GaN-series light emitting diode with high light efficiency

• US 7,772,607 B2
• Filed: 12/29/2006
• Issued: 08/10/2010
• Est. Priority Date: 09/27/2004
• Status: Active Grant

• Current Assignee: Semileds Optoelectronics Company Limited (SemiLEDs Inc)
• Original Assignee: Supernova Optoelectronics Corp.
• Inventors: Hon, Schang-Jin, Lai, Mu-Jen
• Primary Examiner(s): Wilson, Allan R.
• Application Number:
  US11/647,251
• Publication Number:
  US 20070108457A1
• Time in Patent Office: 1,320 Days
• Field of Search: 257/98, 257102-103, 257/E33.025
• US Class Current: 257/98
• CPC Class Codes: H01L 33/10 with a light reflecting structure, e.g. semiconductor Bragg reflector
• CPC Class Codes: H01L 33/14 with a carrier transport control structure, e.g. highly-doped semiconductor layer or current-blocking structure
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/32 containing nitrogen

Abstract

A GaN-series light emitting diode with high light efficiency utilizes a p-type semiconductor layer having a textured surface structure. The optical waveguide effect can be interrupted and formation of hexagonal shaped pits defect can be reduced due to the textured structure. The p-type semiconductor layer is formed on a light emitting layer and includes a p-type cladding layer, p-type transitional layer, and p-type ohmic contact layer. During the manufacturing of the GaN-series LED, the tension and compression of strain is controlled while the p-type cladding layer and the p-type transition layer are formed. Through the control of the epitaxial growth process, it is attained that the surface of the p-type semiconductor layer is textured to increase external quantum efficiency and the operation life of the light emitting device.

Claims

1. A GaN-series light emitting diode having a high light efficiency, comprising:

a substrate;

a semiconductor layer formed on said substrate and including an n-type semiconductor layer;

a p-type semiconductor layer;

a light emitting layer sandwiched between said n-type semiconductor layer and said p-type semiconductor layer;

a reflection layer located between said light emitting layer and said n-type semiconductor layer, said reflection layer having one side thereof in contiguous contact with said light emitting layer and opposing side in contiguous contact with said n-type semiconductor layer;

wherein said p-type semiconductor layer includes a p-type cladding layer, a p-type transition layer, and a p-type ohmic contact layer sequentially formed on said light emitting layer, said p-type semiconductor layer having a predetermined profile of dopant concentration extending therethrough, wherein a first concentration of dopants in said p-type cladding layer is higher than a second concentration of dopants in said p-type transition layer, and wherein a concentration of dopants in said p-type ohmic contact layer falls between said first and second concentrations of dopants; and

wherein said p-type semiconductor layer has a textured surface formed during epitaxial growth of said p-type semiconductor layer as the result of a strain created in said p-type cladding layer and controlled by forming said predetermined profile of said dopants concentration, said textured surface being substantially void of hexagonally shaped defects.

2. The GaN-series light emitting diode in accordance with claim 1, wherein said textured surface of said p-type semiconductor layer interrupts optical waveguide effect in said light emitting diode.

3. The GaN-series light emitting diode in accordance with claim 1, wherein said textured surface of said p-type semiconductor layer is formed by controlling the strain of said p-type cladding layer and said p-type transition layer during the epitaxial growth of said p-type semiconductor layer.

4. The GaN-series light emitting diode in accordance with claim 1, wherein said substrate is selected from a group consisting of sapphire, silicon carbide, zinc oxide, zirconium diboride, gallium arsenide and silicon.

5. The GaN-series light emitting diode in accordance with claim 1, wherein said n-type semiconductor layer is formed from N—

B_xAl_yIn_zGa<sub>1−

x−

y−

z</sub>N_pAs_q (0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, 0≦

p≦

1, 0≦

q≦

1, and x+y+z<

1, p+q=1), or N—

B_xAl_yIn_zGa<sub>1—

x—

y—

z</sub> N_pP_q (0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, 0≦

p≦

1, 0≦

q≦

1, and x+y+z<

1, p+q=1).

6. The GaN-series light emitting diode in accordance with claim 1, wherein said p-type semiconductor layer includes P—

B_xAl_yIn_zGa<sub>1−

x−

y−

z</sub>N_pAs_q (0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, 0≦

p≦

1, 0≦

q≦

1, and x+y+z<

1, p+q=1), or P—

B_xAl_yIn_zGa<sub>1−

x−

y−

z</sub>N_p P_q (0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, 0≦

p≦

1, 0≦

q≦

1, and x+y+z<

1, p+q=1).

7. The GaN-series light emitting diode in accordance with claim 1, wherein said light emitting layer includes B_xAl_yIn_zGa₁₋

x−

y−

zN _pAs_q (0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, 0≦

p≦

1, 0≦

q≦

1, and x+y+z<

1, p+q=1), or B_xAl_yIn_zGa<sub>1−

x−

y−

z</sub>N_pP_q (0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, 0≦

p≦

1, 0≦

q≦

1, and x+y+z<

1, p+q=1), or combination thereof to form quantum well structure.

8. The GaN-series light emitting diode in accordance with claim 1, wherein said p-type cladding layer is a cladding layer having the tension strain controlled during epitaxial growth thereof.

9. The GaN-series light emitting diode in accordance with claim 1, wherein said p-type transition layer is a superlattice structure composed by a semiconductor layer.

10. The GaN-series light emitting diode in accordance with claim 1, wherein said p-type ohmic contact layer is a superlattice structure composed by a semiconductor layer.

11. The GaN-series light emitting diode in accordance with claim 1, wherein said first concentration of dopants in said p-type cladding layer includes a concentration of magnesium in a range from 5×

10¹⁹ to 5×

10²⁰ cm<sup>−

3</sup>.

12. The GaN-series light emitting diode in accordance with claim 1, wherein said second concentration of dopants in said p-type transition layer includes a concentration of magnesium in a range from 5×

10¹⁷ to 5×

10¹⁹ cm<sup>−

3</sup>.

13. The GaN-series light emitting diode in accordance with claim 9 or 10, wherein said superlattice structure includes a plurality of stacked semiconductor layers having different compositions, thickness, and dopants concentrations.

14. The GaN-series light emitting diode in accordance with claim 1, wherein said reflection layer is formed as a Distributed Bragg Reflector including a plurality of stacked semiconductor layers.

15. A GaN-series light emitting diode having a high light efficiency, comprising:

a substrate;

a n-type nitride semiconductor contact layer formed on the said substrate;

a nitride semiconductor light emitting layer formed on said n-type nitride semiconductor contact layer;

a p-type nitride semiconductor cladding layer formed on said nitride semiconductor light emitting layer and having a first concentration of dopants formed therein;

a p-type nitride semiconductor transition layer formed on said p-type nitride semiconductor cladding layer and having a second concentration of dopants formed therein and being lower than said first concentration;

a p-type nitride semiconductor ohmic contact layer formed on said p-type nitride semiconductor transition layer and having a third concentration of dopants formed therein and ranging between said first and second concentrations of dopants; and

at least one metal monolayer structures formed between said p-type nitride semiconductor cladding layer and said p-type nitride semiconductor transition layers.

16. The GaN-series light emitting diode in accordance with claim 15, wherein said metal monolayer structure is selected from a group consisting of aluminum, gallium, indium and other metals from group-III.

17. The GaN-series light emitting diode in accordance with claim 15, wherein said p-type nitride semiconductor ohmic contact layer has a textured surface.

18. The GaN-series light emitting diode in accordance with claim 17, wherein said textured surface of said p-type semiconductor ohmic contact layer is a nitrogen-polarity surface free from defect pits.