JP2007095744A - Semiconductor light-emitting element and manufacturing method thereof, and luminaire using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase luminous efficiency in a semiconductor light-emitting element, where at least an n-type nitride semiconductor layer, a luminous layer, and a p-type nitride semiconductor layer are laminated on a substrate, and an irregular structure is provided on an upper surface. <P>SOLUTION: On a sapphire substrate 2, a buffer layer 3 is formed for film of an n-type gallium nitride compound semiconductor layer 4, the luminous layer 5, and a p-type gallium nitride compound semiconductor layer 6 at a film-forming temperature of 1,000°C. A mask having an opening is formed, the temperature is decreased to 800°C, and a p-type gallium nitride compound semiconductor layer is grown again, thus forming a projection 7 in a square pole shape having a tip in a rectangular pyramid shape, improving the extraction efficiency of light generated by the luminous layer 5 by the projection 7, setting the thickness of the p-type gallium nitride compound semiconductor layer 6 to the minimum required value, reducing resistance, and realizing a blue or ultraviolet light-emitting diode 1 having high luminous efficiency. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a device structure of a gallium nitride-based compound semiconductor light-emitting device capable of generating blue or ultraviolet light, and more specifically, is generated from a light-emitting layer by forming an uneven structure on a p-type gallium nitride-based compound semiconductor layer. The present invention relates to a method for efficiently extracting light to the outside.

  In the gallium nitride compound semiconductor light emitting device, the refractive index of the gallium nitride compound semiconductor layer and the air layer from which the light is extracted are greatly different. Therefore, when light generated from the light emitting layer is incident on the interface at an angle or more. Is totally reflected and cannot be taken out to the air layer side. Therefore, conventionally, in order to realize a blue or ultraviolet semiconductor light emitting device having high luminous efficiency by reducing total reflection of light generated in the light emitting layer, as shown in Patent Documents 1 to 3, light extraction is performed. A method of roughening the surface is used.

In Patent Document 1, an insulating light scattering layer is newly formed on a p-type or n-type gallium nitride compound semiconductor layer serving as a light extraction surface, and the light scattering layer is formed by wet etching of SiO _2. The surface has a concavo-convex structure, and the convex part is composed of a part of spherical particles, or an example in which the convex part is formed in an island shape on the extraction surface is described.

  In Patent Document 2, an opening having a minimum dimension of 1/4 of the emission wavelength λ is provided on the p-type gallium nitride compound semiconductor layer serving as a light extraction surface, and the p-type gallium nitride compound semiconductor layer is formed on the p-type gallium nitride compound semiconductor layer. A process is described in which a resist is stacked and a pattern is formed on the resist, and then an opening is formed by ion milling using the resist as a mask.

Furthermore, in Patent Document 3, the ion milling method, RIE, or the like is applied to the surface of the p-type gallium nitride compound semiconductor layer serving as the light extraction surface or the transparent electrode surface formed on the p-type gallium nitride compound semiconductor layer. It is described that the concavo-convex structure is formed by using the etching method. Specifically, a pattern is formed with a resist or the like, and the opening is etched by an ion milling method using the resist as a mask, so that the p-type gallium nitride compound semiconductor layer or the p-type gallium nitride compound semiconductor layer is formed. A process for forming a concavo-convex structure on the surface of the transparent electrode formed in the above is described.
JP-A-10-163525 JP 2000-91639 A JP 2000-196152 A

In the prior art disclosed in Patent Document 1, since a light scattering layer is newly provided on the light extraction surface, light absorption occurs in the scattering layer. In addition, since SiO ₂ has a smaller refractive index than GaN (SiO ₂ is about 1.7 and GaN is about 2.5), light from the light emitting layer is incident on GaN having a large refractive index to small SiO ₂ . When traveling at an angle or more, there is an escape cone that totally reflects to the GaN side. Furthermore, when the adhesion between the light extraction surface and the light scattering layer is poor, reflection occurs at the interface between the materials having the refractive index difference as described above. As described above, there is a problem that the light extraction efficiency is not sufficiently improved.

On the other hand, in Patent Document 2, since the opening is provided directly on the p-type gallium nitride compound semiconductor layer serving as the light extraction surface, the opening having a depth (0.1 μm or more) that exhibits the light scattering effect is provided. In order to form it, it is necessary to increase the thickness of the p-type gallium nitride compound semiconductor layer. However, the p-type gallium nitride compound semiconductor layer generally has a resistance value of about 10 ⁶ Ω / cm ^2, and has a higher resistance than the n-type gallium nitride compound semiconductor layer. Therefore, although the resistance value from the bottom of the opening to the semiconductor layer is small, the resistance value from the upper surface other than the large-area opening to the semiconductor layer is high, and if the p-type gallium nitride compound semiconductor layer is too thick, There is a problem that the operating voltage of the element is increased and the luminous efficiency is lowered.

  Furthermore, as in Patent Document 3, a part of the p-type gallium nitride compound semiconductor layer is removed by etching by RIE or ion milling to form a concavo-convex structure on the surface of the p-type gallium nitride compound semiconductor layer. In this case, the p-type gallium nitride compound semiconductor layer is damaged, and the ohmic property between the p-type gallium nitride compound semiconductor layer and the p-type electrode material is lowered. As a result, there is a problem that the operating voltage of a semiconductor light emitting device made of a gallium nitride compound is increased as described above.

  An object of the present invention is to form a concavo-convex structure on a p-type gallium nitride semiconductor layer without reducing the ohmic property between the p-type gallium nitride compound semiconductor layer and the p-type electrode material, thereby improving the light extraction efficiency. To provide a semiconductor light-emitting element that can be further improved, a lighting device using the same, and a method for manufacturing the semiconductor light-emitting element.

  The semiconductor light-emitting device of the present invention includes a semiconductor light-emitting device in which at least an n-type nitride semiconductor layer, a light-emitting layer, and a p-type nitride semiconductor layer are stacked on a substrate, and has a concavo-convex structure on the p-type nitride semiconductor layer. In the element, the concavo-convex structure has a quadrangular pyramid-shaped convex portion with a tip including a p-type dopant epitaxially grown from the p-type nitride semiconductor layer.

  According to the above configuration, after the p-type nitride semiconductor layer is formed to a desired thickness, a mask having an opening is formed, and the p-type nitride semiconductor layer contains the p-type dopant, and the tip is Concavities and convexities that improve the light extraction efficiency by diffraction are created by epitaxially growing quadrangular pyramidal and quadrangular columnar projections at low temperatures.

  Therefore, the convex portion can be formed at a sufficient height that can improve the light extraction efficiency by diffraction. In addition, the p-type nitride semiconductor layer can be reduced in resistance by setting the minimum necessary thickness. In addition, the etching for removing the mask does not carve the p-type nitride semiconductor layer, causes little damage, and includes a p-type dopant in the convex portion, so that ohmic contact can be made with the p-type electrode material. By these, a blue or ultraviolet light emitting diode with high luminous efficiency can be realized.

In the semiconductor light emitting device of the present invention, the composition of the outermost surface layer of the convex portion is In _y Ga _1-y N (0 <y ≦ 1).

According to the arrangement, the composition of the outermost layer of the convex portion by the _{In y Ga 1-y N (} 0 <y ≦ 1), the activation energy of the p-type dopant is low, a low-resistance p-type nitride Since an oxide semiconductor layer can be formed, the ohmic property between the p-type nitride semiconductor layer and the p-type electrode material is improved, the operating voltage is reduced, and a blue or ultraviolet semiconductor light emitting device with higher luminous efficiency is realized. be able to.

  Furthermore, the lighting device of the present invention is characterized by using the semiconductor light emitting element.

  According to said structure, the illuminating device which can further improve the light extraction efficiency by forming an unevenness | corrugation in a semiconductor light-emitting device is realizable.

  The method for manufacturing a semiconductor light-emitting device according to the present invention includes a substrate on which at least an n-type nitride semiconductor layer, a light-emitting layer, and a p-type nitride semiconductor layer are stacked, and an unevenness is formed on the p-type nitride semiconductor layer. In the method of manufacturing a semiconductor light emitting device having a structure, after the p-type nitride semiconductor layer is grown to a predetermined film thickness, a mask having an opening is formed, and the p-type nitride semiconductor layer is formed from the p-type nitride semiconductor layer. And a quadrangular prism-shaped convex portion including a type dopant and having a tip thereof formed into a quadrangular pyramid shape, and is epitaxially grown at a low temperature.

  According to the above configuration, when a p-type nitride semiconductor layer is formed to a desired thickness, a mask having an opening is formed, and the crystal is grown again at a reduced temperature. The growth is not carried out in the plane direction as in the case of the above growth, but is first grown in a quadrangular pyramid shape, and then grows in a quadrangular prism shape along the inner peripheral surface of the opening with the tip as a quadrangular pyramid.

  Therefore, when the mask is removed, a concavo-convex structure including a p-type dopant, a quadrangular pyramidal tip, and a quadrangular columnar projection can be formed on the p-type nitride semiconductor layer.

Furthermore, in the method for manufacturing a semiconductor light emitting device of the present invention, the mask is made of a metal oxide film of NiO ₂ or SnO ₂ , a silicon oxide film, a silicon nitride film, or sapphire.

  According to said structure, the mask material is not corroded with respect to the growth gas used during epitaxial growth, and the convex part containing the p-type dopant which has a predetermined shape can be formed easily.

  In addition, the method for manufacturing a semiconductor light-emitting device according to the present invention is characterized in that heat treatment is performed in an atmosphere containing oxygen atoms after epitaxial growth of the convex portion.

  According to said structure, since the dopant in the p-type nitride semiconductor layer containing a convex part is activated and becomes low resistance, the ohmic property of a p-type nitride semiconductor layer and a p-type electrode material becomes favorable. A semiconductor light emitting device with high luminous efficiency can be realized.

  As described above, the semiconductor light-emitting device and the method for manufacturing the same according to the present invention are formed by laminating at least an n-type nitride semiconductor layer, a light-emitting layer, and a p-type nitride semiconductor layer on a substrate. In a semiconductor light emitting device having a concavo-convex structure on a layer, a p-type nitride semiconductor layer is formed to a desired thickness, then a mask having an opening is formed, and a p-type dopant is formed from the p-type nitride semiconductor layer. In addition, the convex and concave portions having a quadrangular pyramid shape and a rectangular column shape are epitaxially grown at a low temperature, thereby creating irregularities that improve the light extraction efficiency by diffraction.

  Therefore, the convex portion can be formed at a sufficient height that can improve the light extraction efficiency by diffraction. In addition, the p-type nitride semiconductor layer can be reduced in resistance by setting the minimum necessary thickness. In addition, the etching for removing the mask does not carve the p-type nitride semiconductor layer, causes little damage, and includes a p-type dopant in the convex portion, so that ohmic contact can be made with the p-type electrode material. By these, a blue or ultraviolet light emitting diode with high luminous efficiency can be realized.

  Furthermore, the illumination device of the present invention uses the semiconductor light emitting element as described above.

  Therefore, it is possible to realize an illumination device that can further improve the light extraction efficiency by forming irregularities in the semiconductor light emitting element.

  FIG. 1 is a cross-sectional view of a light-emitting diode 1 that is a gallium nitride-based compound semiconductor light-emitting element according to an embodiment of the present invention. In this light-emitting diode 1, a buffer layer 3, an n-type gallium nitride compound semiconductor layer 4, a light-emitting layer 5 and a p-type gallium nitride compound semiconductor layer 6 in which a pair layer of AlN and GaN is stacked on a sapphire substrate 2 are sequentially arranged. Laminated. It should be noted that in the present invention, the p-type gallium nitride compound semiconductor layer 6 is followed by the p-type gallium nitride compound semiconductor layer 6 and is dispersed on the p-type gallium nitride compound semiconductor layer 6 so that the tip containing the p-type dopant has a quadrangular pyramid shape. That is, the projection 7 is crystal-grown. A conductive film 8 is stacked on the p-type gallium nitride compound semiconductor layer 6 including the convex portion 7, and a metal layer is further stacked on the conductive film 8 to form the p-type electrode 9. On the other hand, a part of the light emitting diode 1, for example, one corner of a rectangular corner is carved up to the n-type gallium nitride compound semiconductor layer 4 by etching, and an n-type electrode 10 is formed thereon.

  In this light emitting diode 1, the sapphire substrate 2 is used as a support substrate. However, the substrate is not limited to sapphire, and when performing light extraction from the substrate side, the substrate has translucency with respect to the emission wavelength. It goes without saying that anything is acceptable. In that case, although the conductive film 8 and the p-type electrode 9 are materials that reflect light, the substrate is Si or the sapphire substrate 2 is removed by irradiating the YAG laser from the sapphire substrate 2 side. In the case where a conductive film is formed on the buffer layer 3 to form an n-type electrode, the conductive film 8 and the p-type electrode 9 are made of materials that transmit light, and light may be extracted from the p-type electrode 9 side. Good.

The buffer layer 3 is formed by stacking, for example, a pair layer of AlN and GaN with a thickness of 1 nm, and the n-type gallium nitride compound semiconductor layer 4 is, for example, an Al _0.3 Ga _0.7 N layer of 2. The light emitting layer 5 is formed by stacking, for example, an Al _0.2 Ga _0.8 N layer with a thickness of 3 nm, and the p-type gallium nitride compound semiconductor layer 6 is formed, for example, by a p-type layer. An Al _0.3 Ga _0.7 N layer containing a dopant Mg exhibiting electrical conduction is laminated with a thickness of 0.1 μm. On the other hand, the convex part 7 is formed by laminating, for example, Al _0.3 Ga _0.7 N containing a p-type dopant Mg with a thickness of 0.1 μm. However, the outermost layer of the convex portion 7 is formed of In _y Ga _1-y N (0 <y ≦ 1).

In each of the layers 4, 5, 6 and the protrusion 7, the component x of Al _x Ga _1-x N (0 <x ≦ 1) and the thickness thereof are not limited to the above values, and desired electrical characteristics are obtained. It may be appropriately changed within a range where it can be obtained. In the semiconductor light emitting device of the present invention, the composition of the n-type gallium nitride compound semiconductor layer 4, the light emitting layer 5, the p-type gallium nitride compound semiconductor layer 6, and the protrusion 7 is Al _x In _y Ga _1-xy N ( 0 <x ≦ 1, 0 ≦ y ≦ 1). In the above example, y = 0 except for the outermost layer of the convex portion 7.

Below, the crystal growth method of the light emitting diode 1 comprised as mentioned above is demonstrated. The gas used for the growth is hydrogen gas (H ₂ ), nitrogen gas (N ₂ ) as a carrier gas, and ammonia (NH ₃ ), trimethyl gallium (Ga (CH ₃ ) ₃ , hereinafter abbreviated as TMG as gases related to the growth. ), Trimethylaluminum (Al (CH ₃ ) ₃ , hereinafter abbreviated as TMA), silane (SiH ₄ ), and cyclopentadienyl magnesium (Mg (C ₅ H ₅ ) ₂ ).

First, the sapphire substrate 2 is washed with an organic and acid solution. Then, the temperature is raised to 1100 ° C. while flowing H ₂ at 2 (L / min), and the sapphire substrate 2 is vapor-phase etched. Next, the temperature was lowered to 800 ° C., and 1.8 × 10 ⁻⁵ (mol / min) TMA and 1 were added while flowing H ₂ at 20 (L / min) and NH ₃ at 10 (L / min). 1 × 10 ⁻⁵ (mol / min) TMG is alternately supplied to form a buffer layer 3 on which a pair layer of AlN and GaN having a total thickness of 1 nm is stacked on the sapphire substrate 2 Crystal growth.

When the substrate processing is completed in this manner, the semiconductor layer is formed, the temperature is raised to 1000 ° C., and H ₂ is supplied at 20 (L / min) and NH ₃ is supplied at 10 (L / min), and 1.8 × 10 ^−5. (Mol / min) of TMA and 1.1 × 10 ⁻⁵ (mol / min) of TMG are alternately supplied, and silane is further introduced to the thickness of 2.2 μm, and the n-type dopant is Si. An Al _0.3 Ga _0.7 N layer containing N is grown on the buffer layer 3 as the n-type gallium nitride compound semiconductor layer 4.

Subsequently, while maintaining the temperature at 1000 ° C. and flowing H ₂ at 20 (L / min) and NH ₃ at 10 (L / min), 1.8 × 10 ⁻⁵ (mol / min) TMA and 1.1 × 10 ⁻⁵ (mol / min) of TMG is alternately supplied, and silane is further introduced to form the Al _0.2 Ga _0.8 N layer having a thickness of 3 nm as the light emitting layer 5 in the n-type. Crystals are grown on the gallium nitride compound semiconductor layer 4.

Furthermore, while maintaining the temperature at 1000 ° C. and flowing H ₂ at 20 (L / min) and NH ₃ at 10 (L / min), 1.8 × 10 ⁻⁵ (mol / min) TMA and 1.1 × The p-type Al _0.3 Ga _0.7 N layer having a thickness of 0.1 μm was prepared by alternately supplying 10 ⁻⁵ (mol / min) TMG and further introducing cyclopentadienyl magnesium. Then, crystals are grown on the light emitting layer 5 as the p-type gallium nitride compound semiconductor layer 6.

  Thus, when the gallium nitride compound semiconductor layer is laminated, it should be noted that, in the present invention, as shown in FIG. Then, the silicon oxide film 11 is vapor-deposited so as to have a thickness of 0.3 μm, and a resist 12 is applied on the entire surface as shown in FIG. 2B, and the silicon oxide film 11 shown in FIG. Thus, exposure is performed through the mask 13 having a predetermined pattern, and the resist 12 is developed to form a target resist pattern as shown in FIG.

  Thereafter, as shown in FIG. 2 (e), the silicon oxide film 11 in the opening of the resist 12 is etched by BHF, and the resist patterned with acetone is removed as shown in FIG. 2 (f). The silicon oxide film 11 is patterned on the p-type gallium nitride compound semiconductor layer 6.

Using this pattern of the silicon oxide film 11, the temperature is lowered to 800 ° C. and crystal growth is performed again. While H ₂ is supplied at 20 (L / min) and NH ₃ is supplied at 10 (L / min), 1.8% 2 × 10 ⁻⁵ (mol / min) TMA and 1.1 × 10 ⁻⁵ (mol / min) TMG were alternately supplied, and cyclopentadienyl magnesium was further introduced. As shown in FIG. 4, the tip 7 made of p-type Al _0.3 Ga _0.7 N having a thickness of 0.1 μm has a quadrangular pyramid-shaped quadrangular columnar projection 7 on the p-type gallium nitride compound semiconductor layer 6. Then, crystals are grown in the openings 14 of the silicon oxide film 11. The shape of the opening 14 may be a circle or a polygon. When crystal nuclei are grown on the p-type gallium nitride compound semiconductor layer 6 at a low temperature, a square weight is first formed so as to be inscribed in the opening 14. From the weight, a quadrangular column grows along the inner peripheral surface of the opening 14, and the tip becomes the shape of the quadrangular pyramid.

Then, on the outermost layer, the temperature is lowered to 680 ° C. and crystal growth is performed as it is, and 1.8 × 10 ⁻⁵ while flowing H ₂ at 10 (L / min) and NH ₃ at 20 (L / min). (Mol / min) TMA and 3.1 × 10 ⁻⁵ (mol / min) TMG are alternately supplied, and cyclopentadienylmagnesium is further introduced to a thickness of 0.1 μm. In _0.2 Ga _0.8 N is formed.

  Thereafter, the silicon oxide film 11 is removed using BHF or the like, and heat treatment is performed in an atmosphere containing oxygen atoms, whereby the conductive film 8, the p-type electrode 9, and the n-type electrode 10 are formed. become that way.

  When the convex portion 7 is grown, the quadrangular pyramid-shaped convex portion 7 is not formed at about 650 ° C., and the pattern of the silicon oxide film 11 is not less than 1000 ° C. which is a normal film forming temperature of the nitride semiconductor layer. It will also grow in the surface direction. Therefore, it is preferable to grow at 700 to 900 ° C., particularly at the above 800 ° C.

  Thus, by using the pattern of the silicon oxide film 11 which becomes a mask at the time of epitaxial growth and forming the columnar convex portion 7, the convex portion 7 has a height that can sufficiently improve the light extraction efficiency by diffraction ( For example, the emission wavelength λ is ¼ of 460 nm, which is 0.1 μm or more), and the p-type gallium nitride compound semiconductor layer 6 has a necessary minimum thickness (for example, about 0.1 μm), thereby reducing the resistance. Can be planned. Etching with BHF does not carve the p-type gallium nitride compound semiconductor layer 6 but removes the silicon oxide film 11 and causes little damage. Since the convex portion 7 contains a p-type dopant, the conductive layer is conductive. The film 8 can be in ohmic contact. By these, a blue or ultraviolet light emitting diode with high luminous efficiency can be realized.

Further, the composition of the outermost layer of the convex portion 7 is In _y Ga _1-y N (0 <y ≦ 1), so that the activation energy of the p-type dopant is low and the p-type gallium nitride compound semiconductor layer has low resistance. 6 can be formed, the ohmic property between the p-type gallium nitride compound semiconductor layer 6 and the conductive film 8 is improved, the operating voltage is reduced, and a blue or ultraviolet semiconductor light emitting device with higher luminous efficiency is realized. Can do.

  Furthermore, after the epitaxial growth of the convex portion 7, by performing a heat treatment in an atmosphere containing oxygen atoms, the dopant in the p-type gallium nitride compound semiconductor layer 6 including the convex portion 7 is activated (in GaN). The incorporated p-type dopant Mg is not activated because it is bonded to hydrogen in an epitaxially grown state, but by performing heat treatment in an oxygen atmosphere, the bond between Mg and hydrogen is broken. (Hydrogen and oxygen combine to form water vapor), and the p-type dopant Mg is activated.) The ohmic property between the p-type gallium nitride compound semiconductor layer 6 and the conductive film 8 is improved, and more Luminous efficiency can be further improved.

Instead of the silicon oxide film 11, a metal oxide film of NiO ₂ or SnO ₂ , a silicon nitride film, or sapphire can be used as a mask, and these materials are also corroded by a growth gas used during epitaxial growth. In other words, the projection 7 containing the p-type dopant having a predetermined shape can be easily formed. For example, when a silicon nitride film is used, etching with Ar plasma may be performed instead of etching with BHF.

  By using the light-emitting diode 1 configured as described above for the lighting device, it is possible to realize a small-sized and low power consumption lighting device to obtain the same luminous flux (luminance, illuminance).

It is sectional drawing of the light emitting diode which is a gallium nitride type compound semiconductor light emitting element concerning one Embodiment of this invention. It is sectional drawing for demonstrating the manufacturing method of the light emitting diode of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light emitting diode 2 Sapphire substrate 3 Buffer layer 4 N-type gallium nitride compound semiconductor layer 5 Light emitting layer 6 P-type gallium nitride compound semiconductor layer 7 Convex part 8 Conductive film 9 P-type electrode 10 N-type electrode 11 Silicon nitride film 12 Resist 14 Opening

Claims (6)

In a semiconductor light emitting device comprising at least an n-type nitride semiconductor layer, a light emitting layer, and a p type nitride semiconductor layer on a substrate, and having a concavo-convex structure on the p type nitride semiconductor layer,
A semiconductor light emitting device comprising a convex portion having a quadrangular pyramid shape with a tip including a p-type dopant obtained by epitaxially growing the concavo-convex structure from the p-type nitride semiconductor layer. 2. The semiconductor light emitting element according to claim 1, wherein the composition of the outermost layer of the convex portion is In _y Ga _1-y N (0 <y ≦ 1).   An illumination device using the semiconductor light emitting device according to claim 1. In a method for manufacturing a semiconductor light emitting device, comprising at least an n-type nitride semiconductor layer, a light emitting layer, and a p type nitride semiconductor layer on a substrate, and having a concavo-convex structure on the p type nitride semiconductor layer.
After the p-type nitride semiconductor layer is grown to a predetermined film thickness, a mask having an opening is formed, the p-type nitride semiconductor layer includes a p-type dopant, and the tip has a quadrangular pyramid shape. A method for manufacturing a semiconductor light-emitting device, characterized by epitaxially growing a quadrangular columnar convex portion at a low temperature. 5. The method of manufacturing a semiconductor light emitting device according to claim 4, wherein the mask is made of a metal oxide film of NiO ₂ or SnO ₂ , a silicon oxide film, a silicon nitride film, or sapphire.   6. The method for manufacturing a semiconductor light-emitting element according to claim 4, wherein heat treatment is performed in an atmosphere containing oxygen atoms after epitaxial growth of the convex portion.

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