Systems and methods for epitaxial nitride growth without plasma using molecular nitrogen activation by metal atoms

Abstract

Disclosed are plasma-free methods for growing crystalline metal nitride films using intact molecular nitrogen (N2) and in-situ metal-assisted N≡N bond cleavage on a metal-terminated surface. The method includes: providing a substrate bearing a nitride film that is metal-terminated; exposing the surface to N2 in the absence of plasma to adsorb intact N2; delivering metal atoms that activate and cleave the N≡N bond, producing surface-bound nitrogen and an N-terminated region with partial metal coverage; and adsorbing additional metal to complete a crystalline nitride layer, with repetition for multilayer growth. Metals include transition, rare-earth, and actinide elements, enabling binary films (e.g., ScN) and ternaries of the form M1xM21-XN, including, but not limited to, ScxNb1-xN and ScxAI1-xN with controlled x. Metal delivery can be performed by molecular beam epitaxy, thermal chemical vapor deposition, thermal atomic layer deposition, or thermal laser epitaxy under vacuum and substrate heating.

Description

Docket No. MIT26181 PCTSYSTEMS AND METHODS FOR EPITAXIAL NITRIDE GROWTH WITHOUT PLASMA USING MOLECULAR NITROGEN ACTIVATION BY METAL ATOMSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. Provisional Application No. 63 / 704,476, filed 10 / 07 / 2024, which is hereby incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The present invention relates generally to the field of semiconductors and thin films. More specifically, the present invention is related to systems and methods for epitaxial nitride growth without plasma using molecular nitrogen activation by metal atoms. BACKGROUND OF THE INVENTION

[0003] Although our atmosphere is 78.1% N2and 21 % O2, most of the earth’s crust and naturally occurring compounds and minerals are oxides, not nitrides. This is because of the formidable strength of 9.8 eV / molecule of the N=N triple bond in molecular N2, one of the strongest bonds. Lightning and nitrogenase enzymes are two primary mechanisms for breaking the N2triple bond in nature. Electrical discharge in lightning generates the high energy needed to dissociate N2molecules, forming nitrogen oxides (NOX) that contribute to nitrogen deposition in soils. Biological nitrogen fixation is driven by nitrogenase enzymes using energy-efficient processes to break the strong triple bond. The transition metal Fe Mo cofactors in the nitrogenase catalyze the breaking of the strong triple bond of atmospheric N2, thereby facilitating the binding, activation, and conversion of atmospheric N2into ammonia. While natural lightning contributes, most natural nitrogen fixation on earth is efficiently driven by biological nitrogen-fixing microorganisms that carry out the process more efficiently, sustaining life on our planet.

[0004] Although nature has a mechanism to dissociate atmospheric N2, there is a dire need for a low-energy synthetic process to synthesize metal nitrides directly from N2.11531347 1Docket No. MIT26181 PCTToday, the synthesis of inorganic nitride crystalline compound metals and semiconductors that have revolutionized electronic and photonic devices relies on high-power plasma to break N2 bonds akin to natural lightning, or on high temperatures to dissociate NH3. The insufficient reactivity of metal cations with nitrogen requires these epitaxial nitride heterostructures to be synthesized with low impurity levels by high-temperature processes (e.g., > 700 °C) via metalorganic chemical vapor deposition (MOCVD) or plasma-assisted processes via molecular beam epitaxy (MBE) at moderate temperatures (e.g., 400- 700 °C). While the high energy is necessary to promote crystallinity and to overcome the limited reactivity of metal and nitrogen, it also results in physical and chemical defects. It also precludes their use in back-end-of-line (BEOL) semiconductor processing which has a low thermal budget. The ability to deposit nitrides materials by an energy-efficient, lower- temperature process will therefore create significant fundamental and technological opportunities.

[0005] Embodiments of the present invention are an improvement over prior art systems and methods.SUMMARY OF THE INVENTION

[0006] In one embodiment, the present invention provides a method of growing a crystalline nitride without plasma, the method comprising: (a) providing a substrate bearing a nitride film that presents a metal-terminated surface (step 902); (b) exposing the metal- terminated surface to molecular nitrogen (N2) in the absence of plasma, thereby adsorbing intact N2on the surface (step 904); (c) delivering metal atoms to sites of the adsorbed N2so as to activate and cleave the N N bond in situ, forming surface-bound nitrogen atoms and an N-terminated region with partial metal coverage, wherein the metal comprises one or more elements selected from transition metals, rare-earth metals, and actinides (step906); (d) adsorbing additional metal atoms onto the N-terminated region to complete a21531347 1Docket No. MIT26181 PCT crystalline nitride layer (step 908); and (e) optionally repeating steps (a)-(d) to grow successive layers (step 910).

[0007] In one embodiment, the metal consists of a single element, thereby forming a binary metal nitride.

[0008] In one embodiment, the metal is a transition metal selected from the group consisting of scandium (Sc), yttrium (Y), niobium (Nb), titanium (Ti), tantalum (Ta), zirconium (Zr), hafnium (Hf), vanadium (V), tungsten (W), and molybdenum (Mo).

[0009] In one embodiment, the metal is a rare-earth metal selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0010] In one embodiment, the metal is an actinide selected from the group consisting of actinium (Ac), thorium (Th), protactinium (Pa), uranium (U), neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), fermium (Fm), mendelevium (Md), nobelium (No), and lawrencium (Lr).

[0011] In one embodiment, the metal comprises first and second metal elements, Mi and M2, and the layer has composition MlxM2i-xN, where 0<x<1.

[0012] In one embodiment, the nitride is ScxNbi_xN.

[0013] In one embodiment, Mi and M2are independently selected from transition metals and rare-earth metals.

[0014] In one embodiment, one of Mi or M2is Sc or a rare-earth metal and the other is Al, Ga, or In, thereby forming (Sc or RE)X(AI or Ga or ln)i_xN.

[0015] In one embodiment, the nitride is ScxAliXN.31531347 1Docket No. MIT26181 PCT

[0016] In one embodiment, the first and second metal elements are delivered (i) simultaneously or (ii) sequentially in alternating cycles while maintaining the absence of plasma.

[0017] In one embodiment, a flux ratio or pulse-time ratio between Mt and M2is controlled to set x within ±0.02 of a target value.

[0018] In one embodiment, no ionized or radical nitrogen species are introduced during steps (b)-(d) and the N2is undissociated prior to step (c).

[0019] In one embodiment, the metal atoms are provided by thermal evaporation of a metal source under vacuum.

[0020] In one embodiment, the delivering of metal atoms is performed by one or more of molecular beam epitaxy (MBE), thermal chemical vapor deposition (CVD), thermal atomic layer deposition (ALD), or thermal laser epitaxy (TLE), while maintaining the absence of plasma.

[0021] In one embodiment, the chamber is under vacuum during steps (b)-(d).

[0022] In one embodiment, the substrate is heated during steps (b)-(d).

[0023] In one embodiment, the crystalline nitride film has a thickness from 0.5 nm to 10 pm.

[0024] In one embodiment, the nitride film is epitaxial and exhibits registry with the substrate.

[0025] In one embodiment, the (111) Bragg reflection of the nitride film, the X-ray diffraction rocking-curve full-width at half-maximum (FWHM) is between 0.02° and 4°.

[0026] In one embodiment, the nitride film is undoped or unintentionally doped.

[0027] In one embodiment, the nitride film is intentionally doped to n-type or p-type by supplying a dopant flux during growth.

[0028] In one embodiment, the film growth rate is between 1 nm / hr and 5 pm / hr.41531347 1Docket No. MIT26181 PCT

[0029] In one embodiment, the flow into the chamber during step (b) comprises molecular nitrogen (N2).

[0030] In one embodiment, the method further comprises forming non-planar device geometries including one or more of fins, deep trenches, or high-aspect-ratio features.

[0031] In one embodiment, the method further comprising back-end-of-line (BEOL) integration of the nitride film with semiconductor circuits.

[0032] In one embodiment, thin nitride films are employed as a wear-resistant coating, high-temperature-resistant coating, cutting-tool coating, bearing coating, or diffusion barrier.

[0033] In one embodiment, the present invention comprises a nitride film produced by the aforementioned method.

[0034] In one embodiment, the present invention provides an article comprising the aforementioned nitride film, the article selected from: a wear-resistant coating, a high- temperature-resistant coating, a cutting tool, a bearing, or a diffusion barrier.

[0035] In another embodiment, the present invention provides a method of growing a crystalline ternary nitride without plasma, the method comprising: (a) providing a substrate bearing a nitride film that presents a metal-terminated surface (step 1002); (b) exposing the metal-terminated surface to molecular nitrogen (N2) in the absence of plasma, thereby adsorbing intact N2on the surface (step 1004); (c) delivering scandium atoms and M atoms to sites of the adsorbed N2so as to activate and cleave the N N bond in situ, forming surface-bound nitrogen atoms and an N-terminated region with partial metal coverage, wherein M is niobium (Nb) or aluminum (Al) (step 1006); and (d) adsorbing additional scandium atoms and M atoms onto the N-terminated region to complete a crystalline ScxMi_xN layer, where 0 < x < 1 (step 1008).

[0036] In one embodiment, M is niobium (Nb), thereby forming ScxNbi_xN.51531347 1Docket No. MIT26181 PCT

[0037] In one embodiment, M is aluminum (Al), thereby forming ScxAli_xN.

[0038] In one embodiment, 0.01 < x < 0.99.

[0039] In one embodiment, the scandium and M atoms are delivered (i) simultaneously or (ii) sequentially in alternating cycles, while maintaining the absence of plasma.

[0040] In one embodiment, a flux ratio or pulse-time ratio between scandium and M is controlled to set x within ±0.02 of a target value.

[0041] In one embodiment, no ionized or radical nitrogen species are introduced during steps (b)-(d) and the N2is undissociated prior to step (c).

[0042] In one embodiment, the layer is epitaxial on the substrate.

[0043] In one embodiment, the crystalline nitride film has a thickness from 0.5 nm to 10 pm.

[0044] In one embodiment, the delivering of scandium and M atoms is performed by molecular beam epitaxy (MBE), thermal chemical vapor deposition (CVD), thermal atomic layer deposition (ALD), or thermal laser epitaxy (TLE).

[0045] In yet another embodiment, the present invention provides a method of growing crystalline scandium nitride (ScN) without plasma, the method comprising: (a) providing a substrate bearing a nitride film that presents a scandium-terminated surface (step 1102); (b) exposing the scandium-terminated surface to molecular nitrogen (N2) in the absence of plasma, thereby adsorbing intact N2on the surface (step 1104); (c) delivering scandium atoms to sites of the adsorbed N2so as to activate and cleave the N=N bond in situ, forming surface-bound nitrogen atoms and an N-terminated region with partial scandium coverage (step 1106); and (d) adsorbing additional scandium atoms onto the N-terminated region to complete a crystalline ScN layer (step 1108).

[0046] In one embodiment, no ionized or radical nitrogen species are introduced during steps (b)-(d) and the N2is undissociated prior to step (c).61531347 1Docket No. MIT26181 PCT

[0047] In one embodiment, the ScN film is epitaxial and exhibits registry with the substrate.

[0048] In one embodiment, for ScN(111) the X-ray diffraction rocking-curve FWHM is between 0.02° and 4°.

[0049] In one embodiment, the crystalline ScN film has a thickness from 0.5 nm to 10 pm.

[0050] In one embodiment, the ScN film is undoped or unintentionally doped.

[0051] In one embodiment, the ScN film is intentionally doped to n-type or p-type by supplying a dopant flux during growth.

[0052] In one embodiment, delivering scandium atoms is performed by molecular beam epitaxy (MBE), thermal chemical vapor deposition (CVD) performed without plasma, thermal atomic layer deposition (ALD) performed without plasma, or thermal laser epitaxy (TLE).

[0053] In one embodiment, the chamber is under vacuum during steps (b)-(d) and the substrate is heated during steps (b)-(d).

[0054] In one embodiment, the ScN layer is employed as a wear-resistant coating, high- temperature-resistant coating, cutting-tool coating, bearing coating, or diffusion barrier.

[0055] In one embodiment, steps (b)-(d) are performed at 350 °C.BRIEF DESCRIPTION OF FIGURES

[0056] The present disclosure, in accordance with one or more various examples, is described in detail with reference to the following figures. The drawings are provided for purposes of illustration only and merely depict examples of the disclosure. These drawings are provided to facilitate the reader's understanding of the disclosure and should not be considered limiting of the breadth, scope, or applicability of the disclosure. It should be noted that for clarity and ease of illustration these drawings are not necessarily made to scale.71531347 1Docket No. MIT26181 PCT

[0057] FIGS. 1A-1 E show diffraction studies (RHEED, XRD) showing twinned cubic ScN film growth and epitaxial registry with the 6H-SiC substrate. FIG. 1A shows reflection high- electron diffraction (RHEED) pattern of ScN films collected at 40 minutes (top - Ai and A2) and 135 minutes (bottom - A3 and A4) of growth on Si-face 6H-SiC substrate at 550 °C substrate temperature, and Sc flux of 2.5 x 1Q-8torr with plasma (left - A1 and A3), and without plasma (right - A2and A4). Indices in boxes 104 and 106 show diffraction patterns from each domain, and the index in box 102 shows overlapping peaks from each domain. FIG. 1 B is a ScN / 6H-SiC structural schematic showing crystallographic orientations of twin domains of cubic ScN with respect to the 6H-SiC substrate; twin domains of ScN are labeled as “Domain-1” and “Domain-2”. FIG. 10 shows an X-ray diffraction spectra of ScN films grown without plasma on 6H-SiC substrates at different substrate temperatures (350 °C, 550 °C, 750 °C, and 950 °C) showing cubic ScN growth epitaxially in (111) orientation. FIG. 1 D shows skew-symmetric phi (<J>) scans of ScN 242, 6H-SiC 1015 reflections for ScN films grown without plasma at 550 °C. FIG. 1 E shows reciprocal space maps of ScN, 6H-SiC reflections for ScN films grown without plasma at 550 °C indicating epitaxial film registry with 6H-SiC substrate.

[0058] FIGS. 2A-2C show synchrotron-source measured Reciprocal Space Maps for ScN thin films and 6H-SiC substrate, with theoretical simulation. 2D slices of 3D Reciprocal space maps measured at QM2 beamline at CHESS enclosing multiple Bragg reflections related to ScN thin film twinned cubic crystal structure and 6H-SiC substrate hexagonal crystal structure in H = 0 plane for (FIG. 2A) ScN film grown with plasma at 550 °C and (FIG. 2B) ScN film grown without plasma at 550 °C. The data is indexed with respect to the 6H-SiC substrate lattice parameters, and the intensity of all Bragg peaks is shown on a logarithmic scale.81531347 1Docket No. MIT26181 PCT

[0059] FIGS. 2A and 2B show the ScN thin-film’s and 6H-SIC substrate’s Bragg reflections. Strong and intense ScN Bragg peaks indicate a high crystallinity of the ScN film grown without plasma.

[0060] FIG. 2C depicts the simulated diffraction pattern generated from standard Crystallographic Information File for 6H-SiC substrate (white stars, Space group: P62mc,

[0001] out-of-plane, and

[0110] in-plane orientation), twinned ScN (triangles; Space group: Fm3m,

[0111] out-of-plane and

[0211] (up triangles) in-plane orientation, and

[0111] out-of- plane and

[0211] (down triangles) in-plane orientation), Sc (circles, Space group: PG3 / mmc,

[0001] out-of-plane and

[0110] in-plane orientation) by using a tool such as xrayutility tool.

[0061] FIGS. 3A-3E show microstructure and composition analysis of ScN films using HAADF-STEM, XPS.

[0062] FIGS. 3A and 3B show HAADF-STEM micrographs of ScN film grown with plasma.

[0063] FIGS. 3C-3E show ScN film grown without plasma at different magnifications, showing columnar grain growth of ScN, zig-zag facet surface from twinned cubic domains, and two different domains in ScN films.

[0064] FIG. 3F shows XPS Sc2p, N1s core level photoelectron spectra.

[0065] FIG. 3G shows NKU. Auger electron spectra for ScN film grown without plasma, ScN film grown with plasma and a separate metallic Sc film verifying the Sc-N bonding and the presence of nitrogen in the ScN films grown without plasma.

[0066] FIGS. 4A-4F depict growth rate and properties (density, chemical bonding, and optical absorption) of ScN film. FIGS. 4A and 4B show growth rates and densities of ScN films grown at different substrate thermocouple temperatures with plasma and without plasma, respectively, showing comparable growth rates and densities. FIGS. 4C and 4D depict Raman spectra of ScN films grown on 6H-SiC substrates at different substrate temperatures with plasma and without plasma, respectively, showing similar ScN bonding91531347 1Docket No. MIT26181 PCT in films grown. FIGS. 4E and 4F depict Tauc plots from UV-visible absorption spectra for ScN films grown with plasma and without plasma show comparable absorption band edges. The inserts of FIG. 4E and 4F show optical images of the representative ScN film samples grown at 550 °C substrate temperature.

[0067] FIG. 5 depicts Ab initio calculated ScN growth pathways. The nitrogen plasma growth pathway (left) begins with the adsorption of individual N atoms, forming a N layer in a region of the Sc-terminated surface. The molecular nitrogen growth pathway (right) begins with the adsorption of N2molecules in a region of the Sc-terminated surface. Sc atoms then facilitate the breaking of the N2bond on the surface. The two growth pathways converge (center) during the adsorption of Sc atoms to complete the growth of a new ScN layer.

[0068] FIGS. 6(A)-(H) depict the method according to one embodiment of the present invention.

[0069] FIG. 7 depicts X-ray diffraction scans of ScxAli_xN films grown by self-activated (plasma-free) growth on 6H-SiC.

[0070] FIGS. 8(A)-(C) show that opening the heated scandium source shutter getters residual gases — dropping total chamber pressure, suppressing residual gas analyzer (RGA) signals for H2,14N,CH2,15N,CH3, O,CH4,H20,14N2,14 / 15N2,15N2,Ar,CO2, and reducing their mass-spectrum peaks.

[0071] FIG. 9 depicts a flowchart of a plasma-free nitride growth method using intact N2adsorption, metal-assisted N N cleavage, and subsequent metal adsorption to complete each crystalline layer.

[0072] FIG. 10 depicts a flowchart of a plasma-free ternary nitride process forming ScxMi_xN (M = Nb or Al) via intact N2adsorption, Sc+M co-delivery to cleave N=N, and layer completion.101531347 1Docket No. MIT26181 PCT

[0073] FIG. 11 depicts a flowchart of a plasma-free ScN growth method using intact N2adsorption, Sc-assisted N N cleavage, and Sc adsorption to complete the ScN layer.DETAILED DESCRIPTION

[0074] While this invention is illustrated and described in a preferred embodiment, the invention may be produced in many different configurations. There is depicted in the drawings, and will herein be described in detail, a preferred embodiment of the invention, with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and the associated functional specifications for its construction and is not intended to limit the invention to the embodiment illustrated. Those skilled in the art will envision many other possible variations within the scope of the present invention.

[0075] Note that in this description, references to “one embodiment” or “an embodiment” mean that the feature being referred to is included in at least one embodiment of the invention. Further, separate references to “one embodiment” in this description do not necessarily refer to the same embodiment; however, neither are such embodiments mutually exclusive, unless so stated and except as will be readily apparent to those of ordinary skill in the art. Thus, the present invention can include any variety of combinations and / or integrations of the embodiments described herein.

[0076] Unlike naturally occurring oxide crystals such as ruby and gemstones, there are no naturally occurring nitride crystals because the triple bond of the nitrogen molecule is one of the strongest bonds in nature. When the transition metal scandium is subjected to molecular nitrogen, it self-catalyzes to break the nitrogen triple bond to form highly crystalline layers of ScN, a semiconductor. This reaction proceeds even at room temperature, opening a new pathway to ultralow-energy synthesis of crystalline nitride semiconductor layers and beyond.111531347 1Docket No. MIT26181 PCT

[0077] Molecular nitrogen has one of the strongest interatomic bonds, yet experimental results show that a reactive metal, exemplified by scandium, can catalyze its dissociation on a metal-terminated surface to form epitaxial, highly crystalline ScN without plasma. This capability opens new avenues to elucidate how N2is dissociated at surfaces, how metal-nitrogen bonds nucleate and propagate, and how previously unrecognized growth mechanisms govern structure, processing, and property relationships in nitride thin films. It also motivates the design of tailored precursors and catalysts for crystalline nitride growth. Early evidence indicates that this plasma-free pathway produces microstructures distinct from those obtained with conventional plasma-assisted routes. The resulting materials platform spans semiconducting, metallic, superconducting, and catalytic nitrides for devices and circuits. Whereas commercially available high-quality semiconducting nitrides typically require a nitrogen plasma source or very high temperatures to achieve a high degree of atomic ordering, the mechanism described here uses neither, enabling epitaxial nitride synthesis under milder, industry-friendly conditions.

[0078] While investigating the growth of the semiconductor ScN using a plasma-activated source of N2, it was discovered that crystalline layers of semiconducting ScN could be deposited even when Sc is exposed to molecular N2, i.e. , without the plasma. This work describes a study of the synthesis of ScN by two processes: a) in the presence of molecular nitrogen, an entirely thermal process (without nitrogen plasma), and b) with a plasma-assisted process. Owing to a low electronegativity and small nuclear effective charge, Sc has a significant affinity to bond with anions like oxygen and halogens, forming Sc2O3, SCF3, and ScCI3. The heightened reactivity of Sc compared to Ga and Al posed the fundamental question of whether Sc-containing nitride thin films can be grown in a vastly different manner than traditional methods. A strong scavenging effect of scandium metal was observed, highlighting its high reactivity toward nitrogen and oxygen, suggesting that scandium can promote self-activated epitaxial growth at BEOL-compatible121531347 1Docket No. MIT26181 PCT temperatures without an active nitrogen species (i.e., the nitrogen plasma) to facilitate film growth. This mechanism differs entirely from existing growth methods. Self-activated epitaxial ScN film growth was observed under several growth conditions by varying the substrate temperature, Sc flux, and N2flow rate on various substrates of interest. Structural, optical, and physical properties of the ScN films grown from molecular N2show comparable or even better quality than those grown in the standard way with N2plasma. A possible energy-efficient pathway in which Sc facilitates the bond breaking of molecular N2leading to the growth of ScN films is identified by ab initio calculations. These findings open a new window for the low-energy synthesis of novel nitride heterostructures, integration schemes, and applications while enhancing understanding of the synthesis of transition metal nitride compounds and, at the same time, suggesting a reinvestigation of the reactivity of metals with molecular nitrogen.

[0079] In one embodiment, as depicted in FIG. 9, the present invention provides a method of growing a crystalline nitride without plasma, the method comprising: (a) providing a substrate bearing a nitride film that presents a metal-terminated surface (step 902); (b) exposing the metal-terminated surface to molecular nitrogen (N2) in the absence of plasma, thereby adsorbing intact N2on the surface (step 904); (c) delivering metal atoms to sites of the adsorbed N2so as to activate and cleave the N N bond in situ, forming surface-bound nitrogen atoms and an N-terminated region with partial metal coverage, wherein the metal comprises one or more elements selected from transition metals, rare- earth metals, and actinides (step 906); (d) adsorbing additional metal atoms onto the N- terminated region to complete a crystalline nitride layer (step 908); and (e) optionally repeating steps (a)-(d) to grow successive layers (step 910).

[0080] In one embodiment, the metal consists of a single element, thereby forming a binary metal nitride.131531347 1Docket No. MIT26181 PCT

[0081] In one embodiment, the metal is a transition metal selected from the group consisting of scandium (Sc), yttrium (Y), niobium (Nb), titanium (Ti), tantalum (Ta), zirconium (Zr), hafnium (Hf), vanadium (V), tungsten (W), and molybdenum (Mo).

[0082] In one embodiment, the metal is a rare-earth metal selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0083] In one embodiment, the metal is an actinide selected from the group consisting of actinium (Ac), thorium (Th), protactinium (Pa), uranium (U), neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), fermium (Fm), mendelevium (Md), nobelium (No), and lawrencium (Lr).

[0084] In one embodiment, the metal comprises first and second metal elements, Mt and M2, and the layer has composition MlxM2i xN, where 0<x<1.

[0085] In one embodiment, the nitride is ScxNbi_xN.

[0086] In one embodiment, Mt and M2are independently selected from transition metals and rare-earth metals.

[0087] In one embodiment, one of Mt or M2is Sc or a rare-earth metal and the other is Al, Ga, or In, thereby forming (Sc or RE)X(AI or Ga or ln)i_xN.

[0088] In one embodiment, the nitride is ScxAli_xN.

[0089] In one embodiment, the first and second metal elements are delivered (i) simultaneously or (ii) sequentially in alternating cycles while maintaining the absence of plasma.

[0090] In one embodiment, a flux ratio or pulse-time ratio between Mi and M2is controlled to set x within ±0.02 of a target value.141531347 1Docket No. MIT26181 PCT

[0091] In one embodiment, no ionized or radical nitrogen species are introduced during steps (b)-(d) and the N2is undissociated prior to step (c).

[0092] In one embodiment, the metal atoms are provided by thermal evaporation of a metal source under vacuum.

[0093] In one embodiment, the delivering of metal atoms is performed by one or more of molecular beam epitaxy (MBE), thermal chemical vapor deposition (CVD), thermal atomic layer deposition (ALD), or thermal laser epitaxy (TLE), while maintaining the absence of plasma.

[0094] In one embodiment, the chamber is under vacuum during steps (b)-(d).

[0095] In one embodiment, the substrate is heated during steps (b)-(d).

[0096] In one embodiment, the crystalline nitride film has a thickness from 0.5 nm to 10 pm.

[0097] In one embodiment, the nitride film is epitaxial and exhibits registry with the substrate.

[0098] In one embodiment, the (111) Bragg reflection of the nitride film, the X-ray diffraction rocking-curve full-width at half-maximum (FWHM) is between 0.02° and 4°.

[0099] In one embodiment, the nitride film is undoped or unintentionally doped.

[0100] In one embodiment, the nitride film is intentionally doped to n-type or p-type by supplying a dopant flux during growth.

[0101] In one embodiment, the film growth rate is between 1 nm / hr and 5 pm / hr.

[0102] In one embodiment, the flow into the chamber during step (b) comprises molecular nitrogen (N2).

[0103] In one embodiment, the method further comprises forming non-planar device geometries including one or more of fins, deep trenches, or high-aspect-ratio features.

[0104] In one embodiment, the method further comprising back-end-of-line (BEOL) integration of the nitride film with semiconductor circuits.151531347 1Docket No. MIT26181 PCT

[0105] In one embodiment, the nitride film is employed as a wear-resistant coating, high- temperature-resistant coating, cutting-tool coating, bearing coating, or diffusion barrier.

[0106] In one embodiment, the present invention comprises a nitride film produced by the aforementioned method.

[0107] In one embodiment, the present invention provides an article comprising the aforementioned nitride film, the article selected from: a wear-resistant coating, a high- temperature-resistant coating, a cutting tool, a bearing, or a diffusion barrier.

[0108] In another embodiment, as depicted in FIG. 10, the present invention provides a method of growing a crystalline ternary nitride without plasma, the method comprising: (a) providing a substrate bearing a nitride film that presents a metal-terminated surface (step 1002); (b) exposing the metal-terminated surface to molecular nitrogen (N2) in the absence of plasma, thereby adsorbing intact N2on the surface (step 1004); (c) delivering scandium atoms and M atoms to sites of the adsorbed N2so as to activate and cleave the N=N bond in situ, forming surface-bound nitrogen atoms and an N-terminated region with partial metal coverage, wherein M is niobium (Nb) or aluminum (Al) (step 1006); and (d) adsorbing additional scandium atoms and M atoms onto the N-terminated region to complete a crystalline ScxMi_xN layer, where 0 < x < 1 (step 1008).

[0109] In one embodiment, M is niobium (Nb), thereby forming ScxNbi_xN.

[0110] In one embodiment, M is aluminum (Al), thereby forming ScxAli_xN.

[0111] In one embodiment, 0.01 < x < 0.99.

[0112] In one embodiment, the scandium and M atoms are delivered (i) simultaneously or (ii) sequentially in alternating cycles, while maintaining the absence of plasma.

[0113] In one embodiment, a flux ratio or pulse-time ratio between scandium and M is controlled to set x within ±0.02 of a target value.161531347 1Docket No. MIT26181 PCT

[0114] In one embodiment, no ionized or radical nitrogen species are introduced during steps (b)-(d) and the N2is undissociated prior to step (c).

[0115] In one embodiment, the layer is epitaxial on the substrate.

[0116] In one embodiment, the crystalline nitride film has a thickness from 0.5 nm to 10 pm.

[0117] In one embodiment, the delivering of scandium and M atoms is performed by molecular beam epitaxy (MBE), thermal chemical vapor deposition (CVD), thermal atomic layer deposition (ALD), or thermal laser epitaxy (TLE).

[0118] In yet another embodiment, as depicted in FIG. 11 , the present invention provides a method of growing crystalline scandium nitride (ScN) without plasma, the method comprising: (a) providing a substrate bearing a nitride film that presents a scandium- terminated surface (step 1102); (b) exposing the scandium-terminated surface to molecular nitrogen (N2) in the absence of plasma, thereby adsorbing intact N2on the surface (step 1104); (c) delivering scandium atoms to sites of the adsorbed N2so as to activate and cleave the N N bond in situ, forming surface-bound nitrogen atoms and an N-terminated region with partial scandium coverage (step 1106); and (d) adsorbing additional scandium atoms onto the N-terminated region to complete a crystalline ScN layer (step 1108).

[0119] In one embodiment, no ionized or radical nitrogen species are introduced during steps (b)-(d) and the N2is undissociated prior to step (c).

[0120] In one embodiment, the ScN film is epitaxial and exhibits registry with the substrate.

[0121] In one embodiment, for ScN(111) the X-ray diffraction rocking-curve FWHM is between 0.02° and 4°.

[0122] In one embodiment, the crystalline ScN film has a thickness from 0.5 nm to 10 pm.

[0123] In one embodiment, the ScN film is undoped or unintentionally doped.171531347 1Docket No. MIT26181 PCT

[0124] In one embodiment, the ScN film is intentionally doped to n-type or p-type by supplying a dopant flux during growth.

[0125] In one embodiment, delivering scandium atoms is performed by molecular beam epitaxy (MBE), thermal chemical vapor deposition (CVD) performed without plasma, thermal atomic layer deposition (ALD) performed without plasma, or thermal laser epitaxy (TLE).

[0126] In one embodiment, the chamber is under vacuum during steps (b)-(d) and the substrate is heated during steps (b)-(d).

[0127] In one embodiment, the ScN layer is employed as a wear-resistant coating, high- temperature-resistant coating, cutting-tool coating, bearing coating, or diffusion barrier.

[0128] In one embodiment, binary nitride compositions may be represented as TMN, where TM is a transition metal, and REN, where RE is a rare-earth metal. Ternary nitride compositions may be represented as (TM and / or RE)N or as (TM or RE)(AI or Ga or I n)N, including alloy formulations of the form MlxM2 -xN (where 0<x<1) such as ScxNbi_xN and ScxAli_xN. The resulting thin-film compounds can be solid solutions or ordered alloys, with ordering occurring on the cation sublattice.

[0129] In one embodiment, steps (b)-(d) are performed at 350 °C.

[0130] Metal nitrides, including transition metal nitrides (e.g. WN and TaN) and group-ill semiconductor nitrides (e.g. GaN, AIN) are of great technological significance. Their mechanical, thermal, optical, and electronic properties enable a pivotal role in solid-state lighting, acoustic devices, and high-power electronic applications in laser diodes, RF power amplifiers, and acoustic wave resonators for 5G and 6G technologies. Being a transition metal nitride, scandium nitride (ScN) possesses excellent hardness of -21 GPa, elastic modulus of -356 GPa, high melting point of -2600 °C, and thermal stability. Furthermore, ScN is a semiconductor with an energy bandgap of -1.3 eV and can be doped n-type and p-type. ScN also possess a high Seebeck coefficient of ~-86 pVK-1, and181531347 1Docket No. MIT26181 PCT a high thermoelectric power factor of 2.5 x 1O‘3Wnr1K'2at 800 K, surpassing commercially available PbTe. The cubic ScN (111) orientation has a less than 0.1 % lattice mismatch with wurtzite GaN (0001), enabling the utilization of ScN for dislocation reduction, in-situ Ohmic contacts, and current spreading layers in GaN-based devices. The giant polarization discontinuity of ScN with other group-ill nitrides is predicted to make it a suitable candidate for polarization-enhanced tunnel junctions. Incorporation of ScN and alloying nitrides with Sc promises to bring to the established Group-Ill nitride (GaN, AIN, and InN) based electronics and photonics family previously missing properties such as thermoelectric, plasmonic, extremely high piezoelectric, ferroelectric, and high dielectric constant behavior.

[0131] FIGS. 1A-1 E show diffraction studies (RHEED, XRD) showing twinned cubic ScN film growth and epitaxial registry with the 6H-SiC substrate. FIG. 1A shows reflection high- electron diffraction (RHEED) pattern of ScN films collected at 40 minutes (top - Ai and A2) and 135 minutes (bottom - A3 and A4) of growth on Si-face 6H-SiC substrate at 550 °C substrate temperature, and Sc flux of 2.5 x w8torr with plasma (left - A1 and A3), and without plasma (right - A2and A4). Indices in boxes 104 and 106 show diffraction patterns from each domain, and the index in box 102 shows overlapping peaks from each domain. FIG. 1 B is a ScN / 6H-SiC structural schematic showing crystallographic orientations of twin domains of cubic ScN with respect to the 6H-SiC substrate; twin domains of ScN are labeled as “Domain-1” and “Domain-2”. FIG. 1C shows an X-ray diffraction spectra of ScN films grown without plasma on 6H-SiC substrates at different substrate temperatures (350 °C, 550 °C, 750 °C, and 950 °C) showing cubic ScN growth epitaxially in (111) orientation. FIG. 1 D shows skew-symmetric phi (<J>) scans of ScN 242, 6H-SiC 1015 reflections for ScN films grown without plasma at 550 °C. FIG. 1 E shows reciprocal space maps of ScN, 6H-SiC reflections for ScN films grown without plasma at 550 °C indicating epitaxial film registry with 6H-SiC substrate.191531347 1Docket No. MIT26181 PCT

[0132] The ScN films in this study were grown in a molecular beam epitaxy system with and without striking nitrogen plasma from molecular N2 on 6H-SiC substrates to assess the reactivity of Sc with molecular nitrogen and to assess the feasibility of self-activated growth. FIG. 1A shows the in-situ reflection high-energy electron diffraction (RHEED) pattern of ScN films grown at 550 °C with nitrogen plasma (left) and without nitrogen plasma (right), collected at -40 minutes, ~88 nm growth (top) and -135 minutes, -294 nm growth (bottom). These diffraction patterns after 40 minutes of growth (see FIG. 1A; top A1 and A2) indicate rotated domains with two separate overlaid < 110 > zone axes, indexed as pairs of {111} and {002} families of planes, as indexed by red and blue colors on the RHEED pattern. ScN films grown without plasma at different substrate temperatures of 20 °C, 350 °C, 750 °C, and 950 °C show a similar RHEED diffraction pattern. As illustrated in FIG. 1A, all RHEED patterns signify twin cubic ScN film growth (FIG. 1 B) of similar character, with and without striking plasma. Along the

[0001] direction of 6H-SiC, (111) cubic twin ScN domains form instead of a pure hexagonal, wurtzite, or zinc blende phase due to the thermodynamic stability of the rock salt cubic structure of ScN.

[0133] Twin domains are expected to result from the symmetry constraints encountered upon growing a three-fold symmetric cubic crystal on a six-fold symmetric hexagonal substrate. After extended growths of -135 minutes, polycrystalline rings appear in the diffraction pattern for the ScN film grown with plasma, as shown in FIG. 1A, Block A3. In contrast, the spotty twin domain diffraction pattern of ScN films persists for the ScN film grown without plasma, as shown in FIG. 1 A, Block A4. This indicates that thicker ScN films grown without plasma have a high crystalline quality and maintain an excellent epitaxial registry with the substrate.

[0134] Bulk structural properties were analyzed using lab-based and synchrotron X-ray diffraction. FIGS. 1C-E show the crystalline phase, orientation, and epitaxial registry of the201531347 1Docket No. MIT26181 PCTScN film grown without plasma assessed using X-ray diffraction (XRD). The ScN 111 and 222 reflections were observed (See FIG. 1C) for ScN films grown without plasma at substrate temperatures from 20 °C to 950 °C. To test for the in-plane epitaxial relationship between ScN and the substrate, skew-geometry phi-scans of asymmetric ScN 242 and 6H-SiC 1015 reflections are shown in FIG. 1 D. Six peaks at the same positions indicate the 6-fold symmetry and the epitaxial registry of the ScN films with 6H-SiC substrate. The full-width-half-maximum (FWHM) of the individual peaks in the ScN 242 phi scan are ~0.5 degrees, indicating a high degree of in-plane orientation. Similar 6-fold symmetry and epitaxial registry were also observed for the ScN films grown with plasma.

[0135] FIG. 1 E shows a reciprocal space map (RSM) of 6H-SiC and twin-cubic ScN asymmetric reflections, i.e., 242 from the first domain and 313 from the second twin domain, for ScN grown from molecular N2without plasma. No metallic Sc peaks were observed in the reciprocal space corresponding to metallic scandium reflections. The XRD-RSM confirms the high reactivity of Sc with diatomic nitrogen, the growth of (111) ScN films with cubic twin domains over a wide substrate temperature range from 20- 950 °C without plasma, and its epitaxial growth registry with 6H-SiC substrate. Similar twinned-cubic ScN film growth using molecular N2without nitrogen plasma was also observed on other wurtzite (0002) oriented substrates such as GaN and AIN.

[0136] There is a possibility that a small fraction of Sc flux does not form ScN and remains as a secondary phase of metallic Sc. Such metallic inclusions are undesirable in semiconducting ScN. Lab-source XRD has limited X-ray energies and detection range, making the detection of small fractions of secondary phases challenging. To remedy this, a large volume of the 3D reciprocal space was measured using synchrotron X-ray scattering to detect residual unreacted Sc in the ScN film.

[0137] FIGS. 2A and 2B show 2D slices of experimentally measured 3D RSMs in theH - 0 plane for the ScN thin films grown with plasma and without plasma on a 6H-SiC211531347 1Docket No. MIT26181 PCT substrate. FIG. 20 shows a simulated RSM including 6H-SiC substrate (stars), a most likely Sc-metal inclusion phase (circles), and twinned cubic ScN domains (triangles). The comparison between the simulation (FIG. 20) and the data confirms that the observed experimental Bragg reflections measured by the X-ray scattering (See FIGS. 2A-2B) originate from twinned-cubic ScN thin film and 6H-SiC substrate, whereas no Sc-inclusion was observed. Furthermore, extensive phase purity analysis is performed by analyzing the entire large volume of the reciprocal space, and no Bragg reflections are observed for any trace of secondary phases, such as metallic scandium or layered hexagonal ScN, etc., within the large volume of reciprocal space. This confirms the growth of phase pure twin cubic ScN films from molecular N2 without plasma.

[0138] The atomic layer stacking of different twin ScN domains was analyzed using 3D RSM slices at different L-planes. The ScN thin films have a well-ordered crystal lattice with 6-fold symmetry, with discrete ABCA atomic layer stacking from some twin domains and ACBA stacking from others. ScN film grown without plasma exhibits an intense peak with a low FWHM of 0.0865 r.I.u. (relative lattice units) in out-of-plane direction, as shown in Inset FIG. 2B. This indicates that the epitaxial ScN thin film grown without plasma is highly crystalline.

[0139] FIGS. 3A-E show HAADF-STEM images of (111) ScN films grown on (0001) 6H- SiC substrates, highlighting distinct features between films grown with plasma (FIGS. 3A and 3B) and without plasma (FIGS. 3C-3E). EDX spectra validate N incorporation in the ScN films grown without plasma and demonstrate a uniform distribution of Sc and N throughout the film. The top surface of the ScN film grown without plasma (FIG. 30) exhibits a notable surface morphology characterized by sharp pyramid structures of ~18 nm height with {001} facets, providing clear evidence of columnar growth. As highlighted by alternating dark and bright contrasts (see FIG. 3C), these columnar twin domains are rotated by 60 degrees along

[0111] growth direction. Such rotated twin domain formation is221531347 1Docket No. MIT26181 PCT an expected growth feature for cubic crystal growth on hexagonal (wurtzite) crystals, e.g., 6H-SiC, GaN, and AIN.

[0140] Although STEM micrographs of ScN films grown with and without plasma indicate a similar columnar growth, the microstructure differs. Notably, films grown without plasma show large domains extending from the substrate surface to the top of the film (FIGS. 30, 3D), leading to a sharp pyramidal morphology. In contrast, films grown with plasma display smaller rotated domains (FIG. 3B), contributing to a smoother surface morphology (FIG. 3A). The presence of these smaller rotated domains in films grown with plasma suggests a potential influence of plasma on the growth dynamics governing both domain size and orientation. The distinct characteristics observed in films grown without plasma, such as larger continuous domains and well-defined columnar structures, suggest a more controlled and organized growth process in the absence of plasma-induced effects.

[0141] A High-resolution HAADF-STEM image of ScN film grown without plasma (FIG. 3E) shows the nominal structure of cubic ScN projected along < 110 > direction. The interface between ScN and substrate is sharp, and the film has a coherent interface with the substrate. The ScN lattice constant obtained from the Fast Fourier Transform of this region and another region is ~4.3 A, smaller than the relaxed lattice constant of 4.5 A.

[0142] Chemical bonding in the ScN films was analyzed using Sc2p, N1s core level X-ray photoelectron spectra (FIG. 3F), and NKLL Auger electron spectra (FIG. 3G). For reference, a metallic Sc film was used (see methods for growth details). Deconvoluted peaks in the Sc2p core level photoelectron spectra in FIG. 3F indicate Sc-N bonding in the ScN film samples grown without plasma and with plasma. Unlike the metallic Sc film sample, metallic Sc-Sc bonding peaks were not evident in the ScN film samples. Sc-0 bonding is apparent in all samples, likely from the surface oxidation. N1s core level photoelectron spectra and the NKLL Auger electron spectra in FIG. 3G confirm the presence of nitrogen231531347 1Docket No. MIT26181 PCT in the ScN films. A comparable [Sc] / [N] ratio of -1.07 for the ScN films grown with plasma and -1.13 for ScN films grown without plasma was observed by XPS.

[0143] The ScN film thickness and density were measured using X-ray reflectivity (XRR) to examine potential differences in ScN growth kinetics with and without plasma. Growth rates and densities of ScN films grown with and without plasma at varying growth temperatures are shown in FIGS. 4A and 4B. ScN growth rate decreases from -150 nm hour1to -125 nm hour1as substrate temperature is increased from 350 °C to 750 °C. The films were grown in heavily nitrogen-rich conditions, where Sc flux < N* flux < N2flux in all cases of film growth presented here. Comparable growth rates with and without plasma indicate that the ScN growth is not limited by the availability of active N* species but by the flux of Sc and is self-activated. Increasing the growth temperature from 350 °C to 750 °C enhances the density of ScN films from -3.6 g cm-3to -3.9 g cm-3, potentially facilitated by higher adatom surface mobility.

[0144] FIGS. 4C and 4D show the Raman spectra of the ScN films and 6H-SiC substrate for reference. Distinct from 6H-SiC Raman peaks, we observe additional Raman peaks at -365 cm-1, -683 cm-1and -1355 cm-1. The Raman peaks at -365 cm-1correspond to the ScN TO( / “), LA(X) modes, and at -683 cm-1correspond to the ScN LO(L) mode. A ScN second order peak appears at -1300-1360 cm-1. The Raman peaks for ScN films grown without and with nitrogen plasma are at comparable wavenumbers, indicating similar Sc- N bonding.

[0145] Rock-salt crystalline ScN is a semiconductor. The energy bandstructure has a valence band maximum at the f-point and a conduction band minimum at the X-point with an indirect gap in the range of 0.9-1.6 eV corresponding totransition and a direct gap of -2.1-2.4 eV corresponding to transition at X point. The measured Tauc plots for -300 nm thick ScN films grown with plasma are shown in FIG. 4E, and those for -400 nm thick ScN films grown without plasma are shown in FIG. 4F. The extracted optical241531347 1Docket No. MIT26181 PCT absorption edge values of -2.20 (+ / -0.05) eV for all ScN samples align closely with reported values for degenerately doped ScN films. In FIGS. 4E and 4F, insets display ScN film samples, matching the simulated color of uniformly integrated 740 to 565 nm, 1.68 to 2.2 eV light, indicative of ScN's transparency window in the visible regime. The ScN films grown with and without plasma show similar transport properties with comparable electron carrier concentrations of -1.5 x 1019to 8 x 102° cm-3and Hall mobilities of -1 to 5 cm2 / V.s. As observed in XPS, the as-grown ScN films are inherently n-type due to O impurity doping. Comparable optical absorption edges and transport properties in ScN films grown with and without plasma suggest that plasma-free growth is a viable method for obtaining semiconducting ScN films for electronic and photonic applications.

[0146] To study the similarities between growth with and without plasma, the possible paths for growth with nitrogen plasma and molecular N2 are studied via density functional theory (DFT) calculations. For each case, a path that builds one complete ScN layer, connected by several intermediate metastable states which successively lower the energy is identified and summarized in FIG. 5. The total energy is found by summing up the energies of the slab, including any adsorbed atoms / molecules, with the remaining isolated atoms (or molecules), where the nitrogen plasmas are approximated as nitrogen atoms (see Methods section). Our calculations reveal a large energetic push towards the formation of additional ScN layers. With respect to the reference energies for nitrogen plasma and molecular N2 growth, a 13.2 eV / formula unit (nitrogen plasma) and 8.0 eV / formula unit (molecular N2) energy decrease is found. This shows that both processes are highly exothermic, which agrees with the lower growth rate at higher substrate temperatures. Moreover, our nudged elastic band calculations indicate no energy barriers along both paths.

[0147] For the growth process with nitrogen plasma, we find a direct path to the growth of additional ScN layers. Starting with a Sc-terminated surface, nitrogen atoms are adsorbed251531347 1Docket No. MIT26181 PCT to form a N-terminated surface (FIG. 5 left, steps 1-2). After that, the adsorption of Sc atoms completes the new crystalline layer (FIG. 5 middle, steps 3-4). For molecular N2 growth, the initial process (FIG. 5 right, steps 1-3) is different, converging to a shared path with nitrogen plasma in the final step. First, a nitrogen molecule binds onto the Sc- terminated surface (FIG. 5 right, step 1). However, in contrast to the nitrogen plasma pathway, a complete N layer cannot be formed without the assistance of a Sc atom. Once a Sc atom lands on top of the adsorbed surface N2, the surface structure experiences large distortions that involve a significant increase in the N-N bond length, forming a N layer with partial Sc coverage (FIG. 5 right steps 2-3). Finally, additional Sc atoms fall onto the surface to complete the layer.

[0148] FIGS. 6(A)-(H) depict the method according to one embodiment of the present invention. They illustrate two hypothetical reaction pathways, guided by first-principles calculations that plot relative energy (AE per formula unit) on the y-axis, for forming ScN. With nitrogen plasma (left side of FIG. 5 and FIGS. 6(A)-6(C)), radical nitrogen (atomic N) adsorbs on a Sc-terminated surface (step 1 on left side of FIG. 5 & FIG. 6(B)), and adsorption proceeds until a complete N-terminated layer forms (step 2 on left side of FIG. 5 & FIG. 6(C)). This continues to form a complete layer (step 2, left side of FIG. 5 & FIG. 6(C)). Without nitrogen plasma (per the present invention and shown in right side of FIG. 5 & FIGS. 6(F)-6(H)), nitrogen molecules (N2) land on the scandium (Sc) terminated surface (step 1 , right side in FIG. 5 & FIG. 6(G)) and Sc atoms have to initiate bond N2breaking on the surface to start forming a crystal (step 2, right side of FIG. 5 & FIG. 6(G)). The hypothesis is that the individual growth mechanism, growth kinetics, and thermodynamics differs between these processes. In step 3 (middle of FIG. 5 and FIG. 6(E)), after nitrogen terminated layer has been formed, the process repeats to form a ScN crystal, which where the total energy of the system is essentially the same in both cases, which is referred to as the "shared path". Once the nitrogen terminated surface is formed,261531347 1Docket No. MIT26181 PCT scandium can react in either case (plasma free or without plasma) to continue growing the crystal.

[0149] To evaluate the reactive nature of Sc, we studied its gettering or scavenging effect by evaporating scandium from a Knudsen effusion cell at 1408 °C with a Sc beam equivalent flux of 3 10'8torr. The chamber base pressure remained constant before opening the Sc effusion cell shutter. Upon opening the shutter, the M BE chamber pressure immediately dropped (t = 0 min), indicating a gettering effect as Sc captured residual species. Monitoring gas partial pressures with a residual gas analyzer (RGA) during 80 minutes of Sc exposure revealed a rapid decrease in the first 10 minutes and subsequent decay. After Sc exposure, the RGA mass spectra displayed reduced partial pressures of residual gas species (notably, H2 and14N2), highlighting Sc's scavenging capabilities. This behavior, similar to titanium sublimation pumps in ultra-high vacuum systems, showcases Sc's high reactivity. Notably, such pressure reduction wasn't observed when opening Al, Ga, and In shutters, emphasizing Sc's distinct gettering behavior.

[0150] Self-activated ScN films were also grown on other technologically relevant substrates such as (0001) oriented AIN and GaN. RHEED and XRD diffraction patterns show twin cubic ScN (111) film growth on AIN and GaN substrates, akin to 6H-SiC. AFM micrographs of ~120-150 nm thick ScN films grown without plasma reveal a surface roughness of ~2-3.3 nm, aligning with ScN film morphology on 6H-SiC substrate. The ScN film growth rate on GaN, AIN and 6H-SiC substrates were 97.5, 112, and 133 nm hour1, respectively, under the same source fluxes and the corresponding film densities were 4.0, 3.88, and 3.8 g cm-3, correlating with the substrate thermal conductivity: GaN, 130 Wm-1K'1< AIN, 350 Wnr1K’1< 6H-SiC, 490 Wm^K’1. Self-activated growth of ScN is likely exothermic. Substrates with relatively lower thermal conductivity (e.g., GaN) will have higher surface temperatures due to poor heat dissipation, leading to a lower growth rate271531347 1Docket No. MIT26181 PCT due to finite decomposition / thermal desorption of Sc and ScN, and a higher film density due to higher adatom mobility, annealing effects.

[0151] Additionally, Sc flux and nitrogen flow rates were varied during self-activated growth to understand the growth-limiting species during the ScN growth kinetics. At a constant nitrogen flow rate of 3.3 standard cubic centimeters per minute (seem), the ScN film growth rates increase from 17 to 151 nm hour1, with increasing Sc flux from 0.8 x 1C)- 8 to 3 x 10'8torr. Conversely, at a constant Sc flux (of 3 x 1O-8torr), the ScN film growth rate remains constant over an extensive range of N2flow rates from 1.08 to 3 seem. This indicates that ScN growth rates are Sc flux-limited rather than constrained by the availability of active N species.

[0152] Because conventional inorganic synthesis of epitaxial nitrides relies on high-power plasma to break N2bonds, this report of self-activated energy-efficient synthesis of crystalline group ScN films directly from molecular N2bypassing the need for high- temperature reactions or energetic plasma discharge have significant implications in fundamental thin film deposition and making integration of electronic, photonic, acoustic, and quantum devices possible in configurations that were ruled out before.

[0153] The self-activated growth method reported here is significant because: 1) It challenges the conventional paradigms in nitride semiconductor synthesis, potentially lowering manufacturing costs and environmental impact. 2) The self-activated growth of nitrides utilizes molecular N2, which is abundant in the atmosphere, eliminating the need for costly precursors such as NH3, hydrazine, methyl amines, etc. 3) Self-activation growth kinetics and synthesis parameters showcase the versatility of self-activated growth on various technologically significant substrates such as 6H-SiC, AIN, and GaN. The observation of phase-pure semiconducting ScN with atomic layering exhibiting epitaxial registry, and sharp, coherent interfaces with the substrate, and larger continuous domains281531347 1Docket No. MIT26181 PCT and well-defined columnar grain structures suggest that self-activated grown layers lead to higher quality layer growth without plasma-induced effects.

[0154] The observation of a substantial reactivity of scandium with molecular N2 and other residual gas species, coupled with the theoretical insights elucidating the energetically efficient pathway for the self-activated growth of nitride films from molecular N2 expands our understanding of transition metal nitrides and their synthesis route, and motivated similar search in other transition metals also like Ti, Nb, Y, W, Mo, Zr, La, etc. that show scavenging effects [see Gupta et al., “An evaluation of the titanium sublimination pump,” and Haygood et al., Review on the Vacuum Pumping of Hydrogen], This strategy can potentially be extended for the epitaxial growth of other transition metal nitrides (YN, NbN, TiN, TaN, ZrN, etc.), and rare earth nitrides (LaN, LuN, etc.) that host metallic, superconducting, semiconducting, magnetic, and piezoelectric properties. Owing to its scavenging nature, scandium can potentially be considered in sublimation pumps where Ti is currently used. In addition to the several opportunities in electronic, photonic, electroacoustic, and quantum device applications mentioned earlier, the ability of Sc and related metals to self-catalyze growth could be exploited to enable new pathways for the synthesis of other nitride materials that are currently not possible because of the 9.8 eV high energy barrier of the N=N triple bond in molecular N2.

[0155] Self-activated epitaxial growth of a crystalline, phase-pure, semiconducting ScN thin films has been demonstrated from molecular N2, without plasma and at temperatures compatible with back-end-of-line semiconductor processing (< 400 °C). The ability to grow phase pure ScN epitaxially with six-fold rotational symmetry on 6H-SiC substrates with excellent crystallinity, comparable bonding, and a direct bandgap of 2.2 eV (due to degenerate doping) without plasma activation and at temperatures as low as 20 °C results in a completely different paradigm for nitride semiconductors. The observation that Sc itself can break N2bonds with little thermal assistance opens the synthesis and processing291531347 1Docket No. MIT26181 PCT space for transition metal nitrides. It challenges the accepted notion that high temperature and plasma assistance are unavoidable for the growth of transition metal nitrides and their alloys. This has significant implications for energy-efficient processing and for advancing the transition metal nitrides in pioneering devices.

[0156] MATERIALS AND METHODS

[0157] Epitaxial Growth, In-Situ Characterizations

[0158] ScN films were deposited at varying growth conditions on (0001) oriented Si-face 6H-SiC substrates using a Veeco® GenXplor molecular beam epitaxy (MBE) system with the idle-state base pressure of 5 * 10'10torr. Solid Sc source of 99.99% purity on a rare earth element basis from Ames Laboratory was supplied using a Knudsen effusion cell in the MBE environment. A molecular nitrogen gas of 99.99995% purity was used with a growth pressure of approximately 10-5torr. The ScN films were grown without striking the nitrogen plasma, i.e., with 1.08 to 3.3 seem molecular nitrogen gas and with Sc from an effusion cell, to evaluate the feasibility of ScN growth by self-activation. For reference, the ScN films were also grown with nitrogen plasma, wherein 1.95 seem nitrogen was supplied with a Veeco® RF UNI-Bulb plasma source, and a RF plasma of 200 W was used. The ScN films were grown at various thermocouple substrate temperatures (at room temperature, 350 °C, 550°C, 750 °C, 950 °C). Scandium was evaporated from a Knudsen effusion cell to get Sc beam equivalent flux of 2.5 x 1Q-8torr. The films were grown in heavily nitrogen-rich conditions, where the Sc flux was less than molecular N2 flux without plasma and less than the radical nitrogen (N*) flux with plasma. The N* flux is about two orders of magnitude smaller than the N2 flux due to the finite efficiency of a plasma to generate N* from N2. Namely, Sc flux < N* flux < N2 flux in all cases of film growth presented here. Some ScN films were also grown at different Sc fluxes and N2 flow rates. Besides the 6H-SiC substrate, the ScN films were also grown on GaN and AIN template wafers. A metallic Sc film used as a reference for XPS analysis was grown by supplying301531347 1Docket No. MIT26181 PCTSc from an effusion cell and without flowing any nitrogen in the growth chamber at a substrate temperature of 550 °C and a chamber pressure of 4 10-9torr.

[0159] In situ monitoring of film growth was performed using a KSA Instruments reflection high-energy electron diffraction (RHEED) apparatus with a Staib electron gun operating at 14.5 kV and 1.45 A. In-situ monitoring of the residual species in the growth chamber was performed by recording the mass spectra using a Stanford Research Systems (SRS) RGA100 series residual gas analyzer.

[0160] Lab-Source and Synchrotron-based X-Ray Diffraction Measurement

[0161] After epitaxial growth, the film thickness, crystal structure, phase, and orientation were characterized using a Panalytical Empyrean® diffractometer at 45 kV, 40 mA with Cu Ka1 radiation (1.54057 A). X-ray diffraction (XRD) symmetric 2theta-omega scans of the samples were collected with reciprocal space map (RSM) of the ScN 242, ScN twin 313, and 6H-SiC 1015 reflections. Symmetric skew phi scans of ScN 242 and 6H-SiC 1015 reflections were also collected. Film thickness and density were measured by X-ray reflection (XRR) spectra and compared to a simulated spectrum.

[0162] The high dynamic range mapping of a large volume in reciprocal Q-space was also performed with high energy x-ray scattering and a large area detector (Pilatus 6M detector from Dectris) at Cornell High Energy Synchrotron Source. The synchrotron beam's energy was tuned to 37 keV (Wavelength ~ 0.335 A) selected using a double-bounce diamond monochromator with a final spot size of 300 (V) x 800 (H) microns. For all films, we used the unique capability of QM2 Beamline for measuring the reciprocal space containing multiple Bragg reflections, allowing us to characterize several films rapidly. Using standard CeC>2 powder calibrations, geometric parameters of the Pilatus 6M detector, such as detector distance, titling, rotation, and direct beam position, were extracted. The large311531347 1Docket No. MIT26181 PCT volume of 3D reciprocal space data was measured by phi rotation from 0° to 360° at room temperature.

[0163] HAADF-STEM Measurement

[0164] The cross-sectional Scanning Transmission Electron microscopy (STEM) samples were prepared using a standard lift-out process on Helios G4 UX DualBeam focused ion beam system beam with the final milling voltage of 2kV of Ga ions. The Spectra 300 X- CFEG operating at 200 kV with a semi-convergence angle of 30mrad and a High-Angle Annular Dark-Field (HAADF) detector with an angular range of 60-200 mrad was used to collect HAADF-STEM images. The HAADF-STEM images were acquired as a series of 25 images (250 ns per frame), cross-correlated, and subsequently averaged to produce images with a high signal-to-noise ratio. STEM energy-dispersive x-ray spectroscopy (EDX) data were collected using a steradian Dual-X EDX detector.

[0165] XPS (X-ray Photoelectron Spectroscopy) Measurement

[0166] Film bonding and composition were analyzed with a Thermo Scientific Nexsa G2 X-ray photoelectron spectroscopy (XPS) instrument equipped with an Al Ka (1486.6 eV) source. Adventitious carbon and native oxide were removed from the sample surface using a 1 keV Ar+beam for 30s. The photoelectrons were collected by a hemispherical analyzer with a pass energy of 58.7 eV. Prolonged high-resolution C1s, Sc2p, and N1s core level X-ray photoelectron spectra and NKLL Auger electron spectra were collected to obtain a better signal-to-noise ratio. The spectra were analyzed using the CasaXPS software with a charge correction using C1s peak to 284.6 eV and spectral fitting, done with a combination of Lorentzian and Shirley background.

[0167] Raman, Optical, AFM (Atomic Force Microscopy) Measurement

[0168] Raman spectroscopy was performed in a Witec system with a 488 nm wavelength excitation laser under normal-incident-normal-collection geometry. In the transmission geometry, ultraviolet and visible absorption spectra were measured using a Cary-5000-321531347 1Docket No. MIT26181 PCTUV-Vis-NIR-Spectrometer system. Post-growth AFM measurements were performed using an Asylum Research Cypher ES system.

[0169] Ab initio Growth Pathways DFT Calculations

[0170] Density functional theory (DFT) calculations were performed using the Vienna Ab initio Simulation Package (VASP), with projector augmented wave pseudopotentials (Sc: 3s23p64s23d1and N: 2s22p3), Perdew-Burke-Ernzerhof exchange-correlation functional and a kinetic energy cutoff of 520 eV. With the exception of isolated Sc and N atoms, all calculations are non-spin-polarized. Electronic convergence is reached when the difference in total energy is less than 10‘7eV between self-consistent steps, and structural relaxation is complete when the force on each atom is less than 10-3eV / A.

[0171] To obtain the energy of an isolated atom or molecule, it is placed in a large cubic cell, whose dimension is increased until there is no significant change (< 5 meV) in total energy. A single k-point is used in these calculations. The results are Esc = -2.107 eV, EN = -3.125 eV and EN2= -16.666 eV.

[0172] For

[0111] growth, cubic rock salt ScN consists of alternating Sc and N planes forming ScN blocks. The growth at the ScN surface is referenced to an in-plane supercell containing a slab of 10 atomic planes and at least 20 A vacuum out of plane. The in-plane dimension of the cell a = 4.518 A is the lattice parameter of theDFT relaxed conventional cubic rock salt cell of the bulk ScN crystal. For all slab calculations, we use a k-point mesh of 6x8*1 and Gaussian smearing with a small smearing width of 0.02 eV. Only atoms near the top surface of the slab are relaxed. For slabs with a net dipole moment, we apply the dipole correction along the z-direction as implemented in VASP. The growth is modeled by adding additional atoms (Sc, N) or N2molecules above the reference structure. To find intermediate metastable states, we first bring the atom or molecule in proximity to the top surface and relax all atoms near this331531347 1Docket No. MIT26181 PCT surface. We then investigate possible energy barriers between the (meta)stable states through the nudged elastic band method with convergence achieved when the force (tangential + spring) on every atom of the images is below 0.01 eV / A.

[0173] FIG. 7 depicts X-ray diffraction scans of ScxAli_xN films grown by self-activated (plasma-free) growth on 6H-SiC. The intense substrate peak at SiC (006) serves as a reference. Film reflections appear near the ScN (111) position and shift systematically with composition from x ~ 0.07 to 0.28, indicating a single preferred orientation and composition-dependent lattice spacing. The progressive peak shift and comparable line shapes across 7%, 14%, 24%, and 28% compositions are consistent with solid-solution formation rather than phase segregation. A trace from a 100% Al control displays the Al (111) peak at higher 20, further bracketing the alloy positions. Background counts remain low across scans, suggesting good crystalline quality and limited secondary phases. The schematic inset summarizes the architecture: ScxAli_xN grown on a 6H-SiC substrate under self-activated conditions. Overall, the diffraction data support epitaxial, composition- tunable ScxAli_xN growth on SiC using molecular nitrogen without plasma.

[0174] Beyond one-to-one cation-anion nitrides, chemistries include multivalent and multi-oxidation-state compounds such as ScAIN2and LaWN3, where the cation-to-anion ratio differs from unity. Material embodiments also extend to oxynitrides in which oxygen and nitrogen share the anion sublattice, so that any nitride composition described may incorporate a defined fraction of oxygen on the anion site. Additional families include hydrides, oxides, oxynitrides, phosphates, sulfates, and mixtures thereof. If highly reactive metals such as scandium can facilitate dissociation of molecular nitrogen and drive crystalline nitride growth, the same reactivity can be leveraged to dissociate relatively weaker diatomic bonds, including O2, enabling related oxide and oxynitride syntheses.

[0175] In one embodiment, a scavenging element such as Sc, Y, or La is supplied as a metal flux generated by thermal evaporation from a Knudsen effusion cell or by electron-341531347 1Docket No. MIT26181 PCT beam, laser, pulsed-laser, or resistive (current-induced) heating. The flux of the scavenging species corresponds to partial pressures from ~1 x10“9torrto 10 torr, achieved with source temperatures ranging from about 0.4* the melting point up to the boiling, melting, or sublimation point of the material. The process runs in chamber pressures from 1 xio-12torr to 10 torr. Substrate temperature spans 1 K to 1400 K, implemented by resistive or laser heating or by water or liquid N2 / O2 / He cooling. Nitrogen flow is 0.1-10 seem. Self-activated nitride films have thicknesses of 0.5 nm to 10 pm and are crystalline with epitaxial registry to the substrate. For ScN(111), the X-ray diffraction rocking-curve FWHM is 0.02°-4°. Films may be undoped or intentionally doped n-type or p-type via dopant flux during growth. Growth rates are 1 nm / hr to 5 pm / hr. Nitrogen sources include, but are not limited to, N2, forming gas, NH3, or hydrazine.

[0176] Application and device embodiments include semiconducting and superconducting materials, devices, and circuits; vacuum hardware and process uses such as an alternative to commercially available titanium sublimation pumps for achieving ultra-low pressures and for purifying chambers to remove contaminants and residual gases; catalytic functions for dissociating energetic N2bonds; formation of unique heterostructures and growth on substrates stable only at low temperature, including molecular solids and molecular crystals, enabling highly crystalline inorganic films that previously could not be realized at reduced temperatures; and integration as active or passive layers in electronic and photonic devices.

[0177] A purification and evaporation-pumping device is provided in which a scavenging metal such as scandium or yttrium, or a conductive metal coated with a scavenging metal, is heated in a closed chamber to sublimate and release scavenger species that remove residual gases. The scavenging metal may be evaporated by thermal heating, electronbeam heating, laser heating, or by applying current pulses to the scavenging metal or to the conductive substrate coated with the scavenging metal. The vaporized scavenger351531347 1Docket No. MIT26181 PCT captures and getters residual species including, but not limited to, N2, H2, CO2, CHX, and H2O, thereby lowering chamber pressure and reducing contaminants. The device can function as a vacuum pump to decrease system pressure and as in-situ purification equipment to remove undesirable gas species from the chamber. Experimental data demonstrate a strong scavenging effect of scandium consistent with this mechanism.

[0178] FIG. 8(A) depicts chamber pressure (torr) versus Sc shutter open time (minutes). Opening the Sc source causes a rapid pressure drop consistent with gettering; closing the source allows pressure to recover. FIG. 8(B) depicts residual-gas-analyzer (RGA) partial pressure (arbitrary units) versus Sc shutter open time (minutes). Signals for major background species decrease sharply when the Sc shutter is opened and rise after it is closed; traces correspond to 14N2, 15N2 (where 14 and 15 refer to nitrogen 14 and nitrogen 15 isotopes, respectively), 14N / CH2, 15N / CH3 (i.e. , 15N and CH3 have an atomic mass of 15), H2(m / z 2), H2O (18), CO / N2(28), O2(32), CO2(44), and light hydrocarbons. FIG. 8(C) depicts the RGA mass spectrum: pressure (torr) versus mass- to-charge (amu). Peaks at m / z 2, 18, 28, 32, and 44 identify the dominant residuals. During Sc evaporation these peaks are suppressed, indicating capture of hydrogen-, oxygen-, nitrogen-, and carbon-bearing species. Together, FIGS. 8(A)-(C) show that evaporated scandium functions as an effective scavenger, simultaneously lowering total chamber pressure and reducing multiple residual-gas species, consistent with evaporation pumping by a heated scavenging metal (e.g., Sc or Y).

[0179] Nitride growth without plasma minimizes damage to the substrate and underlying device structures. Conventional nitride processes often use energetic plasma, which can induce physical sputtering, charging, and unintended doping in sensitive nanostructures such as fins, nanosheets, and gate-all-around transistors used in commercial semiconductor products. In contrast, self-activated growth with molecular nitrogen and361531347 1Docket No. MIT26181 PCT thermal metal flux proceeds without plasma, mitigating chemical and avoid physical plasma damage and enabling clean, sharp interfaces at substrate-film and film-film boundaries.

[0180] Self-activated nitride films such as ScN, TiN, WN, CrN, and VN combine high hardness, large elastic modulus, and high melting points, making them suitable for mechanical applications including wear-resistant coatings, high-temperature cutting tools, bearings, and diffusion barriers. Beyond mechanics, ScN is promising for thermoelectric applications and can serve functional roles within Ill-nitride device stacks, including dislocation reduction layers, in-situ Ohmic contacts, and current-spreading layers in GaN- based devices.

[0181] The plasma-free, self-activated nitride process is compatible with complex three- dimensional device geometries beyond planar heterostructures, including FinFETs, deep trenches, and other high-aspect-ratio features used in semiconductor logic and memory. Growth below about 400 °C supports back-end-of-line processing and integration with completed circuits by limiting thermal budget and avoiding plasma damage. The approach is adaptable to multiple thin-film synthesis platforms, including atomic layer deposition, chemical vapor deposition, and thermal laser epitaxy, enabling conformal or epitaxial films as required by device architecture. In addition, the chemistry and kinetics are applicable to bulk crystal growth and related bulk synthesis methods for substrate development.

[0182] Various modifications to these aspects will be readily apparent, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, where reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. Pronouns in the masculine (e.g., his) include the feminine and neuter gender (e.g., her371531347 1Docket No. MIT26181 PCT and its) and vice versa. Headings and subheadings, if any, are used for convenience only and do not limit the subject technology.

[0183] A phrase, for example, an “aspect” does not imply that the aspect is essential to the subject technology or that the aspect applies to all configurations of the subject technology. A disclosure relating to an aspect may apply to all configurations, or one or more configurations. A phrase, for example, an aspect may refer to one or more aspects and vice versa. A phrase, for example, a “configuration” does not imply that such configuration is essential to the subject technology or that such configuration applies to all configurations of the subject technology. A disclosure relating to a configuration may apply to all configurations, or one or more configurations. A phrase, for example, a configuration may refer to one or more configurations and vice versa.

[0184] The various embodiments described above are provided by way of illustration only and should not be construed to limit the scope of the disclosure. Those skilled in the art will readily recognize various modifications and changes that may be made to the principles described herein without following the example embodiments and applications illustrated and described herein, and without departing from the spirit and scope of the disclosure.

[0185] While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one381531347 1Docket No. MIT26181 PCT or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[0186] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

[0187] As noted above, particular embodiments of the subject matter have been described, but other embodiments are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In certain implementations, multitasking and parallel processing may be advantageous.CONCLUSION

[0188] A system and method have been shown in the above embodiments for the effective implementation of systems and methods for epitaxial nitride growth without plasma using molecular nitrogen activation by metal atoms. While various preferred embodiments have been shown and described, it will be understood that there is no intent to limit the invention by such disclosure, but rather, it is intended to cover all modifications falling within the spirit and scope of the invention, as defined in the appended claims.391531347 1

Claims

Docket No. MIT26181 PCTWHAT IS CLAIMED IS:1 . A method of growing a crystalline nitride without plasma, the method comprising:(a) providing a substrate bearing a nitride film that presents a metal-terminated surface (step 902);(b) exposing the metal-terminated surface to molecular nitrogen (N2) in the absence of plasma, thereby adsorbing intact N2on the surface (step 904);(c) delivering metal atoms to sites of the adsorbed N2so as to activate and cleave the N=N bond in situ, forming surface-bound nitrogen atoms and an N-terminated region with partial metal coverage, wherein the metal comprises one or more elements selected from transition metals, rare-earth metals, and actinides (step 906);(d) adsorbing additional metal atoms onto the N-terminated region to complete a crystalline nitride layer (step 908); and(e) optionally repeating steps (a)-(d) to grow successive layers (step 910).

2. The method of claim 1 , wherein the metal consists of a single element, thereby forming a binary metal nitride.

3. The method of claim 2, wherein the metal is a transition metal selected from the group consisting of scandium (Sc), yttrium (Y), niobium (Nb), titanium (Ti), tantalum (Ta), zirconium (Zr), hafnium (Hf), vanadium (V), tungsten (W), and molybdenum (Mo).

4. The method of claim 2, wherein the metal is a rare-earth metal selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

5. The method of claim 2, wherein the metal is an actinide selected from the group consisting of actinium (Ac), thorium (Th), protactinium (Pa), uranium (U), neptunium (Np),401531347 1Docket No. MIT26181 PCT plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Of), einsteinium (Es), fermium (Fm), mendelevium (Md), nobelium (No), and lawrencium (Lr).

6. The method of claim 1 , wherein the metal comprises first and second metal elements, Mi and M2, and the layer has composition MlxM21-xN, where 0<x<1.

7. The method of claim 6, wherein the nitride is ScxNbi_xN.

8. The method of claim 6, wherein Mi and M2are independently selected from transition metals and rare-earth metals.

9. The method of claim 6, wherein one of Mi or M2is Sc or a rare-earth metal and the other is Al, Ga, or In, thereby forming (Sc or RE)X(AI or Ga or ln)i_xN.

10. The method of claim 9, wherein the nitride is ScxAli_xN.

11. The method of claim 6, wherein the first and second metal elements are delivered (i) simultaneously or (ii) sequentially in alternating cycles while maintaining the absence of plasma.

12. The method of claim 6, wherein a flux ratio or pulse-time ratio between Mi and M2is controlled to set x within ±0.02 of a target value.

13. The method of claim 1 , wherein no ionized or radical nitrogen species are introduced during steps (b)-(d) and the N2is undissociated prior to step (c).

14. The method of claim 1 , wherein the metal atoms are provided by thermal evaporation of a metal source under vacuum.

15. The method of claim 1 , wherein the delivering of metal atoms is performed by one or more of molecular beam epitaxy (MBE), thermal chemical vapor deposition (CVD), thermal atomic layer deposition (ALD), or thermal laser epitaxy (TLE), while maintaining the absence of plasma.

16. The method of claim 1 , wherein the chamber is under vacuum during steps (b)-(d).

17. The method of claim 1 , wherein the substrate is heated during steps (b)-(d).411531347 1Docket No. MIT26181 PCT18. The method of claim 1, wherein the crystalline nitride film has a thickness from 0.5 nm to10 pm.

19. The method of claim 1 , wherein the nitride film is epitaxial and exhibits registry with the substrate.

20. The method of claim 1 , wherein, for the (111) Bragg reflection of the nitride film, the X- ray diffraction rocking-curve full-width at half-maximum (FWHM) is between 0.02° and 4°.

21. The method of claim 1 , wherein the nitride film is undoped or unintentionally doped.

22. The method of claim 1 , wherein the nitride film is intentionally doped to n-type or p-type by supplying a dopant flux during growth.

23. The method of claim 1 , wherein the film growth rate is between 1 nm / hr and 5 pm / hr.

24. The method of claim 1 , wherein the flow into the chamber during step (b) comprises molecular nitrogen (N2).

25. The method of claim 1 , further comprising forming non-planar device geometries including one or more of fins, deep trenches, or high-aspect-ratio features.

26. The method of claim 1 , further comprising back-end-of-line (BEOL) integration of the nitride film with semiconductor circuits.

27. The method of claim 1 , wherein the nitride film is employed as a wear-resistant coating, high-temperature-resistant coating, cutting-tool coating, bearing coating, or diffusion barrier.

28. A nitride film produced by the method of any one of claims 1-27.

29. An article comprising the nitride film of claim 28, selected from: a wear-resistant coating, a high-temperature-resistant coating, a cutting tool, a bearing, or a diffusion barrier.

30. A method of growing a crystalline ternary nitride without plasma, the method comprising:(a) providing a substrate bearing a nitride film that presents a metal-terminated surface (step 1002);(b) exposing the metal-terminated surface to molecular nitrogen (N2) in the absence of plasma, thereby adsorbing intact N2on the surface (step 1004);421531347 1Docket No. MIT26181 PCT(c) delivering scandium atoms and M atoms to sites of the adsorbed N2so as to activate and cleave the N=N bond in situ, forming surface-bound nitrogen atoms and an N-terminated region with partial metal coverage, wherein M is niobium (Nb) or aluminum (Al) (step 1006); and(d) adsorbing additional scandium atoms and M atoms onto the N-terminated region to complete a crystalline ScxMi_xN layer, where 0 < x < 1 (step 1008).

31. The method of claim 1 , wherein M is niobium (Nb), thereby forming ScxNbi_xN.

32. The method of claim 1 , wherein M is aluminum (Al), thereby forming ScxAli_xN.

33. The method of any one of claims 30-32, wherein 0.01 < x < 0.99.

34. The method of any one of claims 30-33, wherein the scandium and M atoms are delivered (i) simultaneously or (ii) sequentially in alternating cycles, while maintaining the absence of plasma.

35. The method of any one of claims 30-34, wherein a flux ratio or pulse-time ratio between scandium and M is controlled to set x within ±0.02 of a target value.

36. The method of any one of claims 30-35, wherein no ionized or radical nitrogen species are introduced during steps (b)-(d) and the N2is undissociated prior to step (c).

37. The method of any one of claims 30-36, wherein the layer is epitaxial on the substrate.

38. The method of any one of claims 30-37, wherein the crystalline nitride film has a thickness from 0.5 nm to 10 pm.

39. The method of any one of claims 30-38, wherein the delivering of scandium and M atoms is performed by molecular beam epitaxy (MBE), thermal chemical vapor deposition (CVD), thermal atomic layer deposition (ALD), or thermal laser epitaxy (TLE).

40. A method of growing crystalline scandium nitride (ScN) without plasma, the method comprising:(a) providing a substrate bearing a nitride film that presents a scandium-terminated surface(step 1102);431531347 1Docket No. MIT26181 PCT(b) exposing the scandium-terminated surface to molecular nitrogen (N2) in the absence of plasma, thereby adsorbing intact N2on the surface (step 1104);(c) delivering scandium atoms to sites of the adsorbed N2so as to activate and cleave the N=N bond in situ, forming surface-bound nitrogen atoms and an N- terminated region with partial scandium coverage (step 1106); and(d) adsorbing additional scandium atoms onto the N-terminated region to complete a crystalline ScN layer (step 1108).

41. The method of claim 40, wherein no ionized or radical nitrogen species are introduced during steps (b)-(d) and the N2is undissociated prior to step (c).

42. The method of claim 40 or 41 , wherein the ScN film is epitaxial and exhibits registry with the substrate.

43. The method of any one of claims 40-42, wherein for ScN(111) the X-ray diffraction rocking-curve FWHM is between 0.02° and 4°.

44. The method of any one of claims 40-43, wherein the crystalline ScN film has a thickness from 0.5 nm to 10 pm.

45. The method of any one of claims 40-44, wherein the ScN film is undoped or unintentionally doped.

46. The method of any one of claims 40-45, wherein the ScN film is intentionally doped to n- type or p-type by supplying a dopant flux during growth.

47. The method of any one of claims 40-46, wherein delivering scandium atoms is performed by molecular beam epitaxy (MBE), thermal chemical vapor deposition (CVD) performed without plasma, thermal atomic layer deposition (ALD) performed without plasma, or thermal laser epitaxy (TLE).

48. The method of any one of claims 40-47, wherein the chamber is under vacuum during steps (b)-(d) and the substrate is heated during steps (b)-(d).441531347 1Docket No. MIT26181 PCT 49. The method of any one of claims 40-48, wherein the ScN layer is employed as a wear- resistant coating, high-temperature-resistant coating, cutting-tool coating, bearing coating, or diffusion barrier.

50. The method of any one of the claims 40-49, wherein steps (b)-(d) are performed at 350 °C.451531347 1

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