LIGHT EMITTING DIODE AND METHOD FOR MANUFACTURING LIGHT EMITTING DIODES

• US 20140306176A1
• Filed: 11/18/2013
• Published: 10/16/2014
• Est. Priority Date: 04/15/2013
• Status: Active Grant

• Current Assignee: Advanced Optoelectronic Technology, Inc.
• Original Assignee: Advanced Optoelectronic Technology, Inc.
• Inventors: CHIU, CHING-HSUEH, LIN, YA-WEN, TU, PO-MIN, HUANG, SHIH-CHENG
• Granted Patent: US 9,029,831 B2
• Time in Patent Office: Days
• US Class Current: 257/13
• CPC Class Codes: H01L 33/007 comprising nitride compounds
• CPC Class Codes: H01L 33/06 within the light emitting region, e.g. quantum confinement structure or tunnel barrier
• CPC Class Codes: H01L 33/10 with a light reflecting structure, e.g. semiconductor Bragg reflector
• CPC Class Codes: H01L 33/60 Reflective elements

Abstract

An exemplary light emitting diode includes a substrate and a first undoped gallium nitride (GaN) layer formed on the substrate. The first undoped GaN layer defines a groove in an upper surface thereof. A distributed Bragg reflector is formed in the groove of the first undoped GaN layer. The distributed Bragg reflector includes a plurality of second undoped GaN layers and a plurality of air gaps alternately stacked one on the other. An n-type GaN layer, an active layer and a p-type GaN layer are formed on the distributed Bragg reflector and the first undoped GaN layer. A p-type electrode and an n-type electrode are electrically connected with the p-type GaN layer and the n-type GaN layer, respectively. A method for manufacturing plural such light emitting diodes is also provided.

Claims

1. A light emitting diode, comprising:

a substrate;

a first undoped gallium nitride (GaN) layer formed on the substrate, the first undoped GaN layer defining a groove in an upper surface thereof;

a distributed Bragg reflector formed in the groove of the first undoped GaN layer, the distributed Bragg reflector comprising a plurality of second undoped GaN layers and a plurality of air gaps alternately stacked one on the other;

an n-type GaN layer, an active layer and a p-type GaN layer formed in that sequence on the first undoped GaN layer and the distributed Bragg reflector; and

a p-type electrode and a n-type electrode, electrically connected with the p-type GaN layer and the n-type GaN layer, respectively.

2. The light emitting diode of claim 1, wherein a thickness D1 of each air gap follows the formula D1=λ

/(4n₁), a thickness D2 of each second undoped GaN layer follows the formula D2=λ

/(4n₂), λ

represents a wavelength of light emitted by the active layer, n₁ represents a refractive index of air, and n₂ represents a refractive index of the second undoped GaN layer.

3. The light emitting diode of claim 2, wherein the active layer emits a light with a peak wavelength of 365 nm, the thickness D1 of each air gap is about 91.2 nanometers (nm), and the thickness D2 of each second undoped GaN layer is about 36.7 nm.

4. The light emitting diode of claim 1, wherein the substrate is one of a sapphire substrate, a silicon (Si) substrate and a silicon carbide (SiC) substrate.

5. A method for manufacturing a plurality of light emitting diodes, the method comprising:

providing a substrate;

forming a first undoped gallium nitride (GaN) layer on the substrate, an upper surface of the first undoped GaN layer being divided into a plurality of first areas and a plurality of second areas;

etching the first areas of the upper surface of the first undoped GaN layer to form a plurality of grooves;

forming a semiconductor structure inside each of the grooves and on each of the second areas of the upper surface of the first undoped GaN layer, each semiconductor structure comprising a plurality of second undoped GaN layers and a plurality of aluminum nitride (AlN) layers alternately stacked one on the other, a topmost one of the second undoped GaN layers being located at a top side of the semiconductor structure, and a bottommost one of the AlN layers being located at a bottom side of the semiconductor structure;

etching away the AlN layers on the second areas thereby removing the AlN layers and the second undoped GaN layers from the second areas;

forming an n-type GaN layer, an active layer and a p-type GaN layer, in that sequence, on upper surfaces of the topmost second undoped GaN layers and the second areas of the upper surface of the first undoped GaN layer;

removing the AlN layers inside the grooves to form air gaps, the second undoped GaN layers and the air gaps in each groove cooperatively forming a distributed Bragg reflector; and

cutting the substrate to form a plurality of individual light emitting diodes.

6. The method of claim 5, further comprising, before etching away the AlN layers on the second areas, forming a silicon dioxide (SiO₂) protecting layer around the entire periphery of the first undoped GaN layer, wherein the SiO₂ protecting layer covers side surfaces of the first undoped GaN layer and end faces of the semiconductor structures in the grooves in order to prevent the AlN layers inside the grooves from being etched when the AlN layers on the second areas are etched away.

7. The method of claim 6, further comprising removing the SiO₂ protecting layer after etching away the AlN layers on the second areas.

8. The method of claim 6, wherein the SiO₂ protecting layer has a thickness of about 300 nanometers (nm).

9. The method of claim 6, wherein the AlN layers on the second areas are etched away by using a potassium hydroxide (KOH) solution.

10. The method of claim 6, further comprising, before removing the AlN layers inside the grooves, forming a plurality of cutting channels, wherein each cutting channel extends from the p-type GaN layer to the first undoped GaN layer to expose end surfaces of the AlN layers inside the grooves, and the cutting channels are arranged in the form of a grid.

11. The method of claim 10, further comprising cutting the substrate along the cutting channels to form the plurality of individual light emitting diodes.

12. The method of claim 5, wherein a thickness D1 of each air gap follows the formula D1=λ

/(4n₁), a thickness D2 of each second undoped GaN layer follows the formula D2=λ

/(4n₂), λ

represents a wavelength of light emitted by the active layer, n₁ represents a refractive index of air, and n₂ represents a refractive index of the second undoped GaN layer.

13. The method of claim 5, wherein the grooves formed by etching the first areas are totally inside the first undoped GaN layer.

14. A method for manufacturing a plurality of light emitting diodes, the method comprising:

providing a substrate;

forming a first undoped gallium nitride (GaN) layer on the substrate, an upper surface of the first undoped GaN layer being divided into a plurality of first areas and a plurality of second areas;

etching the first areas of the upper surface of the first undoped GaN layer to form a plurality of grooves;

forming a semiconductor structure inside each of the grooves and on each of the second areas of the upper surface of the first undoped GaN layer, each semiconductor structure comprising a plurality of n-type GaN layers and a plurality of second undoped GaN layers alternately stacked one on the other, a topmost one of the second undoped GaN layers being located at a top side of the semiconductor structure, and a bottommost one of the n-type GaN layers being located at a bottom of the semiconductor structure;

etching away the n-type GaN layers on the second areas thereby removing the n-type GaN layers and the second undoped GaN layers from the second areas;

forming an n-type GaN layer, an active layer and a p-type GaN layer, in that sequence, on upper surfaces of the topmost second undoped GaN layers and the second areas of the upper surface of the first undoped GaN layer;

removing the n-type GaN layers inside the grooves to form air gaps, the second undoped GaN layers and the air gaps in each groove cooperatively forming a distributed Bragg reflector; and

cutting the substrate to form a plurality of individual light emitting diodes.

15. The method of claim 14, further comprising, before etching away the n-type GaN layers on the second areas, forming a silicon dioxide (SiO₂) protecting layer around the entire periphery of the first undoped GaN layer, wherein the SiO₂ protecting layer covers side surfaces of the first undoped GaN layer and end faces of the semiconductor structures in the grooves in order to prevent the n-type GaN layers inside the grooves from being etched when the n-type GaN layers on the second areas are etched away.

16. The method of claim 15, further comprising removing the SiO₂ protecting layer after etching away the n-type GaN layers on the second areas.

17. The method of claim 15, wherein the SiO₂ protecting layer has a thickness of about 300 nanometers (nm).

18. The method of claim 15, wherein the n-type GaN layers on the second areas are etched away by using a potassium hydroxide (KOH) solution.

19. The method of claim 14, wherein the n-type GaN layer has an ion doping concentration in the range of from about 8*10¹⁸ cm⁻

3 to about 1*10²⁰ cm<sup>−

3</sup>.

20. The method of claim 14, wherein a thickness D1 of each air gap follows the formula D1=λ

/(4n₁), a thickness D2 of each second undoped GaN layer follows the formula D2=λ

/(4n₂), λ

represents a wavelength of light emitted by the active layer, n₁ represents a refractive index of air, and n₂ represents a refractive index of the second undoped GaN layer.