SEMICONDUCTOR LIGHT-EMITTING DEVICES HAVING CONCAVE MICROSTRUCTURES PROVIDING IMPROVED LIGHT EXTRACTION EFFICIENCY AND METHOD FOR PRODUCING SAME

• US 20110155999A1
• Filed: 12/08/2010
• Published: 06/30/2011
• Est. Priority Date: 12/08/2009
• Status: Active Grant

• Current Assignee: Lehigh University
• Original Assignee: Lehigh University
• Inventors: Gilchrist, James F., Ee, Yik-Khoon, Kumnorkaew, Pisist, Tansu, Nelson
• Granted Patent: US 8,586,963 B2
• Time in Patent Office: Days
• US Class Current: 257/13
• CPC Class Codes: H01L 2933/0058 relating to optical field-shaping elements
• CPC Class Codes: H01L 2933/0091 Scattering means in or on the semiconductor body or semiconductor body package H01L33/22 takes precedence
• CPC Class Codes: H01L 33/06 within the light emitting region, e.g. quantum confinement structure or tunnel barrier
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/58 Optical field-shaping elements

Abstract

A conventional semiconductor LED is modified to include a microlenslayer over its light-emitting surface. The LED may have an active layer including at least one quantum well layer of InGaN and GaN. The microlens layer includes a plurality of concave microstructures that cause light rays emanating from the LED to diffuse outwardly, leading to an increase in the light extraction efficiency of the LED. The concave microstructures may be arranged in a substantially uniform array, such as a close-packed hexagonal array. The microlens layer is preferably constructed of curable material, such as polydimethylsiloxane (PDMS), and is formed by soft-lithography imprinting by contacting fluid material of the microlens layer with a template bearing a monolayer of homogeneous microsphere crystals, to cause concave impressions, and then curing the material to fix the concave microstructures in the microlens layer and provide relatively uniform surface roughness.

Claims

1. A light emitting device comprising:

at least one n-type layer;

at least one p-type layer disposed adjacent said at least one n-type layer; and

a microlens layer disposed adjacent said at least one p-type layer, said microlens layer comprising a plurality of concave microstructures.

2. the light-emitting device of claim 1, wherein said plurality of concave microstructures are arranged in a substantially uniform array.

3. The light-emitting device of claim 1, wherein said plurality of concave microstructures are arranged in a plurality of comprises close-packed hexagonal array.

4. The light emitting device of claim 1, wherein each of said plurality of concave microstructures has a maximum diameter measuring approximately 1 micron in diameter.

5. The light emitting device of claim 1, wherein said microlens layer comprises polydimethylsiloxane (PDMS).

8. The light emitting device of claim 1, wherein the microlens layer is deposited on a top emission surface of an InGaN quantum well.

9. The light emitting device of claim 8, wherein InGaN quantum well comprises a quantum well active region comprising a GaN layer sandwiched between two InGaN layers.

6. The light emitting device of claim 6, wherein said microlens layer is formed by imprinting fluid PDMS with a template comprising a plurality of microsphere crystals, and curing the imprinted PDMS.

7. The light emitting device of claim 7, wherein said template comprises an array an array of SiO₂ microsphere crystals.

10. A light emitting device comprising:

a substrate;

a first contact layer disposed over said substrate, said first contact layer comprising a GaN-based material having a first conduction type;

an active layer disposed over said first contact layer, said active layer comprising at least one GaN-based material;

a second contact layer disposed over said active layer, said second contact layer comprising a GaN-based material having a second conduction type opposite to the first conduction type; and

a microlens layer disposed over said second contact layer, said microlens layer comprising a plurality of concave microstructures.

11. The light emitting device of claim 10, wherein said active region comprises multiple InGaN-GaN pairs of quantum well layers.

12. The light emitting device of claim 10, wherein each of said plurality of concave microstructures has a maximum diameter within a range of from about 0.05 micron up to about 4 microns.

13. The light emitting device of claim 10, wherein each of said plurality of concave microstructures has a maximum diameter within a range of from about 0.5 micron up to about 1 micron.

14. A method for improving light extraction efficiency of a light emitting device, the method comprising:

providing a light emitting device having a top emission surface;

depositing a layer of fluid curable material on the top emission surface;

imprinting the layer of fluid material by contacting the layer of fluid material with a template comprising a plurality of microspheres;

heat treating the imprinted layer of fluid material to provide a microlens layer of cured material comprising a plurality of concave microstructures; and

removing the template from contact with the microlens layer of cured material.

15. The method of claim 14, further comprising:

providing the template comprising the plurality of microspheres by;

providing a substrate; and

depositing a monolayer of close-packed SiO₂ microspheres onto the substrate.

16. The method of claim 14, wherein depositing a monolayer of close-packed SiO₂ microspheres onto the substrate comprises:

providing a colloidal suspension of SiO₂ microspheres;

providing a deposition blade above the substrate;

depositing the colloidal suspension on the substrate; and

sweeping the deposition blade over the substrate to distribute the SiO₂ over the substrate.

17. The method of claim 14, wherein depositing a layer of fluid curable material on the top emission surface comprises spin-coating fluid polydimethylsiloxane (PDMS) onto the light emitting device.

18. The method of claim 17, wherein heat treating the imprinted layer of fluid PDMS1 comprises heating the fluid PDMS to a temperature of at least 80 degrees Celsius for a period of at least 45 minutes.

19. An optoelectronic device comprising:

a multilayer semiconductor structure comprising a GaN layer and an active region, the active region comprising at least one quantum well layer of InGaN and GaN, wherein the electron quantum well layers and hole quantum well layer form a first quantum well stage, and wherein the active region comprises a plurality of quantum well stages adjacent to each other having the same structure as the first quantum well stage; and

a microlens layer disposed over the multilayer semiconductor, said microlens layer comprising a plurality of concave microstructures.

20. A method for making an optoelectronic device, the method comprising:

providing a multilayer semiconductor structure comprising a GaN layer and an active region, the active region comprising at least one quantum well layer of InGaN and GaN, wherein the electron quantum well layers and hole quantum well layer form a first quantum well stage, and wherein the active region comprises a plurality of quantum well stages adjacent to each other having the same structure as the first quantum well stage; and

providing a microlens layer comprising a plurality of concave microstructures over the multilayer semiconductor.

21. A method for generating optical emission from an optoelectronic device, the method comprising:

providing a GaN layer and an active region, the active region comprising at least one quantum well layer of InGaN and GaN, wherein the electron quantum well layers and hole quantum well layer form a first quantum well stage, and wherein the active region comprises a plurality of quantum well stages adjacent to each other having the same structure as the first quantum well stage;

providing a microlens layer comprising a plurality of concave microstructures over the active region; and

exciting the active region to produce optical emission through the microlens layer.