Inorganic nitrides with wurtzite crystal structures are well-known semiconductors used in optical and electronic devices. In contrast, rocksalt-structured nitrides are known for their superconducting ...and refractory properties. Breaking this dichotomy, herewe report ternary nitride semiconductors with rocksalt crystal structures, remarkable electronic properties, and the general chemical formula MgₓTM
1−xN (TM = Ti, Zr, Hf, Nb). Our experiments show that these materials form over a broad metal composition range, and that Mg-rich compositions are nondegenerate semiconductors with visible-range optical absorption onsets (1.8 to 2.1 eV) and up to 100 cm² V−1·s−1 electron mobility for MgZrN₂ grown on MgO substrates. Complementary ab initio calculations reveal that these materials have disorder-tunable optical absorption, large dielectric constants, and electronic bandgaps that are relatively insensitive to disorder. These ternary MgₓTM
1−xN semiconductors are also structurally compatible both with binary TMN superconductors and main-group nitride semiconductors along certain crystallographic orientations. Overall, these results highlight MgₓTM
1−xN as a class of materials combining the semiconducting properties of main-group wurtzite nitrides and rocksalt structure of superconducting transition-metal nitrides.
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Nitride materials feature strong chemical bonding character that leads to unique crystal structures, but many ternary nitride chemical spaces remain experimentally unexplored. The search for ...previously undiscovered ternary nitrides is also an opportunity to explore unique materials properties, such as transitions between cation-ordered and -disordered structures, as well as to identify candidate materials for optoelectronic applications. Here, we present a comprehensive experimental study of MgSnN2, an emerging II–IV–N2 compound, for the first time mapping phase composition and crystal structure, and examining its optoelectronic properties computationally and experimentally. We demonstrate combinatorial cosputtering of cation-disordered, wurtzite-type MgSnN2 across a range of cation compositions and temperatures, as well as the unexpected formation of a secondary, rocksalt-type phase of MgSnN2 at Mg-rich compositions and low temperatures. A computational structure search shows that the rocksalt-type phase is substantially metastable (>70 meV/atom) compared to the wurtzite-type ground state. Spectroscopic ellipsometry reveals optical absorption onsets around 2 eV, consistent with band gap tuning via cation disorder. Finally, we demonstrate epitaxial growth of a mixed wurtzite-rocksalt MgSnN2 on GaN, highlighting an opportunity for polymorphic control via epitaxy. Collectively, these findings lay the groundwork for further exploration of MgSnN2 as a model ternary nitride, with controlled polymorphism, and for device applications, enabled by control of optoelectronic properties via cation ordering.
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Recently theorized hybrid II-IV-N2/III-N heterostructures, based on current commercialized (In,Ga)N devices, are predicted to significantly advance the design space of highly efficient ...optoelectronics in the visible spectrum, yet there are few epitaxial studies of II-IV-N2 materials. In this work, we present heteroepitaxial ZnGeN2 grown on GaN buffers and AlN templates. We demonstrate that a GaN nucleating surface is crucial for increasing the ZnGeN2 crystallization rate to combat Zn desorption, extending the stoichiometric growth window from 215 °C on AlN to 500 °C on GaN buffers. Structural characterization reveals well-crystallized films with threading dislocations extending from the GaN buffer. These films have a critical thickness for relaxation of 20–25 nm as determined by reflection high energy electron diffraction (RHEED) and cross-sectional scanning electron microscopy (SEM). The films exhibit a cation-disordered wurtzite structure, with lattice constants a = 3.216 ± 0.004 Å and c = 5.215 ± 0.005 Å determined by RHEED and X-ray diffraction (XRD). This work demonstrates a significant step toward the development of hybrid ZnGeN2-GaN integrated devices.
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Interest in inorganic ternary nitride materials has grown rapidly over the past few decades, as their diverse chemistries and structures make them appealing for a variety of applications. Due to ...synthetic challenges posed by the stability of N
2
, the number of predicted nitride compounds dwarfs the number that has been synthesized, offering a breadth of opportunity for exploration. This review summarizes the fundamental properties and structural chemistry of ternary nitrides, leveraging metastability and the impact of nitrogen chemical potential. A discussion of prevalent defects, both detrimental and beneficial, is followed by a survey of synthesis techniques and their interplay with metastability. Throughout the review, we highlight applications (such as solid-state lighting, electrochemical energy storage, and electronic devices) in which ternary nitrides show particular promise.
Combinatorial experiments involve synthesis of sample libraries with lateral composition gradients requiring spatially resolved characterization of structure and properties. Because of the maturation ...of combinatorial methods and their successful application in many fields, the modern combinatorial laboratory produces diverse and complex data sets requiring advanced analysis and visualization techniques. In order to utilize these large data sets to uncover new knowledge, the combinatorial scientist must engage in data science. For data science tasks, most laboratories adopt common-purpose data management and visualization software. However, processing and cross-correlating data from various measurement tools is no small task for such generic programs. Here we describe COMBIgor, a purpose-built open-source software package written in the commercial Igor Pro environment and designed to offer a systematic approach to loading, storing, processing, and visualizing combinatorial data. It includes (1) methods for loading and storing data sets from combinatorial libraries, (2) routines for streamlined data processing, and (3) data-analysis and -visualization features to construct figures. Most importantly, COMBIgor is designed to be easily customized by a laboratory, group, or individual in order to integrate additional instruments and data-processing algorithms. Utilizing the capabilities of COMBIgor can significantly reduce the burden of data management on the combinatorial scientist.
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Cation-disordered ZnGeN2 shows promise for application as a blue-green emitter in light-emitting devices, but more foundational work is necessary to understand structure–property relationships. In ...this work, we present a combinatorial exploration of the experimental phase space of wurtzite (cation-disordered) ZnGeN2 using high-throughput co-sputtering. Structure, morphology and optical properties are explored as a function of cation composition and synthesis temperature. ZnGeN2 is found to crystallize in the wurtzite structure ranging from Zn-rich to Ge-rich compositions. X-ray diffraction refinements reveal a continuous shift in cell volume with off-stoichiometry, indicating alloy-like structural behavior. The optical absorption of all films examined is lower in energy than the value predicted for cation-ordered ZnGeN2, suggesting that cation disorder is decreasing the bandgap. Additionally, the absorption threshold shifts continuously to higher energy for Ge-rich samples, consistent with bandgap shifts due to alloy-like structural behavior. Defect formation energy diagrams are calculated to help guide understanding of off-stoichiometry from a defect complex perspective. This work paves the way toward use of ZnGeN2 as a bandgap-tunable optoelectronic semiconductor.
•Conversion of single-crystal layered-2D Bi2Se3 to β-In2Se3.•The β-In2Se3 is also single crystal, with the crystal structure and orientation of the Bi2Se3 substrate.•Bi-rich layered-2D BixSey ...compounds (such as Bi4Se3) are created between the Bi2Se3 and In2Se3.
In this work, we demonstrate that the surface layers of single-crystal layered-2D Bi2Se3 can be converted to layered-2D rhombohedral β-In2Se3 by annealing under a trimethylindium (TMIn) flux. Samples were prepared in a metalorganic chemical vapor deposition (MOCVD) chamber, then transferred under vacuum to a surface analysis chamber for analysis with low-energy electron diffraction (LEED) and Auger electron spectroscopy. Additional ex situ characterization included x-ray diffraction, transmission-electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS) elemental mapping, and Raman spectroscopy. The resulting single-crystal β-In2Se3 adopts the rhombohedral crystal structure (space group R-3m) and orientation of the underlying Bi2Se3, and the excess Bi atoms generated by this process create an underlying region of Bi-rich BixSey. Due to the difference in bandgap between Bi2Se3 and In2Se3, this conversion reaction presents a pathway to lateral heterojunctions if only selected regions are converted by masking the surface to spatially define the TMIn exposure. The conversion may also have implications for heteroepitaxy, because the in-plane lattice constants of Bi2Se3 and In2Se3 (0001) surfaces match those of InP and GaAs (111), respectively, and the natural cleavage planes of a layered-2D crystal facilitate substrate removal and reuse.
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Emerging photovoltaic materials need to prove their viability by demonstrating excellent electronic properties. In ternary and multinary semiconductors, disorder and off-stoichiometry often cause ...defects that limit the potential for high-efficiency solar cells. Here we report on Zn-rich ZnSnN 2 (Zn/(Zn + Sn) = 0.67) photoluminescence, high-resolution X-ray diffraction, and electronic structure calculations based on Monte-Carlo structural models. The mutual compensation of Zn excess and O incorporation affords a desirable reduction of the otherwise degenerate n-type doping, but also leads to a strongly off-stoichiometric and disordered atomic structure. It is therefore remarkable that we observe only near-edge photoluminescence from well-resolved excitons and shallow donors and acceptors. Based on first principles calculations, this result is explained by the mutual passivation of Zn Sn and O N defects that renders both electronically benign. The calculated bandgaps range between 1.4 and 1.8 eV, depending on the degree of non-equilibrium disorder. The experimentally determined value of 1.5 eV in post-deposition annealed samples falls within this interval, indicating that further bandgap engineering by disorder control should be feasible via appropriate annealing protocols.
We report controlling site disorder in ternary and multinary compounds enables tuning optical and electronic properties at fixed lattice constants and stoichiometries, moving beyond many of the ...challenges facing binary alloy systems. Here, we consider possible enhancements to energy-related applications through the integration of disorder-tunable materials in devices such as light-emitting diodes, photonics, photovoltaics, photocatalytic materials, batteries, and thermoelectrics. However, challenges remain in controlling and characterizing disorder. Focusing primarily on II–IV–V2 materials, we identify three metrics for experimentally characterizing cation site disorder. Complementary to these experiments, we discuss simulation methods to understand disordered materials. Nonidealities, such as off-stoichiometry and oxygen incorporation, can occur while synthesizing metastable disordered materials. While nonidealities may seem undesirable, we describe how if harnessed they could provide another knob for tuning disorder and subsequently properties. To illustrate the effects of disorder on device-relevant properties, we provide case examples of disordered materials and their potential in device applications.
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II-IV-V
2
materials, ternary analogs to III-V materials, are emerging for their potential applications in devices such as LEDs and solar cells. Controlling cation ordering in II-IV-V
2
materials ...offers the potential to tune properties at nearly fixed compositions and lattice parameters. While tuning properties at a fixed lattice constant through ordering has the potential to be a powerful tool used in device fabrication, cation ordering also creates challenges with characterization and quantification of ordering. In this work, we investigate two different methods to quantify cation ordering in ZnGeP
2
thin films: a stretching parameter calculated from lattice constants
, and an order parameter determined from the cation site occupancies (
S
). We use high resolution X-ray diffraction (HRXRD) to determine
and resonant energy X-ray diffraction (REXD) to extract
S
. REXD is critical to distinguish between elements with similar
Z
-number (
e.g.
Zn and Ge). We found that samples with a
corresponding to the ordered chalcopyrite structure had only partially ordered
S
values. The optical absorption onset for these films occurred at lower energy than expected for fully ordered ZnGeP
2
, indicating that
S
is a more accurate descriptor of cation order than the stretching parameter. Since disorder is complex and can occur on many length scales, metrics for quantifying disorder should be chosen that most accurately reflect the physical properties of interest.
Resonant energy X-ray diffraction was used to quantify cation site ordering in ZnGeP
2
thin films.
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