High brightness electroluminescent device emitting in the green to ultraviolet spectrum and method of making the same

• US 5,661,074 A
• Filed: 05/24/1995
• Issued: 08/26/1997
• Est. Priority Date: 02/03/1995
• Status: Expired due to Term

• Current Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Original Assignee: Advanced Technology Materials, Inc. (Entegris Incorporated)
• Inventors: Tischler, Michael A.
• Primary Examiner(s): KUNEMUND, ROBERT M
• Application Number:
  US08/448,743
• Time in Patent Office: 825 Days
• Field of Search: 117/90, 117/97, 117/95, 117/952, 437/127, 437/129
• US Class Current: 438/32
• CPC Class Codes: H01L 33/007 comprising nitride compounds
• CPC Class Codes: H01L 33/105 with a resonant cavity structure
• CPC Class Codes: H01L 33/32 containing nitrogen

Abstract

A green-blue to ultraviolet light-emitting optical device, e.g. a green-blue to ultraviolet emitting laser or a green-blue to ultraviolet emitting diode, comprising a green-blue to ultraviolet light emitting gallium nitride material on a base structure including a silicon carbide substrate, which preferably consists of 2H--SiC, 4H--SiC, or a-axis oriented 6H--SiC. The carrier mobility and the transparency of the silicon carbide substrate are optimized by the selection of orientation and polytype, thus enhancing device performance. The light-emitting diodes may incorporate a structural modification to increase the light output comprising a dielectric Bragg mirror beneath the LED structure, made of alternating layers of AlN, GaN, InN or their alloys. Methods for making such light-emitting diodes are provided, including a technique for defining individual devices by mesa etching which avoids possible damage to the active area during dicing.

Claims

1. A method of making a green-blue to ultraviolet light-emitting diode comprising forming a green-blue to ultraviolet light emitting material selected from the group consisting of:

GaN;

MGaN; and

MM'"'"'GaN

wherein;

M is a metal which is compatible with Ga and N in the composition MGaN and the composition MGaN is stable at 25°

C. and one atmosphere pressure conditions, and

M'"'"' is a compatible metal providing quaternary compounds of the formula M_1-x-y M'"'"'_y Ga_x N, wherein x and y range from 0 to 1, on a base structure comprising a SiC substrate selected from the group consisting of 2H--SiC, 4H--SiC and a-axis oriented 6H--SiC.

2. A method according to claim 1, wherein said base structure comprises at least one mesa on a top surface thereof, with said green-blue to ultraviolet light emitting material deposited on at least one mesa.

3. A method according to claim 2, wherein said at least one mesa on said base structure includes a main mesa surface having an equivalent diameter of less than 350 micrometers.

4. A method according to claim 2, wherein said at least one mesa on said base structure includes a main mesa surface having an equivalent diameter of less than 200 micrometers.

5. A method according to claim 2, wherein said at least one mesa is formed on a top surface on said base structure by etching a masked precursor base structure to a predetermined depth to yield said at least one mesa.

6. A method according to claim 1, wherein at least one mesa is formed on a top surface on said base structure after deposition of said green-blue to ultraviolet light emitting material on said base structure by etching of said deposited green-blue to ultraviolet light emitting material and underlying base structure to a predetermined depth to yield said at least one mesa.

7. A method according to claim 2, wherein said mesa structure formation comprises patterning said base structure with a metal mask defining said mesa structure, etching said patterned base structure to a predetermined depth, removing said metal mask, and depositing said green-blue to ultraviolet light emitting material on upper surfaces of said mesa structure.

8. A method according to claim 1, wherein the light-emitting green-blue to ultraviolet light emitting material includes a quantum well region.

9. A method according to claim 1, further comprising forming a Bragg mirror layer between the SiC substrate and the light-emitting green-blue to ultraviolet light emitting material.

10. A method according to claim 9, wherein the dielectric Bragg mirror comprises of green-blue to ultraviolet light emitting material.

11. A method according to claim 1, wherein the base structure comprises a buffer layer on said SiC substrate, between said SiC substrate and said light-emitting green-blue to ultraviolet light emitting material.

12. A method according to claim 11, wherein said buffer layer comprises a strained layer green-blue to ultraviolet light emitting superlattice.

13. A method according to claim 1, wherein the green-blue to ultraviolet light emitting material is selected from the group consisting of:

GaN, AlGaN, InGaN, and AllnGaN.

14. A method according to claim 1, wherein the green-blue to ultraviolet light emitting material is selected from the group consisting of:

GaN, AlGaN, InGaN, and AllnGaN.

15. A method according to claim 1, wherein the green-blue to ultraviolet light emitting material is GaN.