Scalable led with improved current spreading structures

• US 6,614,056 B1
• Filed: 11/21/2000
• Issued: 09/02/2003
• Est. Priority Date: 12/01/1999
• Status: Expired due to Term

• Current Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Original Assignee: Cree Lighting Company (Ideal Industries Incorporated)
• Inventors: Mack, Michael, Ibbetson, James, Tarsa, Eric J., Thibeault, Brian
• Primary Examiner(s): Le, Vu A.
• Assistant Examiner(s): MENZ, DOUGLAS M
• Application Number:
  US09/721,352
• Time in Patent Office: 1,015 Days
• Field of Search: 257/91, 257/94, 257/99, 257/773, 257/88
• US Class Current: 257/91
• 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 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/38 with a particular shape
• CPC Class Codes: H01L 33/64 Heat extraction or cooling elements

Abstract

An LED with improved current spreading structures that provide enhanced current injection into the LED'"'"'s active layer, improving its power and luminous flux. The current spreading structures can be used in LEDs larger than conventional LEDs while maintaining the enhanced current injection. The invention is particularly applicable to LEDs having insulating substrates but can also reduce the series resistance of LEDs having conductive substrates. The improved structures comprise conductive fingers that form cooperating conductive paths that ensure that current spreads from the p-type and n-type contacts into the fingers and uniformly spreads though the oppositely doped layers. The current then spreads to the active layer to uniformly inject electrons and holes throughout the active layer, which recombine to emit light.

Claims

1. A semiconductor LED with current spreading structures, comprising:

two or more adjacent layers doped with impurities;

at least one groove etched through one or more of said layers, exposing a surface on or within one of said layers, said at least one groove beginning at a first edge of said layers and extending toward the opposite second edge;

a first contact having at least one elongated first conductive finger on said exposed surface within said at least one groove, such that current flows from said contact into said at least one first finger and into said layer with said exposed surface, said first contact and said at least one finger beginning at said first edge and extending toward said second edge; and

a second contact having at least one elongated second conductive finger on the surface of said adjacent layers such that current flows from said second contact into said at least one conductive second finger and into said adjacent layers, said second contact and said at least one second conductive finger at said second edge and extending toward said first edge.

2. The semiconductor LED of claim 1, wherein said at least one second conductive finger and said at least one first conductive finger are generally parallel for a portion of their lengths.

3. The semiconductor LED of claim 1, wherein said at least one second conductive finger and adjacent said at least one first conductive finger are approximately uniform distance from one another to provide nearly uniform current injection into said two or more adjacent layers doped with impurities.

4. The semiconductor LED of claim 1, including one said first conductive finger, wherein said second contact and at least one conductive finger form a generally U-shaped conductive path, said first contact and said first conductive finger forming an elongated conductive path within said U-shaped path.

5. The semiconductor LED of claim 1, including one said first conductive finger, wherein said first contact and at least one conductive finger form a generally U-shaped conductive path, said second contact and said second conductive finger forming an elongated conductive path within said U-shaped path.

6. The semiconductor LED of claim 1, including a plurality of said first and second conductive fingers, said second conductive fingers forming a plurality of conductive paths from said second contact toward said opposite edge, said first fingers forming a plurality of conductive paths from said first contact toward said second contact, interdigitated between said second fingers.

7. A semiconductor LED with current spreading structures, comprising:

two or more adjacent layers doped with impurities;

at least one groove etched through one or more of said layers, exposing a surface on or within one of said layers;

a first contact having at least one first conductive finger on said exposed surface within said at least one groove, such that current flows from said contact into said at least one first finger, and into said layer with said exposed surface; and

a second contact having at least one second conductive finger on the surface of said adjacent layers such that current flows from said second contact, into said at least one conductive second finger and into said adjacent layers, wherein said second contact is located near the center of the surface of said adjacent layers and said second conductive fingers form conductive paths from said second contact toward the edge of said surface of said adjacent layers, and said first conductive fingers form conductive paths from said first contact, toward said second contact interdigitated between said second conductive fingers.

8. A semiconductor LED with current spreading structures, comprising:

two or more adjacent layers doped with impurities;

at least one groove etched through one or more of said layers, exposing a surface on or within one of said layers;

a first contact having at least one first conductive finger on said exposed surface within said at least one groove, such that current flows from said contact into said at least one first finger, and into said layer with said exposed surface; and

a second contact having at least one second conductive finger on the surface of said adjacent layers such that current flows from said second contact, into said at least one conductive second finger and into said adjacent layers, wherein said second contact is located in the center of the surface of said adjacent layers and further comprises two conductive branches forming conductive paths in opposite respective directions from said contact down a centerline of said surface, said second conductive fingers forming conductive paths generally orthogonal to said branches, said first fingers forming conductive paths from said first contact and from the edge of said surface, toward said branches interdigitated between said second fingers.

9. A semiconductor LED with current spreading structures, comprising:

two or more adjacent layers doped with impurities;

at least one groove etched through one or more of said layers, exposing a surface on or within one of said layers;

a first contact having at least one first conductive finger on said exposed surface within said at least one groove, such that current flows from said contact into said at least one first finger, and into said layer with said exposed surface; and

a second contact having at least one second conductive finger on the surface of said adjacent layers such that current flows from said second contact, into said at least one conductive second finger and into said adjacent layers, wherein said at least one first and second conductive fingers comprises a plurality of said first and second conductive fingers, wherein said second fingers form generally parallel zig-zag conductive paths from said second contact, and said first fingers form generally parallel zig-zag conductive paths from said first contact interdigitated between said second zig-zag fingers.

10. A scalable light emitting diode (LED) with enhanced current spreading structures, comprising:

an epitaxially grown p-type layer;

an epitaxially grown n-type layer;

an epitaxially grown active layer between said p-type and n-type layers;

a first contact having at least one first conductive finger;

at least one groove etched through said p-type and active layers to said n-type layer, said groove extending from a first edge of said n-type layer toward its opposite edge, said first contact and at least one finger on said n-type layer in said groove;

a second contact and at least one second conductive finger on said p-type layer, wherein said second contact is at the edge of said p-type layer opposite said n-type first edge and said at least one second finger extending toward said n-type first edge, said at least one first and second conductive fingers are generally parallel for at least a portion of their lengths.