Inverted LED Structure with Improved Light Extraction

• US 20100065866A1
• Filed: 09/15/2008
• Published: 03/18/2010
• Est. Priority Date: 09/15/2008
• Status: Active Grant

• Current Assignee: Toshiba Techno Center Inc. (Toshiba Corporation)
• Original Assignee: Ghulam Hasnain
• Inventors: Hasnain, Ghulam
• Granted Patent: US 7,741,134 B2
• Time in Patent Office: Days
• US Class Current: 257/98
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate

Abstract

A light source and method for fabricating the same are disclosed. The light source includes a substrate and a light emitting structure. The substrate has a first surface and a second surface, the second surface including a curved, convex surface with respect to the first surface of the substrate. The light emitting structure includes a first layer of a material of a first conductivity type overlying the first surface, an active layer overlying the first layer, the active layer generating light when holes and electrons recombine therein, and a second layer includes a material of a second conductivity type overlying the active layer and a second surface opposite to the first surface. A mirror layer overlies the light emitting structure.

Claims

1. A device comprising:

a substrate having a first surface and a second surface, said second surface comprising a curved, convex surface with respect to said first surface of said substrate;

a first layer overlying said first surface, said first layer comprising a material of a first conductivity type;

an active layer overlying said first layer, said active layer generating light when holes and electrons recombine therein; and

a second layer comprising a material of a second conductivity type, said second layer having a first surface overlying said active layer and a second surface opposite to said first surface, said substrate being transparent to light generated by said active layer.

2. The device of claim 1 wherein said first layer, said second layer, and said active layer comprise materials from the GaN family of materials.

3. The device of claim 1 wherein said substrate comprises sapphire.

4. The device of claim 1 wherein said curved convex surface is chosen such that a light ray generated in said active layer that is initially reflected from said surface due to internal reflection subsequently strikes said surface at an angle that is less than the critical angle to said surface at that point on said surface.

5. The device of claim 1 wherein said curved convex surface is non-spherical.

6. The device of claim 1 wherein said curved convex surface is substantially parabolic.

7. A method of fabricating a light emitting device comprising:

providing a substrate having a first surface and a second surface that are substantially parallel to one another;

fabricating a light emitting structure on said first surface, said light emitting structure comprising;

a first layer of semiconductor material of a first conductivity type deposited on said substrate;

an active layer overlying said first layer; and

a second layer of semiconductor material of an opposite conductivity type from said first conductivity type overlying said active layer; and

etching said second surface of said substrate to provide a curved, convex surface with respect to said first surface.

8. The method of claim 7 wherein etching said second surface of said substrate comprises:

depositing a layer of photoresist on said second surface;

patterning said deposited photoresist layer;

heating said photoresist to a temperature at which a surface of said photoresist layer assumes a curved convex shape; and

etching said photoresist layer and said substrate.

9. The method of claim 7 wherein said curved convex surface is chosen such that a light ray generated in said active layer that is initially reflected from said curved convex surface due to internal reflection subsequently strikes said curved convex surface at an angle that is less than the critical angle to said surface at that point on said surface.