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

• US 7,521,727 B2
• Filed: 03/15/2007
• Issued: 04/21/2009
• Est. Priority Date: 04/26/2006
• Status: Active Grant

• Current Assignee: Rohm and Haas Company (Dow, Inc.)
• Original Assignee: Rohm and Haas Company (Dow, Inc.)
• Inventors: Mosley, David Wayne, Khanarian, Garo
• Primary Examiner(s): Doan; Theresa T
• Application Number:
  US11/724,399
• Publication Number:
  US 20070284601A1
• Time in Patent Office: 768 Days
• Field of Search: 257/98, 257/100, 257 79- 82, 257E33056-E33059, 257/E25.032
• US Class Current: 257/98
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/508 having a non-uniform spatial arrangement or non-uniform concentration, e.g. patterned wavelength conversion layer, wavelength conversion layer with a concentration gradient of the wavelength conversion material
• CPC Class Codes: H01L 33/52 Encapsulations

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.

Claims

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/cm³ and no more than 0.60 g/cm³.

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, TiO₂ 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/cm³ and no more than 7.0 g/cm³.

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.