Method of forming green light emitting diode in silicon carbide

• US 5,604,135 A
• Filed: 08/12/1994
• Issued: 02/18/1997
• Est. Priority Date: 08/12/1994
• Status: Expired due to Term

• Current Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Original Assignee: Cree Research, Inc.
• Inventors: Suvorov, Alexander V., Edmond, John A.
• Primary Examiner(s): Bowers, Jr., Charles L.
• Assistant Examiner(s): Radomsky, Leon
• Application Number:
  US08/290,020
• Time in Patent Office: 921 Days
• Field of Search: 437/22, 437/23, 437/25, 437/100, 437/127, 437/905, 148/DIG. 148, 117/902, 117/951, 257/77, 257/87, 257/102, 257/103
• US Class Current: 438/45
• CPC Class Codes: H01L 33/0054 for devices with an active region comprising only group IV elements
• CPC Class Codes: H01L 33/16 with a particular crystal structure or orientation, e.g. polycrystalline, amorphous or porous
• CPC Class Codes: H01L 33/34 containing only elements of Group IV of the Periodic Table
• CPC Class Codes: Y10S 148/148 Silicon carbide
• CPC Class Codes: Y10S 438/931 Silicon carbide semiconductor

Abstract

A light emitting diode is disclosed that emits in the green portion of the visible spectrum, along with a method of producing the diode. The light emitting diode comprises a 6H silicon carbide substrate having a planar surface inclined more than one degree off axis toward one of the <11 20> directions; an ohmic contact to the substrate; a first epitaxial layer of 6H silicon carbide on the inclined surface of the substrate and having a first conductivity type; a second epitaxial layer of 6H silicon carbide on the first layer and having the opposite conductivity type for forming a p-n junction between the first and second layers; and an ohmic contact to the second epitaxial layer. The diode produces a peak wavelength of between about 525 and 535 nanometers with a spectral half width of no more than about 90 nanometers.

Claims

1. A method of producing a true green light emitting diode in silicon carbide, the method comprising:

depositing a first epitaxial layer of 6H silicon carbide having a first conductivity type on a prepared planar surface of a 6H silicon carbide substrate in which the planar surface is inclined more than one degree off axis with respect to a basal plane thereof substantially towards one of the <

11 20>

directions;

directing an ion implantation beam of dopant ions onto the first epitaxial layer while maintaining the layer at a temperature high enough to position dopant atoms at substitutional lattice sites in the epitaxial layer but less than the temperature at which excessive graphitization of the silicon carbide would occur to produce an implanted layer on said first epitaxial layer having the opposite conductivity type from said first layer, and to thereby produce a p-n junction between said first layer and said implanted layer; and

removing graphite from the surface of the implanted layer without affecting the electronic characteristics of the implanted layer or the junction.

2. A method of producing a light emitting diode according to claim 1 wherein the step of directing an ion implantation beam while maintaining the layer at a high temperature comprises maintaining the layer at a temperature above about 1500°

C. and below about 1900°

C.

3. A method of producing a light emitting diode according to claim 1 wherein the step of directing an ion implantation beam while maintaining the layer at a high temperature comprises maintaining the layer at a temperature of between about 1700°

and 1800°

C.

4. A method of producing a light emitting diode according to claim 1 wherein the step of removing graphite from the surface of the implanted layer comprises annealing the surface in the presence of a dopant that would produce a conductivity type the same as that of the dopant implanted.

5. A method of producing a light emitting diode according to claim 4 wherein the step of annealing the surface further comprises depositing a thin epitaxial layer of 6H silicon carbide on the implanted layer having the same conductivity type as the implanted layer.

6. A method of producing a light emitting diode according to claim 4 wherein:

the step of depositing a first layer comprises depositing an n-type layer;

the step of directing an ion beam comprises directing a beam of acceptor dopant ions to form a p-type implanted layer; and

the step of annealing the surface comprises annealing the surface in the presence of aluminum.

7. A method of producing a light emitting diode according to claim 4 wherein:

the step of depositing a first layer comprises depositing a p-type layer;

the step of directing an ion beam comprises directing a beam of donor dopant ions to form an n-type implanted layer; and

the step of annealing the surface comprises annealing the surface in the presence of nitrogen.

8. A method of producing a light emitting diode according to claim 1 wherein the step of removing graphite from the surface of the implanted layer comprises exposing the surface to an oxygen plasma.

9. A method according to claim 1 further comprising the step of depositing an additional epitaxial layer of 6H silicon carbide upon the implanted layer to encourage current spreading and the resulting light output of the diode.

10. A method of producing a light emitting diode according to claim 1 wherein the step of ion implantation comprises directing the ion beam at an energy of between about 20 and 200 keV at a dosage of between about 5×

10¹⁵ and 5×

10¹⁷ ions per square centimeter.

11. A method of producing a true green light emitting diode in silicon carbide, the method comprising:

depositing a first epitaxial layer of 6H silicon carbide on a prepared planar surface of a 6H silicon carbide substrate in which the planar surface is inclined more than one degree off axis with respect to a basal plane thereof substantially towards one of the <

11 20>

directions;

directing an ion implantation beam of dopant ions onto the first epitaxial layer while maintaining the layer at a temperature high enough to position dopant atoms at substitutional lattice sites in the epitaxial layer but less than the temperature at which excessive graphitization of the silicon carbide would occur to produce an implanted layer on said first epitaxial layer having the opposite conductivity type from said first layer, and to thereby produce a p-n junction between said first layer and said implanted layer;

annealing the surface in the presence of a dopant that would produce a conductivity type the same as that of the dopant implanted; and

depositing an additional epitaxial layer of 6H silicon carbide upon the implanted layer to encourage current spreading and the resulting light output of the diode.

12. A method according to claim 11 wherein the step of depositing the additional epitaxial layer on the implanted layer comprises depositing an epitaxial layer with the same conductivity type as the implanted layer.

13. A method according to claim 11 wherein:

the step of depositing a first layer comprises depositing an n-type layer;

the step of directing an ion beam comprises directing a beam of acceptor dopant ions to form a p-type implanted layer;

the step of annealing the surface comprises annealing the surface in the presence of aluminum; and

the step of depositing an additional epitaxial layer comprises depositing a p-type layer.

14. A method of producing a light emitting diode according to claim 11 wherein:

the step of depositing a first layer comprises depositing a p-type layer;

the step of directing an ion beam comprises directing a beam of donor dopant ions to form an n-type implanted layer;

the step of annealing the surface comprises annealing the surface in the presence of nitrogen; and

the step of depositing an additional epitaxial layer comprises depositing an n-type layer.

15. A method according to claim 11 wherein the step of directing the ion implantation beam comprises directing the beam against the (0001) silicon face of said first epitaxial layer.

16. A method according to claim 11 wherein the step of directing the ion implantation beam comprises directing the beam against the (0001) carbon face of said first epitaxial layer.

17. A method of producing a light emitting diode according to claim 11 wherein the step of ion implantation comprises directing the ion beam at an energy of between about 20 and 200 keV at a dosage of between about 5×

10¹⁵ and 5×

10¹⁷ ions per square centimeter.