Source: http://www.google.com/patents/US7453092?dq=4,923,986
Timestamp: 2016-02-09 18:07:38
Document Index: 389157788

Matched Legal Cases: ['art 4', 'art 4', 'art 4', 'art 4', 'art 4', 'art 4']

Patent US7453092 - Light emitting device and light emitting element having predetermined ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inPatentsA light emitting device having: a predetermined optical form that is provided on a surface of an LED element mounted on a base, the predetermined optical form being made to allow an increase in efficiency of taken out light from an inside of the LED element; and a sealing material that seals the predetermined...http://www.google.com/patents/US7453092?utm_source=gb-gplus-sharePatent US7453092 - Light emitting device and light emitting element having predetermined optical formAdvanced Patent SearchPublication numberUS7453092 B2Publication typeGrantApplication numberUS 11/214,018Publication dateNov 18, 2008Filing dateAug 30, 2005Priority dateAug 31, 2004Fee statusPaidAlso published asDE102005041095A1, US20060043402Publication number11214018, 214018, US 7453092 B2, US 7453092B2, US-B2-7453092, US7453092 B2, US7453092B2InventorsYoshinobu Suehiro, Koji TasumiOriginal AssigneeToyoda Gosei Co., Ltd.Export CitationBiBTeX, EndNote, RefManPatent Citations (27), Non-Patent Citations (1), Referenced by (14), Classifications (26), Legal Events (2) External Links: USPTO, USPTO Assignment, EspacenetLight emitting device and light emitting element having predetermined optical form
n1�sin45�<n2
In the LED element that is described in Japanese Patent Application Laid-Open No. 2003-69075 (FIG. 1, [0011]), however, ability to take out light that has been confined within a GaN based semiconductor layer (light confined within a layer) depend on a difference in the refractive index vis-�-vis the sealing member around the element, and a sufficient ability to take out light cannot be gained in a state where a reflection from the interface occurs on the basis of the difference in the refractive index vis-�-vis the sealing member, even in the case where unevenness processing has been carried out on the surface of the element. In addition, though an increase in the efficiency of taking out light car be achieved by scattering light that has been confined within a GaN based semiconductor layer, this is not an ideal form or anything close to this. A problem also arises concerning this light that is confined within a layer, where the amount of light is reduced when it propagates over a long distance within a layer having a large optical absorption coefficient so as to attenuate, and in addition, the amount of generated heat increases within the element.
(2) Furthermore, according to the first embodiment, sapphire substrate S is removed, and instead, SiO2-Nb2O5 based glass having n=1.8 is used, and thereby, the critical angle θc with LED element 2 becomes approximately 50 degrees. The sealing material may be selected so that critical angle θc between this LED element 2 and glass sealing part 4 becomes no less than 45�, and thereby, the amount of light confined within a layer that propagates laterally through GaN based semiconductor layer 100 can be reduced, in comparison with sapphire substrate S having n =1.7, and furthermore, the probability of light confined within a layer of GaN based semiconductor layer 100 being radiated to the outside of the element when entering into portion in uneven form 20A becomes high. In addition to this, GaN based semiconductor layer 100 has a thickness of 10 μm, and the probability of light being reaching portion in uneven form 20A is high, and therefore, light can be radiated to the outside with extremely high efficiency at an ideal level. In addition, even in the case where the flatness of the uneven surface is not sufficient, due to restriction in processing, the sealing material having a high refractive index compensates for this, and thus, properties which provide an efficiency that is close to the limit of what can be theoretically realized can be achieved. Here, the formation of unevenness is carried out on p-GaN: Si layer 20 which is at a distance from MQW 24 that is the light emitting layer in GaN based semiconductor layer 100, and therefore, damage to the light emitting layer can be avoided at the time of the formation of unevenness. Therefore, the internal quantum efficiency can be maintained, and the efficiency of radiation of light to the outside of LED element 2 can be greatly increased.
(4) In addition, the thermal expansion coefficients of Al2O3 substrate 3 and glass sealing part 4, which form the package, are approximately the same, and thereby, a structure where inconveniences, such as cracking caused by thermal stress, do not easily occur can be provided. As a result, effects are gained where the value of current that is allowed to flow can be increased, in addition to reliability against thermal impacts. Conventional epoxy resin sealing restricts the current that is allowed to flow, due to the glass transition temperature (Tg point) of the epoxy resin. This is because the thermal expansion coefficient becomes great at a temperature that is no lower than the Tg point, and disconnection easily occurs in electrical connection portions. The Tg point of glass sealing part 4 is higher than that of epoxy resins by 300� C. or more, and the thermal expansion coefficient is no greater than 1/7 of epoxy resins at a temperature that is no higher than the Tg point.
(7) Sapphire substrate S is peeled after LED element 2 is mounted on Al2O3 substrate 3, which is a base, and then, portion in uneven form 20A is provided, and therefore, it becomes possible to easily form a package of a variety of sealing materials which are sealing materials other than glass sealing part 4, such as, for example, epoxy resin materials, fluorophore containing light transmitting resin materials and glass materials that contain a fluorophore. In addition, it is also easy to fabricate portion in uneven form 20A of which the uneven form corresponds to the difference in the refractive index vis-�-vis the sealing material.
According to the fifth embodiment, GaP substrate 200 is polished to a desired thickness on the side from which light is taken out, and in addition, portion in uneven form 20A is provided through cutting by a dicer, and thereby, LED element 2 having excellent properties of taking out light is gained. In addition, at this time, the light emitting layer can be prevented from being damaged during processing on the side of GaP substrate 200. In the case of a GaP substrate 200 of n=3.5, a sealing material of approximately n=2.4 is used to make it possible for light that has been emitted from an end portion of LED element 2 to be radiated to the outside of LED element 2 without total reflection of light that laterally propagates when entering into portion in uneven form 20A when portion in uneven form 20A is formed so as to have the above described size. It is difficult in practice to implement a sealing material for LED element 2 that exceeds n=2, which is the current level. Even in the case where radiation of light to the outside cannot be implemented at an ideal level, however, light can be made to radiate from the uneven side in approximately vertical step form to the outside at a solid angle in a large angular range that covers the direction from 90�−sin−1 (n1/n2) to 90� (here, n1 is the refractive index of the light emitting layer of LED element 2, and n2 is the refractive index of the sealing material) relative to the direction of the normal line of the light emitting layer. In particular, this form and a sealing material of n=1.6 or greater are combined, and thereby, a gain that is much higher than that in the case where the form is not processed and an epoxy resin sealing of n=1.5 is used can be gained.
Here, tapers (inclined angles) with the limit of the critical angle between the light emitting layer and the sealing material of the LED element may be formed in the uneven step portions. Within this limit, an effective uneven side in step form can be provided. That is to say, the inclinations are provided so as to make light radiate to the outside in the direction 90� relative to the direction of the normal of the light emitting layer, which makes the solid angle maximum. In addition, the LED element may be formed by combining a light emitting layer of LED element 2 and a substrate having the same refractive index as the light emitting element, for example, a GaN substrate and a GaN based semiconductor layer, or an SiC substrate and a GaN based semiconductor layer, instead of the layered structure which is formed of GaP substrate 200 and AlInGaP based semiconductor layer 201.
FIGS. 8A and 8B show an LED element according to a sixth embodiment; FIG. BA is a plan view of the LED element as viewed from the side from which light is taken out, and FIG. 8B is a diagram for illustrating how light is taken out in the portion in protrusion form of FIG. 8A. This LED element 2 has portion in uneven form 20A where collective bodies in hexagonal form are arranged in staggered form via flat portions 20 b (with intervals of 10 μm), and in each of these collective bodies, three protrusions 20 a (having a height of 2 μm) in diamond form (adjacent step sides form 60� or 120�) are combined on the surface of an n-GaN: Si layer from which light is taken out, as shown in FIG. BA.
When glass sealing part 4 in hemispherical form is provided, surface in optical form 42 around LED element 2 is ideally in an optical form into which light that is radiated from LED element 2 can perpendicularly enter. Here, critical angle 9 of surface in optical form 42 becomes θ=sin−1 (n0/n2)=31.8�, where the refractive index of air is n0=1.0 and the refractive index of glass sealing part 4 is n2=1.9, and the reflectance from the interface tends to increase in the vicinity of −5�, which is critical angle θ, though total reflection does not occur to light that enters at an angle that is within the limit of this critical angle θ, and it is preferable to provide an optical form that allows the amount of light that enters at an angle in a range that makes the reflectance from the interface small to increase.
The layer of a material having a high refractive index 119 is formed on the surface of n-GaN layer 113 so as to have a film thickness of 1 μm, by heating and vaporizing Ta2O5, which is a raw material by means of an electron beam vapor deposition method. Ta2O5 has an refractive index of n=2.2, and critical angle θc becomes 66� on the basis of the ratio of indices of refraction relative to n-GaN layer 113. In addition, a coarse surface portion 119A is formed on the surface of layer of a material having a high refractive index 119 on the side from which light is taken out, in accordance with an electron beam deposition method.
This flip chip type LED element 2 has a configuration where an ITO contact electrode 120 of which the thermal expansion coefficient is 7.0�10−6/� C. is provided instead of p side electrode 118 of LED element 1 that is described in the ninth embodiment.
In FIG. 16, curve A shows the ratio of efficiency of radiation to the outside of an LED element (standard element) in rectangular parallelepiped form using a sapphire substrate, curve B0 shows the ratio of efficiency of radiation to the outside of an LEE element in rectangular parallelepiped form using a substrate which is GaN or has an refractive index that is the same as that of GaN, and curve B1 shows the ratio of efficiency of radiation to the outside of an LED element in rectangular parallelepiped form using a substrate which is GaN or has an refractive index that is the same as that of GaN, and on which surface processing has been carried out The dimensions of all of the rectangular parallelepiped forms are W=300 μm, the thickness of semiconductor layer t=6 μm, and the thickness of substrate is 84 μm (thickness of 72% of 116 μm) This is a case where the processed form on the surface is a prism having an inclination angle of 45� (with bottom sides of 2 μm). Here, the characteristics curves do not change greatly, and stay approximately the same, even in the case where the inclination angle is changed within a range of �15�. This is because it becomes easier for light to be radiated from the light emitting element to the sealing material while it also becomes easier for light to reenter into the adjacent surface in processed form as the angle of inclination is increases.
This flip chip type LED element 2 is gained by providing cut portions 130A having an inclination angle of 45� in the corners of GaN substrate 130 (in the form where surfaces C are rounded in the corners of the substrate) of LED element 2 of the eleventh embodiment.
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257/E33.054, 257/93, 257/E33.001, 257/103, 257/E33.074, 257/777International ClassificationH01L33/62, H01L33/56, H01L33/06, H01L33/22, H01L33/32Cooperative ClassificationH01L2224/16225, H01L33/22, H01L33/56, H01L33/486, H01L33/32, H01L33/0079European ClassificationH01L33/22Legal EventsDateCodeEventDescriptionNov 15, 2005ASAssignmentOwner name: TOYODA GOSEI CO., LTD., JAPANFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:SUEHIRO, YOSHINOBU;TASUMI, KOJI;REEL/FRAME:017019/0627Effective date: 20050914Apr 25, 2012FPAYFee paymentYear of fee payment: 4RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services