality of the structure of the light emitting device and the increase in efficiency, it can be said that the method of improving the extraction efficiency by introducing a periodic photonic crystal structure on the surface of the light emitting device.

As shown in FIG. 3, the horizontal GaN series light emitting device has a structure grown on a sapphire (n = 1.76) substrate 10 having a relatively lower refractive index than GaN. Since the total thickness of the GaN semiconductor layer 20 reaches about 5 μm, it can be regarded as a waveguide structure in which various higher order modes exist. An upper layer of the GaN semiconductor layer 20 starts from the p-type GaN semiconductor layer 21, and a multi-quantum well layer corresponding to the light emitting layer 22 region is positioned below it.

An n-type GaN semiconductor layer 23 is positioned below the light emitting layer 22, and a buffer layer 24 may be positioned between the n-type GaN semiconductor layer 23 and the substrate 10. In addition, the reflective film 50 may be formed on the opposite side of the substrate 10.

In the horizontal GaN series light emitting device, a transparent electrode layer 30 such as ITO is usually deposited on the p-type GaN semiconductor layer 21 to supply current evenly over the entire area. Therefore, when the photonic crystal 40 is introduced into the horizontal GaN series light emitting device, the maximum range that can be etched is the sum of the thickness of the transparent electrode layer 30 and the thickness of the p-type GaN semiconductor layer 21. In general, the thickness of the transparent electrode layer 30 and the p-type GaN semiconductor layer 21 is between 100 and 300 nm.

Therefore, when the photonic crystal 40 is introduced into the horizontal GaN series light emitting device, the maximum range that can be etched is limited by the thickness (100 to 300 nm) of the p-type GaN semiconductor layer 21 described above. Therefore, there may be a limit in the extraction efficiency.

On the other hand, one example of the vertical light emitting device structure as shown in Figure 4, by removing the sapphire used as a substrate during the growth process of the GaN semiconductor layer 20 by laser absorption method, and on the p-type GaN semiconductor layer 21 The reflective ohmic electrode 50 is formed by using a multilayer metal thin film including Ni, Ag, and the like, which can simultaneously serve as a mirror and an electrode.

Among the differences between the vertical GaN light emitting devices, which are distinguished from the general horizontal GaN light emitting devices, the current direction is vertical due to the removal of sapphire, which is an insulator, and the output plane of light is reversed in the case of FIG. For example).

The fact that the current flows in the vertical direction in the vertical light emitting device structure means that the probability that the supplied current can reach the quantum well layer, which is the light emitting layer 22, is high. This, in turn, contributes to the improvement of the internal quantum efficiency.

In addition, the vertical light emitting device structure has a characteristic that heat dissipation is easy because the sapphire as an insulator is removed and a conductor is formed on the p-type GaN semiconductor layer 21. This may serve as an advantageous aspect, especially when designing a high output light emitting device.

In fact, in the case of a conventional GaN series blue light emitting device having a sapphire substrate, when the supplied current value exceeds several hundred mA, the output decreases. This can be interpreted as the internal quantum efficiency of the quantum well is degraded due to the temperature increase inside the device due to the weak thermal conductivity of the sapphire substrate.

The vertical blue light emitting device structure has a feature that can be carefully considered optically in connection with the improvement of light extraction efficiency in addition to the physical characteristics that the current flows and heat is easily discharged. This is summarized as follows.

First, since the upper portion of the vertical light emitting device structure is the n-type GaN semiconductor layer 23, the photonic crystal 60 is introduced into the n-type GaN semiconductor layer 23 that is relatively thicker than the p-type GaN semiconductor layer 21. The advantage is that you can. In general, the extraction efficiency improvement effect through the photonic crystal 60 has a property that is proportional to the etching depth until the extraction efficiency is saturated.

Therefore, without limiting the resistance of the p-type GaN semiconductor layer, which is one of the difficulties in introducing a photonic crystal in a horizontal GaN-based light emitting device, or the surface non-emitting coupling effect of the active layer quantum well layer etching, A photonic crystal structure of depth can be formed. In addition, since the period of providing the maximum extraction efficiency is slightly different depending on the etching depth, it is possible to utilize the structural conditions allowed by a given etching technique.

In addition, the vertical light emitting device is positioned in a position smaller than the wavelength of light from which the quantum well layer (light emitting layer) 22, which is a light emitting region, and the mirror (reflective ohmic electrode) 50 having a high reflectance are emitted.

That is, as described above, in the structure of the vertical light emitting device, a reflective ohmic electrode 50 which simultaneously serves as a mirror and an electrode is formed on the p-type GaN semiconductor layer 21. Therefore, the thickness of the p-type GaN semiconductor layer 21 corresponds to the distance between the light emitting layer 22 and the metal mirror of the light emitting device.

In general, when there is a mirror having a high reflectance in a position close to the light emitting layer 22, the light emission performance is greatly changed as compared with the case where there is no mirror. That is, the decay rate may vary according to the distance between the light emitting layer 22 and the mirror, and the radiation pattern may be adjusted. By using these characteristics well, the light extraction efficiency of the light emitting device can be significantly improved.

Hereinafter, the process of determining the structural factors of the photonic crystal applicable to the vertical GaN light emitting device through computer simulation calculation (3D-FDTD) and calculating the relative extraction efficiency increase ratio obtained from each structural factor will be described. .

Unlike the horizontal structure, the vertical light emitting device structure does not have radiation through the side surface of the substrate, and thus the overall efficiency corresponds to the efficiency due to vertical radiation. At this time, an example of the structure of the light emitting device for analysis on the computer simulation is made of a light emitting device semiconductor layer 100, the photonic crystal 60 is formed, as shown in Figure 5, the refractive index that can be used as an encapsulant outside the photonic crystal 60 The structure in which the epoxy 70 of 1.4 is located is used.

The size of a typical light emitting device cannot be included in the computational structure due to computer memory limitations. In order to solve this problem, a case where a full mirror (not shown) is positioned at both ends of the light emitting device structure having a finite size (12 μm) is applied instead.

In addition, as shown in FIG. 6, an absorption rate (k = 0.045) was applied to the light emitting layer (quantum well layer) 22 of the light emitting device 100. At the bottom of the structure, however, for ease of analysis, instead of the actual metal mirror with absorbance, it was replaced with a full mirror that also has a reflectance of 100%.

Since the vertical structure must always consider the effect of interference by the mirror, the relative position of the light emitting layer 22 with respect to the mirror in the structure is an important variable. This is because when the radiation pattern is changed by the interference effect between the mirror and the light emitting layer 22, there is a possibility that the photonic crystal 60 functioning factor effectively changes. In other words, it can be said that the angle of light in which extraction is efficiently performed by the diffraction process varies depending on the period of the photonic crystal 60.

Here, only the effect by the photonic crystal 60 is calculated purely in a state where the mirror effect is excluded. In order to exclude the interference effect by the mirror, the distance between the mirror and the light emitting layer 22 is set far, or the distance is set at about halfway point between the constructive interference and the cancellation interference condition.

Thus, the radiation pattern when the light emitting layer 22 is free from the interference effect of the mirror is as shown in FIG. Looking at such a radiation pattern, a fine interference fringe is still visible depending on the angle, but can be considered as a spherical wave.

Referring to the extraction efficiency change with respect to the photonic crystal 60 cycle, as shown in Figure 8, the photonic crystal 60 cycle (a) that can obtain the maximum extraction efficiency is about 800nm, the relative increase ratio of the extraction efficiency is about 2 times It is enough. At this time, the etching depth is 225nm, the radius of the hole 61 constituting the photonic crystal is fixed to 0.25a when the period is a.

Next, a change in extraction efficiency according to the size of the hole 61 constituting the photonic crystal 60 is shown in FIG. 9. At this time, the etching depth was fixed to 225nm, the cycle was selected to 800nm. Looking at the results, it can be seen that when the size of the hole 61 of the photonic crystal 60 is 0.35a, the extraction efficiency is maximum, and the relative increase is increased by 2.4 times.

As described above, an advantage of the vertical GaN light emitting device is that the limitation on the etching depth is small. The maximum etch depth of the horizontal structure is determined by the thickness of the p-type GaN semiconductor layer (actually about half the thickness of the p-GaN layer, considering the increase in resistance), but the vertical structure is relatively thicker than the n-type The thickness (about 3 micrometers) of a GaN semiconductor layer can be utilized.

In order to take advantage of such a vertical structure, as shown in FIG. 10, the optimum period according to the etching depth was investigated while sequentially changing the etching depth for forming the photonic crystal.

The extraction efficiency tends to saturate over a certain level of etch depth, as mentioned in the horizontal structural studies.

However, it is interesting to note that the deeper the etching depth, the more efficient the extraction efficiency due to the photoperiodic structure, which has a long period of time. This is remarkable in that there is room for utilizing a photonic crystal structure with a large period of time that can be easily implemented in practice while deepening the etching depth.

As described above, the reason why the extraction efficiency of the photonic crystal structure with a large period continues to increase as the etching depth increases (see FIG. 11) may be considered.

First, in order for light to pass through two media having different refractive indices, a phase-matching condition in the planar direction must be satisfied.

Second, when light proceeds from a medium having a high refractive index to a medium having low refractive index, phase matching conditions cannot be satisfied above a certain angle. This particular angle is called the critical angle, and total reflection occurs above the critical angle.

Third, the photonic crystal helps to extract light corresponding to the total reflection angle to the outside. That is, when the photonic crystal and the light are combined, the momentum of the photonic crystal is added, so that the light corresponding to total reflection can satisfy the phase matching condition.

Fourth, the momentum of the photonic crystal is inversely proportional to the period. That is, since the photonic crystal having a small period can make a large momentum, it is possible to effectively extract the light traveling near the horizontal direction far from the critical angle among the lights corresponding to the total reflection. On the other hand, photonic crystals with large periods are effective for extracting light traveling relatively close to the vertical direction.

Fifth, according to the wave optical theory, the total reflection process in the waveguide structure can be described corresponding to the mode. For example, light having an incident angle close to the horizontal direction corresponds to the basic waveguide mode, and the closer the incident angle is to the vertical direction, the higher order mode.

Sixth, GaN light emitting devices can also be regarded as waveguide structures having a thickness of several microns or more.

Therefore, in consideration of this fact, when the photonic crystal is applied to the GaN light emitting device, it can be seen that the photonic crystal with short period is suitable for extracting the fundamental waveguide mode, and the photonic crystal with long period is suitable for extracting the higher waveguide mode. .

In general, the basic waveguide mode tends to saturate the extraction efficiency for more than a certain degree of photonic crystal etching depth (~ λ / n), while the extraction efficiency tends to increase steadily for the photonic crystal etching depth toward higher order modes. .

In conclusion, as the etching depth increases, the extraction efficiency continues to increase in the higher order mode due to the photonic crystal structure having a long period.

In order to maximize the extraction efficiency as described above, optimization of photonic crystal structural factors was performed through computer simulation. Extraction efficiency was found to be closely correlated with etch depth, pore size and period.

In particular, in the case of a vertical GaN light emitting device, since a relatively thick n-type GaN semiconductor layer is used to form a photonic crystal, there is virtually no restriction on the depth of etching. The chances of choosing the period will also increase.

As described above, the angle of incidence of light acting efficiently varies depending on the period of the photonic crystal. That is, in the photonic crystal composed of one cycle, the region of the incident angle where the diffraction efficiency is relatively small exists.

However, in order to maximize the extraction efficiency, it must have a high diffraction efficiency for all angles larger than the critical angle. Therefore, the photonic crystal structure in which two or more kinds of cycles are mixed may exhibit better extraction efficiency than the photonic crystal in which only one cycle exists independently.

Similar principles can be applied to horizontal GaN light emitting devices. When a photonic crystal is introduced to increase external light extraction efficiency in a horizontal GaN light emitting device, the photonic crystal may be classified into two categories according to the position at which the photonic crystal is introduced.

One of them is etching the region of the p-type GaN semiconductor layer 21 located at the top of the light emitting element among the semiconductor layers 20 formed on the sapphire substrate 10 as shown in FIG. When the transparent conductive layer 30 is formed on the p-type semiconductor layer 21, the conductive layer 30 is also etched together.

The other is to grow the GaN semiconductor layer 20 on the patterned sapphire substrate (PSS) 12 having the pattern 11 formed thereon as shown in FIG. 13.

On the other hand, as shown in Figure 14, it is also conceivable to apply the two structures at the same time. A graph comparing the extraction efficiency for each of the above structures is shown in FIG. 15.

In this graph, the horizontal axis represents the distance that light travels within the computational space. The vertical axis represents the amount of light extracted to the outside according to the light travel distance.

Looking at the results of the graph, the horizontal structure (Reference) that does not apply the periodic structure, the extraction efficiency is saturated before the light traveling distance is less than 10㎛. In the horizontal structure, only light within a critical angle can be extracted, so most of the light comes out through one transmission (reflection) process.

In contrast, in the case where the sapphire substrate 12 having the photonic crystal 40 structure or the pattern 11 is applied, the extraction efficiency increases steadily until the light traveling distance reaches 100 μm. This is because the light is extracted to the outside through the diffraction process whenever the light corresponding to the total reflection meets the periodic structure.

At this time, the extraction efficiency is eventually saturated due to the absorption rate of the internal material constituting the device. Therefore, the basic principle when introducing a deformation or periodic structure of the structure to increase the external light extraction efficiency is to extract light to the outside with less absorption loss within the shortest traveling distance.

Returning to the results, it can be seen that the extraction efficiency is maximized when the photonic crystal 40 structure and the sapphire substrate 12 structure with the pattern 11 are simultaneously applied, that is, when two kinds of periodic structures are simultaneously applied. Can be.

If the GaN semiconductor layer 20 is grown on the sapphire substrate 12 having the pattern 11 in the horizontal GaN light emitting device, and the structure in which the photonic crystal 40 is applied again to the upper layer is technically defined, different periods It can be said that photonic crystals with are applied to different planes independently.

Since the vertical GaN light emitting device has a structure in which the substrate has already been removed, the mixed cycle photonic crystal structure having the same structure as the horizontal light emitting device cannot be adopted. However, by taking advantage of the fact that the etching depth is virtually unlimited, in this case it is possible to apply photonic crystal structures with different periods in the same plane.

16 illustrates a structure of a photonic crystal layer 200 in which photonic crystals of different periods are mixed in a vertical GaN light emitting device. 17 and 18 are electron micrographs when the photonic crystal layer 200 is experimentally implemented.

In the mixed cycle photonic crystal layer 200 structure of the electron micrograph, the plasma of the gas used for etching and the surface of the GaN semiconductor layer react when the pattern of the n-type GaN semiconductor layer of the vertical structure is formed through a general etching process. It is caused by the addition of a fine pattern.

Therefore, the mixed cycle photonic crystal layer 200 formed by the formation process may be regarded as a structure in which a random structure having a shorter average period is added to the periodic photonic crystal structure.

In order to arithmetically evaluate the effect of the mixed-cycle photonic crystal layer 200 structure, the extraction efficiency was compared using the structures shown in FIGS. 19A and 19B through computer simulation.

The structure of the mixed period photonic crystal layer 200 can be expressed in various forms. However, in order to simplify the structure, the mixed cycle photonic crystal layer 200 is expressed according to the following principle.

First, a first photonic crystal 210 structure having a long first period is introduced, and the etching depth of the first photonic crystal 210 structure is set to 450 nm.

The second photonic crystal 220 structure having a relatively short period was introduced to an unetched portion of the first photonic crystal 210 structure having a long period, and the etching depth of the second photonic crystal 220 structure having a short period was 225 nm. Set.

The structure expressed in the calculation space describes a method of experimentally defining the second photonic crystal 220 having a short period first and then introducing the first photonic crystal 210 having a longer etching depth later.

In this case, since the period, etching depth, shape, etc. of each of the mixed photonic crystals 210 and 220 may be expressed in various ways, various combinations of the mixed periodic photonic crystal layer 200 may be considered.

Referring to the calculation result, as shown in FIG. 20, the photonic crystal structure in which different periods are mixed always shows an effect of improving light extraction efficiency better than the other structures. Therefore, if a method is provided to reliably produce a mixed-cycle photonic crystal structure experimentally, it is possible to always expect improved extraction efficiency than a single photonic crystal structure, regardless of the combination of each photonic crystal structure.

As described above, when the photonic crystal is introduced into the vertical GaN light emitting device, when the n-type GaN semiconductor layer having a thickness of 3 μm or more is etched to form the photonic crystal, the photonic crystal is formed in the p-type GaN semiconductor layer. Compared to the structure, the electrical properties can be preserved, and the restriction on the etching depth is substantially eliminated.

First, when the light extraction efficiency effect on the etching depth in the single crystal photonic crystal structure is summarized, when the photonic crystal etching depth of the photonic crystal introduced into the n-type GaN semiconductor layer is 300 nm or more, the period of the photonic crystal introduced is 1 μm or more, 5 When less than m, the photonic crystal structure satisfying the above two conditions shows a tendency to approach the maximum light extraction efficiency, while the extraction efficiency increases steadily in proportion to the etching depth.

In addition, as the etching depth deepens, the optimum period moves in a longer direction. For example, when the etching depth is 225 nm, the optimum photonic crystal period is about 800 nm, whereas for the 900 nm etching depth, the optimal photonic crystal period is 1400 nm.

As such, when the constraint on the etching depth is substantially removed, various types of mixed period photonic crystal structures may be proposed. Mixing cycle photonic crystal structure shapes can be classified as follows according to the production method.

As shown in FIG. 21, the mixed period photonic crystal layer 200 is formed on the semiconductor layer 100, and after the first photonic crystal 210 having a long period is formed through an etching process, the mixed photonic crystal layer 200 is shorter than this. The second photonic crystal 220 having a period may be formed through an etching process. In this case, as described above, the second photonic crystal 220 may have a random structure in which an average period is shorter than that of the first photonic crystal 210.

As such, when the first photonic crystal 210 of the long period is formed first and then the second photonic crystal 220 of the short period is formed, as illustrated, the inside of the hole 211 constituting the first photonic crystal 210 is also shown. The second photonic crystal 220 is formed, so that the second photonic crystal 220 may also be formed on the entire light emitting surface.

The period of the first photonic crystal 210 having the longest period of the photonic crystal layer 200 may be 800 nm to 5000 nm, and the depth of the pattern of the first photonic crystal 210 having the longest period of the photonic crystal layer 200 is formed. May be from 300 nm to 3000 nm.

In addition, the period of the second photonic crystal 220 with the shortest period of the photonic crystal layer 200 may be 50 nm to 1000 n, and the pattern of the pattern of the second photonic crystal 220 with the shortest period of the photonic crystal layer 200 is formed. The depth can be 50 nm to 500 nm.

On the other hand, when the period of the photonic crystal layer 200 is a, the depth of the hole forming the photonic crystal of the photonic crystal layer 200 may be 0.1a to 0.45a.

In FIG. 22, in forming the mixed period photonic crystal layer 200 on the semiconductor layer 100, first, a second photonic crystal 220 having a short period is formed through an etching process, and then a first photonic crystal having a longer period is formed. The structure formed by the etching process 210 is shown.

As shown in FIG. 23, after the first photonic crystal 210 having a long period is formed through an etching process, the second photonic crystal 220 having a shorter period may be formed through a deposition process.

In this case, when the second photonic crystal 220 is formed through the deposition process, the second photonic crystal 220 is formed by the pattern of the particles 221 protruding on the structure of the first photonic crystal 210 instead of the intaglio shape. The shape of the particles 221 may be hemispherical, or may be hexagonal by the shape of the GaN crystal.

As such, when the first photonic crystal 210 of the long period is formed first and then the second photonic crystal 220 of the short period is formed, as illustrated, the inside of the hole 211 constituting the first photonic crystal 210 is also shown. The second photonic crystal 220 is formed, so that the second photonic crystal 220 may also be formed on the entire light emitting surface.

In FIG. 24, the second photonic crystal 220 having a short period is first formed through a deposition process, and then the first photonic crystal 210 having a longer period is formed through an etching process.

Since the mixed-cycle photonic crystal layer 200 structure is obtained by adding photonic crystals 210 and 220 having two independent periods, various combinations are possible depending on the structural factors of the photonic crystals 210 and 220.

Basically, the extraction efficiency varies depending on how the cycles of the two photonic crystals 210 and 220 are combined, and the etching depth and the shape of the photonic crystal may also be variables. In addition, when introducing a new material by the deposition process, the refractive index of the introduced material may also be a variable.

In the present invention, when the photonic crystal is introduced into the n-type GaN semiconductor layer of the vertical GaN light emitting device to improve the external light extraction efficiency, the etching depth of the photonic crystal is deeply formed, thereby making it easy to manufacture a long period (1 μm or more). ) Can ensure maximum extraction efficiency.

In addition, it is possible to maximize the extraction efficiency by providing a mixed-cycle photonic crystal structure in which two or more kinds of cycles are mixed in the same plane in addition to the single-crystal photonic crystal structure.

25 illustrates a vertical light emitting device structure having the above-described mixed period photonic crystal layer 200. In the light emitting device structure, the semiconductor layer 100 in which the photonic crystals 210 and 220 are formed, in turn, includes an n-type semiconductor layer 110, a light emitting layer 120, and a p-type semiconductor layer 130. As described, the photonic crystal 200 is formed on the surface of the n-type semiconductor layer 110.

An ohmic electrode layer or a reflective ohmic electrode layer 300 is positioned below the semiconductor layer 100, and the light emitting device structure may be positioned on a support layer 400 made of a semiconductor or metal such as silicon.

In this case, the n-type electrode 500 may be positioned on the n-type semiconductor layer 110 on which the photonic crystal layer 200 is formed.

As described above, as described above, the photonic crystals 210 and 220 are formed by etching the n-type GaN semiconductor layer 110, thereby hardly affecting the increase in resistance in the semiconductor layer 100. In addition, since the vertical GaN light emitting device is easy to discharge heat, the light extraction effect following the introduction of the photonic crystal layer 200 can be preserved in the high output region.

In addition, since the thickness of the n-type GaN semiconductor layer 110 may be generally greater than 3 μm, the extraction efficiency may far exceed the etch depth of the photonic crystal.

As described above, as the etching depth of the photonic crystal increases, the period for ensuring the maximum extraction efficiency moves in a longer direction. In particular, the photonic crystal having a period of 1 μm or more continuously increases the extraction efficiency for the deeper etching depth than the saturation point of the short period. Can rise.

On the other hand, the mixed period photonic crystal layer 200 structure in which different periods are mixed in the same plane described above has an effect of improving extraction efficiency better than the structure having a single period regardless of the combination of the combined photonic crystals 210 and 2200 structures. The optimal periodic shift and mixed periodic photonic crystal layer 200 structure according to the etching depth may be applied to other light emitting device structures having a thickness of 300 nm or more.

The above embodiment is an example for explaining the technical idea of the present invention in detail, and the present invention is not limited to the above embodiment, various modifications are possible, and various embodiments of the technical idea are all protected by the present invention. It belongs to the scope.

The present invention as described above has the following effects.

First, in applying a photonic crystal for improving the light extraction efficiency, the electrical characteristics of the device can be preserved.

Second, the same light extraction effect can be exhibited in the high power region.

Third, the photonic crystal etch depth can be extended until the extraction efficiency is saturated.

Fourth, it is possible to exhibit the optimal extraction efficiency in a long period (more than 1㎛) photonic crystal structure.

Fifth, the extraction efficiency may always be superior to that of the single crystal photonic crystal structure.

Sixth, the present invention is applicable to other types of light emitting device structures in which photonic crystals may be formed in a thick layer of 300 nm or more to improve external light extraction efficiency.

Claims (17)

  1. In the light emitting device,
    And a photonic crystal layer comprising at least two photonic crystal structures having different periods on the same plane on the semiconductor layer.
  2. The nitride-based light emitting device according to claim 1, wherein the photonic crystal layer is a pattern of a plurality of hole patterns or a plurality of protruding particles.
  3. The nitride-based light emitting device of claim 1, wherein a period of the photonic crystal having the longest period is 800 nm to 5000 nm.
  4. The nitride-based light emitting device of claim 1, wherein a depth of the pattern of which the photonic crystal layer has the longest photonic crystal is 300 nm to 3000 nm.
  5. The nitride-based light emitting device of claim 1, wherein a period of the photonic crystal having the shortest period is 50 nm to 1000 nm.
  6. The nitride-based light emitting device of claim 1, wherein a depth of a pattern of which the photonic crystal layer has the shortest photonic crystal is 50 nm to 500 nm.
  7. The nitride-based light emitting device according to claim 1, wherein when a period of the photonic crystal layer is a, a depth of a hole forming the photonic crystal layer of the photonic crystal layer is 0.1a to 0.45a.
  8. The method of claim 1, wherein the semiconductor layer,
    a p-type semiconductor layer;
    A light emitting layer on the p-type semiconductor layer;
    A nitride-based light emitting device comprising an n-type semiconductor layer located on the light emitting layer.
  9. The nitride-based light emitting device of claim 8, wherein the photonic crystal layer is formed on an n-type semiconductor layer.
  10. The nitride-based light emitting device of claim 1, wherein a reflective ohmic electrode layer is disposed on the other side of the semiconductor layer.
  11. The nitride-based light emitting device according to claim 10, wherein a support layer made of a semiconductor or a metal is positioned on the reflective ohmic electrode layer.
  12. The method of claim 1, wherein the photonic crystal layer,
    A first photonic crystal having a first period;
    And a second photonic crystal having a longer period than the first period.
  13. The nitride-based light emitting device according to claim 12, wherein the first photonic crystal or the second photonic crystal has a plurality of hole patterns.
  14. The nitride-based light emitting device according to claim 13, wherein the second photonic crystal layer is formed in a plurality of holes of the first photonic crystal.
  15. The nitride-based light emitting device according to claim 12, wherein the second photonic crystal is a plurality of protruding particles.
  16. In the light emitting device,
    And a photonic crystal layer comprising a periodic first photonic crystal and a second photonic crystal having a random structure on the same plane on the semiconductor layer.
  17. The nitride-based light emitting device according to claim 16, wherein the second photonic crystal has an average period smaller than that of the first photonic crystal.
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KR1020060041006A KR100736623B1 (en) 2006-05-08 2006-05-08 Led having vertical structure and method for making the same
KR1020070037416A KR20080093558A (en) 2007-04-17 2007-04-17 Nitride light emitting device
US11/797,727 US7652295B2 (en) 2006-05-08 2007-05-07 Light emitting device having light extraction structure and method for manufacturing the same
EP11167034A EP2362440A3 (en) 2006-05-08 2007-05-07 Semiconductor light emitting device
EP11167036.0A EP2362441B1 (en) 2006-05-08 2007-05-07 Semiconductor light emitting device
EP11167038A EP2362442A3 (en) 2006-05-08 2007-05-07 Method for manufacturing a semiconductor light emitting device
EP07107655A EP1855327B1 (en) 2006-05-08 2007-05-07 Semiconductor light emitting device
EP11167031A EP2362439A3 (en) 2006-05-08 2007-05-07 Semiconductor light emitting device
EP14175657.7A EP2808909A1 (en) 2006-05-08 2007-05-07 Semiconductor light emitting device
CNA2007101049636A CN101071840A (en) 2006-05-08 2007-05-08 Light emitting device and method for manufacturing the same
JP2007123894A JP5179087B2 (en) 2006-05-08 2007-05-08 Light emitting element
CN201410116298.2A CN103928580B (en) 2006-05-08 2007-05-08 Light emitting device
US12/637,661 US7939840B2 (en) 2006-05-08 2009-12-14 Light emitting device having light extraction structure and method for manufacturing the same
US12/637,653 US8008103B2 (en) 2006-05-08 2009-12-14 Light emitting device having light extraction structure and method for manufacturing the same
US12/637,646 US7893451B2 (en) 2006-05-08 2009-12-14 Light emitting device having light extraction structure and method for manufacturing the same
US12/637,637 US8003993B2 (en) 2006-05-08 2009-12-14 Light emitting device having light extraction structure
US13/214,871 US8283690B2 (en) 2006-05-08 2011-08-22 Light emitting device having light extraction structure and method for manufacturing the same
US13/612,343 US8648376B2 (en) 2006-05-08 2012-09-12 Light emitting device having light extraction structure and method for manufacturing the same
JP2013001743A JP2013062552A (en) 2006-05-08 2013-01-09 Light-emitting device
US14/151,613 US9246054B2 (en) 2006-05-08 2014-01-09 Light emitting device having light extraction structure and method for manufacturing the same
US14/974,991 US9837578B2 (en) 2006-05-08 2015-12-18 Light emitting device having light extraction structure and method for manufacturing the same

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WO2010101332A1 (en) * 2009-03-03 2010-09-10 엘지이노텍주식회사 Light-emitting device
WO2011021753A1 (en) * 2009-08-18 2011-02-24 우리엘에스티 주식회사 Group iii-nitride semiconductor light emitting device and fabrication method thereof
US8049239B2 (en) 2008-11-26 2011-11-01 Lg Innotek Co., Ltd. Light emitting device and method of manufacturing the same
KR101134802B1 (en) * 2010-02-01 2012-04-13 엘지이노텍 주식회사 Light emitting device, method for fabricating the same and light emitting device package
KR101283062B1 (en) * 2010-09-27 2013-07-05 엘지이노텍 주식회사 substrate and light emitting diode having nano-structure, and fabrication method thereof
KR101316619B1 (en) * 2011-05-13 2013-10-15 (주)버티클 Semiconductor devices and fabrication method thereof
KR101707116B1 (en) * 2010-07-30 2017-02-15 엘지이노텍 주식회사 A light emitting Device, and a method of fabricating the light emitting device
US9806231B2 (en) 2010-08-23 2017-10-31 Intellectual Discovery Co., Ltd. Semiconductor light-emitting device having a photonic crystal pattern formed thereon, and method for manufacturing same

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US8049239B2 (en) 2008-11-26 2011-11-01 Lg Innotek Co., Ltd. Light emitting device and method of manufacturing the same
US8823029B2 (en) 2008-11-26 2014-09-02 Lg Innotek Co., Ltd. Light emitting device and method of manufacturing the same
WO2010101332A1 (en) * 2009-03-03 2010-09-10 엘지이노텍주식회사 Light-emitting device
US8569084B2 (en) 2009-03-03 2013-10-29 Lg Innotek Co., Ltd. Method for fabricating light emitting device including photonic crystal structures
KR101134810B1 (en) * 2009-03-03 2012-04-13 엘지이노텍 주식회사 Light emitting device and method for fabricating the same
WO2011021753A1 (en) * 2009-08-18 2011-02-24 우리엘에스티 주식회사 Group iii-nitride semiconductor light emitting device and fabrication method thereof
KR101134802B1 (en) * 2010-02-01 2012-04-13 엘지이노텍 주식회사 Light emitting device, method for fabricating the same and light emitting device package
KR101707116B1 (en) * 2010-07-30 2017-02-15 엘지이노텍 주식회사 A light emitting Device, and a method of fabricating the light emitting device
US9806231B2 (en) 2010-08-23 2017-10-31 Intellectual Discovery Co., Ltd. Semiconductor light-emitting device having a photonic crystal pattern formed thereon, and method for manufacturing same
KR101283062B1 (en) * 2010-09-27 2013-07-05 엘지이노텍 주식회사 substrate and light emitting diode having nano-structure, and fabrication method thereof
KR101316619B1 (en) * 2011-05-13 2013-10-15 (주)버티클 Semiconductor devices and fabrication method thereof

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