Transparent substrate light emitting diodes with directed light output

• US 6,015,719 A
• Filed: 04/24/1998
• Issued: 01/18/2000
• Est. Priority Date: 10/24/1997
• 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): Fahmy, Wael
• Assistant Examiner(s): Pham, Long
• Application Number:
  US09/066,089
• Time in Patent Office: 634 Days
• Field of Search: 438/47, 438/24, 438/29, 438/46, 257/94, 257/96, 257/97, 257/84, 257/85, 257/90
• US Class Current: 438/29
• 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 33/0093 Wafer bonding; Removal of the growth substrate
• 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 method for fabricating a light emitting diode with a transparent substrate comprising the steps of:

fabricating at least a first distributed Bragg reflector reflecting light that strikes it within a first range of angles of incidence less than 25 degrees from normal and transmitting light with absorption less than 25% that strikes it within a second range of angles of incidence greater than 25 degrees from normal; and

placing the first distributed Bragg reflector in the light emitting diode with the transparent substrate.

2. The method of claim 1 wherein the distributed Bragg reflector reflects light emitted by an active region of the light emitting diode 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 method of claim 2 wherein the active region is wafer bonded to a combination of the transparent substrate and the distributed Bragg reflector.

4. The method of claim 2 wherein the transparent substrate is wafer bonded to a combination of distributed Bragg reflector and active region.

5. The method of claim 1 wherein:

the transparent substrate has a top and a bottom surface; and

the first distributed Bragg reflector is placed between an active region and one of the top and bottom surfaces of the transparent substrate.

6. The method of claim 5 further comprising the steps of:

fabricating a transparent window that has a top and bottom surface;

placing the bottom surface of the transparent window adjacent to the active region and opposing the top surface of the transparent substrate; and

placing a second distributed Bragg reflector, that reflects light which strikes it within the first range of angles of incidence and transmits light which strikes it within the second range of angles of incidence, between the active region and one of the top and bottom surfaces of the transparent window.