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

• US 5,874,747 A
• Filed: 11/24/1997
• Issued: 02/23/1999
• Est. Priority Date: 02/05/1996
• Status: Expired due to Term

• Current Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Original Assignee: Advanced Technology Materials, Inc. (Entegris Incorporated)
• Inventors: Redwing, Joan, Tischler, Michael A.
• Primary Examiner(s): MONIN, DONALD L JR
• Application Number:
  US08/894,609
• Time in Patent Office: 456 Days
• Field of Search: 257/77, 257/94, 257/103, 257/461, 257/81, 257/85, 257/99, 438/107, 438/133, 438/68, 438/87
• US Class Current: 257/77
• 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
• CPC Class Codes: H01L 33/44 characterised by the coatings, e.g. passivation layer or anti-reflective coating

Abstract

A green-blue to ultraviolet light emitting semiconductor laser having a top contact, a Bragg reflector, cladding layer, active layer, cladding layer, buffer, substrate, bottom contact and a passivation layer. The key aspect is a Ga*N material on a base structure comprising a SiC substrate selected from a group consisting of 2H-SiC, 4H-SiC and a-axis oriented 6H-SiC. Furthermore, the cladding layers have larger band gaps than the active layer and are complimentarily doped.

Claims

1. A semiconductor device or precursor thereof, comprising a layer of single crystal silicon carbide and a layer of single crystal gallium nitride, having a buffer layer therebetween comprising a compositionally graded Ga*N layer.

2. A semiconductor device or precursor thereof according to claim 1, wherein the silicon carbide comprises a polytype selected from the group consisting of 2H-SiC, 4H-SiC, and 6H-SiC.

3. A semiconductor device or precursor thereof according to claim 1, wherein said compositionally graded Ga*N layer comprise a compositionally graded Al_x Ga_1-x N buffer layer between the gallium nitride and silicon carbide layers, wherein x can range from 0 to 1, and the buffer layer is compositionally graded from an interface of the the buffer layer with the silicon carbide layer at which x is 0, to an interface of the buffer layer with the gallium nitride layer at which x is 1.

4. A semiconductor device or precursor thereof, comprising a silicon carbide substrate and an epitaxial layer of gallium nitride, having a buffer layer therebetween comprising a compositionally graded (Al,Ga)N buffer layer.

5. A semiconductor device or precursor thereof according to claim 4, wherein said buffer layer comprises an AlGal-,N buffer layer where the Al composition (x) is graded from 1 at the buffer-SiC interface to 0 at the GaN-buffer interface.

6. A semiconductor device or precursor thereof according to claim 4, wherein the thickness of said buffer layer is from 200 Å

to 5 μ

m.

7. A semiconductor device or precursor thereof according to claim 4, wherein the thickness of said buffer layer is from 500 Å

to 1 μ

m.

8. A semiconductor device or precursor thereof, comprising a silicon carbide substrate and an epitaxial layer of gallium nitride, having a buffer material therebetween comprising an AlN buffer layer on the silicon carbide substrate, and a compositionally graded (Al,Ga)N buffer layer between the AlN buffer layer and the gallium nitride epitaxial layer.

9. A semiconductor device or precursor thereof according to claim 8, wherein the thickness of said AlN buffer layer is from 50 Å

to 5 μ

m.

10. A semiconductor device or precursor thereof according to claim 8, wherein the thickness of said AlN buffer layer is from 100 Å

to 1 μ

m.

11. A semiconductor device or precursor thereof, comprising a silicon carbide substrate and an epitaxial layer of gallium nitride, having a buffer material therebetween comprising a conductive buffer layer of the formula Al_x Ga_1-x N wherein the buffer layer includes a lower Al composition layer that is doped to render it highly conductive in character.

12. A semiconductor device or precursor thereof according to claim 11, wherein x is in the range of from x=1 to x=0.3.

13. A semiconductor device or precursor thereof according to claim 11, wherein x is in the range of from x=0.7 to x=0.4.

14. A semiconductor device or precursor thereof according to claim 11, wherein the buffer material comprises an end composition adjacent said gallium nitride epitaxial layer, selected from the group consisting of GaN and a lower Al_y Ga_1-y N composition, where y<

x.

15. A semiconductor device or precursor thereof according to claim 14, wherein the buffer material comprises a s said end composition Al_y Ga_1-y N and the gallium nitride epitaxial layer comprises (Al, Ga)N.

16. A semiconductor device or precursor thereof according to claim 11, wherein the conductive buffer layer is an n-type material.

17. A semiconductor device or precursor thereof according to claim 11, wherein the conductive buffer layer is a p-type material.

18. A semiconductor device or precursor thereof, comprising a silicon carbide substrate and an epitaxial layer of gallium nitride, having a buffer material therebetween comprising a buffer layer selected from the group consisting of (Al, Ga)N compositionally graded layers, (Al, In)N compositionally graded layers, and (Al, Ga, In)N compositionally graded layers.

19. A semiconductor device or precursor thereof according to claim 18, wherein the epitaxial layer of gallium nitride contains In.

20. A semiconductor device or precursor thereof according to claim 19, wherein the epitaxial layer of gallium nitride comprises an epitaxial layer formed of material selected from the group consisting of (In, Ga)N, (In, Ga)N, and (Al, Ga, In)N.

21. A semiconductor device or precursor thereof according to claim 19, wherein the epitaxial layer of gallium nitride comprises In₀.1 Ga₀.9 N,and the buffer material includes AlN grading through (Al, Ga)N to GaN, and grading from GaN to In₀.1 Ga₀.9 N.

22. A semiconductor device or precursor thereof, comprising a SiC substrate element including a mesa-shaped portion having a Ga*N quantum well structure or other Ga*N s tructure formed thereon, where in t he mesa-shaped portion has an equivalent diameter in the range of from 50 to 300 μ

m, and a height of from 1 to 15 μ

m.

23. A semiconductor device or precursor thereof according to claim 22, wherein the SiC substrate comprise an SiC polytype selected from the group consisting of 2H-SiC, 4H-SiC, and a-axis oriented 6H-SiC.

24. A semiconductor device or precursor thereof according to claim 22, wherein said mesa-shaped portion has a quantum well structure thereon, and said quantum well structure includes a well having a well width of from 150 Å

to 750 Å

.

25. A method for fabricating a light emitting diode comprising the steps of:

a. forming an M_x M'"'"'_y M"_1-x-y N barrier layer on a conductive substrate, wherein M, M'"'"', and M" are metals compatible with nitrogen (N) in the composition M_x M'"'"'_y M"_1-x-y N, and the composition M_x M'"'"'_y M"_1-x-y N is stable at room temperatures and pressures;

b. forming an M_a M'"'"'_b M"_1-a-b N active region on the M_x M'"'"'_y M"_1-x-y N barrier layer;

c. forming an M_c M'"'"'_d M"_1-c-d N barrier layer on the M_a M'"'"'_b M"_1-a-b N active region;

d. forming a heavily doped contact layer on the M_c M'"'"'_d M"_1-c-d N barrier layer; and

e. forming a first contact on the heavily doped contact layer and a second contact on the substrate, wherein x, y, a, b, c, and d are numbers, each number having a magnitude between zero and one and wherein x+y, a+b, and c+d, each have a magnitude between zero and one.

26. The method of claim 25 wherein the substrate is a selected polytype of silicon carbide (SiC) selected from a group of polytypes of SiC including 2H-SiC, 4H-SiC, and a-axis oriented 6H-SiC.

27. The method of claim 26 wherein the SiC substrate is oriented to have a high mobility axis aligned with the direction of electron current.

28. A method for fabricating a light emitting diode comprising the steps of:

a. forming a first barrier layer on a conductive substrate, the first barrier layer being a first selected composition;

b. forming an active region of a second selected composition on the first barrier layer;

C. forming a second barrier layer of a third selected composition on the active region;

d. forming a heavily doped contact layer of a fourth selected composition on the second barrier layer; and

e. forming a first contact on the heavily doped contact layer and a second contact on the substrate, wherein the first, second, third and fourth selected compositions are selected from a group of compositions M_x M'"'"'_y M"_1-x-y N, M_a M'"'"'_b M"_1-a-b N, M_c M'"'"'_d M"_1-c-d N and M_e M'"'"'_f M"_1-e-f N, respectively, wherein x, y, a, b, c, d, e, and f are numbers, each number having a magnitude between zero and one and wherein x+y, a+b, c+d, and e+f, each has a magnitude between zero and one.

29. The method of claim 28 wherein the substrate is a selected polytype of silicon carbide (SC) selected from a group of polytypes of SC including 2H-SiC, 4H-SiC, and a-axis oriented 6H-SiC.

30. The method for fabricating a light emitting diode with a Bragg mirror, the method comprising the steps of:

a. forming a Bragg mirror including alternating layers of AlN, GaN, InN, or their alloys on a conductive substrate;

b. forming an M_x M'"'"'_y M"_1-x-y N barrier layer on a conductive substrate, wherein M, M'"'"', and M" are metals compatible with nitrogen (N) in the composition M_x M'"'"'_y M"_1-x-y N, and the composition M_x M'"'"'_y M"_1-x-y N is stable at room temperatures and pressures;

c. forming an M_a M'"'"'_b M"_1-a-b N active region on the M_x M'"'"'_y M"_1-x-y N barrier layer;

d. forming an M_c M'"'"'_d M"_1-c-d N barrier layer on the M_a M'"'"'_b M"_1-a-b N active region;

e. forming a heavily doped contact layer on the M_c M'"'"'_d M"_1-c-d N barrier layer; and

f. forming a first contact on the heavily doped contact layer and a second contact on the substrate, wherein x, y, a, b, c, and d are numbers, each number having a magnitude between zero and one and wherein x+y, a+b, and c+d, each have a magnitude between zero and one.

31. The method of claim 30 wherein the substrate is a selected polytype of silicon carbide (SiC), selected from a group of polytypes of SiC including 2H-SiC, 4H-SiC, and a-axis oriented 6H-SiC.

32. The method for fabricating light emitting diodes (LEDs) comprising the steps of:

a. forming a first barrier layer on a conductive substrate;

b. forming an active region on the first barrier layer;

C. forming a second barrier layer on the active region;

d. forming a heavily doped contact layer on the second barrier layer;

e. masking each LED device area;

f. mesa etching trenches between the LED device areas and leaving the LEDs as mesas separated by the trenches;

g. passivating sidewalls of the LEDs;

h. forming a first contact on the heavily doped contact layer and a second contact on the substrate; and

i. slicing the substrate only in the trenches.