WO2020023725A1

WO2020023725A1 - Methods of growing single crystal materials

Info

Publication number: WO2020023725A1
Application number: PCT/US2019/043398
Authority: WO
Inventors: Hayder AL-ATABI; James H. Edgar
Original assignee: Higher Committee For Education Development; Kansas State University Research Foundation
Priority date: 2018-07-25
Filing date: 2019-07-25
Publication date: 2020-01-30

Abstract

Apparatus and methods of growing crystalline materials, especially single-crystal materials are provided. The apparatus includes heat transfer structure in conductive heat transfer relationship with a seed material upon which the crystalline material is to be grown. The heat transfer structure is operable to cool the seed so as to favor crystal growth on the seed as opposed to other parts of the apparatus. The seed may comprise a single crystal material that is especially suited for growing single crystal epitaxial films of a semiconductor, thermoelectric, or piezoelectric material.

Description

METHODS OF GROWING SINGLE CRYSTAL MATERIALS

CROSS-REFERENCE TO RELATED APPLICATION This application claims the benefit of U.S. Provisional Patent Application No.

62/703,265, filed July 25, 2018, which is incorporated by reference herein in its entirety.

STATEMENT REGARDING GOVERNMENT SPONSORED RESEARCH

This invention was made with government support under contract No. 1508172 awarded by the National Science Foundation. The government has certain rights in the invention.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention is generally directed toward an apparatus that is capable of selectively growing crystalline materials, especially crystalline semiconductor materials, on a seed material located within a specially configured crucible. In certain embodiments, the seed material comprises a single crystal material and is especially adapted toward growing single crystal epitaxial films of semiconductor materials. Also, in certain embodiments, the specially configured crucible comprises a heat transfer fin that is in a heat-conductive relationship with the seed material and is configured to produce a temperature gradient between the seed material and the surrounding parts of the crucible so as to create conditions favorable for crystal formation on the seed as opposed to the adjacent portions of the crucible.

Description of the Prior Art

There has been recent interest in the use of early transition-metal and rare-earth nitrides, such as ScN and CrN, in fabricating electrical components given their semiconductor, thermoelectric, and/or piezoelectric characteristics. See, Saha et al., Appl. Phys. Lett. 110, 252104 (2017), and Eklund et al., J Mater. Chem. C., 4, 3905 (2016).

Crystal growth using physical vapor transport processes has been studied as a way of growing crystalline materials having use in semiconductor devices. Generally, this type of crystal growth is conducted in a growth chamber (e.g., a crucible) in which a source material is heated and sublimed. The sublimed material is then caused to recrystallize on a seed. See, e.g., U.S. Patent Application Publication 2012/0103249 (disclosing a sublimation crystal growth process an apparatus for growing SiC single crystals), and Shin- ichi et al., Mat. Res. Soc. Symp., Vol 640, (2001) (disclosing SiC bulk single crystal growth by sublimation). However, several challenges have been identified with this general process. First, it can be difficult getting the sublimed material to crystallize in the desired location. For example, under certain conditions, the sublimed material may crystallize on portions of the growth chamber instead of the seed. This results in reduced crystal growth rates on the seed and longer sublimation processing times. Second, it can be difficult to achieve single-crystal epitaxial growth on substrates that are not chemically and/or structurally identical to the sublimed material. This can be due, at least in part, to large lattice constant mismatch, poor chemical stability toward the sublimed material, or poor thermal stability.

Therefore, a need exists in the art for an apparatus that overcomes these problems by providing a way to direct recrystallization of the sublimed material to a desired location within the growth chamber, and also to achieve single-crystal epitaxial growth on a variety of substrates.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention there is provided an apparatus for growing a crystalline material via physical vapor transport of the material onto a seed. The apparatus comprises a vessel having an interior that is configured to contain a source of the material. The vessel comprises a heat source configured to vaporize at least a portion of the source of the material. The apparatus also comprises a lid for the vessel that is configured to receive the seed. The seed, when held by or affixed to the lid, has a surface that faces the interior of the vessel and is adapted for growing the crystalline material thereon. The apparatus further comprises a heat transfer device that is in contact with a surface of the seed that faces away from the interior of the vessel. The heat transfer device is configured to conduct heat away from the seed and the interior of the vessel.

According to another embodiment of the present invention there is provided a method of growing a single crystal material. The method comprises vaporizing a source of the single crystal material within an apparatus comprising a vessel having an interior that is configured to receive a source of the single crystal material. The apparatus further comprises a lid for the vessel into which a seed is received. The seed has a surface that faces the interior of the vessel and is adapted for growing the single crystal material thereon. The vaporized source of the single crystal material is caused to deposit on the seed by inducing a temperature gradient between the surface of the seed that faces the interior of the vessel and a surface of the lid that faces the interior of the vessel thereby creating conditions that favor growth of the single crystal material on the seed as opposed to the surface of the lid.

According to yet another embodiment of the present invention there is provided a method of growing a single crystal epitaxial layer. The method comprises vaporizing a source of the single crystal epitaxial layer within an apparatus comprising a vessel having an interior that is configured to receive a source of the crystalline material and a lid for the vessel into which a single crystal seed is affixed or held. The seed has a surface that faces the interior of the vessel that is adapted for growing the epitaxial layer thereon. The vaporized source of the single crystal material is caused to deposit on the seed and form the single crystal epitaxial layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram of an apparatus made in accordance with an embodiment of the present invention and illustrates a crucible having a lid configured to receive a seed and a heat transfer device in contact with the seed;

Figs. 2a and 2b depict an exemplary lid forming a part of the apparatus, the lid comprises an orifice there through that is configured to hold the seed;

Figs. 3a and 3b depict two exemplary heat transfer devices that are configured to contact a surface of the seed;

Fig. 4 is a photograph of a post-growth tungsten seed upon which scandium nitride was grown;

Fig. 5 is a schematic illustration of an exemplary tungsten furnace into which a crucible according to one embodiment of the present invention may be received; Fig. 6 is a photograph of a crucible lid containing a tungsten seed post crystal growth, the left inset depicts the single-crystal ScN grown on the single-crystal tungsten seed, the right inset depicts the polycrystalline ScN grown on the crucible lid;

Fig. 7 is a schematic illustration of the orientation of ScN (100) grown on a single- crystal tungsten (100) seed with a rotational angle of 45° between the ScN layer and the tungsten seed;

Fig. 8 is the XRD pattern of ScN crystal grown on a single-crystal of tungsten (100), the growth temperature was l860°C at a pressure of 35 torr;

Fig. 9 is a chart illustrating the effect of growth temperature on ErN crystal growth rate;

Fig. 10 is a chart illustrating the effect of pressure on ErN crystal growth rate; and

Figs. 11 and 12 are SEM images of ErN crystals produced according to embodiments of the present invention.

While the drawings do not necessarily provide exact dimensions or tolerances for the illustrated components or structures, the drawings are to scale with respect to the relationships between the components of the structures illustrated in the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The crystal growth location and rate can be influenced through creation of a temperature gradient not only within the growth chamber, but also among adj acent surfaces within the growth chamber. For example, material deposition occurs most favorably on cooler surfaces. The present invention seeks to exploit this phenomenon by creating a cool surface within the growth chamber, and particularly on the seed material, that presents more favorable conditions for crystal growth as compared to other surfaces within the growth chamber. Certain embodiments of the present invention are directed toward conducting heat away from the seed upon which crystal growth is desired. This may be accomplished by attaching one or more heat transfer devices to the seed, so the seed becomes cooler than other regions of the growth chamber. Consequently, the material deposition is directed to the seed instead of other surfaces within the growth chamber. This improves the overall efficiency of the growth process and reduces the possibility of crystal growth in other regions, thereby suppressing polycrystalline growth. Tuming now to Fig. 1, apparatus 10 is an exemplary device made in accordance with the present invention. Apparatus 10 comprises a vessel 12, which may also be referred to herein as a crucible. Vessel 12 comprises an interior volume 14 that is configured to receive a source of the crystalline material, which is described in greater detail below. The apparatus 10 further comprises a lid 16 for the vessel 12 that is configured to receive a seed 18 upon which deposition of the source of the crystalline material is desired to occur. The seed 18 is received within an orifice 20 formed through lid 16. An exemplary crucible lid 16 is shown in Figs. 2a and 2b. As can be seen, lid 16 comprises a disc-like configuration with a central orifice 20. It is understood that other types of vessel closures may be used without departing from the scope of the present invention.

In certain embodiments, orifice 20 comprises a shoulder 22 that is configured to engage a lip 24 of seed 18 and prevent seed 18 from falling through orifice 20 when installed within lid 16. Thus, seed 18 may be configured with a surface 26 that faces the interior of vessel 12 that has a smaller diameter than an opposite surface 28 that faces away from the interior of vessel 12. In particular embodiments, surface 26 of the seed 18 extends past an interior margin 27 of the lid 16 into the vessel interior 14.

It is understood that other vessel configurations and ways of affixing the seed to or holding the seed on the lid may be used. In these embodiments, the lid need not be configured with an orifice through which the seed is received. Rather, the seed could be welded, glued or clipped onto the surface of the lid that faces the interior of the vessel.

Apparatus 10 further comprises a heat transfer device 30 that is configured to contact surface 28, directly or indirectly, so as to conduct heat away from the seed 18 and the vessel interior 14. In certain embodiments, device 30 comprises a fin section 32 and a base section 34 that extends transversely therefrom. In preferred embodiments, and as illustrated, base section 34 has a diameter that is smaller than the diameter of the fin 32 and may be sized to be received within orifice 20. This particular arrangement also produces a primary heat transfer surface 33, which is oriented to face away from lid 16, and a secondary heat transfer surface 35 that faces lid 16. It is understood, however, that other configurations are possible for device 30 so long as the device is capable of radiative and convective heat transfer with the environment outside of the vessel 12. In certain embodiments, surface 36 of base section 34 may be placed in direct, abutting contact with surface 28 of seed 18. This positioning permits conductive heat transfer to occur between seed 18 and device 30 thereby providing a cooling effect relative to seed 18 (i.e., seed 18 is cooled and device 30 is warmed). However, it is within the scope of the present invention for an intermediate material to be positioned in between seed

18 and device 30, in order to secure device 30 and seed 18 together, or to improve the conductive heat transfer between these two members. For example, an intermediate metallic layer (not shown), such as a solder, may be located between device 30 and seed 18 to affix these members together. It is also within the scope of the present invention for device 30 and seed 18 to be unitarily formed from a common piece of material. For example, the seed 18 and device 30 may be machined or cast as a single piece, rather than two individual components. Thus, in certain embodiments, it is preferable for the seed 18 and device 30 to be formed from the same material, such as tungsten. Although, the crystallographic characteristics of the seed 18 and heat transfer device 30 do not necessarily need to be identical (i.e., the seed 18 may be single crystalline, whereas the device 30 may be polycrystalline).

As depicted in the figures, device 30 is configured such that fin 32 is circular. However, any other geometry may be employed, such as rectangular, so long as the device 30 is capable of inducing a temperature gradient sufficient to drive deposition of the source material onto surface 26 of the seed 18. Moreover, device 30 may be configured so that fin section 32 may have a geometry that is adjustable or continuously variable to suit whatever conditions are present within vessel 12. In certain embodiments, the primary heat transfer surface 33 of fin section 32, which is responsible for a major portion of the radiative and/or convective heat transfer of the device 30 to the outside environment, has a surface area that is at least twice as great, and preferably at least 3 times, or at least 5 times as great as the surface area of surface 26 of seed 18.

As indicated previously, device 30 is configured so as to induce a temperature gradient between the surface 26 of the seed 18 that faces the vessel interior 14 and surface 27 of the lid 16 that faces the vessel interior 14. In preferred embodiments, the induced temperature gradient is aimed at making the seed surface 26 cooler than the lid surface (i.e., a negative temperature gradient) so as to create conditions that favor crystal deposition and growth on the seed 18 as opposed to the lid 16. In particular embodiments, this temperature gradient may be as little as 5°C, but is preferably at least lO°C, at least l5°C, or at least 20°C.

Turning to Fig. 5, an exemplary furnace 37 for subliming a source material for deposition on seed 18 is shown. Note this furnace is described for illustrative purposes only and should not be taken as limiting upon the scope of the present invention. The furnace 37 comprises a heating element 38, preferably a tungsten wire mesh heating element, that is configured to heat to a crucible 40, preferably a tungsten crucible, to a temperature that is sufficient to vaporize at least a portion of the source material. In certain embodiments, heating element 38 is configured to heat the interior 14 of vessel 12 to a temperature of at least l750°C, at least l850°C, or at least 2000°C. However, the required heat output by heating element 38 will be dependent upon the characteristics of the source material. Generally, for many of the uses described herein, the sublimation temperature of the source material will be in the range of about l750°C to about 2200°C. Given these extreme temperatures, furnace 37 may be equipped with a plurality of heat shields 42, preferably layers of tungsten plate, to contain heat radiated from the heating element 38 and insulate the furnace from the outside environment. The furnace chamber 45 is preferably made of stainless steel, although other materials can be used. As one alternative to the furnace 37 depicted in Fig. 5, an induction heating furnace could be used in which the crucible is heated directly by an external inductive coil. Insulation, such as graphite foam, can be used in place of the heat shields 42 to contain the heat generated within the crucible. In certain embodiments, furnace 37 comprises a cooling system that surrounds the heat shields 42, such as a shell and tube copper jacket heat exchanger. The heat exchanger may be placed between the heat shields 42 and the furnace chamber inner walls 46 to ensure that the furnace chamber outer walls 48 are at a safe temperature, preferably room temperature. In certain embodiments, the top of the crucible 40 is not insulated with heat shields. This lack of insulation can provide an axial temperature difference, which can be the driving force for crystal growth. In the examples below, growth temperature is measured using a pyrometer 50 that is focused on the top of the crucible 40.

In certain embodiments the apparatus includes a quantity of the source material 44 placed within the vessel 12. In preferred embodiments, the source material 44 comprises, consists of, or consists essentially of a member selected from the group consisting of scandium nitride, silicon carbide, other transition metal nitrides and carbides, post- transition metal nitrides (e.g., aluminum nitride) and carbides, lanthanide nitrides (e.g., erbium nitride) and carbides, and actinide metal nitrides and carbides. Most commonly, the source material 44 is a polycrystalline solid material, although this need not always be the case. For instance, it is also within the scope of the present invention for the source material to be a liquid, which is then evaporated and deposited on the seed.

The seed material may be formed of any number of materials. However, in certain embodiments, selection of the seed material is dependent upon certain critical parameters. First, the seed 18 should be formed from a material that is stable at the temperatures under which the furnace must operate to sublime the source material 44. Second, the seed 18 may be formed from a material having a close lattice match and chemical and thermal stability with the source material 44. The close lattice match is an important characteristic in the ability to successfully grow a single crystal epitaxial layer on the seed 18. In certain embodiments, the lattice mismatch, defined as the percent difference between the lattice constants of the seed and deposited materials, is less than 4%, less than 3%, less than 2%, or less than 1%.

In certain embodiments the seed 18 comprises, consists of, or consists essentially of a member selected from the group consisting of tungsten, silicon, sapphire, magnesium oxide, zirconium nitride (ZrN), zirconium diboride (ZrB₂), niobium carbide (NbC) and tantalum carbide (TaC). When the source material is ScN, tungsten, ZrN, ZrB₂, NbC, and TaC are preferred seed materials. In particularly preferred embodiments, the seed 18 comprises a single-crystal material, such as single crystal tungsten, as it has been discovered that single crystal seed materials appear to favor formation of single crystal epitaxial layers. But, as mentioned previously, the principles of the present invention can be extended to a broad range of materials provided that the seed and source materials are matched with the aforementioned considerations in mind. In certain embodiments, the seed 18, preferably tungsten, is required to have a very smooth surface to produce large crystal grains. Thus, in preferred embodiments, the seed 18 is polished to remove oxidized metal and generally form a smooth, uniform surface on one, and preferably both, sides of the seed. The present invention also provides methods of growing a crystalline material, especially single crystal materials. These methods comprise, utilizing apparatus 10 to vaporize the source 44 of the crystalline material, described above, which is placed within the interior volume 14 of vessel 12. The vaporization of the source material 44 may be effected by heating element 38, for example. In certain embodiments, the furnace chamber 45 can be charged with nitrogen and/or forming gas (95% Ar and 5% Eb) during vaporization of the source material 44. The vaporized source of the crystalline material is caused to recrystallize (or recondense or deposit) on the surface 26 of the seed 18 that faces the vessel interior 14 by inducing a temperature gradient between surface 26 and the surface 27 of the lid 16 that faces the interior of the vessel. This temperature gradient creates conditions that favor growth of the crystalline material on the seed 18 as opposed to the surface 27 of the lid 16, namely cooler conditions on the seed than on the lid. In certain embodiments, the crystalline material is deposited on the seed in the form of an epitaxial film. The step of inducing the temperature gradient may be achieved through use of a heat transfer device 30 that conducts heat away from the seed 18 and radiates or convectively transfers it to the environment outside of the vessel 12, especially via fin section 32. In particular embodiments, this temperature gradient may be as little as 5°C, but is preferably at least l0°C, at least l5°C, or at least 20°C.

The present invention can be used to create materials useful in a number of electronic devices including energy harvesting devices, such as thermoelectrics and piezoelectrics, and p-type semiconductors.

EXAMPLES

The following Examples describe use of a heat transfer device to drive crystal growth to the seed and also use of a single crystal seed for epitaxial crystal growth thereon. These examples are presented for illustrative purposes and should not be taken as limiting the scope of the present invention.

Example 1 : ETse of Fin to Enhance Mass Transfer Rate of Seeded Grown Crystals via Physical Vapor Transport Process. In this example, a specially designed tungsten crucible was used to grow crystalline ScN upon a tungsten seed via a physical vapor transport process. The apparatus used is illustrated in Fig. 5. In order to increase the mass transfer rate of ScN from the source of ScN to the seed, two heat transfer devices having fins of different sizes were manufactured and placed in direct contact with the seed during the growth process. The fins are illustrated in Figs. 3a and 3b. The fin of Fig. 3a has a primary surface 33a comprising an area that is approximately 4 times larger than the fin 33b of Fig. 3b.

The source of ScN was placed into the crucible and a tungsten seed was positioned within an orifice located in the crucible lid. One trial was conducted with no heat transfer device placed in contact with the seed, one trial with the small heat transfer device placed in contact with the seed (Fig. 3b), and one trial with the large heat transfer device placed in contact with the seed (Fig. 3a). The crucible was then heated to a temperature sufficient to sublime the ScN from the source material. Crystal growth was permitted for 100 hours in each run. . The surface of the seed facing the interior of the crucible had an area of approximately 0.5 cm², and the surface of the lid facing the interior of the crucible had an area of approximately 4.41 cm². The results are shown in Table 1.

Table 1

As can be seen, use of either heat transfer device resulted in increased mass of ScN crystal on the seed and decreased crystal growth on the lid. The use of the device with the larger fin, however, showed significantly better crystal growth on the seed, as compared to the smaller fin. This suggests that the more heat that can be removed from the seed by the fin, the greater mass that can be deposited on the seed as opposed to the adjacent lid. The epitaxial layer of ScN 46 deposited on the interior-facing surface of the seed 18 is visible in Fig. 4. Example 2: Epitaxial Growth of ScN ETsing Single Crystal Tungsten Substrate

Single crystal tungsten with the (100) crystallographic orientation was employed as a seed crystal for producing a single crystal of ScN. The apparatus used is the same as that for Example 1 and is depicted in Fig. 5. The source of ScN was placed into the crucible and the tungsten seed was positioned within an orifice located in the crucible lid. Runs were conducted using both the large and small fins described in Example 1. The crucible was then heated to a temperature sufficient to sublime the ScN from the source material. The growth temperature was l860°C, and the pressure within the crucible was 35 torr.

A thick ScN layer (500 microns) was produced on the tungsten single crystal with the (100) orientation by the sublimation-recondensation method (also known as physical vapor transport). The single crystal nature of the scandium nitride was demonstrated by x- ray diffraction techniques. See, Fig. 8. In addition, the single-crystalline growth was visible in photographs taken of the ScN grown on the seed and compared with the ScN deposited on the crucible lid. As can be seen in Fig. 6, the left inset depicts the single crystal ScN grown on the single-crystal tungsten seed. This is contrasted with the polycrystalline ScN growth on the crucible lid that can be seen in the right inset.

Figure 7 schematically illustrates the orientation of ScN (100) grown on the single crystal tungsten (100) with a 45° angle interface. XRD analysis gave values of a and b of approximately 3.16 A, each. ETsing the Pythagorean Theorem, C (distance between adjacent atoms in the crystal lattice) would have a value of approximately 4.48 A. This closely agrees with the reported ScN lattice of 4.5 A indicating that the single crystalline tungsten has a very small lattice constant mismatch with ScN, which along with its high melting point of 3422°C, renders it a very good seed for growing single crystal ScN.

Example 3: Sublimation Growth and Characterization of Erbium Nitride Crystals

Erbium nitride (ErN) is a rare earth nitride notable for its magnetic and optical properties. This example pertains to its growth on a non-native substrate, namely tungsten foil, via physical vapor transport, and its characterization. The source material employed in this example was erbrium metal that was converted to ErN by heating in nitrogen. Subsequently, the ErN was sublimed to form ErN crystals.

The sublimation growth was conducted in a tungsten furnace as previously described. The erbium nitride crystals were grown unseeded on polycrystalline tungsten foils with a predominately (100) textures. These foils were cleaned by acetone, methanol, and iso-propyl alcohol, respectively. The distance between ErN source and the growth area was kept constant at approximately 2 cm.

The sublimation was carried out over the temperature range of 1620 -1770 °C and in ultra-high-purity nitrogen at pressures of 150-510 Torr. During start-up, the temperature of the furnace was increased at a rate of 240 °C/hr up to the growth temperature. The ErN crystals were grown by maintaining that dwell temperature for 20 hr. Overall, each experiment needed 30 to 36 hr to complete, depending on the growth temperature.

The ErN source was synthesized by heating small chunks of Er metal (99.9 % purity) in pure nitrogen at 1500 °C. The starting pressure at room temperature was 400 Torr, and it increased gradually to 427 Torr at the nitridizing temperature. After stopping the experiment, the pressure was 350 Torr which means 50 Torr of N2 was consumed. The resulting ErN source was blue-grey and brittle.

The morphology and size of the resulting deposits were characterized by optical and scanning electron microscopy. X-ray diffraction patterns were taken to determine the structure, lattice constant, and orientation of the crystals. A copper Ka x-ray source was employed with a wavelength of 0.15418 nm. Raman spectra was employed to characterize the ErN’s vibrational properties. The elemental analysis was estimated via X-ray Photoelectron Spectroscopy (XPS) and Energy Dispersive x-ray Spectroscopy (EDS).

The following reversible reaction takes place in the tungsten furnace:

1

^ErN(s) «® ^Er(g) + 2 ^N2( )

The solid ErN sublimes dissociatively at the hotter point in the crucible (at the ErN source) via the forward reaction and condensates at the colder tungsten foil via the reverse reaction. Figure 9 shows the effect of growth temperature on the crystal growth rate. The growth rate increased exponentially with increasing temperature. This trend is attributed to increasing the sublimation rate, thus the tungsten substrate was saturated with ErdNh gases.

Figure 10 illustrates the effect of pressure on crystal growth rate. Since sublimation has an inverse relationship to pressure, the growth rate was inversely proportional to pressure.

The SEM images of Figs. 11 and 12 elucidate how the crystal morphology was influenced by growth temperature. At a temperature of 1620 °C, grain boundary defects appeared, and the facets of the crystals were rough. See, Fig. 11. However, as the temperature increased, the crystal facets became smooth, suggesting higher adatom diffusion rates. See, Fig. 12.

The ErN crystals were highly faceted, bound by (100) and (111) crystal planes, see, Fig. 11. The (111) facet has the highest growth rate, while (100) facet has the lowest growth rate. Facets with higher growth rate usually inclined to the ones having lower growth rate during the growth process.

The lattice constant was 4.853 A. The ErN compound deviated from stoichiometry: the Er:N atomic ratio ranged from 1 : 1.15 to 1 : 1.2 according to EDX and XPS elemental analysis.

It was concluded from this example that the growth temperature had a dramatic impact on the ErN crystal growth, both the rate and crystal morphology. The growth rate increased exponentially with increasing temperature. At 1620 °C, small crystals with rough surfaces were grown. As the temperature increased (>1620 °C), the crystal size increased, and the surface morphology changed from rough to smooth. On the other hand, the growth rate was found to be inversely proportional to the growth pressure. XRD pattern revealed that there was a strong preference for (200) orientation which is attributed to the dominant orientation of the tungsten substrate (200).

Claims

We claim:

1. An apparatus for growing a crystalline material via physical vapor transport of the material onto a seed, the apparatus comprising:

a vessel having an interior that is configured to contain a source of the material, the vessel comprising a heat source configured to vaporize at least a portion of the source of the material;

a lid for the vessel into which the seed is affixed or held, wherein the seed, when affixed to or held by the lid, has a surface that faces the interior of the vessel and is adapted for growing the crystalline material thereon; and

a heat transfer device that is in contact with a surface of the seed that faces away from the interior of the vessel, the heat transfer device being configured to conduct heat away from the seed and the interior of the vessel.

2 The apparatus of claim 1, wherein the heat source is configured to heat the interior of the vessel to a temperature of at least l750°C.

3. The apparatus of claim 1, wherein the surface of the seed that faces the interior extends past an interior margin of the lid into the interior of the vessel.

4. The apparatus of claim 1, wherein the seed is formed from tungsten.

5. The apparatus of claim 4, wherein the tungsten is single crystal tungsten.

6. The apparatus of claim 1, wherein the apparatus includes a quantity of the source material placed within the interior of the vessel, the source material comprising a member selected from the group consisting of scandium nitride, silicon carbide, transition metal nitrides and carbides, post-transition metal nitrides and carbides, lanthanide and actinide metal nitrides and carbides.

7. The apparatus of claim 1 , wherein the heat transfer device comprises a fin.

8. The apparatus of claim 7, wherein the fin is comprised of the same material as the seed.

9. The apparatus of claim 7, wherein the fin is comprised of a different material from the seed.

10. The apparatus of claim 7, wherein the fin has a surface area that is at least twice the area of the surface of the seed that faces the interior of the vessel.

11. The apparatus of claim 1, wherein the heat transfer device is configured to induce a negative temperature gradient between the surface of the seed that faces the interior of the vessel and a surface of the lid that faces the interior of the vessel.

12. The apparatus of claim 11, wherein the induced negative temperature gradient is at least l0°C.

13. A method of growing a crystalline material comprising the steps of: vaporizing a source of the crystalline material within an apparatus comprising a vessel having an interior that is configured to receive a source of the crystalline material, a lid for the vessel into which a seed is affixed or held, the seed having a surface that faces the interior of the vessel and is adapted for growing the crystalline material thereon; and

causing the vaporized source of the crystalline material to deposit on the seed by inducing a temperature gradient between the surface of the seed that faces the interior of the vessel and a surface of the lid that faces the interior of the vessel thereby creating conditions that favor growth of the crystalline material on the seed as opposed to the surface of the lid.

14. The method of claim 13, wherein the seed that is received in the lid of the vessel is a single crystal of seed material.

15. The method of claim 14, wherein the seed material is selected from the group consisting of tungsten, zirconium nitride, zirconium diboride, niobium carbide, and tantalum carbide.

16. The method of claim 15, wherein the seed comprises a single crystal of tungsten.

17. The method of claim 13, wherein the apparatus further comprises a heat transfer device that is in contact with a surface of the seed that faces away from the interior of the vessel, the heat transfer device being configured to conduct heat away from the seed and the interior of the vessel.

18. The method of claim 17, wherein the step of inducing the temperature gradient comprises the device conducting heat away from the seed so as to cool the surface of the seed that faces the interior of the vessel to at least lO°C lower than the surface of the lid that faces the interior of the vessel.

19. The method of claim 17, wherein the heat transfer device comprises a heat transfer fin.

20. The method of claim 198, wherein the fin comprises the same material as the seed.

21. The method of claim 19, wherein the fin is comprised of a different material from the seed.

22. The method of claim 13, wherein the step of vaporizing the source of the crystalline material comprises heating the interior of the vessel to a temperature of at least l750°C.

23. The method of claim 13, wherein the source of the crystalline material comprises a member selected from the group consisting of scandium nitride, silicon carbide, transition metal nitrides and carbides, post-transition metal nitrides and carbides, and lanthanide and actinide metal nitrides and carbides.

24. The method of claim 13, wherein the crystalline material deposited on the seed is in the form of an epitaxial film.

25. A method of growing a single crystal epitaxial layer comprising the steps of:

vaporizing a source of the single crystal epitaxial layer within an apparatus comprising a vessel having an interior that is configured to receive a source of the crystalline material and a lid for the vessel into which a single crystal seed is affixed or held, the seed having a surface that faces the interior of the vessel that is adapted for growing the epitaxial layer thereon; and causing the vaporized source of the single crystal material to deposit on the seed and form the single crystal epitaxial layer.

26. The method of claim 25, wherein the source of the single crystal epitaxial layer comprises a member selected from the group consisting of scandium nitride, silicon carbide, transition metal nitrides and carbides, post-transition metal nitrides and carbides, and lanthanide and actinide metal nitrides and carbides.

27. The method of claim 25, wherein the single crystal seed comprises a member selected from the group consisting of tungsten, zirconium nitride, zirconium diboride, niobium carbide, and tantalum carbide.

28. The method of claim 25, wherein the single crystal seed comprises a single crystal of tungsten, and wherein the source of the single crystal epitaxial layer comprises scandium nitride.

29. The method of claim 25, wherein the vaporized source of the single crystal material is caused to deposit on the seed by inducing a temperature gradient between the surface of the seed that faces the interior of the vessel and a surface of the lid that faces the interior of the vessel thereby creating conditions that favor growth of the single crystal epitaxial layer on the seed as opposed to the surface of the lid.

30. The method of claim 29, wherein the apparatus further includes a heat transfer device that is configured to conduct heat away from the seed, and wherein the step of inducing a temperature gradient comprises conducting heat away from the seed and the interior of the vessel to the heat transfer device which transfers heat to an environment outside of the vessel.