Light-emitting diode with a thick transparent layer

• US 5,233,204 A
• Filed: 01/10/1992
• Issued: 08/03/1993
• Est. Priority Date: 01/10/1992
• Status: Expired due to Term

• Current Assignee: Philips Lumileds Lighting Company LLC (Apollo Global Management, Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Yu, Jiann, Huang, Kuo-Hsin, Kuo, Chihping, Fletcher, Robert M., Osentowski, Timothy D.
• Primary Examiner(s): MINTEL, WILLIAM A
• Application Number:
  US07/819,542
• Time in Patent Office: 571 Days
• Field of Search: 357/17, 357/52, 357/52 E, 357/16, 357/55, 372/45, 372/49, 257/13, 257/94, 257/96, 257/97, 257/103, 257/98
• US Class Current: 257/13
• CPC Class Codes: H01L 33/0062 for devices with an active region comprising only III-V compounds
• CPC Class Codes: H01L 33/02 characterised by the semiconductor bodies

Abstract

A light emitting diode (LED) including a light generation region situated on a light-absorbing substrate also includes a thick transparent layer which ensures that an increased amount of light is emitted from the sides of the LED and only a minimum amount of light is absorbed by the substrate. The thickness of the transparent layer is determined as a function of its width and the critical angle at which light is internally reflected within the transparent layer. The thick transparent layer is located either above, below or both above and below the light generation region. The thick transparent layer may be made of materials and with fabrication processes different from the light generation region.

Claims

1. A light emitting diode, positioned in a medium having a refractive index, η

₁, the light emitting diode having a width, A, and comprising;

a light absorbing substrate;

a light generation region overlaying the substrate;

a top transparent layer overlaying the light generation region, the top transparent layer having sides with a thickness, D, which is greater than a minimum thickness of 0.06 times A and

wherein the top transparent layer increases the light generation efficiency of the light emitting diode by increasing an amount of light emitted from the sides and reducing an amount of light absorbed by the light absorbing substrate.

2. A light emitting diode as recited in claim 1, wherein:

the top transparent layer has a refractive index, η

₂ ;

η

₁ and η

₂ define a critical angle θ

_c =Sin^-1 (η

₁ /η

₂);

the critical angle θ

_c ≦

45°

°

; and

the thickness, D, of the top transparent layer is less than 4 times (A * tan θ

_c)/2.

3. A light emitting diode as recited in claim 2, wherein the thickness, D, of the top transparent layer is substantially equal to (A * tan θ

_c)/2.

4. A light emitting diode as recited in claim 3, wherein the top transparent layer is selected from the group comprising GaP, GaAsP and AlGaAs.

5. A light emitting diode as recited in claim 1, wherein:

the top transparent layer has a refractive index, η

₂ ;

η

₁ and θ

₂ define a critical angle θ

_c =Sin^-1 (η

₁ /η

₂);

the critical angle θ

_c >

45°

; and

the thickness, D, of the top transparent layer is less than 4 times (A * tan (90°

-θ

_c))/2.

6. A light emitting diode as recited in claim 5, wherein the thickness, D, of the top transparent layer is substantially equal to (A * tan (90°

-θ

_c))/2.

7. A light emitting diode as recited in claim 6, wherein the top transparent layer is selected from the group comprising GaP, GaAsP and AlGaAs.

12. A light emitting diode as recited in claim 1, further comprising a bottom transparent layer between the light generation region and the light absorbing substrate.

13. A light emitting diode as recited in claim 12, wherein:

the bottom transparent layer has a refractive index, η

₂ ;

η

₁ and η

₂ define a critical angle θ

_c =Sin^-1 (η

₁ /η

₂); and

the thickness, D_B, of the bottom transparent layer is less than 4 times A * tan θ

_c.

14. A light emitting diode as recited in claim 13, wherein the thickness, D_B, of the bottom transparent layer is substantially equal to A * tan θ

_c.

15. A light emitting diode as recited in claim 14, wherein:

the top transparent layer is selected from the group comprising GaP, GaAsP and AlGaAs.

16. A light emitting diode as recited in claim 1, wherein:

the light generation region is fabricated by a first process; and

the top transparent layer is fabricated by a second process which is different from the first process.

18. A light emitting diode as recited in claim 12, wherein:

the light generation region is fabricated by a first process;

the top transparent layer is fabricated by a second process which is different from the first process; and

the bottom transparent layer is fabricated by a third process which is different from the first process.

8. A light emitting diode, positioned in a medium having a refractive index, η

₁, the light emitting diode comprising;

a light absorbing substrate;

a bottom transparent layer overlaying the substrate;

a confirming layer overlaying the bottom transparent layer;

a light generation region overlaying the confining layer; and

wherein the transparent layer is thicker than the total thickness of the light generation region and the confining layer.

9. A light emitting diode as recited in claim 8, wherein:

the light emitting diode has a width, A;

the bottom transparent layer has a refractive index, η

₂ ;

η

_a and η

₂ define a critical angle θ

_c =Sin^-1 (η

₁ /η

₂);

the thickness, D, of the bottom transparent layer is less than 4 times A * tan θ

_c.

10. A light emitting diode as recited in claim 9, wherein the thickness, D, of the bottom transparent layer is substantially equal to A * tan θ

_c.

11. A light emitting diode as recited in claim 10, wherein the bottom transparent layer is selected from the group comprising GaP, GaAsP and AlGaAs.

17. A light emitting diode as recited in claim 8, wherein:

the light generation region is fabricated by a first process; and

the bottom transparent layer is fabricated by a second process which is different from the first process.