Light-Emitting Diode Chip With High Light Extraction And Method For Manufacturing The Same
This invention provides a light-emitting diode chip with high light extraction, which includes a substrate, an epitaxial-layer structure for generating light by electric-optical effect, a transparent reflective layer sandwiched between the substrate and the epitaxial-layer structure, and a pair of electrodes for providing power supply to the epitaxial-layer structure. A bottom surface and top surface of the epitaxial-layer structure are roughened to have a roughness not less than 100 nm root mean square (rms). The light generated by the epitaxial-layer structure is hence effectively extracted out. A transparent reflective layer not more than 5 μm rms is formed as an interface between the substrate and the epitaxial-layer structure. The light toward the substrate is more effectively reflected upward. The light extraction and brightness are thus enhanced. Methods for manufacturing the light-emitting diode chip of the present invention are also provided.
1 . A light-emitting diode chip, comprising:
a substrate;
a transparent refractive layer formed on said substrate, said transparent refractive layer having a refractive index greater than that of the air;
an epitaxial-layer structure with a bottom surface connecting to said transparent refractive layer and a top surface opposite to the bottom surface, said epitaxial-layer structure generating light and having a refractive index greater than that of said transparent refractive layer, and both of the bottom surface and top surface having a roughness not less than 100 nm root mean square (rms); and
an electrode unit having a pair of electrodes separately disposed on said epitaxial-layer structure to form ohmic contact and supply electric energy to said epitaxial-layer structure.
2 . The light-emitting diode chip as claimed in claim 1 , wherein said transparent refractive layer has a thickness not more than 5 μm rms and the refractive index between 1 and 2.
3 . The light-emitting diode chip as claimed in claim 1 , wherein said transparent refractive layer is formed of polymer or dielectric material having thermal conductivity up to 0.2 W/m.K or more.
4 . The light-emitting diode chip as claimed in claim 2 , wherein said transparent refractive layer is formed of polymer or dielectric material having thermal conductivity up to 0.2 W/m.K or more.
5 . The light-emitting diode chip as claimed in claim 1 , further comprising a reflective mirror layer having a reflective efficiency not less than 50% and formed between said substrate and said transparent refractive layer.
6 . The light-emitting diode chip as claimed in claim 1 , wherein said substrate is formed of silicon, ceramic or metallic material.
7 . The light-emitting diode chip as claimed in claim 5 , wherein said reflective mirror layer has a material selected from a group consisting of Al, Ag, Au, Pt, Pd, Rb and a combination thereof.
8 . The light-emitting diode chip as claimed in claim 5 , wherein said reflective mirror layer is formed of high-refractive index dielectric layers and low-refractive-index dielectric layers alternately disposed to each other.
9 . The light-emitting diode chip as claimed in claim 1 , wherein said epitaxial-layer structure is formed of GaN-based material and comprises an N-type first cladding layer having the bottom surface, a P-type second cladding layer having the top surface and an active layer sandwiched between said first cladding layer and said second cladding layer.
10 . The light-emitting diode chip as claimed in claim 1 , further comprising a transparent electrical conductive layer formed on the top surface of said epitaxial-layer structure.
11 . The light-emitting diode chip as claimed in claim 10 , wherein said transparent electrical conductive layer has a roughed top surface.
12 . The light-emitting diode chip as claimed in claim 1 , wherein said substrate surrounds said transparent refractive layer.
13 . A method for manufacturing a light-emitting diode chip with high light extraction efficiency, comprising:
forming an epitaxial-layer structure for generating light by electro-optical effect on a substrate, said epitaxial-layer structure having a first cladding layer of first conductivity type, a second cladding layer of second conductivity type and an active layer sandwiched between said first cladding layer and said second cladding layer;
performing a first roughening step for making a top surface of said second cladding layer have roughness not less than 100 nm rms;
forming a pair of electrodes respectively in ohmic contact with said first cladding layer and said second cladding layer;
forming a provisional substrate separately on said second cladding layer and removing said substrate under said epitaxial-layer structure to expose a bottom surface of said first cladding layer;
performing a second roughening step for making the bottom surface of said first cladding layer having a roughness not less than 100 nm rms;
forming a substrate under the bottom surface of said first cladding layer; and
removing said provisional substrate.
14 . The method for manufacturing a light-emitting diode chip as claimed in claim 13 , further comprising forming a transparent electrical conductive layer on a top surface of said second cladding layer.
15 . The method for manufacturing a light-emitting diode chip as claimed in claim 14 , wherein the step for forming said transparent electrical conductive layer further comprises roughening the top surface of said transparent electrical conductive layer.
16 . The method for manufacturing a light-emitting diode chip as claimed in claim 13 , wherein said first roughening step and said second roughening step are performed by epitaxial growth, wet etching, inductively-coupled plasma etching or photo-assisted chemical etching.
17 . The method for manufacturing a light-emitting diode chip as claimed in claim 13 , wherein said provisional substrate is attached on said second cladding layer with wax or removable glue.
18 . The method for manufacturing a light-emitting diode chip as claimed in claim 13 , wherein said substrate is removed by chemical etching, laser lift-off or smart cut.
19 . The method for manufacturing a light-emitting diode chip as claimed in claim 13 , wherein the step for forming a substrate under the bottom surface of said first cladding layer comprises attaching said substrate onto said first cladding layer with a glue having a refractive index greater than that of the air and less than that of the epitaxial-layer structure.
20 . The method for manufacturing a light-emitting diode chip as claimed in claim 19 , wherein the glue is transparent to the light emitted from said epitaxial-layer structure.
21 . The method for manufacturing a light-emitting diode chip as claimed in claim 19 , wherein the glue has a thickness not more than 5 μm rms.
22 . The method for manufacturing a light-emitting diode chip as claimed in claim 20 , wherein the glue has a thickness not more than 5 μm rms.
23 . The method for manufacturing a light-emitting diode chip as claimed in claim 13 , wherein said first conductivity type is N-type or P-type.
24 . A method for manufacturing a light-emitting diode chip with high light extraction efficiency, comprising:
forming an epitaxial-layer structure for generating light by electro-optical effect on a substrate, said epitaxial-layer structure having a first cladding layer of first conductivity, a second cladding layer of second conductivity and an active layer sandwiched between said first cladding layer and said second cladding layer;
performing a first roughening step for making a top surface of said second cladding layer have roughness not less than 100 nm rms;
forming a pair of electrodes respectively in ohmic contact with said first cladding layer and said second cladding layer;
forming a provisional substrate separately on said second cladding layer and removing said substrate under said epitaxial-layer structure to expose a bottom surface of said first cladding layer;
performing a second roughening step for making the bottom surface of said first cladding layer having a roughness not less than 100 nm rms;
forming a transparent refractive layer having a refractive index greater than that of the air and less than that of the epitaxial-layer structure connecting to said first cladding layer;
forming a substrate connecting to said transparent refractive layer; and
removing said provisional substrate.
25 . The method for manufacturing a light-emitting diode chip as claimed in claim 24 , further comprising forming a transparent electrical conductive layer on a top surface of said second cladding layer.
26 . The method for manufacturing a light-emitting diode chip with high light extraction as claimed in claim 25 , wherein the step for forming said transparent electrical conductive layer further comprises roughening the top surface of said transparent electrical conductive layer.
27 . The method for manufacturing a light-emitting diode chip as claimed in claim 24 , wherein said first roughening step and said second roughening step are performed by epitaxial growth, wet etching, inductively-coupled plasma etching or photo-assisted chemical etching.
28 . The method for manufacturing a light-emitting diode chip as claimed in claim 24 , wherein said provisional substrate is attached on said second cladding layer with wax or removable glue.
29 . The method for manufacturing a light-emitting diode chip as claimed in claim 24 , wherein said substrate is removed by chemical etching, laser lift-off or smart cut.
30 . The method for manufacturing a light-emitting diode chip with high light extraction as claimed in claim 24 , wherein the transparent refractive layer is formed by film deposition.
31 . The method for manufacturing a light-emitting diode chip as claimed in claim 24 , wherein the step for forming a substrate includes forming a seed layer with thin-film deposition process on the transparent refractive layer and then performing an electroplating process to form the substrate from the seed layer.
32 . The method for manufacturing a light-emitting diode chip as claimed in claim 24 , wherein the first conductivity type is N-type or P-type.
33 . The method for manufacturing a light-emitting diode chip as claimed in claim 24 , wherein the transparent refractive layer has a thickness not more than 5 μm rms.
34 . The method for manufacturing a light-emitting diode chip with high light extraction as claimed in claim 24 , wherein further comprising forming a reflective mirror layer on the transparent refractive layer prior to the step of forming the substrate.
35 . The method for manufacturing a light-emitting diode chip as claimed in claim 34 , wherein the reflective mirror layer includes electrical conductive material, electrical insulating material or a combination thereof.
36 . The method for manufacturing a light-emitting diode chip as claimed in claim 34 , wherein the reflective mirror layer is formed of high-refractive index dielectric layers and low-refractive-index dielectric layers alternately disposed to each other.