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Patent Issued for Nitride Semiconductor Light-Emitting Element, Nitride Semiconductor Light-Emitting Device, and Method of Manufacturing Nitride...

July 23, 2014



Patent Issued for Nitride Semiconductor Light-Emitting Element, Nitride Semiconductor Light-Emitting Device, and Method of Manufacturing Nitride Semiconductor Light-Emitting Element

By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventor Weng, Yufeng (Osaka, JP), filed on August 22, 2012, was published online on July 8, 2014.

The patent's assignee for patent number 8772790 is Sharp Kabushiki Kaisha (Osaka-shi, JP).

News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates to a nitride semiconductor light-emitting element, a nitride semiconductor light-emitting device and a method of manufacturing a nitride semiconductor light-emitting element.

"Conventionally, in a general nitride semiconductor light-emitting element, on a sapphire substrate, an n-type nitride semiconductor layer, a nitride semiconductor light-emitting layer, a p-type nitride semiconductor layer and the like are sequentially provided. On each of the side of the n-type nitride semiconductor layer and the side of the p-type nitride semiconductor layer, an n-side electrode and a p-side electrode for connection with an external power supply are formed. On the substantially entire surface of the p-type nitride semiconductor layer, in order to assist current diffusion within the p-type nitride semiconductor layer, a transparent conductive film or the like formed with, for example, ITO (indium tin oxide) is deposited as a current diffusion layer.

"Furthermore, on the upper portion of the current diffusion layer, a reflective film is deposited. This reflective film is provided in order to reflect light emitted from the nitride semiconductor light-emitting layer to the current diffusion layer toward the sapphire substrate and thereby enhance the efficiency of extracting light by the nitride semiconductor light-emitting element. The reflective film is generally formed with a metal material, such as Ag or Al, that has a high reflectivity. For example, JP-A-2011-71444 and JP-A-2006-108161 propose a nitride semiconductor light-emitting element in which a metal reflective film is formed through an insulating film on a transparent conductive film. Moreover, JP-A-2006-120913 proposes a nitride semiconductor light-emitting element in which a metal reflective film is formed on a transparent conductive film through a multiple reflective film formed with a plurality of dielectric layers.

"However, when the metal reflective film is formed in the nitride semiconductor light-emitting element as in JP-A-2011-71444 and JP-A-2006-108161, a phenomenon called migration occurs due to the effects of as an electric field, an ambient humidity and the like acting on the metal reflective film, and thus a reliability problem occurs. When the multilayer reflective film is formed as in JP-A-2006-120913, since it is necessary to deposit a few tens of reflective films so as to obtain a high reflectivity, disadvantageously, it takes a long time, and it is uneconomical in terms of cost."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventor's summary information for this patent: "The present invention is made to overcome the above problem; an object of the present invention is to provide a nitride semiconductor light-emitting element including a reflective mirror in which its cost is low, its reflectivity is high and its reliability is high, a nitride semiconductor light-emitting device and a method of manufacturing a nitride semiconductor light-emitting element.

"To achieve the above object, according to the present invention, there is provided a nitride semiconductor light-emitting element including: a substrate; a nitride semiconductor multilayer portion provided on the substrate; and a protective layer provided on an upper portion of the nitride semiconductor multilayer portion, in which the nitride semiconductor multilayer portion includes a light-emitting layer, and an air gap layer is formed in at least one of an area between the substrate and the light-emitting layer and an area between the light-emitting layer and the protective layer.

"In the configuration described above, the reflective mirror including the air gap layer is formed in at least one of the area between the substrate and the light-emitting layer and the area between the light-emitting layer and the protective layer. The reflective mirror has a high reflectivity for the light emitted from the light-emitting layer. The reflective mirror has no metal reflective film. This prevents the reliability from being decreased due to the migration phenomenon. It is therefore possible to obtain the nitride semiconductor light-emitting element including the reflective mirror that has a low cost, a high reflectivity and a high reliability.

"Alternatively, in the nitride semiconductor light-emitting element configured as described above, a current diffusion layer provided on the nitride semiconductor multilayer portion is further included, and the air gap layer is provided between the current diffusion layer and the protective layer.

"In the configuration described above, the reflective mirror that is formed with 'the current diffusion layer/the air gap layer/the protective layer' and that has a three-layer structure is formed. The refractive index contrast of the interface between the current diffusion layer and the reflective mirror is high. Hence, the reflective mirror has a high reflectivity for the light emitted from the light-emitting layer.

"Alternatively, in the nitride semiconductor light-emitting element configured as described above, the nitride semiconductor multilayer portion further includes: a first nitride semiconductor layer provided between the substrate and the light-emitting layer; and a second nitride semiconductor layer provided between the light-emitting layer and the protective layer, and the air gap layer is formed in at least one of an area within the first nitride semiconductor layer and an area within the second nitride semiconductor layer.

"In the configuration described above, the reflective mirror including the air gap layer is formed in at least one of the area within the first nitride semiconductor layer and the area within the second nitride semiconductor layer. Hence, the reflective mirror can be formed in a position closer to the light-emitting layer. Thus, the light emitted from the light-emitting layer can be more effectively reflected off the reflective mirror. It is therefore possible to more enhance the efficiency of utilizing the light emitted from the light-emitting layer.

"Alternatively, in the nitride semiconductor light-emitting element configured as described above, a solid layer that is provided adjacent to the air gap layer in a direction of a normal to a main surface of the light-emitting layer is further included, and the solid layer has a high refractive index contrast for the air gap layer, and pairs with the air gap layer to form a reflective mirror.

"In the configuration described above, the solid layer that is adjacent to the air gap layer in the direction of the normal to the main surface of the light-emitting layer and that has a high refractive index contrast for the air gap layer is provided. The solid layer pairs with the air gap layer to form a DBR (distributed bragg reflector) mirror functioning as the reflective mirror. Hence, in the interface between the air gap layer and the solid layer, a high refractive index contrast is obtained. It is therefore possible to further enhance the reflectivity of the reflective mirror for the light emitted from the light-emitting layer.

"Alternatively, in the nitride semiconductor light-emitting element configured as described above, a joining electrode provided on an upper portion of the nitride semiconductor multilayer portion and a first highly reflective electrode layer provided between the nitride semiconductor multilayer portion and the joining electrode are further included.

"In the configuration described above, the first highly reflective electrode layer is provided between the nitride semiconductor multilayer portion and the joining electrode. Hence, the light emitted from the light-emitting layer can be reflected off the first highly reflective electrode layer. It is therefore possible to prevent the light emitted from the light-emitting layer from being absorbed by the joining electrode.

"Alternatively, in the nitride semiconductor light-emitting element configured as described above, the nitride semiconductor multilayer portion further includes a first nitride semiconductor layer provided between the substrate and the light-emitting layer, and the nitride semiconductor light-emitting element further includes: a contact electrode provided on an upper portion of the first nitride semiconductor layer; and a second highly reflective electrode layer provided between the first nitride semiconductor layer and the contact electrode.

"In the configuration described above, the second highly reflective electrode layer is provided between the first nitride semiconductor layer and the contact electrode. Hence, the light emitted from the light-emitting layer can be reflected off the second highly reflective electrode layer. It is therefore possible to prevent the light emitted from the light-emitting layer from being absorbed by the contact electrode.

"To achieve the above object, according to the present invention, there is provided a nitride semiconductor light-emitting device including: a nitride semiconductor light-emitting element including: a substrate; a nitride semiconductor multilayer portion provided on the substrate and having a light-emitting layer; and a protective layer provided on an upper portion of the nitride semiconductor multilayer portion; a package substrate on which the nitride semiconductor light-emitting element is mounted; and an optically transparent resin sealing portion that seals the nitride semiconductor light-emitting element mounted on the package substrate, in which an air gap layer is formed in at least one of an area between the substrate and the light-emitting layer in the nitride semiconductor light-emitting element, an area between the light-emitting layer and the protective layer in the nitride semiconductor light-emitting element and an area in the package substrate.

"In the configuration described above, the reflective mirror including the air gap layer is formed in at least one of the area between the substrate and the light-emitting layer in the nitride semiconductor light-emitting element, the area between the light-emitting layer and the protective layer in the nitride semiconductor light-emitting element and the area in the package substrate. The reflective mirror has a high reflectivity for the light emitted from the light-emitting layer. The reflective mirror has no metal reflective film. This prevents the reliability from being decreased due to the migration phenomenon. It is therefore possible to obtain the nitride semiconductor light-emitting device including the reflective mirror that has a low cost, a high reflectivity and a high reliability.

"To achieve the above object, according to the present invention, there is provided a method of manufacturing a nitride semiconductor light-emitting element including: a step of providing, on a substrate, a nitride semiconductor multilayer portion having a light-emitting layer; a step of providing a protective layer on an upper portion of the nitride semiconductor multilayer portion; and a step of forming an air gap layer in at least one of an area between the substrate and the light-emitting layer and an area between the light-emitting layer and the protective layer.

"In the configuration described above, the reflective mirror including the air gap layer is formed in at least one of the area between the substrate and the light-emitting layer and the area between the light-emitting layer and the protective layer. The reflective mirror has a high reflectivity for the light emitted from the light-emitting layer. The reflective mirror has no metal reflective film. This prevents the reliability from being decreased due to the migration phenomenon. It is therefore possible to obtain the method of manufacturing the nitride semiconductor light-emitting element including the reflective mirror that has a low cost, a high reflectivity and a high reliability.

"In the method of manufacturing the nitride semiconductor light-emitting element configured as described above, a step of providing a solid layer that is adjacent to the air gap layer in a direction of a normal to a main surface of the light-emitting layer, that has a high refractive index contrast for the air gap layer and that pairs with the air gap layer to form a reflective mirror may be further included.

"In the configuration described above, the solid layer that is adjacent to the air gap layer in the direction of the normal to the main surface of the light-emitting layer and that has a high refractive index contrast for the air gap layer is provided. The solid layer pairs with the air gap layer to form the DBR mirror functioning as the reflective mirror. Hence, in the interface between the air gap layer and the solid layer, a high refractive index contrast is obtained. It is therefore possible to more enhance the reflectivity of the reflective mirror for the light emitted from the light-emitting layer."

For additional information on this patent, see: Weng, Yufeng. Nitride Semiconductor Light-Emitting Element, Nitride Semiconductor Light-Emitting Device, and Method of Manufacturing Nitride Semiconductor Light-Emitting Element. U.S. Patent Number 8772790, filed August 22, 2012, and published online on July 8, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8772790.PN.&OS=PN/8772790RS=PN/8772790

Keywords for this news article include: Electronics, Semiconductor, Sharp Kabushiki Kaisha.

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Source: Electronics Newsweekly


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