High speed surface plasmon coupled light emitting diodes

• US 9,768,347 B2
• Filed: 04/28/2014
• Issued: 09/19/2017
• Est. Priority Date: 04/26/2013
• Status: Active Grant

• Current Assignee: Agency For Science Technology and Research, National University of Singapore
• Original Assignee: Agency For Science Technology and Research, National University of Singapore
• Inventors: Teo, Ee Jin, Teng, Jinghua, Yang, Chengyuan, Bettiol, Andrew
• Primary Examiner(s): Wilson, Allan R
• Application Number:
  US14/787,122
• Publication Number:
  US 20160087143A1
• Time in Patent Office: 1,240 Days
• CPC Class Codes: H01L 2933/0016 relating to electrodes
• CPC Class Codes: H01L 2933/0025 relating to coatings
• 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 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/32 containing nitrogen
• CPC Class Codes: H01L 33/38 with a particular shape
• CPC Class Codes: H01L 33/50 Wavelength conversion elements

Abstract

A light emitting diode device (LED) is provided. The LED comprises a first-doped layer on a substrate, an active layer on the first-doped layer, a second-doped layer on the active layer, and a metal layer on the second-doped layer. The second-doped layer is patterned on a surface opposite to the active layer to define a first portion and a second portion. The first portion of the second-doped layer has a first portion thickness constrained for electron-hole pairs in the active layer to couple efficiently to a surface plasmon mode at an interface of the metal layer and the second-doped layer thereby increasing the spontaneous emission rate of the LED. The second portion of the second-doped layer has a second portion thickness sufficient to ensure formation of a p-n junction in the LED.

Claims

1. A light emitting diode device (LED) comprising:

a first-doped layer on a substrate;

an active layer on the first-doped layer, the active layer being configured to emit electron-hole pairs;

a second-doped layer on the active layer; and

a metal layer on the second-doped layer, wherein the second-doped layer is textured with a plurality of V-pits on a surface opposite to the active layer to define a surface plasmon thickness that is configured to allow the electron-hole pairs in the active layer to couple efficiently to a surface plasmon mode at an interface of the metal layer and the second-doped layer thereby increasing the spontaneous emission rate of the LED, and wherein light is emitted from a rear side of the LED when the metal layer has a thickness of approximately 30 nm or thicker, wherein the rear side comprises a surface of the substrate opposite the first-doped layer.

2. The LED of claim 1, wherein the active layer comprises one or more quantum well layers comprising material selected from semiconductor emitting material and organic molecules.

3. The LED of claim 1, wherein the substrate comprises a material selected from quartz, fused silica, silicon, sapphire and polymer.

4. The LED of claim 1, wherein the first-doped layer is an n-doped layer and the second-doped layer is a p-doped layer.

5. The LED of claim 1, wherein the first-doped layer comprises a material selected from the group comprising Si,Ge, SiC, GaAs, InGaP, InGaAs, InGaN, GaN, AlGaN, ZnSe, ZnCdSe, AlGaAs, InP and a molecule doped polymer, or wherein the second- doped layer comprises a material selected from the group comprising Si, Ge, SiC, GaAs, InGaP, InGaAs, InGaN, GaN, AlGaN, ZnSe, ZnCdSe, AlGaAs, lnP and a molecule doped polymer.

6. The LED of claim 1, wherein the active layer comprises a material selected from the group comprising Si,Ge, SiC, GaAs, InGaP, InGaAs, InGaN, GaN, AlGaN, ZnSe,Zn CdSe, CdS, AlGaAs and InP.

7. The LED of claim 1, wherein the metal layer comprises a metal selected from the group consisting of Au, Ag, Al, Cu, Ti, Ni, Cr, Zn, and an alloy formed from one or more of Au, Ag, Al, Cu, Ti, Ni, Cr, and Zn.

8. The LED of claim 1, wherein the metal layer is formed on a first portion of the second-doped layer but not on a second portion of the second-doped layer, or wherein the metal layer is formed on the first and second portions of the second-doped layer.

9. The LED of claim 1, wherein the metal layer comprises a random array of metal nanoparticles formed through annealing or spincoating of metallic nanoparticles;

or wherein the metal layer comprises patterned metallic nanostructures fabricated using lithography and deposition processes.

10. The LED of claim 1, wherein the second-doped layer is patterned with any one of the following:

plasmonic nanostructures, metamaterial nanostructures, a structure of sub wavelength grating, a structure of nanoantennas, and a structure of nanoapertures.

11. The LED of claim 1, further comprising a first electrode in contact with the first-doped layer and an electrode layer forming a second electrode in contact with the second-doped layer, or comprising a phosphors layer on a surface of the LED.

12. The LED of claim 1, wherein the second-doped layer is textured with the plurality of V-pits on the surface opposite to the active layer to further define a second portion that is configured to form a p-n junction in the LED.

13. A method for fabricating a light emitting diode (LED), the method comprising:

depositing a first-doped GaN layer with first impurities on a substrate;

forming one or more quantum well layers on the first-doped layer;

depositing a second-doped GaN layer with second impurities on the quantum well layer;

depositing a metal layer over the second-doped layer,

wherein depositing the second-doped GaN layer comprises texturing a plurality of sharp V-pits so that a first portion of the second doped GaN layer has a first thickness and a second portion of the second doped GaN layer has a second thickness, the first thickness defining a surface plasmon thickness that is configured to allow electron-hole pairs in the one or more quantum well layers to couple efficiently to a surface plasmon mode at an interface of the metal layer and the second-doped layer for an increased spontaneous emission rate of the LED and the second thickness being determined to ensure formation of a p-n junction in the LED, and wherein a thinnest portion of the second-doped layer and a thinnest portion of the metal layer over the thinnest portion of the second doped layer both are within the surface plasmon coupling thickness.

14. The method of claim 13, further comprises forming an electrode pad being a first electrode in contact with the first-doped GaN layer and an electrode layer forming a second electrode in contact with the second-doped GaN layer.

15. The method of claim 13 wherein depositing the metal layer over the second-doped layer comprises at least one of depositing the metal layer over an electrode layer, annealing or spincoating of metallic nanoparticles.

16. A method for fabricating a light emitting diode (LED), the method comprising:

depositing a first-doped GaN layer with first impurities on a substrate

forming one or more quantum well layers on the first-doped layer;

depositing a second-doped GaN layer with second impurities on the quantum well layer;

depositing a metal layer over the second-doped layer; and

avoiding the second-doped layer where an electrode layer is formed when depositing the metal layer over the second-doped layer, or avoiding a second portion of the second-doped layer when depositing the metal layer over the second-doped layer,

wherein depositing the second-doped GaN layer comprises texturing a plurality of sharp V-pits so that a first portion of the second doped GaN layer has a first thickness and the second portion of the second doped GaN layer has a second thickness, the first thickness defining a surface plasmon thickness that is configured to allow electron-hole pairs in the one or more quantum well layers to couple efficiently to a surface plasmon mode at an interface of the metal layer and the second-doped layer for an increased spontaneous emission rate of the LED and the second thickness being determined to ensure formation of a p-n junction in the LED.