Semi-insulating silicon carbide without vanadium domination

• US 6,396,080 B2
• Filed: 05/25/2001
• Issued: 05/28/2002
• Est. Priority Date: 05/18/1999
• Status: Expired due to Term

• Current Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Brady, Mark, Tsvetkov, Valeri F., Carter, Calvin H. Jr.
• Primary Examiner(s): Clark, Sheila V.
• Application Number:
  US09/866,129
• Publication Number:
  US 20010023945A1
• Time in Patent Office: 368 Days
• Field of Search: 257/77,76,78
• US Class Current: 257/77
• CPC Class Codes: C30B 23/00 Single-crystal growth by condensing evaporated or sublimed materials
• CPC Class Codes: C30B 29/36 Carbides
• CPC Class Codes: C30B 33/00 After-treatment of single crystals or homogeneous polycrystalline material with defined structure C30B31/00 takes precedence
• CPC Class Codes: H01L 29/1608 Silicon carbide
• CPC Class Codes: H01L 29/778 with two-dimensional charge carrier gas channel, e.g. HEMT ; with two-dimensional charge-carrier layer formed at a heterojunction interface H01L29/803 takes precedence
• CPC Class Codes: H01L 29/78 with field effect produced by an insulated gate H01L29/7725, H01L29/775, H01L29/778 take precedence
• CPC Class Codes: H01L 29/812 with a Schottky gate H01L29/7725, H01L29/775, H01L29/778, H01L29/806 take precedence; with Schottky contact on top of heterojunction gate H01L29/802

Abstract

A semi-insulating bulk single crystal of silicon carbide is disclosed that has a resistivity of at least 5000 Ω-cm at room temperature and a concentration of trapping elements that create states at least 700 meV from the valence or conduction band that is below the amounts that will affect the resistivity of the crystal, preferably below detectable levels. A method of forming the crystal is also disclosed, along with some resulting devices that take advantage of the microwave frequency capabilities of devices formed using substrates according to the invention.

Claims

1. A semi-insulating silicon carbide single crystal comprising:

donor dopants, acceptor dopants, and intrinsic point defects in said silicon carbide single crystal;

wherein the number of dopants of a first conductivity type is greater than the number of dopants of a second conductivity type; and

the number of intrinsic point defects in said silicon carbide crystal that act to compensate the predominating first type dopant is greater than the numerical difference by which said first type of dopant predominates over said second type of dopant; and

the concentration of transition elements is less than 1×

10¹⁶;

said silicon carbide single crystal having a resistivity of at least 5000 ohm-cm at room temperature.

2. A silicon carbide single crystal according to claim 1 having a concentration of nitrogen atoms below 1×

10¹⁷ cm<sup>−

3</sup>.

3. A silicon carbide single crystal according to claim 1 wherein the concentration of vanadium is less than 1×

10¹⁶ cm<sup>−

3</sup>.

4. A semi-insulating silicon carbide crystal according to claim 1 wherein said first type dopants are donors, said second type dopants are acceptors and said intrinsic point defects act as acceptors.

5. A semi-insulating silicon carbide crystal according to claim 4 wherein said acceptors include boron.

6. A semi-insulating silicon carbide crystal according to claim 1 wherein said first type dopants are acceptors, said second type dopants are donors and said intrinsic point defects act as donors.

7. A silicon carbide single crystal according to claim 1 wherein the polytype of the silicon carbide is selected from the group consisting of the 3C, 4H, 6H and 15R polytypes.

8. A silicon carbide single crystal according to claim 1 wherein the concentration of nitrogen is 5×

10¹⁶ cm<sup>−

3</sup> or less.

9. A silicon carbide single crystal according to claim 1 wherein the concentration of vanadium is below the level that can be detected by secondary ion mass spectroscopy (SIMS).

10. A silicon carbide single crystal according to claim 1 wherein the concentration of vanadium is less than 1×

10¹⁴ cm<sup>−

3</sup>.

11. A silicon carbide single crystal according to claim 1 having a resistivity of at least 10,000 Ω

-cm at room temperature.

12. A silicon carbide single crystal according to claim 1 having a resistivity of at least 50,000 Ω

-cm at room temperature.

13. A transistor having a substrate that comprises the bulk single crystal according to claim 1.

14. A transistor according to claim 13 selected from the group consisting of:

metal-semiconductor field-effect transistors, metal-insulator field effect transistors, and high electron mobility transistors.

15. A semi-insulating bulk single crystal of silicon carbide having a resistivity of at least 5000 Ω

-cm at room temperature and a concentration of trapping elements that create states at least 700 meV from the valence or conduction band that is below the amount that affects the electrical characteristics of the crystal.

16. A silicon carbide single crystal according to claim 15 having a concentration of nitrogen atoms below 1×

10¹⁷ cm<sup>−

3</sup>.

17. A silicon carbide single crystal according to claim 15 wherein the concentration of vanadium is less than 1×

10¹⁶ cm<sup>−

3</sup>.

18. A silicon carbide single crystal according to claim 15 wherein the polytype of the silicon carbide is selected from the group consisting of the 3C, 4H, 6H and 15R polytypes.

19. A silicon carbide single crystal according to claim 15 wherein the concentration of nitrogen is 5×

10¹⁶ cm<sup>−

3</sup> or less.

20. A silicon carbide single crystal according to claim 15 wherein the concentration of vanadium is below the level that can be detected by secondary ion mass spectroscopy (SIMS).

21. A silicon carbide single crystal according to claim 15 wherein the concentration of vanadium is less than 1×

10¹⁴ cm<sup>−

3</sup>.

22. A silicon carbide single crystal according to claim 15 having a resistivity of at least 10,000 Ω

-cm at room temperature.

23. A silicon carbide single crystal according to claim 15 having a resistivity of at least 50,000 Ω

-cm at room temperature.

24. A transistor having a substrate that comprises the bulk single crystal according to claim 15.

25. A transistor according to claim 24 selected from the group consisting of:

metal-semiconductor field-effect transistors, metal-insulator field effect transistors, and high electron mobility transistors.