Group lll nitride emitting devices with gallium-free layers

• US 20040051108A1
• Filed: 06/27/2003
• Published: 03/18/2004
• Est. Priority Date: 12/28/2000
• Status: Active Grant

• Current Assignee: Thomson Licensing (Vantiva SA)
• Original Assignee: Thomson Licensing (Vantiva SA)
• Inventors: Nortrup, Kevin Eugene
• Granted Patent: US 7,345,700 B2
• Time in Patent Office: Days
• US Class Current: 257/82
• CPC Class Codes: H01L 33/32 containing nitrogen
• CPC Class Codes: H04N 17/045 Self-contained testing apparatus
• CPC Class Codes: H04N 21/47 End-user applications
• CPC Class Codes: H04N 21/4884 for displaying subtitles

Abstract

The present invention is a semiconductor structure for light emitting devices that can emit in the red to ultraviolet portion of the electromagnetic spectrum. The semiconductor structure includes a first cladding layer of a Group III nitride, a second cladding layer of a Group III nitride, and an active layer of a Group III nitride that is positioned between the first and second cladding layers, and whose bandgap is smaller than the respective bandgaps of the first and second cladding layers. The semiconductor structure is characterized by the absence of gallium in one or more of these structural layers.

Claims

1. A semiconductor structure (10) for light emitting devices that can emit in the red to ultraviolet portion of the electromagnetic spectrum, said structure (10) comprising:

a first cladding layer (11) of Al_xIn_yGa_1-x-yN, where 0≦

x≦

1 and 0≦

y≦

1 and (x+y)≦

1;

a second cladding layer (12) of Al_xIn_yGa_1-x-yN, where 0≦

x≦

1 and 0≦

y≦

1 and (x+y)≦

1; and

an active layer (13) of Al_xIn_yGa_1-x-yN, where 0≦

x≦

1 and 0≦

y≦

1 and 0≦

(x+y)≦

1, said active layer (13) positioned between said first cladding layer (11) and said second cladding layer (12);

wherein said first and second cladding layers (11-12) have respective bandgaps that are each larger than the bandgap of said active layer (13); and

wherein at least one of the layers selected from the group consisting of said first cladding layer (11), said second cladding layer (12), and said active layer (13) is characterized by the absence of gallium.

2. A semiconductor structure (10) according to claim 1, wherein said first cladding layer (11) consists essentially of Al_xIn_1-xN, where 0<

x≦

1, and is characterized by the absence of gallium.

3. A semiconductor structure (10) according to claim 1, wherein said second cladding layer (12) consists essentially of Al_xIn_1-xN, where 0<

x≦

1, and is characterized by the absence of gallium.

4. A semiconductor structure (10) according to claim 1, wherein:

said first cladding layer (11) and said second cladding layer (12) have opposite conductivity types; and

said active layer (13) consists essentially of Al_xIn_1-xN, where 0≦

x<

1, and is characterized by the absence of gallium.

5. A semiconductor structure (10) according to claim 1, wherein said active layer (13) has a first surface (14) and a second surface (15), said first surface (14) of said active layer (13) being in contact with said first cladding layer (11) and said second surface (15) of said active layer (13) being in contact with said second cladding layer (12).

6. A semiconductor structure (10) according to any of claims 1-5, wherein said first cladding layer (11) is characterized by the absence of gallium.

7. A semiconductor structure (10) according to any of claims 1-5, wherein said second cladding layer (12) is characterized by the absence of gallium.

8. A semiconductor structure (10) according to any of claims 1-5, wherein said active layer (13) is characterized by the absence of gallium.

9. A semiconductor structure (10) according to any of claims 1-5, wherein said active layer (13) is doped.

10. A semiconductor structure (10) according to any of claims 1-5, wherein said active layer (13) is undoped.

11. A semiconductor structure (10) according to any of claims 1-5, wherein said first cladding layer (11) and said second cladding layer (12) have opposite conductivity types.

12. A semiconductor structure (10) according to any of claims 1-5, further comprising:

a silicon carbide substrate (17);

wherein said first cladding layer (11) is positioned between said silicon carbide substrate (17) and said active layer (13); and

wherein said silicon carbide substrate (17) and said first cladding layer (11) have the same conductivity type.

13. A semiconductor structure (10) according to claim 12, wherein said silicon carbide substrate (17) is in contact with said first cladding layer (11), opposite said active layer (13).

14. A semiconductor structure (10) according to claim 13, wherein:

said first cladding layer (11) has a first surface (21) and a second surface (22), said first surface (21) of said first cladding layer (11) being in contact with said silicon carbide substrate (17), and said second surface (22) of said first cladding layer (11) being in contact with said active layer (13); and

wherein the composition of said first cladding layer (11) is progressively graded such that the crystal lattice at said first surface (21) of said first cladding layer (11) more closely matches the crystal lattice of said silicon carbide (17), and the crystal lattice at said second surface (22) of said first cladding layer (11) more closely matches the crystal lattice of said active layer (13).

15. A semiconductor structure (10) according to claim 12, wherein said silicon carbide substrate (17) is a single crystal.

16. A semiconductor structure (10) according to claim 12, wherein said silicon carbide (17) is a polytype selected from the group consisting of 3C, 4H, 6H, and 15R.

17. A semiconductor structure (10) according to claim 12, wherein said silicon carbide (17) is a single crystal silicon carbide substrate (17) of a polytype selected from the group consisting of 3C, 4H, 6H, and 15R.

18. A semiconductor structure (10) according to claim 12, further comprising discrete crystal portions (28) selected from the group consisting of gallium nitride and indium gallium nitride, said discrete crystal portions (28) positioned between said first cladding layer (11) and said silicon carbide substrate (17), said discrete crystal portions (28) being present in an amount sufficient to reduce the barrier between said first cladding layer (11) and said silicon carbide substrate (17), but less than an amount that would detrimentally affect the function of any resulting light emitting device formed on said silicon carbide substrate (17).

19. A semiconductor structure (10) according to claim 12, further comprising:

a first ohmic contact (25), wherein said silicon carbide substrate (17) is positioned between said first ohmic contact (25) and said first cladding layer (11); and

a second ohmic contact (26), wherein said second cladding layer (12) is positioned between said second ohmic contact (26) and said active layer (13).

20. A semiconductor structure (10) according to claim 19, wherein said first and second ohmic contacts (25-26) comprise at least one metal selected from the group consisting of aluminum, nickel, titanium, gold, platinum, and vanadium, and layers, alloys, and blends thereof.

21. A semiconductor structure (10) according to claim 19, further comprising:

a Group III nitride contact layer (27), wherein said contact layer (27) is positioned between said second ohmic contact (26) and said second cladding layer (12), and said contact layer (27) and said second cladding layer (12) have the same conductivity type.

22. A semiconductor structure (10) according to claim 21, wherein said contact layer (27) is a p-type contact layer (27) formed of a Group III nitride selected from the group consisting of gallium nitride, indium nitride, Al_xIn_1-xN, where 0<

x<

1, Al_xGa_1-xN, where 0<

x<

1, In_xGa_1-xN, where 0<

x<

1, and Al_xIn_yGa_1-x-yN, where 0<

x<

1 and 0<

y<

1 and (x+y)<

1.

23. A semiconductor structure (10) according to claim 21, wherein said contact layer (27) is a p-type superlattice formed from a plurality of Group III nitride layers selected from the group consisting of gallium nitride, indium nitride, Al_xIn_1-xN, where 0<

x<

1, Al_xGa_1-xN, where 0<

x<

1, In_xGa_1-xN, where 0<

x<

1, and Al_xIn_yGa_1-x-yN, where 0<

x<

1 and 0<

y<

1 and (x+y)<

1.

24. A semiconductor structure (10) according to claim 23, wherein said superlattice is formed from alternating layers of two Group III nitride layers selected from the group consisting of gallium nitride, indium nitride, Al_xIn_1-xN, where 0<

x<

1, Al_xGa_1-xN, where 0<

x<

1, In_xGa_1-xN, where 0<

x<

1, and Al_xIn_yGa_1-x-yN, where 0<

x<

1 and 0<

y<

1 and (x+y)<

1.

25. A semiconductor structure (10) according to claim 24, wherein said superlattice is formed from either a plurality of alternating layers of gallium nitride and In_xGa_1-xN, where 0<

x<

1, or a plurality of alternating layers of gallium nitride and Al_xGa_1-xN, where 0<

x<

1.

26. A semiconductor structure (10) according to any of claims 1-5, further comprising a Group III nitride contact layer (27), wherein said contact layer (27) is in contact with said second cladding layer (12), opposite said active layer (13), and said contact layer (27) and said second cladding layer (12) have the same conductivity type.

27. A semiconductor structure (10) according to any of claims 1-5, further comprising:

a silicon carbide substrate (17), wherein said silicon carbide substrate (17) and said first cladding layer (11) have the same conductivity type; and

a conductive buffer layer (23);

wherein said first cladding layer (11) is positioned between said silicon carbide substrate (17) and said active layer (13); and

wherein said conductive buffer layer (23) is positioned between said silicon carbide substrate (17) and said first cladding layer (11).

28. A semiconductor structure (10) according to claim 27, wherein said conductive buffer layer (23) is a Group III nitride selected from the group consisting essentially of aluminum gallium nitride having the formula Al_xGa_1-xN, where 0≦

x≦

1, and aluminum indium nitride having the formula Al_xIn_1-xN, where 0≦

x≦

1.

29. A semiconductor structure (10) according to claim 27, further comprising a Group III nitride transition layer (24), said transition layer (24) being positioned between said conductive buffer layer (23) and said first cladding layer (11), and having the same conductivity type as said first cladding layer (11).

30. A semiconductor structure (10) according to claim 27, further comprising:

a first ohmic contact (25), wherein said silicon carbide substrate (17) is positioned between said first ohmic contact (25) and said conductive buffer layer (23); and

a second ohmic contact (26), wherein said second cladding layer (12) is positioned between said second ohmic contact (26) and said active layer (13).

31. A semiconductor structure (10) according to claim 27, further comprising:

a Group III nitride contact layer (27), wherein said contact layer (27) and said second cladding layer (12) have the same conductivity type;

a first ohmic contact (25), wherein said silicon carbide substrate (17) is positioned between said first ohmic contact (25) and said conductive buffer layer (23); and

a second ohmic contact (26), wherein said contact layer (27) is positioned between said second ohmic contact (26) and said second cladding layer (12).

32. A semiconductor structure (10) according to claim 31, wherein said contact layer (27) is a p-type superlattice formed from a plurality of Group III nitride layers selected from the group consisting of gallium nitride, indium nitride, Al_xIn_1-xN, where 0<

x<

1, Al_xGa_1-xN, where 0<

x<

1, In_xGal_1-xN, where 0<

x<

1, and Al_xIn_yGa_1-x-yN, where 0<

x<

1 and 0<

y<

1 and (x+y)<

1.

33. A semiconductor structure (10) according to claim 32, wherein said superlattice is formed from alternating layers of two Group III nitride layers selected from the group consisting of gallium nitride, indium nitride, Al_xIn_1-xN, where 0<

x<

1, Al_xGa_1-xN, where 0<

x<

1, In_xGa_1-xN, where 0<

x<

1, and Al_xIn_yGa_1x-yN, where 0<

x<

1 and 0<

y<

1 and (x+y)<

1.

34. A semiconductor structure (10) according to any of claims 1-5, further comprising:

a Group III nitride transition layer (24), said transition layer (24) in contact with said first cladding layer (11) and opposite said active layer (13), and having the same conductivity type as said first cladding layer (11);

a conductive buffer layer (23) in contact with said transition layer (24) and opposite said first cladding layer (11), said conductive buffer layer (23) being a Group III nitride selected from the group consisting of aluminum gallium nitride having the formula Al_xGa_1-xN, where 0≦

x≦

1, and aluminum indium nitride having the formula Al_xIn_1-xN, where 0≦

x≦

1;

a single crystal silicon carbide substrate (17) in contact with said conductive buffer layer (23) and opposite said transition layer (24), said silicon carbide substrate (17) having a polytype selected from the group consisting of 3C, 4H, 6H, and 15R, and said silicon carbide substrate (17) and said first cladding layer (11) having the same conductivity type;

a first ohmic contact (25) to said silicon carbide substrate (17) and opposite said conductive buffer layer (23), said first ohmic contact (25) comprising at least one metal selected from the group consisting of aluminum, nickel, titanium, gold, platinum, and vanadium, and layers, alloys, and blends thereof;

a Group III nitride contact layer (27) on said second cladding layer (12) and opposite said active layer (13), wherein said contact layer (27) is a p-type superlattice formed from a plurality of Group III nitride layers selected from the group consisting of gallium nitride, indium nitride, Al_xIn_1-xN, where 0<

x<

1, Al_xGa_1-xN, where 0<

x<

1, In_xGa_1-xN, where 0<

x<

1, and Al_xIn_yGa_1-x-yN, where 0<

x<

1 and 0<

y<

1 and (x+y)<

1;

a second ohmic contact (26) to said Group III nitride contact layer (27) and opposite said second cladding layer (12), said second ohmic contact (26) comprising at least one metal selected from the group consisting of aluminum, nickel, titanium, gold, platinum, and vanadium, and layers, alloys, and blends thereof; and

wherein said first cladding layer (11) and said second cladding layer (12) have opposite conductivity types.