Light emitting device having improved light extraction efficiency and method of making same Number:7,521,727 from the United States Patent and Trademark Office (PTO) owispatent A light emitting device including a multi-layer stack and an encapsulant layer having a patterned encapsulant region in optical proximity to a luminous stack surface of the multi-layer stack is disclosed. A method of making that encapsulant layer and of affixing that encapsulant layer to a luminous stack surface is also disclosed.<H efficiency, extraction, Light, emitting, , 7521727.html, Patent, pto, 7521727

Title: Light emitting device having improved light extraction efficiency and method of making same

Abstract: A light emitting device including a multi-layer stack and an encapsulant layer having a patterned encapsulant region in optical proximity to a luminous stack surface of the multi-layer stack is disclosed. A method of making that encapsulant layer and of affixing that encapsulant layer to a luminous stack surface is also disclosed.

Patent Number: 7,521,727 Issued on 04/21/2009 to Khanarian, et al.

Inventors: Khanarian; Garo (Princeton, NJ), Mosley; David Wayne (Philadelphia, PA)
Assignee: Rohm and Haas Company (Philadelphia, PA)

Appl. No.: 11/724,399

Filed: March 15, 2007

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
60795220	Apr., 2006

Current U.S. Class: 257/98 ; 257/100; 257/79

Current International Class: H01L 33/00 (20060101)

Field of Search: 257/98,100,79-82,E33.056-E33.059,E25.032

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Primary Examiner: Doan; Theresa T
Attorney, Agent or Firm: Baskin; Jonathan D.

Parent Case Text

This application claims the benefit of priority under 35 U.S.C. .sctn.119(e) of U.S. Provisional Patent Application No. 60/795,220 filed on Apr. 26, 2006.

Claims

I claim:

1. A light emitting device comprising: a) a multi-layer stack comprising: an n-doped layer; a light-generating layer; and a p-doped layer, wherein said multi-layer stack has a luminous stack surface; and b) an encapsulant layer comprising: a proximal patterned encapsulant region comprising: a first recess set comprising at least one first recess comprising first recess filler; optionally, a second recess set comprising at least one second recess comprising a second recess filler; and a proximal patterned encapsulant surface disposed upon said luminous stack surface; and wherein at least one of said first recess set and said second recess set has a pattern wherein: said pattern is a periodic pattern, said pattern has a feature size, in at least one lateral dimension, of at least 5 nanometers and no more than 5,000 microns; said periodic pattern has a period, in at least one lateral dimension, of at least 10 nanometers and no more than 5,000 microns; said first recess has a maximum recess depth of at least 25 nanometers and no more than 10,000 microns; and said second recess has a maximum recess depth of at least 25 nanometers and no more than 10,000 microns; wherein at least one of said first recess and said second recess has a recess opening coincident with said proximal patterned encapsulant surface; and optionally, an unpatterned encapsulant region comprising an encapsulant material; wherein said first recess filler differs in refractive index from at least one of second recess filler and said encapsulant material by at least 0.001 and no more than 3.0; and wherein at least one of said first recess filler, said second recess filler, and said encapsulant material has a mean density of at least 0.03 g/cm.sup.3 and no more than 0.60 g/cm.sup.3.

2. The light emitting device of claim 1, wherein at least one of said first recess filler and said second recess filler is selected from GIaN, SiC, AlN, ZnS, TiO.sub.2 ZnO, GaP, and high RI glass.

3. The light emitting device of claim 1, wherein at least one of said first recess filler and said second recess filler has a mean density greater than 0.60 g/cm.sup.3 and no more than 7.0 g/cm.sup.3.

4. The light emitting device of claim 1 wherein at least one of said first recess filler, said second recess filler, and said encapsulant material is a cured B-staged optical material.

5. The light emitting device of claim 4 wherein said cured B-staged optical material further comprises pores, and wherein said cured B-staged optical material has a porosity of at least 0.1 volume percent to 95 volume percent, based on the volume of said cured B-staged optical material.

6. The light emitting device of claim 1, further comprising a reflective layer capable of reflecting at least 50% of the light generated by said light-generating layer that impinges upon said reflective layer, wherein said reflective layer is disposed opposite said multi-layer stack from said luminous stack surface.

7. The light emitting device of claim 1, wherein said multi-layer stack further comprises an intervening high refractive index layer disposed between said luminous stack surface and said proximal patterned encapsulant surface, wherein said intervening high refractive index layer has a refractive index no lower than 0.5 below the refractive index of the luminous stack surface, for the wavelength of light to be extracted.

8. The light emitting device of claim 1, wherein said multi-layer stack further comprises a bonding layer disposed between said luminous stack surface and said proximal patterned encapsulant surface, wherein said bonding layer has a thickness between 1 nm and 50 nm.

Description

The present invention relates to a multi-layer stack based light emitting device having improved light extraction efficiency, and to a method of making the light emitting device.

Light emitting devices, for example light emitting diodes (LEDs), generate light using one or more materials having refractive indices (typically n.about.2.5) much higher than that of air (n=1.0). Typically, light is generated in a multi-layer stack, at least one exterior surface, a luminous stack surface, is intended to release light generated within the multi-layer stack. This luminous stack surface may be in contact with, for example, an encapsulant material. Such encapsulant materials typically have refractive indices in the range n=1.4 to 1.8. The drop in refractive index encountered by light impinging upon the interface between a luminous stack surface and the encapsulant layer is, therefore, substantial, with the result that much of the light generated within the multi-layer stack is reflected back into the multi-layer stack by that interface. That is, instead of exiting the multi-layer stack with concomitant entry into the encapsulant layer, a large fraction of the light is channeled back into the interior of multi-layer stack where a similar large fraction is absorbed, thereby drastically reducing the external quantum yield of light useful for illumination.

U.S. Pat. No. 6,831,302 discloses patterning of an exterior surface of an n-doped GaN layer which is an exterior layer of the multi-layer stack. Portions of that n-doped layer are removed to create openings which are then covered over, but not filled, with encapsulant material, creating a smooth layer of encapsulant surface against the openings to the depressions in the surface of the n-doped GaN layer. This patterning within the outermost semiconductor layer creates a plurality of disruptive high and low refractive index regions normal to the encapsulant surface. These disruptive regions interrupt the low angle reflection of light at the interface as well as the tendency of light reflected at low angle to be guided back and forth, parallel to and near the luminous stack surface, within the n-doped semiconductor layer, until that trapped light is absorbed without ever exiting the multi-layer stack.

While the formation of depressions in the exterior surface of the multi-layer stack may improve quantum yield for semi-conductor based light emitting devices, the patterning process can be time consuming, requiring, for example, etching of epitaxial surfaces which typically requires expensive equipment. The patterning process may also disrupt the electronic structure of the light emitting layer which in term may decrease light emitting efficiency.

We have surprisingly discovered that by patterning a region of the encapsulant layer, a region in optical proximity to a luminous stack surface of a multi-layer stack, such that there is a variation in the refractive index in that region, and by further forming a portion of the encapsulant layer having a density less than 0.6 g/cc, a plurality of light scattering extractive centers is created, and light is efficiently transmitted to the air environment such that the external quantum yield of light useful for illumination is increased.

One aspect of the present invention is directed to a light emitting device comprising: a) a multi-layer stack comprising: an n-doped layer; a light-generating layer; and a p-doped layer, wherein said multi-layer stack has a luminous stack surface; and b) an encapsulant layer comprising: a proximal patterned encapsulant region comprising: a first recess set comprising at least one first recess comprising first recess filler; optionally, a second recess set comprising at least one second recess comprising a second recess filler; and a proximal patterned encapsulant surface disposed upon said luminous stack surface; and wherein at least one of said first recess set and said second recess set has a pattern wherein: said pattern is selected from random pattern, periodic pattern, or a combination thereof, said pattern has a feature size, in at least one lateral dimension, of at least 5 nanometers and no more than 5,000 microns; said periodic pattern has a period, in at least one lateral dimension, of at least 10 nanometers and no more than 5,000 microns; said first recess has a maximum recess depth of at least 25 nanometers and no more than 10,000 microns; and said second recess has a maximum recess depth of at least 25 nanometers and no more than 10,000 microns; wherein at least one of said first recess and said second recess has a recess opening coincident with said exterior patterned encapsulant surface; and optionally, an unpatterned encapsulant region comprising an encapsulant material; wherein said first recess filler differs in refractive index from at least one of second recess filler and said encapsulant material by at least 0.001 and no more than 3.0; and wherein at least one of said first recess filler, said second recess filler, and said encapsulant material has a mean density of at least 0.03 g/cm.sup.3 and no more than 0.60 g/cm.sup.3.

A second aspect of the present invention is directed to a method of preparing an encapsulated light emitting device, comprising the steps of: A) providing an encapsulant block comprising encapsulant material; and B) forming a light extraction encapsulant sheet having a patterned encapsulant region, said region having an exterior patterned encapsulant surface, on a surface of said encapsulant block; wherein said step of forming said patterned encapsulant region comprises: a) forming a first recess set comprising at least one first recess; b) filling said first recess with a first recess filler; c) optionally, forming a second recess set comprising at least one second recess; and filling said second recess with a second recess filler; wherein at least one of said first recess set and said second recess set has a pattern wherein: said pattern is selected from random pattern, periodic pattern, or a combination thereof, said pattern has a feature size, in at least one lateral dimension, of at least 5 nanometers and no more than 5,000 microns; said periodic pattern has a period, in at least one lateral dimension, of at least 10 nanometers and no more than 5,000 microns; said first recess has a maximum recess depth of at least 25 nanometers and no more than 10,000 microns; said second recess has a maximum recess depth of at least 25 nanometers and no more than 10,000 microns; at least one of said first recess and said second recess has a recess opening coincident with said exterior patterned encapsulant surface; and said first recess filler differs in refractive index from at least one of second recess filler and said encapsulant material by at least 0.001 and no more than 3.0; wherein at least one of said first recess filler, said second recess filler, and said encapsulant material has a mean density of at least 0.03 g/cm.sup.3 and no more than 0.60 g/cm.sup.3. C) affixing said light extraction encapsulant sheet to a multi-layer stack, wherein said multi-layer stack comprises: an n-doped layer; a light-generating layer; and a p-doped layer, wherein said multi-layer stack has a luminous stack surface; and wherein said exterior patterned encapsulant surface is disposed upon said luminous stack surface; wherein said luminous stack surface has a topography selected from smooth surface and patterned multilevel surface; and wherein said patterned multilevel surface has a pattern selected from a random pattern, a periodic pattern, and combinations thereof; and D) optionally removing all or a portion of said encapsulant material from contact with any or said first recess set and said second recess set.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 side views 1a-1b each represent an light emitting device including encapsulant layer 109 having proximal patterned encapsulant region 117.

FIG. 2 LED side views 2a-2f each represent a portion of an light emitting device including n-doped layer 107 and encapsulant layer 109 having a proximal patterned encapsulant region 117.

FIG. 3 light emitting device views 3a-3d each represent proximal patterned encapsulant surface 113, including first recess openings 119-1 and inter-recess volume element 118.

FIG. 4 views 4a, 4c, 4e, and 4h each represent a first recess 112-1 having a first recess opening 119-1 at proximal patterned encapsulant surface 113 and inter-recess volume element 118. Views 4b, 4d, 4f, and 4g each represent a first recess opening 119-1 at proximal patterned encapsulant surface 113.

FIG. 5 light emitting device views 5a-5e each represent a proximal patterned encapsulant surface 113, including first recess openings 119-1 and inter-recess volume element 118.

FIG. 6 views 6a-6d each represent a side view of encapsulant block 120 and of a patterned mold which forms first recesses 112-1 in the surface of encapsulant block 120 that is being transformed into proximal patterned encapsulant surface 113 of an encapsulant layer 109.

FIG. 7 views 7a-7e each represent a side view during transformation of encapsulant block 120, coated with first recess filler layer 125, into an encapsulant layer 109 having proximal patterned encapsulant region 117 which includes first recesses 112-1 having first recess walls 111-1. First recess 112-1 is filled, completely or partially, with first recess filler derived from first recess filler layer 125. Views 7a-7c each further include a side view of a patterned mold used to form a relief pattern in the encapsulant block 120. View 7d represents proximal patterned encapsulant region 117, the first recess 112-1 of which contains first recess filler derived from first recess filler layer 125 and second recesses 112-2 containing second recess filler. FIG. 7d represents a case in which first recess filler surface excess 126 has not been removed, or has been partially removed. View 7e represents a proximal patterned encapsulant region 117 formed by removal of first recess filler surface excess 126 during planarization.

FIG. 8 views 8a-8d each represent a side view of proximal patterned encapsulant region 117. FIG. 8a represents first recesses 112-1 having more than one size, and inter-recess volume element 118. FIGS. 8b and 8c includes first recess 112-1 and second recess 112-2. In FIGS. 8b and 8c, second recesses 112-2 have the same shape and size. In FIG. 8d, second recesses 112-2 differ in shape and size. FIG. 8a further indicates first recess depth 129-1 and maximum first recess depth 130-1 for a given first recess 112-1. FIGS. 8c and 8d show second recess wall 111-2 and second recess opening 119-2, and FIG. 8d indicates second recess depth 129-2 and maximum second recess depth 130-2 for a given second recess 112-2.

FIG. 9 represents a side view of multi-layer stack 115 as in FIG. 1b, except that multi-layer stack 115 further includes optional auxiliary light transmitting layer 131 and and optional cover slip 127. In addition to the luminous stack surface 114 shown in FIG. 1b, two luminous stack surfaces 114 of auxiliary light transmitting layer 131 are shown, each having a proximal patterned encapsulant region 117 disposed upon it. Auxiliary light transmitting layer 131 further has a luminous stack surface 114, opposite p-doped layer 105, which is disposed upon reflective layer 103, and which does not have a proximal patterned encapsulant region 117 disposed thereupon.

FIG. 10 views 10a-10e represent a recess patterns, indicating lateral feature sizes and periods with which pattern features repeat in lateral dimensions x and y. FIGS. 10a and 10c-10e are side views of proximal patterned encapsulant region 117. FIG. 10b is a view of proximal patterned encapsulant region 117 from a vantage point above the distal surface of region 117.

DETAILED DESCRIPTION

TABLE-US-00001 TABLE 1 Index to components identified numerically in the Drawings. Numerical Identifier Description 100 light emitting diode (LED) 101 submount 102 bonding layer 103 reflective layer 104 support 105 p-doped layer 106 light generating layer 107 n-doped layer 108 n-side contact pad 109 encapsulant layer 110 unpatterned encapsulant region 111-1 first recess wall 111-2 second recess wall 112-1 first recess 112-2 second recess 113 proximal patterned encapsulant surface 114 luminous stack surface 115 multi-layer stack 116 p-side contact layer 117 proximal patterned encapsulant region 118 inter-recess volume element 119-1 first recess opening 119-2 second recess opening 120 encapsulant block 121 encapsulant block unpatterned proximal surface 122 patterned mold 123 mold patterned surface 124 mold protrusions 125 first recess filler layer 126 first recess filler surface excess 127 cover slip 128 proximal patterned encapsulant region thickness 129-1 first recess depth 129-2 second recess depth 130-1 maximum first recess depth 130-2 maximum second recess depth 131 auxiliary light transmitting layer 132 x-dimension feature size 133 x-dimension period 134 y-dimension feature size 135 y-dimension period

FIG. 1 side views 1a-1b represent side views of an example of a light emitting device 100 in the form of a packaged die. FIG. 1a represents a full packaged die. FIG. 1b represents a portion of that packaged die, emphasizing the disposition of encapsulant layer 109. Light emitting device 100 includes a multi-layer stack 115. Multi-layer stack 115 includes: p-doped layer 105, light generating layer 106, and n-doped layer 107. P-doped layer 105 of multi-layer stack 115 is disposed upon reflective layer 103 which, in turn is disposed upon bonding layer 102 which, in turn, is disposed upon submount 101. N-side contact pad 108 provides electrical contact to n-doped layer 107. P-side contact pad 116 provides electrical contact to p-doped layer 105. Encapsulant layer 109, including unpatterned encapsulant region 110 is disposed upon multi-layer stack 115 at luminous stack surface 114 which is, in this case, an exterior surface of n-doped layer surface. Encapsulant layer 109 further extends to p-side contact pad 116 at reflective layer 103. Proximal patterned encapsulant region 117, including its patterned encapsulant surface 113, is patterned by first recesses 112-1 which are bounded by first recess walls 111-1. Here, light emitting device 100 further includes support 104.

FIG. 2 side views 2a-2f each represent a portion of an light emitting device 100 including n-doped layer 107, luminous stack surface 114 (which is, in this case, an exterior surface of n-doped layer surface), proximal patterned encapsulant surface 113, first recesses 112-1, first recess walls 111-1, unpatterned encapsulant region 110 and encapsulant layer 109. Views 2a, 2b, 2c, 2e, and 2f include cross-sectional views of periodic arrays of first recesses 112-1 having, respectively, cone, right cylindrical, right cylindrical with curved base, truncated cone, and hemispherical shapes. View 2d represents a random arrangement of randomly shaped first recesses 112-1.

FIG. 3 views 3a-3d each represent a proximal patterned encapsulant surface 113 of encapsulant layer 109, having first recess openings 119-1 included in proximal patterned encapsulant surface 113. FIG. 3a represents a square array of circular first recess openings 119-1. The shape of an individual first recess 112-1 having a first recess opening of FIG. 3a is depicted in FIGS. 4a and 4b. FIG. 3b represents a random distribution of randomly shaped first recess openings 119-1. FIG. 3c represents a diagonal array of circular first recess openings 119-1. The shape of an individual first recess having a first recess opening of FIG. 3c is depicted in FIGS. 4a and 4b. FIG. 3d represents a diagonal array of first recess openings 119-1 having a circular shell shape. The shape of an individual first recess having a first recess opening 119-1 of FIG. 3d is depicted in FIGS. 4c and 4d.

FIGS. 4a, 4c, 4e, and 4g are side views of individual first recesses 112-1 viewed from the same side view perspective as FIGS. 1 and 2. FIGS. 4b, 4d, 4f, and 4h are views of the proximal patterned encapsulant surface 113 of proximal patterned encapsulant region 117 which includes first recess openings 119-1. FIG. 4a represents a right cylindrical first recess 112-1, and FIG. 4b represents the first recess opening 119-1 of that regular cylindrical first recess 112-1. FIG. 4c represents a right cylindrical shell first recess 112-1, wherein that recess is bounded both outside and inside by inter-recess volume element 118, and FIG. 4d represents a first recess opening 119-1 of that right cylindrical shell. FIG. 4e represents a right parallelepiped first recess 112-1, and FIG. 4f represents the rectangular first recess opening 119-1 of that right parallelepiped first recess 112-1. FIG. 4g represents a first recess 112-1 which is a right parallelepiped shell, wherein that first recess is bounded both outside and inside by inter-recess volume element 118, and FIG. 4h represents a first recess opening 119-1 of that right parallelepiped shell 112-1.

FIGS. 5a-5e each represent a proximal patterned encapsulant surface 113, including first recess openings 119-1 and inter-recess volume element 118. All of these are viewed from the same perspective as FIGS. 3a-3d, i.e., facing luminous stack surface 114 (see FIGS. 1 and 2).

FIGS. 6a-6d each represent a side view of an encapsulant block and of a patterned mold which forms first recesses 112-1 during formation what will become proximal patterned encapsulant region 117. FIG. 6a (top) represents encapsulant block 120 having encapsulant block unpatterned proximal surface 121; and FIG. 6a (bottom) represents patterned mold 122 having mold patterned surface 123 having mold protrusions 124. FIG. 6b represents penetration of mold protrusions 124 into encapsulant block 120, converting the FIG. 6a encapsulant block unpatterned proximal surface 121 into what will become proximal patterned encapsulant region 117, and forming first recess walls 111-1. FIG. 6c represents partial withdrawal of mold protrusions 124 from newly formed first recesses 112-1 having first recess walls 111-1. FIG. 6d represents fully withdrawn patterned mold 122 and encapsulant block 120 including what will become proximal patterned encapsulant region 117.

FIGS. 7a-7e each represent a side view during transformation of encapsulant block 120, coated with first recess filler layer 125, into proximal patterned encapsulant layer 109 having proximal patterned encapsulant region 117, itself having proximal patterned encapsulant surface 113, first recess walls 111-1, and first recesses 112-1 filled, partially or completely, with first recess filler derived from first recess filler layer 125. FIGS. 7a-7c further include a side view of patterned mold 122 which forms relief patterns during formation of the proximal patterned encapsulant region 117 of the proximal patterned encapsulation layer 109 prior to incorporation of layer 109 into a light emitting device. FIG. 7a (top) represents encapsulant block 120, coated with first recess filler layer 125. FIG. 7a (bottom) represents patterned mold 122 having mold surface 123 having mold protrusions 124. FIG. 7b represents formation of relief patterned first recess filler layer 125 by action of patterned mold 122 upon first recess filler layer 125 which, in turn, penetrates encapsulant block 120 to form a relief pattern in the encapsulant material of encapsulant block 120. FIG. 7c (top) represents encapsulant block 120 having patterned first recess filler layer 125. First recess filler penetrates encapsulant block 120 while patterning the surface of that block and creating inter-recess volume elements 118 containing encapsulant material (see FIGS. 7d and 7e) and extends leaving first recess filler surface excess 126. FIG. 7c (bottom) represents withdrawn patterned mold 122. FIG. 7d represents encapsulant layer 109 having proximal patterned encapsulant region 117, first recesses 112-1 and second recesses 112-2. First recess filler surface excess is no longer an excess, but has become first recess filler for an extended first recess 112-1. Second recesses 112-2 are filled with a second recess filler to form proximal patterned encapsulant surface 113. FIG. 7e represents encapsulant layer 109, including unpatterned encapsulant region 110 and proximal patterned encapsulant region 117, having first recesses 112-1, and second recesses 112-2. First recesses 112-1 are filled with first recess filler derived from first recess filler layer 125, and excess first recess filler material has been removed by planarization to form proximal patterned encapsulant surface 113. When the term "proximal" is used FIG. 7, or any other figures, and an encapsulant layer 109 is not associated with a multi-layer stack 115, the use of "proximal" indicates a region or surface of that encapsulant layer 109 suitable for being disposed upon a luminous stack surface 114.

FIG. 8 views 8a-8d each represent a side view of proximal patterned encapsulant region 117. FIG. 8a represents proximal patterned encapsulant region 117, having patterned region thickness 128 disposed upon luminous stack surface 114 of n-doped layer 107, and including first recesses 112-1 having more than one size. A first recess depth 129-1 is depicted for a first recess 112-1, as is the maximum first recess depth 130-1 for that first recess 112-1. FIGS. 8b and 8c represent a first recess 112-1 having first recess openings 119-1 and second recesses 112-2 having second recess openings 119-2. FIG. 8c indicates second recesses 112-2, included in proximal patterned encapsulant region 117, having second recess walls 111-2 and second recess openings 119-2 coincident with proximal patterned encapsulant surface 113. In FIGS. 8b and 8c, second recesses 112-2 have the same shape and size. In FIG. 8d second recesses 112-2 differ in shape and size. For a given second recess 112-2, the second recess depth 129-2 associated with a given point on second recess wall 111-2 may be equal to or less than the maximum second recess depth 130-2 for that second recess 112-2 (see FIG. 8d). The maximum second recess depth 130-2 is indicated for each of FIG. 8d second recesses 112-2.

FIG. 9 represents a side view of multi-layer stack 115 as in FIG. 1b, except that multi-layer stack 115 further includes optional auxiliary light transmitting layer 131 and cover slip 127. P-doped layer 105 is disposed upon auxiliary light transmitting layer 131, which is disposed upon reflective layer 103. Encapsulant layers 109, having proximal patterned encapsulant regions 117, are disposed upon luminous stack surfaces 114 of auxiliary light transmitting layer 131 along with being disposed upon luminous stack surface 114 of n-doped layer 107.

FIG. 10 views 10a-10e represent recess patterns, indicating lateral feature sizes and periods. FIGS. 10a and 10c-10e are side views of proximal patterned encapsulant region 117. FIG. 10b is a view of proximal patterned encapsulant region 117 from a vantage point above the distal surface of proximal patterned encapsulant region 117. FIGS. 10a and 10b represent the same proximal patterned encapsulant region 117 having the same pattern of first recesses 112-1. In FIG. 10a, x-dimension feature size 132 and x-dimension period 133 are indicated for a pattern of first recesses 111-1. FIG. 10b further indicates y-dimension feature size 134 and y-dimension period 135 for the recess pattern of first recesses 112-1. FIG. 10c represents a first recess 112-1 which is a single recess having no patterning at the distal surface of proximal patterned encapsulant region 117, but having a proximal recess pattern having first recess openings 119-1 at proximal patterned encapsulant surface 113. Second recesses 112-2 form a complementary pattern. X-dimension feature size 132 and x-dimension period 133 are indicated for each pattern. The proximal patterned encapsulant region of FIG. 10d is identical to that of 10c, except that first recess 112-1 is further patterned at the distal surface of proximal patterned excapsulant region 117. In this case, inter-recess volume elements 118 are present, forming a complementary pattern. Each of the two patterns of first recess 112-1 has an x-dimension feature size 132 and an x-dimension period 133. FIG. 10e is identical to FIG. 10d, except that x-dimension feature size 132 and an x-dimension period 133 are indicated for the pattern of second recesses 112-2.

The figures of the drawings are intended to illustrate embodiments of the present invention and to visually provide further clarification of numbered portions of the light emitting device which are defined in the text. These figures are not, in any way, intended to limit the scope of the present invention. One of skill in the art will recognized that there are other specific embodiments of the present invention which differ in detail from those embodiments encompassed by the figures.

The terminology of this specification includes words specifically mentioned herein, derivatives thereof, and words of similar import.

Used herein, the following terms have these definitions:

The words "a" and "an" as used in the specification mean "at least one."

"Range". Disclosures of ranges herein take the form of lower and upper limits. There may be one or more lower limits and, independently, one or more upper limits. A given range is defined by selecting one lower limit and one upper limit. The selected lower and upper limits then define the boundaries of that particular range. All ranges that can be defined in this way are inclusive and combinable, meaning that any lower limit may be combined with any upper limit to delineate a range.

A "submount" 101 is a support substrate upon which a multi-layer stack may be affixed directly, or affixed indirectly through intervening layers.

A "multi-layer stack" 115 is a stack of layers, including p-doped layer 105, light generating layer 106, and n-doped layer 107, within which light is generated. Multi-layer stack 115 may be inorganic, small molecule organic, or polymer/small molecule organic. Herein, the terms "multi-layer stack" and "stack" are used interchangeably. A multi-layer stack 115 may, optionally, include additional layers such as, for example, auxiliary light transmitting layer 131.

A "p-doped layer" 105 includes a p-doped material. The p-doped material may be an organic material, an inorganic material, or an organic-inorganic hybrid material.

An "n-doped layer" 107 includes an n-doped material.

A "p-side contact pad" 116 includes an electrically conducting material, and provides electrical contact to p-doped layer 105.

An "n-side contact pad" 108 includes an electrically conducting material, and provides electrical contact to n-doped layer 107.

A "light generating layer" 106 includes a light generating material, and is disposed between p-doped layer 105 and n-doped layer 107. The light generating layer generates light in response to a voltage difference and current flow between the p-doped layer and the n-doped layer.

A "reflective layer" 103 includes a reflective material that is capable of reflecting at least 50% of light generated by the light generating layer that impinges upon that reflective layer. When a reflective layer is disposed upon a luminous stack surface, the effect is to redirect light generated in multi-layer stack 115, and impinging upon that surface, to another luminous surface 114, one that has been designated for light output.

A "bonding layer" 102 includes a bonding material suitable for bonding adjacent layers (e.g., reflective layer 103 and submount 101) external to multi-layer stack 115. A bonding layer is typically an adhesive material. Where optical clarity is desired, a bonding material having transparency to light over the desired wavelength range is used. An example of an adhesive having transparency to visible light is Optical Adhesive Norland 74.

An "exterior stack surface" of multi-layer stack 115 is a surface that is part of that stack, and beyond which that stack does not extend.

A "luminous stack surface" 114 is an exterior stack surface of multi-layer stack 115 upon which light generated within multi-layer stack 115 impinges. In FIGS. 1 and 2, a surface of n-doped layer 107 is an exterior n-doped layer surface. Therefore, in FIGS. 1 and 2, the exterior n-doped layer surface is a luminous stack surface 114. One skilled in the art will recognize that, although it will often be the case that an exterior n-doped layer surface will be a luminous stack surface 114 of a given light emitting device, a surface of another layer, of multi-layer stack 115, may also have an exterior stack surface which is a luminous stack surface 114. For example, if a surface of p-doped layer 105 is also exterior to multi-layer stack 115 (see FIG. 1), that exterior surface may also be a luminous stack surface 114. It will also be recognized that other configurations of layers within a multi-layer stack are possible. Multi-layer stack 115 may further include an optional "auxiliary light transmitting layer" 131 (see FIG. 9), having an "exterior auxiliary transmitting surface" which is a luminous stack surface 114. A multi-layer stack may have one luminous stack surface 114 or plural luminous stack surfaces 114.

A "distal surface" of an encapsulant layer 109 is a surface of that layer which is most distant from the luminous stack surface 114 upon which that encapsulant layer 109 is disposed. Luminous stack surface 114 is chosen as a convenient spatial reference for indicating the relative positioning of surfaces of encapsulant layer 109. An example of a distal surface of encapsulant layer 109 is the topmost surface of encapsulant layer 109, as depicted in FIG. 1a.

A "proximal surface" of an encapsulant layer 109 is the surface of that layer which is closest to the luminous stack surface 114 upon which that encapsulant layer 109 is disposed. For example (see FIG. 1), the surface of n-doped layer 107 which is an exterior surface of multi-layer stack 115 is a luminous stack surface 114. Patterned surface 113 is disposed upon luminous stack surface 114, and is the surface of encapsulant layer 109 closest to luminous stack surface 114. Therefore, patterned surface 113 is "proximal patterned encapsulant surface 113". The opposing surface of encapsulant layer 109, (i.e., the surface of encapsulant layer 109 which is topmost in FIG. 1a) is then "distal" to luminous stack surface 114, and is the distal surface of the encapsulant layer 109 of FIG. 1a. As indicated in the illustrative example of FIG. 1a, a portion of encapsulant layer 109 extends to p-side contact pad 116 and reflective layer 103 and, as such, includes an additional proximal encapsulant surface at the interface with reflective layer 103.

One skilled in the art will recognize that the light emitting devices of the present invention may vary in detail from the light emitting devices of illustrative FIG. 1a. FIG. 1a includes an extension of encapsulant layer 109 to regions of the device including the a side edge of multi-layer stack 115. Although that side edge may be considered to also be a luminous stack surface 114 of multi-layer stack 115, in the case shown the proximal encapsulant surface along that side edge is not patterned. One skilled in the art will further know that design decisions regarding patterning of proximal encapsulant surfaces will depend upon many considerations, including, for example, the tradeoff between additional amount of light that will be captured from a given luminous stack surface as a result of such patterning and the cost and degree of difficulty of disposing a proximal patterned encapsulant region 117, with its proximal patterned encapsulant surface 113, upon that luminous stack surface 114.

A "proximal patterned encapsulant region" 117 is a region of encapsulant layer 109 extending from "proximal patterned encapsulant surface" 113 into encapsulant layer 109 to a plane, parallel to proximal patterned encapsulant surface 113, which is the plane farthest from proximal patterned encapsulant surface 113 that still passes through a recess 112. In the same way that the distal surface of encapsulant layer 109 is defined supra, that plane is the "distal surface" of proximal patterned encapsulant region 117, and the distance, along a straight line normal to proximal patterned encapsulant surface 113, between proximal and distal patterned encapsulant surfaces of a given proximal patterned encapsulant region 117 is the "proximal patterned encapsulant region thickness" 128. Proximal patterned encapsulant region 117 has a dielectric function that varies spatially according to a pattern. All, a portion of, or none of proximal patterned encapsulant region 117 is in optical proximity to luminous stack surface 114. If proximal patterned encapsulant region 117 is directly bonded to luminous stack surface 114, typically all, or a portion of that proximal patterned encapsulant region 117 will be in optical contact with luminous stack surface 114. Proximal patterned encapsulant region 117 will typically not be in optical contact with luminous stack surface 114 if there is an intervening high refractive index layer. An "intervening high refractive index layer" (not shown in the figures) disposed between luminous stack surface 114 and proximal patterned encapsulant region 117 has a refractive index, for the wavelength of light to be extracted, that is: no lower than 0.5; 0.1; or 0.01 below; and preferably equal to or greater than the refractive index, for the wavelength of light to be extracted, of luminous stack surface 114. In one embodiment an intervening high RI layer is formed when an LED having a luminous stack surface 114 further has a high RI top layer disposed upon it prior to affixing the light extraction encapsulation sheet.

A "recess set" is the set of "recesses" 112, typically formed during a step of applying a filler layer 125 (see FIG. 7), a patterning step (see FIGS. 6 and 7), or a combination of steps of applying a filler layer and patterning. A recess set may contain a single recess or plural recesses. Plural recesses of a given recess set are related to each other such that they form a pattern which may be random or periodic, or a combination of random and periodic. When a recess set contains a single recess, that recess is typically a continuous layer having one or more patterned recess walls 111. In some cases, however recess 112 of a recess set containing a single recess 112 may be unpatterned (i.e., a layer that is smooth on both of its main surfaces).

"Topography" refers to the state of roughness of a surface. For example a surface may be smooth, or may have a multi-level pattern.

An "inter-recess volume element" 118 is a volume element of proximal patterned encapsulant region 117 that is derived from encapsulant block 120. Inter-recess volume element 118 includes "inter-recess filler". "Inter-recess filler" includes "encapsulant material". During formation of recesses 112 by patterning, a smooth surface of an encapsulant block may remain smooth (i.e., may not be deformed), in which case there will be no inter-recess volume element 118. Alternatively, the surface of encapsulant block 120 may be deformed, in which case a portion of the encapsulant material becomes part of proximal patterned encapsulant region 117. The volume occupied by that encapsulant material is the inter-recess volume element 118.

To illustrate that a given proximal patterned encapsulant region may contain one recess set or plural recess sets, a "first recess set" and a "second recess set" are indicated in the figures. The two illustrative sets are differentiated using numerical identifiers (see Table 1). Numerical identifiers relating to a recess or recesses 112 contained in the first recess set include the hyphenated numerical suffix "-1" (see FIGS. 1-9), while those relating to a recess or recesses 112 contained in the second recess set include suffix "-2" (see FIGS. 7 and 8). The designations of first recess and second recess are made for illustrative purposes. Therefore, it is understood that a given proximal patterned encapsulant region may include a single recess set, two recess sets, three recess sets, or more than three recess sets, with no particular limit on the number of such recess sets.

A "recess wall" 111 is a surface of recess 112 which forms a boundary of recess 112 within proximal patterned encapsulant region 117. When a recess 112 does not extend to proximal patterned encapsulant surface 113, its recess wall is a continuous boundary surrounding that recess. When a recess 112 extends to proximal patterned encapsulant surface 113 to form a recess opening 119 coincident with that surface, its recess wall is contiguous with that recess opening. "First recess walls" 111-1 (see FIGS. 1, 2, and 6-9) and "second recess walls" 111-2 (see FIG. 8) illustrate recess walls, respectively, for a first set of recesses 112-1 and a second set of recesses 112-2. It will further be recognized that there may be an "intervening high refractive index layer" ("intervening high RI layer") disposed between proximal patterned encapsulant region 117 and luminous stack surface 114.

A "recess opening" 119 is a surface of recess 112 that is coincident with proximal patterned encapsulant surface 113. As such, for a given recess, the recess opening of that recess is the boundary of that recess at proximal patterned encapsulant surface 113. "First recess openings" 119-1 (see FIGS. 3, 4, 5, and 8) and "second recess openings" 119-2 (see FIG. 8) illustrate recess openings, respectively, for a first set of recesses and a second set of recesses.

A "recess depth" 129 for a given recess 112 is a distance within that recess between first and last encounter with recess wall 111-1, along a straight line, normal to and extending from proximal patterned encapsulant surface 113. The "maximum recess depth" 130 for a given recess 112 is its largest recess depth.

A "lateral dimension" is a dimension running parallel to the plane of proximal patterned encapsulant surface 113. In FIG. 10, x-dimension and y-dimension are lateral dimensions that are perpendicular to one another.

A "pattern feature size" is the size of a recess, measured in a lateral dimension, when plural recesses form a pattern (see FIGS. 10a, 10b and 10e, x-dimension feature size 132). Alternatively, a "pattern feature size" is the size of a feature of a pattern on a single recess, measured in a lateral dimension (see FIGS. 10c and 10d, x-dimension feature size 132).

A "pattern period" is the period of repetition of a pattern of recesses, measured in a lateral dimension, when plural recesses form a pattern (see FIGS. 10a, 10b and 11e, x-dimension period 133). Alternatively, a "pattern period" is the period of repetition of a pattern on a single recess, measured in a lateral dimension (see FIGS. 10c and 10d, x-dimension feature size 132).

A "recess filler" is a material included in a recess 112. Recess 112 may be completely filled with a single recess filler, or may be partially filled with each of two or more recess fillers.

A "cover slip" 127 is a layer of transparent material having a surface disposed upon a distal surface of encapsulant layer 109 and a surface typically in contact with air, or other environment external to light emitting device 100. One skilled in the art will recognize that the presence of cover slip 127 in a light emitting device is optional.

An "exterior stack surface" of multi-layer stack 115 is a surface which is part of that stack, and beyond which that stack does not extend. Luminous stack surface 114 is an example of an exterior stack surface.

A "light extraction encapsulation sheet" is a free standing sheet identical to an encapsulant layer having a proximal patterned encapsulant region. By "sheet" is meant any film of thickness appropriate to encapsulate a light emitting device. There are no particular limits to the lateral (in-plane) dimensions of a sheet. Typically, the thickness of a sheet will be: at least 1 micron, at lest 10 microns, or at least 100 microns; and no more than 10,000 microns, or no more than 1,000 microns, Although the light extraction encapsulation sheet is suitable for being affixed to a luminous stack surface of a multi-layer stack, it has not yet been affixed to that multi-layer stack. The term "proximal patterned encapsulant region" is used in reference to the patterned region of the light extraction encapsulation sheet to indicate that it is that region which may later be affixed to a luminous stack surface of a multi-layer stack.

An "auxiliary light transmitting layer" 131 is an optional layer of multi-layer stack 115 that is non-absorbing, or substantially non-absorbing, with respect to wavelengths of light generated within multi-layer stack 115 which are desired to be included in the light emitted by light emitting device 100. An "exterior auxiliary transmitting surface" of auxiliary light transmitting layer 131 is a surface of that layer which is a luminous stack surface 114. The light emitting device represented in FIG. 9 has multi-layer stack 115 which includes an auxiliary light transmitting layer 131 which has more than one exterior auxiliary transmitting surface. In FIG. 9, two of those exterior auxiliary transmitting surfaces are luminous multi-stack surfaces 114, each having a proximal patterned encapsulant region 117 disposed upon it. A third exterior auxiliary transmitting surface is also a luminous stack surface 114, however, that surface has reflective surface 103 disposed upon it. Therefore, a luminous stack surface 114 may or may not have a proximal patterned encapsulant region 117 disposed upon it. It is further noted that, although two of the exterior auxiliary transmitting surfaces depicted in FIG. 9 as encapsulated appear to be two different surfaces, those apparently different surfaces could be separate, or could be part of the same surface, as might be the case for a circular light emitting device.

A "phosphor layer" which includes a phosphor, may be used to change the frequency of light generated in light generating layer 106. An example of "phosphor host" is YAG (yttrium aluminum garnet, Y.sub.3Al.sub.5O.sub.12). Typical phosphor emitters are, for example, cerium (Ce), neodymium (Nd), and erbium (Er). YAG:Ce is excited by blue light with a wavelength of 460 nm and radiates yellow excited light with a wavelength of 520 to 550 nm The yellow excited light is mixed with blue light, thereby generating white light. A phosphor layer is positioned so that light emitted by luminous stack surface 114 encounters that phosphor layer before exiting the light emitting device. Phosphor layers typically contain particles on size on the order of a micron or more, and tend to be rough. If a micron scale phosphor layer is utilized to change the frequency of light exiting luminous stack 114 of the present invention, that micron scale phosphor layer will be positioned at a distance from luminous stack surface 114 that is greater than the distance to the distal surface of proximal patterned encapsulant region 117. Phosphors typically include mixtures of rare earth elements, the compositions and ratios of which are adjusted based upon the wavelength of light generated in light generating layer 106 and upon the desired output wavelength. A non-exhaustive list of phosphors includes: YAG:Ce; nitride silicates:Eu; Sr-Aluminate:Eu; thiogallates; ZnS:Cu, YBO.sub.3; and LaBO.sub.3. A non-exhaustive list of specific phosphors, and their output wavelengths, includes: (Y,Gd).sub.3(Al,Ga).sub.5O.sub.12:Ce; SrB.sub.4O.sub.7:Eu (368 nm); Sr.sub.2P.sub.2O.sub.7:Eu (420 nm); BaMgAl.sub.10O.sub.17:Eu (453 nm); Sr.sub.4Al.sub.14O.sub.25:Eu (490 nm); Ba.sub.2SiO.sub.4:Eu (505 nm); SrGa.sub.2S.sub.4:Eu (535 nm); Sr.sub.2SiO.sub.4:Eu (575 nm); SrS:Eu (615 nm) and combinations thereof.

Alternatively, a recess may include a recess filler which includes plural nanophosphors. In such case, the nanophosphors are located within proximal patterned encapsulant region 177. Nanophosphors are phosphor particles having a mean particle diameter of: at least 1 nm; at least 2 nm, or at least 5 nm; and no more than 50 nm, no more than 30 nm, no more than 20 nm, no more than 10 nm.

"Planarization" refers to any method that causes a smooth surface to be formed within or upon a proximal patterned encapsulant surface. Spin coating and sputtering techniques are useful methods to achieve planarization. Planarization can also be achieved by filling in recesses in a surface with a fluid recess filler and then removing excess with, for example, a doctor blade, typically followed by a curing process. Planarization can also be achieved with abrasive pads.

It will be recognized by one of skill in the art that multi-layer stack 115 is well known. It will further be recognized that use and placement of: reflective layer 103 to redirect light; submount 101 to provide positional and dimensional stability; bonding layer 102 to affix adjacent layers to one another; and cover slip 127 will vary from device to device, and that any of these are optional based upon design requirements of a given light emitting device 100. Further, additional layers may be included within multi-layer stack 115. These additional layers may include, but are not limited to: metallic electrodes, transparent electrodes such as those made from indium tin oxide ("ITO"), and phosphor layers.

It will be further recognized by one of skill in the art that light emitting device 100 is illustrative of light emitting devices of the present invention, and that such devices may vary substantially in the details of design.

Proximal patterned encapsulant surface 113 of encapsulant layer 109 is indented with a first recess or first recesses 112-1 arranged in a pattern. The pattern can be a periodic pattern, a random pattern, or a combination of periodic and random pattern. When a pattern is periodic, the pattern may be periodic: in a first dimension along proximal patterned encapsulant surface 113; in a second dimension, perpendicular to the first dimension, along proximal patterned encapsulant surface 113; in a third dimension normal to proximal patterned encapsulant surface 113; or any combination. That is, a pattern may be periodic in one, two, or three dimensions. First recess 112-1 can have a regular shape or an irregular shape. When proximal patterned encapsulant region 117 includes plural first recesses 112-1, all of those first recesses may be identical in size and shape, or individual first recesses may vary in size, shape, or both. When first recess shapes are selected from two or more regular shapes and the pattern is a periodic pattern, first recesses having a particular regular shape can be distributed in a periodic "subpattern" which may or may not have a periodic relationship to first recesses having different shapes. Alternatively, when first recess shapes are selected from two or more regular shapes, and the pattern is a periodic pattern, first recesses having a particular regular shape can be distributed in a random "subpattern". The first recess shape of a first recess of the present invention can also be irregular and recurring according to periodic or random pattern. When first recess shapes are selected from two or more irregular shapes, the pattern formed by those first recesses is a periodic pattern, first recesses having a particular irregular shape can be distributed in a periodic or random subpatt