Vanadium compensated, SI SiC single crystals of NU and PI type and the crystal growth process thereof

Abstract

In a crystal growth apparatus and method, polycrystalline source material and a seed crystal are introduced into a growth ambient comprised of a growth crucible disposed inside of a furnace chamber. In the presence of a first sublimation growth pressure, a single crystal is sublimation grown on the seed crystal via precipitation of sublimated source material on the seed crystal in the presence of a flow of a first gas that includes a reactive component that reacts with and removes donor and/or acceptor background impurities from the growth ambient during said sublimation growth. Then, in the presence of a second sublimation growth pressure, the single crystal is sublimation grown on the seed crystal via precipitation of sublimated source material on the seed crystal in the presence of a flow of a second gas that includes dopant vapors, but which does not include the reactive component.

Description

Reaction (1) is, in essence, CVD deposition of metal Me, and it yields elemental metal in the form of solid precipitate, Me↓. This reaction is partial and does not consume the entire amount of gaseous metal halide present in the reactive atmosphere.

In the second step, which follows the first step and which occurs as gas mixture 26 carrying the remaining metal halide vapor permeates the intermediate layer 22b of thermal insulation, said intermediate layer 22b situated at temperatures approximately between 300 and 900° C., gaseous metal halide reacts with hydrogen and nitrogen according to the following reaction (2) (reaction (2) is written without stoichiometric coefficients):
MeX+H₂+N₂⇒MeN↓+HX,  (2)
where MeN↓ is a precipitate of solid metal nitride MeN. This reaction leads to the removal of residual N₂ from the atmosphere by binding nitrogen into solid metal nitride, MeN. Reaction (2) is, in essence, CVD deposition of metal nitride MeN. The residual nitrogen in reaction (2) comes from N₂ released into the furnace chamber 20 from graphite parts, such as graphite crucible 21 and thermal insulation 22.

In the third step which follows the second step, the gas mixture 26 carrying the remaining metal halide vapor moves to inner layer 22c of thermal insulation, said inner layer 22c situated at temperatures above 900° C., the remaining metal halide reacts with hydrogen and carbon of thermal insulation to form metal carbide according to the following reaction (3) (reaction (3) is written without stoichiometric coefficients):
MeX+H₂+C⇒MeC↓+HX,  (3)
where Med↓ is a precipitate of solid metal carbide. Reaction (3) is, in essence, CVD deposition of metal carbide, MeC.

All three aforementioned reactions produce gaseous hydrogen halide, HX, as a byproduct. Driven by the flow of gas mixture 26 into chamber 20 and diffusion, gaseous hydrogen halide permeates the bulk (the walls, the lid, and the base) of graphite crucible 21 situated at temperatures between 2000 and 2400° C., where said gaseous hydrogen halide reacts with carbon-bound boron and converts it into volatile boron halides according to the following reaction (4) (reaction (4) is written without stoichiometric coefficients):
BC+HX⇒BX_n↑+CH_m↑,  (4)
where BC symbolizes carbon-bound boron, BX_n↑ symbolizes volatile boron-halogen molecular associates and CH_m↑ symbolizes gaseous hydrocarbons. In the case of hydrogen chloride, HCl, the dominant products of reaction (4) are BCl, BCl₂ and C₂H₂.

The volatile products of reactions (1)-(4) are removed from the crystal growth cell and then from the chamber by the flow of gas mixture 26 into chamber 20, as symbolized by arrows 25a in FIG. 2.

Due to reactions (1)-(3), the bulk of thermal insulation 22, becomes coated with thin deposits of metal, metal nitride and metal carbide. Such coatings reduce to some degree the ability of the insulation 22 to absorb gases, but they do not affect adversely thermal properties of said insulation.

At high temperatures of SiC sublimation growth (2000-2400° C.), gaseous hydrogen halide also reacts with silicon carbide leading to the appearance of volatile silicon-halogen and hydrocarbon molecular associates according to the following reaction (5) (reaction (5) is written without stoichiometric coefficients):
SiC+HX⇒SiX_m↑+CH_n↑,  (5)
where SiX_m↑ symbolizes volatile silicon halides and CH_n↑ symbolizes gaseous hydrocarbons. In the case of hydrogen chloride, HCl, the dominant products of reaction (5) are SiCl₂ and C₂H₂. In practical terms, the yield of reaction (5) is insignificant, and no noticeable silicon or carbon losses from the crucible occur.

FIG. 3 shows a SiC crystal growth apparatus for the growth of high-purity SiC crystals. In one desirable, non-limiting embodiment, the metal halide used for the removal of nitrogen and boron from the growth ambient is tantalum pentachloride, TaCl₅.

With reference to FIG. 3, the growth process is carried out in a growth cell 8 (e.g., the growth cell 8 of FIG. 1) which includes a chamber 10, which includes growth crucible 11 and thermal insulation 12. Growth crucible 11 is made of dense, fine-grain, isostatically-molded graphite, such as “ATJ” available from UCAR Carbon Company of New York, N.Y. Thermal insulation 12 is made from light-weight, fibrous graphite, such as Calcarb® CBCF available from Mersen USA, St. Mary's, PA. Prior to use in SiC growth, all graphite parts and components are commercially halogen-purified to the total ash level of 5 ppm by weight. At present, this is the purest graphite available commercially.

Growth crucible 11 is charged with SiC sublimation source 14 disposed at the crucible bottom and SiC seed crystal 15 disposed at the crucible top. RF coil 16 provides heating to growth crucible 11. Upon reaching SiC sublimation growth temperatures between 2000 and 2400° C., source 14 vaporizes and fills the interior of crucible 11 with SiC vapors 19 that include volatile molecules of Si₂C, SiC₂ and Si. Driven by temperature gradients, the SiC vapors 19 migrate towards seed 15, as symbolized by arrows 19, and precipitate on SiC seed crystal 15 causing growth of SiC single crystal 17 on SiC seed crystal 15.

The SiC growth apparatus of FIG. 3 includes gas delivery system 30, which serves to generate the vapor of metal halide, mix the vapor with the carrier gas (Ar+H₂) and bring the gas mixture 26 into the furnace chamber 10 through a heated inlet 10a. This gas mixture has the following composition: H₂ (desirably, between 2 and 5% by volume), TaCl₅ vapor (desirably, between 100 and 1000 ppm by volume), Ar (the balance). Argon pre-mixed with hydrogen to a desired level can be used as a carrier gas.

The pressure and the flows of the gaseous components are controlled using means known in the art, e.g., U.S. Pat. No. 6,410,433, such as upstream valves 35 and 36, mass flow controllers 35a, 36a, valves 35b and 36b, downstream valve 39 and vacuum pump 37. Other common and conventional parts of the gas delivery system, such as pressure gauges, solenoid valves, filters, electronic control, etc. are not shown. During growth of SiC single crystal 17, the total pressure in chamber 10 is maintained, desirably, between 5 and 50 Torr.

In FIG. 3, the source of gaseous TaCl₅ is solid tantalum pentachloride 32, which is contained in a sealed vessel 31 having an interior volume of about 100 cm³. Vessel 31 is made of corrosion resistant alloy, such as type 316 stainless steel, and is heated by a heater 31a to create a spatially uniform temperature distribution in the vessel. During growth of SiC single crystal 17, the temperature of vessel 31 is maintained, desirably between 75 and 120° C. At these temperatures, solid TaCl₅ vaporizes and generates a TaCl₅ vapor pressure between 0.1 and 1 Torr.

The Ar+H₂ mixture is supplied into vessel 31 at a flow rate, desirably, between 20 and 50 sccm. Inside vessel 31, the Ar+H₂ mixture mixes with the TaCl₅ vapor and carries it through the valve 36b to manifold 38. Valve 36b and manifold 38 are heated by flexible tape-heaters 38a to a temperature equal or above that of the vessel 31 and, desirably, to a temperature between 100 and 200° C.

The main flow of the Ar+H₂ mixture is supplied through the valve 35, mass flow controller 35a and valve 35b to manifold 38 at a flow rate, desirably, between 50 and 300 sccm. The gaseous byproducts of the reactions taking place in chamber 10 flow through an outlet 10b, a valve 39 and vacuum pump 37 to a scrubber (not shown) for neutralization.

Results of high-purity 6H SiC growth runs carried out in the apparatus shown in FIG. 3 are shown in the following Table 1. The nitrogen concentration in grown SiC single crystal 17 was between 4·10¹⁵ and 7·10¹⁵ cm⁻³, and the boron concentration was between 2·10¹⁵ and 8·10¹⁵ cm⁻³. Compared to the prior art, a 4-10 fold reduction in the levels of background N and B in SiC single crystals 17 were observed.

TABLE 1
			Activation
			Energy of
	Impurity Content, cm−3	Rho @ RT,	Resistivity
	Nitrogen	Boron	Vanadium	Ohm-cm	(RT-400° C.)
Crystals	Type of Growth	Background	Introduced	Background	Introduced	Background	Introduced	Measured	Extrapolated	eV
6H	Prior Art	8e15-1e17		8e15-3e16			9e16-2e17	1e5-2e11		Variable
6H	High	4e15-7e15		2e15-8e15		<1e14		1e3-1e7		Variable
	Purity
6H	Pl-Type	4e15-7e15			8e15-2e16		9e16-2e17		1e12-1e21	0.9-1.5
4H	Pi-Type								1e14-1e18	1.1-1.5
6H	Nu-Type		8e15-2e16	2e15-8e15				(1-2)e11		0.78-0.80
4H	Nu-Type							(2-4)e11		0.79-0.82

Growth of SI SiC Single Crystals of PI-Type

The growth process for SI SiC single crystals of PI-type includes two phases, phase (a) and phase (b). Phase (a) is growth under reactive atmosphere aimed at removal of background N and B from the growth ambient, as described above in connection with FIG. 3. The duration of phase (a) of the growth process is, desirably, between 12 and 24 hours. Phase (b) of the process is growth of the final product—fully compensated, semi-insulating PI-type SiC single crystal—said growth carried out using co-doping with V (vanadium) and B (boron).

FIG. 4 shows a SiC crystal growth apparatus for growth of SiC crystals of PI-type. The apparatus is similar to the one shown in FIG. 3, with the exception of the growth crucible 11′. The presence of vanadium and boron dopants in the heated growth crucible during phase (a) of the process is undesirable. Therefore, growth crucible 11′ was devised to permit vanadium and boron dopants to be stored at low temperatures during phase (a) and be subsequently brought into the growth crucible in phase (b). Details regarding growth crucible 11′ and its operation are shown in FIGS. 5A and 5B.

With reference to FIGS. 4, 5A and 5B, growth crucible 11′ is made of dense, fine grain graphite and has a graphite tube 42 attached, i.e., at the bottom. Desirably, the outside diameter of tube 42 is between 30 and 40 mm, while the inner diameter is between 15 and 20 mm. A doping capsule 45 containing the dopant(s) is disposed inside the tube 42 on pushrod 44. Desirably, doping capsule 45 and pushrod 44 are made of an inert material, such as graphite. The prior art use of a doping capsule is disclosed in U.S. Pat. No. 7,608,524 and U.S. Pat. No. 8,216,369, both of which are incorporated herein by reference.

As shown in FIG. 4, tube 42 is supported in the chamber by a structure 42a that has an opening 42b that facilitates evacuation and back filling of the inner space of chamber 10 with process gases. Tube 42, doping capsule 45 and pushrod 44 are included in chamber 10 and are exposed to the same pressure and flows of gaseous components as chamber 10.

At its bottom, graphite pushrod 44 is connected to a metal pushrod 44a using means known in the art, such as threading. The threaded union between graphite pushrod 44 and metal pushrod 44a is shown schematically as item 44b in FIG. 4. Metal pushrod 44a extends to the exterior of the chamber 10 and is sealed via a seal 44c, which forms a vacuum-tight, linear motion feed-through. Seal 44c can be an O-ring seal, a Ferrofluidic linear motion feed-through (e.g., available from FerroTec, Inc. 33 Constitution Drive Bedford, N.H., USA 03110), or a bellows-based vacuum feed-through (e.g., available from Standard Bellows Company, 375 Ella T. Grasso Turnpike, Windsor Locks, Conn., USA 06096).

During growth of SiC single crystal 17, the total pressure in chamber 10, including Tube 42, doping capsule 45 and pushrod 44, is maintained, desirably, between 5 and 50 Torr.

In phase (a) of the process, where growth is carried out in crucible 11′ in the manner described above in connection with FIG. 3, doping capsule 45 is disposed at a distance from crucible 11′, while the opening of tube 42 is sealed with graphite plug 43, as shown in FIG. 5a, Desirably, the substantially undoped portion of SiC single crystal 17 grown during phase (a) is a sacrificial portion. Due to the distance between doping capsule 45 and heated crucible 11′, the temperature of the doping capsule 45 is lower than that of the crucible 11′. Desirably, the temperature of the doping capsule 45 during phase (a) of the process does not exceed 1000° C.

SiC source material 14 is disposed in a source crucible 40 at a distance from the bottom of the crucible 11′ via one or more standoffs 46 that are configured to permit the doping vapors 56 (discussed hereafter) to migrate toward the top of crucible 11′, thus forming a gap or free space 41. Source crucible 40 also forms an annular gap 41a between the outer diameter of the source crucible 40 and the inner diameter of the crucible 11′. During phase (b) of the process, free space 41 and annular gap 41a serve as conduits for doping vapors 56 to reach the growing SiC single crystal 17.

Two non-limiting embodiments of doping capsule 45 are shown in FIGS. 6A and 6B. FIG. 6A is a doping capsule 45a that includes a single compartment 63 for a single dopant 62, for instance, vanadium, while FIG. 6B is a doping capsule 45b that includes two compartments 63a and 63b for two separate dopants 62a and 62b, for instance, vanadium and boron. Each doping capsule 45a and 45b has tapered top 60. Doping capsule 45a has at least one calibrated capillary 61 in communication with compartment 63 serving as a passageway for doping vapors 56. Doping capsule 45b has at least two calibrated capillaries 61a and 61b in communication with compartments 63a and 63b serving as passageways for the doping vapors 56a and 56b.

The principle of operation of each capsule 45a and 45b is based on the well-known phenomenon of effusion, i.e., the slow escape of vapor from a sealed vessel through a small orifice. At high temperatures, the vapor pressure of dopant (62, 62a, or 62b) inside of its space (63, 63a, or 63b) forces the vapor (56, 56a, or 56b) to escape via each capillary (61, 61a, or 61b) in communication with the corresponding space. If the cross section of each capillary is sufficiently small, the vapor pressure of the doping vapors in the capsule does not differ substantially from an equilibrium value.

The laws of effusion are well known and, for given growth conditions, temperature, vapor pressure of inert gas, volatility of the dopant (62, 62a, or 62b), and the diameter and/or length of the capillary (61, 61a, or 61b), the flux of molecules of doping vapors 56, 56a, or 56b escaping the corresponding capsule via the corresponding capillary can be readily calculated. Thus, the dimension of each capillary and the number of capillaries in communication with each space (63, 63a, and/or 63b) can be tailored to achieve a steady and well-controlled flux of doping vapors from the capsule to the growing SiC crystal 17.

Referring back to FIG. 4 and with continuing reference to FIGS. 5A-6, at the completion of phase (a) of the process described above in connection with FIG. 3, valves 36 and 36b of the gas delivery system 30 are closed, thus stopping the flow of metal halide vapor into the furnace chamber 10.

Following termination of the flow of metal halide vapor into the furnace chamber 10, doping capsule 45 i.e., either doping capsule 45a or doping capsule 45b, is moved upward (FIG. 5B) via upward movement of pushrod 44. In FIG. 4, the upward movement of pushrod 44 is accomplished via upward movement of the pushrod 44a through the vacuum seal 44c, said seal operational to preserve the integrity of the atmosphere in the chamber 10. The outside diameter of the doping capsule is sized to the inside diameter of tube 42, so that the doping capsule can be moved via push rod 44 without undue force. The tapered top 60 of the doping capsule pushes plug 43 out of the end of tube 42, thus bringing the doping capsule into the crucible interior, as shown in FIG. 5B. The outside diameter of the doping capsule is sized to the inside diameter of tube 42, so that the doping capsule can be moved via push rod 44 without undue force. The tapered top 60 of the doping capsule pushes plug 43 out of the end of tube 42, thus bringing the doping capsule into the crucible interior, as shown in FIG. 5B.

During phase (b) of the growth process, co-doping of the growing SiC single crystal 17 with vanadium and boron takes place. The dopant(s) are chosen from a group that includes, without limitation, elemental vanadium, elemental boron, vanadium carbide (VC_0.9), boron carbide (B₄C), vanadium boride (VB) and/or vanadium diboride (VB₂).

In one embodiment, for vanadium-boron co-doping, doping capsule 45a is used. Alternatively, doping capsule 45b can be used with vanadium and boron in spaces 63a and 63b, respectively, or vice versa. Doping capsule 45a comprises a single capillary which is 1 mm in diameter and 6 mm long. The single-compartment 63 in doping capsule 45a contains vanadium metal as a source of vanadium and vanadium diboride, VB₂, as a source of boron. Vanadium diboride is taken in the weight ratio to vanadium, desirably, between 1 and 10%.

Results of growth runs aimed at producing vanadium-compensated, semi-insulating PI-type 6H SiC crystals are shown in Table 1 above. Based on SIMS impurity analysis, the grown crystals included between 4·10¹⁵ and 7·10¹⁵CM³ of unintentional background nitrogen. The levels of intentionally introduced boron and vanadium were between 9·10¹⁵ and 2·10¹⁶ cm³ and between 9·10¹⁶ and 2·10¹⁷ cm³, respectively.

The resistivity of the wafers sliced from the grown SI SiC crystals was measured at room temperature using COREMA, a non-contact capacitance-based instrument. The results were, typically, above the measurement limit of 1·10¹² Ohm-cm of the instrument. In order to approximately estimate the room-temperature resistivity, the wafers were measured at elevated temperatures between 100 and 400° C. using a Variable Temperature version of COREMA (VT-COREMA). The results were extrapolated to room temperature, yielding room-temperature resistivity values on the order of 10¹²-10²¹ Ohm-cm with the activation energies between about 0.9 and 1.5 eV. This indicated PI-type with full compensation of boron shallow acceptors by vanadium.

Growth of SI SiC Single Crystals of NU-Type

In similarity to the growth of semi-insulating SI SiC single crystals of PI-type, the growth process for SI SiC crystals of NU-type also includes two phases. Phase (a) of the process is growth of substantially undoped, sacrificial portion of the SiC single crystal under reactive atmosphere aimed at removal of background N and B from the growth ambient. Phase (a) of the growth process is carried out as described above in connection with FIG. 3. The duration of phase (a) is, desirably, between 12 and 24 hours. Phase (b) of the process is growth of NU-type SiC using co-doping with V (vanadium) and N (nitrogen).

FIG. 7 shows a SiC crystal growth apparatus for the growth of semi-insulating SiC single crystals of NU-type. The apparatus shown in FIG. 7 is similar to the one shown in FIG. 4, with the exception of gas delivery system 30. For simplicity of illustration, pushrod 44a, vacuum seal 44c, threading 44b, and structure 42a including opening 44b have been omitted from FIG. 7. However, it is to be appreciated these elements or their equivalents would also present in the apparatus shown in FIG. 7. In order to achieve precise co-doping with nitrogen, gas delivery system 30 includes an additional gas line comprising valves 74, 74b and mass flow controller 74a which is not required for the gas delivery system 30 of FIG. 4. Other than the addition of the gas line comprising valves 74, 74b, and mass flow controller 74a, the SiC crystal growth apparatus shown in FIG. 7 is the same as the SiC crystal growth apparatus shown in FIG. 4. Accordingly, details regarding the elements common to the SiC crystal growth apparatuses shown in FIGS. 4 and 7 will not be described further herein to avoid unnecessary redundancy.

An Ar+N₂ gas mixture is supplied to valve 74. The concentration of N₂ in the Ar+N₂ gas mixture is, desirably, between 50 and 200 ppm by volume.

In one embodiment, metallic vanadium is used as a dopant. During growth of SiC single crystal 17, vanadium is disposed in doping capsule 45a shown in FIG. 6A. Doping capsule 45a comprises a single capillary 61 which is 1 mm in diameter and 6 mm long.

With ongoing reference to FIG. 7, the growth process for vanadium-compensated SiC single crystals 17 of NU-type is carried out as follows. At the completion of phase (a) of the process, described above in connection with FIG. 3, valves 36 and 36b are closed, thus stopping the flow of metal halide vapor into furnace chamber 10. Recall that during phase (a) of the process, Ar+H₂ flows into furnace chamber 10 via valves 35 and 35b and mass flow controller 35a. Desirably, the portion of SiC single crystal 17 grown during phase (a) is a sacrificial portion.

In phase (b) of the process and following termination of the flow of metal halide vapor into furnace chamber 10, valves 74 and 74b are opened, and the mass flow controller 74a is activated allowing the Ar+N₂ mixture to flow into the furnace chamber 10 with the flow of Ar+H₂. Desirably, the flow of the Ar+N₂ mixture is between 1 and 10% of the flow of the Ar+H₂ mixture.

Following this, doping capsule 45a is moved upward using pushrod 44. The tapered top of doping capsule 45a pushes plug 43 out of the tube 42, thus bringing doping capsule 45a into the crucible interior, as shown for example in FIG. 5B.

Results of the growth runs of vanadium-compensated, SI SiC crystals of NU-type are shown in Table 1 above. Based on SIMS impurity analysis, the grown SI SiC single crystals included between 2·10¹⁵ and 8·10¹⁵ cm⁻³ of unintentional background boron. The levels of intentionally introduced nitrogen and vanadium were between 8·10¹⁵ and 2·10¹⁶ cm³ and 9·10¹⁶ and 2·10¹⁷ cm³, respectively.

The resistivity of the wafers sliced from the grown SI SiC crystals was measured at room temperature using COREMA. The resistivity values were between 1·10¹¹ Ohm-cm and 4·10¹¹ Ohm-cm. The activation energy of resistivity in the temperature range between 25 and 400° C. measured using VT COREMA was between 0.78 and 0.82 eV. This pointed to NU-type with full compensation of nitrogen shallow donors by vanadium.

The present invention has been described with reference to the accompanying figures. Obvious modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

1. A crystal growth method comprising:

(a) providing a sic single crystal seed and a polycrystalline sic source material in spaced relation inside of a growth crucible that is disposed inside of a furnace chamber, the growth crucible disposed inside of a furnace chamber defining a growth ambient; and

(b) sublimation growing a sic single crystal on the sic seed crystal via precipitation of sublimated sic source material on the sic seed crystal; and

(c) causing a reactive atmosphere to form in the growth ambient that reacts with background nitrogen and boron present in the growth ambient forming a solid nitride compound with the background nitrogen and a gaseous boron halide compound with the background boron.

2. The method of claim 1, wherein the reactive atmosphere includes a halide vapor compound and one or more gases.

3. The method of claim 2, wherein:

the halide vapor compound is comprised of (1) fluorine or chlorine, and (2) tantalum or niobium; and

the one or more gases includes argon, hydrogen, or a mixture of argon+hydrogen.

4. The method of claim 2, further including:

(d) following step (c), changing the atmosphere in the growth ambient to a non-reactive atmosphere; and

(e) following step (d), introducing into the growth ambient a vanadium dopant that causes the portion of the sic single crystal sublimation growing on the sic seed crystal after step (d) to be fully compensated and semi-insulating doped with vanadium.

5. The method of claim 4, wherein step (e) further includes introducing into the growth ambient a dopant of boron or nitrogen.

6. The method of claim 4, wherein, in step (e), the vanadium dopant is introduced into the growth ambient via controlled effusion.

7. The method of claim 4, wherein introducing the vanadium dopant into the growth ambient in step (e) includes moving the vanadium dopant from a position outside the growth crucible where the vanadium dopant is a solid to a position inside the growth crucible where the vanadium dopant produces vanadium vapors during sublimation growth of the sic single crystal.

8. The method of claim 4, wherein a pressure inside of the growth crucible during sublimation growth of the sic single crystal is between 1 and 100 Torr.

9. A crystal growth method comprising:

(a) introducing a polycrystalline source material and a seed crystal into a growth ambient comprised of a growth crucible disposed inside of a furnace chamber;

(b) in the presence of a first sublimation growth pressure in the growth ambient, sublimation growing a single crystal on the seed crystal via precipitation of sublimated source material on the seed crystal in the presence of a flow of a first gas that includes a reactive component that reacts with gaseous nitrogen in the growth ambient forming a solid nitride compound, reacts with boron in the growth ambient forming a gaseous boron halide compound, or both; and

(c) following step (b) and in the presence of a second sublimation growth pressure in the growth ambient, sublimation growing the single crystal on the seed crystal via precipitation of sublimated source material on the seed crystal in the presence of a flow of a second gas that includes dopant vapors, but which does not include the reactive component.

10. The method of claim 9, wherein:

each sublimation growth pressure is between 1 and 100 Torr; and

the first and second sublimation growth pressures can be the same or different.

11. The method of claim 9, further including introducing a source of the dopant vapors into the growth crucible between steps (b) and (c).

12. The method of claim 9, wherein steps (b) and (c) are performed without exposing the growth ambient to room ambient atmosphere between said steps.

13. The method of claim 9, wherein:

the reactive component of the first gas is a gaseous metal halide;

the dopant vapors of the second gas comprise gaseous vanadium; and

the second gas further comprises hydrogen, nitrogen or hydrogen+nitrogen.

14. A sic crystal growth method comprising:

(a) providing a sic single crystal seed and a polycrystalline sic source material in spaced relation inside of a growth crucible that is disposed in a furnace chamber, wherein the crucible disposed in the furnace chamber defines a growth ambient;

(b) initiating sublimation growth of a sic single crystal on the sic single crystal seed in the growth ambient;

(c) following step (b), substantially removing background impurities of nitrogen and boron from the growth ambient during sublimation growth of the sic single crystal on the sic single crystal seed in the growth ambient; and

(d) following step (c), introducing vanadium and boron dopants into the growth ambient during sublimation growth of the sic single crystal on the sic single crystal seed in the growth ambient thereby sublimation growing a PI-type sic single crystal on the sic seed crystal, wherein the grown PI-type sic single crystal is semi-insulating, has a room-temperature resistivity of at least 10¹⁰ Ohm-cm, and an activation energy of resistivity in the range between approximately 0.9 and 1.5 eV in the temperature range between room temperature and 400° C.

15. The sic crystal growth method of claim 14 A sic crystal growth method comprising:

(a) providing a sic single crystal seed and a polycrystalline sic source material in spaced relation inside of a growth crucible that is disposed in a furnace chamber, wherein the crucible disposed in the furnace chamber defines a growth ambient;

(b) initiating sublimation growth of a sic single crystal on the sic single crystal seed in the growth ambient;

(c) following step (b), substantially removing background impurities of nitrogen and boron from the growth ambient during sublimation growth of the sic single crystal on the sic single crystal seed in the growth ambient; and

(d) following step (c), introducing vanadium and boron dopants into the growth ambient during sublimation growth of the sic single crystal on the sic single crystal seed in the growth ambient thereby sublimation growing a PI-type sic single crystal on the sic seed crystal, wherein the PI-type sic single crystal further comprises:

shallow acceptors present in larger concentrations than shallow donors; and

vanadium present in concentrations sufficient to achieve full compensation.

16. The sic crystal growth method of claim 14 A sic crystal growth method comprising:

(a) providing a sic single crystal seed and a polycrystalline sic source material in spaced relation inside of a growth crucible that is disposed in a furnace chamber, wherein the crucible disposed in the furnace chamber defines a growth ambient;

(b) initiating sublimation growth of a sic single crystal on the sic single crystal seed in the growth ambient;

(c) following step (b), substantially removing background impurities of nitrogen and boron from the growth ambient during sublimation growth of the sic single crystal on the sic single crystal seed in the growth ambient; and

(d) following step (c), introducing vanadium and boron dopants into the growth ambient during sublimation growth of the sic single crystal on the sic single crystal seed in the growth ambient thereby sublimation growing a PI-type sic single crystal on the sic seed crystal, wherein the PI-type sic single crystal further comprises:

background nitrogen intentionally reduced in a concentration between 4·10¹⁵ and 7·10¹⁵ atoms-cm⁻³; and

intentionally introduced boron and vanadium dopants in concentrations between 9·10¹⁵ and 2·10¹⁶ atoms-cm⁻³, and 9·10¹⁶ and 2·10¹⁷ atoms-cm⁻³, respectively.

17. The sic crystal growth method of claim 14 15, wherein the PI-type sic single crystal further comprises a 4H or 6H polytype.

18. A sic crystal growth method comprising:

(a) providing a sic single crystal seed and a polycrystalline sic source material in spaced relation inside of a growth crucible that is disposed in a furnace chamber, wherein the crucible disposed in the furnace chamber defines a growth ambient;

(b) initiating sublimation growth of a sic single crystal on the sic single crystal seed in the growth ambient;

(c) following step (b), substantially removing background impurities of nitrogen and boron from the growth ambient during sublimation growth of the sic single crystal on the sic single crystal seed in the growth ambient; and

(d) following step (c), introducing vanadium and nitrogen dopants into the growth ambient during sublimation growth of the sic single crystal on the sic single crystal seed in the growth ambient thereby sublimation growing a NU-type sic single crystal on the sic seed crystal, wherein the grown NU-type sic single crystal is semi-insulating, has a room-temperature resistivity of at least 10¹⁰ Ohm-cm, and an activation energy of resistivity between approximately 0.78 and 0.82 eV in the temperature range between room temperature and 400° C.

19. The sic crystal growth method of claim 18 A sic crystal growth method comprising:

(a) providing a sic single crystal seed and a polycrystalline sic source material in spaced relation inside of a growth crucible that is disposed in a furnace chamber, wherein the crucible disposed in the furnace chamber defines a growth ambient;

(b) initiating sublimation growth of a sic single crystal on the sic single crystal seed in the growth ambient;

(c) following step (b), substantially removing background impurities of nitrogen and boron from the growth ambient during sublimation growth of the sic single crystal on the sic single crystal seed in the growth ambient; and

(d) following step (c), introducing vanadium and nitrogen dopants into the growth ambient during sublimation growth of the sic single crystal on the sic single crystal seed in the growth ambient thereby sublimation growing a NU-type sic single crystal on the sic seed crystal, wherein the NU-type sic single crystal further comprises:

shallow donors present in larger concentrations than shallow acceptors, and

vanadium present in concentrations sufficient to achieve full compensation.

20. The sic crystal growth method of claim 18 A sic crystal growth method comprising:

(a) providing a sic single crystal seed and a polycrystalline sic source material in spaced relation inside of a growth crucible that is disposed in a furnace chamber, wherein the crucible disposed in the furnace chamber defines a growth ambient;

(b) initiating sublimation growth of a sic single crystal on the sic single crystal seed in the growth ambient;

(c) following step (b), substantially removing background impurities of nitrogen and boron from the growth ambient during sublimation growth of the sic single crystal on the sic single crystal seed in the growth ambient; and

(d) following step (c), introducing vanadium and nitrogen dopants into the growth ambient during sublimation growth of the sic single crystal on the sic single crystal seed in the growth ambient thereby sublimation growing a NU-type sic single crystal on the sic seed crystal, wherein the NU-type sic single crystal further comprises:

background boron intentionally reduced in a concentration between 2·10¹⁵ and 8·10¹⁵ atoms-cm⁻³; and

intentionally introduced nitrogen and vanadium dopants in concentrations between 8·10¹⁵ and 2·10¹⁶ atoms-cm⁻³, and 9·10¹⁶ and 2·10¹⁷ atoms-cm⁻³, respectively.

21. The sic crystal growth method of claim 18 19, wherein the NU-type sic single crystal further comprises a 4H or 6H polytype.

22. The method of claim 4, wherein the portion of the sic single crystal that is doped with vanadium is fully compensated and semi-insulating.

23. A sic crystal growth method comprising:

(a) providing a sic single crystal seed and a polycrystalline sic source material in spaced relation inside of a growth crucible that is disposed in a furnace chamber, wherein the crucible disposed in the furnace chamber defines a growth ambient;

(b) initiating sublimation growth of a sic single crystal on the sic single crystal seed in the growth ambient;

(c) following step (b), substantially removing background impurities of nitrogen and boron from the growth ambient during sublimation growth of the sic single crystal on the sic single crystal seed in the growth ambient; and

(d) following step (c), introducing vanadium and boron dopants into the growth ambient during sublimation growth of the sic single crystal on the sic single crystal seed in the growth ambient thereby sublimation growing a PI-type sic single crystal on the sic seed crystal, wherein the grown PI-type sic single crystal is semi-insulating, has a room-temperature resistivity of at least 10¹⁰ Ohm-cm, and an activation energy of resistivity in the range between approximately 0.9 and 1.5 eV in the temperature range between room temperature and 400° C.

24. A sic crystal growth method comprising:

(a) providing a sic single crystal seed and a polycrystalline sic source material in spaced relation inside of a growth crucible that is disposed in a furnace chamber, wherein the crucible disposed in the furnace chamber defines a growth ambient;

(b) initiating sublimation growth of a sic single crystal on the sic single crystal seed in the growth ambient;

(c) following step (b), substantially removing background impurities of nitrogen and boron from the growth ambient during sublimation growth of the sic single crystal on the sic single crystal seed in the growth ambient; and

(d) following step (c), introducing vanadium and nitrogen dopants into the growth ambient during sublimation growth of the sic single crystal on the sic single crystal seed in the growth ambient thereby sublimation growing a NU-type sic single crystal on the sic seed crystal, wherein the grown NU-type sic single crystal is semi-insulating, has a room-temperature resistivity of at least 10¹⁰ Ohm-cm, and an activation energy of resistivity between approximately 0.78 and 0.82 eV in the temperature range between room temperature and 400° C.

25. The sic crystal growth method of claim 16, wherein the PI-type sic single crystal further comprises a 4H or 6H polytype.

26. The sic crystal growth method of claim 23, wherein the PI-type sic single crystal further comprises a 4H or 6H polytype.

27. The sic crystal growth method of claim 20, wherein the NU-type sic single crystal further comprises a 4H or 6H polytype.

28. The sic crystal growth method of claim 24, wherein the NU-type sic single crystal further comprises a 4H or 6H polytype.