Transparent substrate light emitting diodes with directed light output

• US 5,793,062 A
• Filed: 10/24/1997
• Issued: 08/11/1998
• Est. Priority Date: 08/10/1995
• Status: Expired due to Term

• Current Assignee: Lumileds LLC (Apollo Global Management, Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Kish, Fred A. Jr., Stockman, Stephen A.
• Primary Examiner(s): JACKSON JR, JEROME
• Application Number:
  US08/962,944
• Time in Patent Office: 291 Days
• Field of Search: 257/98, 372/99
• US Class Current: 257/98
• CPC Class Codes: H01L 21/24 Alloying of impurity materials, e.g. doping materials, electrode materials, with a semiconductor body H01L21/182 takes precedence
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 33/10 with a light reflecting structure, e.g. semiconductor Bragg reflector
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers

Abstract

Methods for the fabrication of TS LED chips with improved light extraction and optics, particularly increased top surface emission, and the TS LEDs so fabricated are described. Non-absorbing DBRs within the chip permit the fabrication of the LEDs. The transparent DBRs redirect light away from absorbing regions such as contacts within the chip, increasing the light extraction efficiency of the LED. The non-absorbing DBRs can also redirect light toward the top surface of the chip, improving the amount of top surface emission and the on-axis intensity of the packaged LED. These benefits are accomplished with optically non-absorbing layers, maintaining the advantages of a TS LED, which advantages include ˜6 light escape cones, and improved multiple pass light extraction.

Claims

1. A light emitting diode that does not emit coherent radiation, comprising:

an active region for generating light;

a substrate transparent to the light generated by the active region, the substrate underlying the active region and having a top and bottom surface and a plurality of exposed side surfaces, light generated by the active region being capable of leaving the light emitting diode through the exposed side surfaces of the substrate;

a window layer transparent to the light generated by the active region, overlying the active region, the window layer having at least one top exposed surface through which light generated by the active region can pass;

a first contact and a second contact for applying a voltage across the active region, at least the first and second contacts absorbing light generated by the active region;

at least a first distributed Bragg reflector, substantially transparent to the light generated by the active region, the distributed Bragg reflector reflecting light striking the distributed Bragg reflector within a predefined range of angles of incidence and transmitting light generated by the active region with minimal absorption when the light strikes the distributed Bragg reflector outside the predefined range of angles of incidence, the distributed Bragg reflector redirecting light generated by the active region away from absorbing regions of the light emitting diode and towards at least one exposed surface.

2. The light emitting diode of claim 1 wherein the distributed Bragg reflector reflects light emitted by the active region in at least a first of two directions, the two directions being away from light absorbing areas of the light emitting diode and towards at least a first preferential direction.

3. The device of claim 2 wherein the active region comprises In(AlGa)P, the substrate comprises GaP, and the distributed Bragg reflector comprises a multi-layer stack of any combination of In_X Al_Y Ga_Z P(0≦

X,Y,Z≦

1) and Al_X'"'"' Ga_1-x As(0≦

X'"'"'≦

1).

4. The light emitting diode of claim 2 wherein the transparent substrate is patterned with a plurality of trenches and the Bragg reflector and the active region are grown on the patterned substrate.

5. The light emitting diode of claim 4 wherein the trenches have sidewalls angled 45°

from the vertical.

6. The light emitting diode of claim 2 wherein the distributed Bragg reflector is placed between the active region and a portion of the substrate, the portion of the substrate including the surfaces of the substrate closest to and furthest from the active region.

7. The light emitting diode of claim 6 wherein a second distributed Bragg reflector is placed between the active region and at least a portion of the transparent window, the portion of the transparent window including the surfaces of the transparent window closest to and furthest from the active region.

8. The light emitting diode of claim 1 wherein the substrate is wafer bonded to a combination of the distributed Bragg reflector and active region.

9. The light emitting diode of claim 8 wherein the distributed Bragg reflector reflects light emitted by the active region in at least a first of two directions, the two directions being away from light absorbing areas of the light emitting diode and towards at least a first preferential direction.

10. The light emitting diode of claim 9 wherein scattering centers are incorporated into the wafer bond between the substrate and the active region/reflector combination.

11. The light emitting diode of claim 1 wherein a combination of the substrate and distributed Bragg reflector is wafer bonded to the active region.

12. The light emitting diode of claim 11 wherein the distributed Bragg reflector reflects light emitted by the active region in at least a first of two directions, the two directions being away from light absorbing areas of the light emitting diode and towards at least a first preferential direction.

13. The light emitting diode of claim 12 wherein scattering centers are incorporated into the wafer bond between the substrate/reflector combination and the active region.