Nitrides feature many interesting properties, such as a wide range of bandgaps suitable for optoelectronic devices including light-emitting diodes (LEDs), and piezoelectric response used in ...microelectromechanical systems (MEMS). Nitrides are also significantly underexplored compared to oxides and other chemistries, with many being thermochemically metastable, sparking interest from a basic science point of view. This paper reports on experimental and computational exploration of the Mg–Sb–N material system, featuring both metastable materials and semiconducting properties. Using sputter deposition, we discovered a new Mg2SbN3 nitride with a wurtzite-derived crystal structure and synthesized the antimonide-nitride Mg3SbN with an antiperovskite crystal structure for the first time in thin film form. Theoretical calculations indicate that Mg2SbN3 is metastable and has properties relevant to LEDs and MEMS, whereas Mg3SbN has a large dielectric constant (28ε0) and low hole effective masses (0.9m 0), of interest for photovoltaic solar cell absorbers. The experimental solar-matched 1.3 eV optical absorption onset of the Mg3SbN antiperovskite agrees with the theoretical prediction (1.3 eV direct, 1.1 eV indirect), and with the measurements of room-temperature near-bandgap photoluminescence. These results make an important contribution toward understanding semiconductor properties and chemical trends in the Mg–Sb–N materials system, paving the way to future practical applications of these novel materials.
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IJS, KILJ, NUK, PNG, UL, UM
Silicon anodes are promising for next-generation lithium-ion batteries due to high theoretical capacity. However, their performance and lifetime are currently limited by continuous electrolyte ...reduction and solid-electrolyte interphase (SEI) formation. Thus, SEI studies are important but often complicated due to the rough morphology of samples, buried interfaces, and the presence of binders. Here, we demonstrate the chemical origin of SEI formation by electrolyte reduction on lithium silicide thin films, synthesized by the diffusion of pure evaporated lithium into smooth sputtered silicon. These model samples allowed for the accurate estimation of irreversible capacity loss due to electrolyte reduction and for the precise characterization of the resulting SEI by vibrational and photoelectron spectroscopies. Spectroscopic characterizations showed clear evidence that lithium silicide reduced electrolyte directly upon contact. Negligible first-cycle irreversible capacity loss was observed for lithium silicide compared to that for silicon, indicating that the decomposition product of electrolyte on lithium silicide is able to stop further electrolyte reduction to a large extent. Fluoro-ethylene carbonate was shown to significantly affect the chemistry of electrolyte reduction on lithium silicide and subsequent cycling performance. The results of this basic study reveal the chemistry occurring at the interface of the lithium silicide and electrolyte and help in understanding the limited calendar lifetime of Li-ion batteries with Si anodes.
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IJS, KILJ, NUK, PNG, UL, UM
A2BO4 spinels constitute one of the largest groups of oxides, with potential applications in many areas of technology, including (transparent) conducting layers in solar cells. However, the ...electrical properties of most spinel oxides remain unknown and poorly controlled. Indeed, a significant bottleneck hindering widespread use of spinels as advanced electronic materials is the lack of understanding of the key defects rendering them as p‐type or n‐type conductors. By applying first‐principles defect calculations to a large number of spinel oxides the major trends controlling their dopability are uncovered. Anti‐site defects are the main source of electrical conductivity in these compounds. The trends in anti‐sites transition levels are systemized, revealing fundamental “doping rules”, so as to guide practical doping of these oxides. Four distinct doping types (DTs) emerge from a high‐throughput screening of a large number of spinel oxides: i) donor above acceptor, both are in the gap, i.e., both are electrically active and compensated (DT‐1), ii) acceptor above donor, and only acceptor is in the gap, i.e., only acceptor is electrically active (DT‐2), iii) acceptor above donor, and only donor is in the gap, i.e., only donor is electrically active (DT3), and iv) acceptor above donor in the gap, i.e., both donor and acceptor are electrically active, but not compensated (DT‐4). Donors and acceptors in DT‐1 materials compensate each other to a varying degree, and external doping is limited due to Fermi level pinning. Acceptors in DT‐2 and donors in DT‐3 are uncompensated and may ionize and create holes or electrons, and external doping can further enhance their concentration. Donor and acceptor in DT‐4 materials do not compensate each other, and when the net concentration of carriers is small due to deep levels, it can be enhanced by external doping.
First‐principle defect calculations reveal that cation anti‐sites dominate doping in spinel oxides. Based on their ionization level we found four doping types (DTs). Most of the DT‐1 spinels are compensated (c) n‐ or p‐ or insulators, while DT‐2 are exclusively p‐type (p), DT‐3 are exclusively n‐type (n) and DT‐4 are mostly intrinsic (i). A number of compounds belonging to DT‐1, DT‐2, and DT‐4 is presented.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Currently, there is a lack of nonvolatile memory (NVM) technology that can operate continuously at temperatures > 200 °C. While ferroelectric NVM has previously demonstrated long polarization ...retention and >1013 read/write cycles at room temperature, the largest hurdle comes at higher temperatures for conventional perovskite ferroelectrics. Here, we demonstrate how AlScN can enable high-temperature (>200 °C) nonvolatile memory. The c-axis textured thin films were prepared via reactive radiofrequency magnetron sputtering onto a highly textured Pt (111) surface. Photolithographically defined Pt top electrodes completed the capacitor stack, which was tested in a high temperature vacuum probe station up to 400 °C. Polarization–electric field hysteresis loops between 23 and 400 °C reveal minimal changes in the remanent polarization values, while the coercive field decreased from 4.3 MV/cm to 2.6 MV/cm. Even at 400 °C, the polarization retention exhibited negligible loss for up to 1000 s, demonstrating promise for potential nonvolatile memory capable of high−temperature operation. Fatigue behavior also showed a moderate dependence on operating temperature, but the mechanisms of degradation require additional study.
A high-speed and high-power current measurement instrument is described for measuring rapid switching of ferroelectric samples with large spontaneous polarization and coercive field. Instrument ...capabilities (±200 V, 200 mA, and 200 ns order response) are validated with a LiTaO
single crystal whose switching kinetics are well known. The new instrument described here enables measurements that are not possible using existing commercial measurement systems, including the observation of ferroelectric switching in large coercive field and large spontaneous polarization Al
Sc
N thin films.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Polycrystalline thin film copper chalcogenide solar cells show remarkable efficiencies, and analogous but less-explored semiconducting materials may hold similar promise. With consideration of ...elemental abundance and process scalability, we explore the potential of the Cu–Sb–S material system for photovoltaic applications. Using a high-throughput combinatorial approach, Cu–Sb–S libraries were synthesized by magnetron co-sputtering of Cu2S and Sb2S3 targets and evaluated by a suite of spatially resolved characterization techniques. The resulting compounds include Cu1.8S (digenite), Cu12Sb4S13 (tetrahedrite), CuSbS2 (chalcostibite), and Sb2S3 (stibnite). Of the two ternary phases synthesized, CuSbS2 was found to have the most potential, however, when deposited at low temperatures its electrical conductivity varied by several orders of magnitude due to the presence of impurities. To address this issue, we developed a self-regulated approach to synthesize stoichiometric CuSbS2 films using excess Sb2S3 vapor at elevated substrate temperatures. Theoretical calculations explain that phase-pure CuSbS2 is expected to be formed over a relatively wide range of temperatures and pressures, bound by the sublimation of Sb2S3 and decomposition of CuSbS2. The carrier concentration of CuSbS2 films produced within this regime was tunable from 1016–1018cm−3 through appropriate control of Sb2S3 flux rate and substrate temperature. CuSbS2 displayed a sharp optical absorption onset indicative of a direct transition at 1.5eV and an absorption coefficient of 105cm−1 within 0.3eV of the onset. The results of this study suggest that CuSbS2 holds promise for solar energy conversion due to its tolerant processing window, tunable carrier concentration, solar-matched band gap, and high absorption coefficient.
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•The Cu–Sb–S material system is briefly introduced.•Carrier density identifies CuSbS2 as the most promising ternary for solar absorber applications.•A method for sputter deposition of phase pure CuSbS2 using high temperatures and excess Sb2S3 is described.•The process is extended to control doping levels between 1016 and 1018cm−3.•Optoelectronic properties of the resulting phase pure films are reported Eg=1.5eV, abs. coeff.>105cm−1.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The opportunity for enhanced functional properties in semiconductor solid solutions has attracted vast scientific interest for a variety of novel applications. However, the functional versatility ...originating from the additional degrees of freedom due to atomic composition and ordering comes along with new challenges in characterization and modeling. Developing predictive synthesis–structure–property relationships is prerequisite for effective materials design strategies. Here, a first‐principles based model for property prediction in such complex semiconductor materials is presented. This framework incorporates nonequilibrium synthesis, dopants and defects, and the change of the electronic structure with composition and short range order. This approach is applied to ZnSnN2 (ZTN) which has attracted recent interest for photovoltaics. The unintentional oxygen incorporation and its correlation with the cation stoichiometry leads to the formation of a solid solution with dual sublattice mixing. A nonmonotonic doping behavior as a function of the composition is uncovered. The degenerate doping of near‐stoichiometric ZTN, which is detrimental for potential applications, can be lowered into the 1017 cm−3 range in highly off‐stoichiometric material, in quantitative agreement with experiments.
A predictive synthesis–structure–property model from first principles is presented for nonideal semiconductor solid solutions, accounting for off‐stoichiometry, impurities, disorder, and metastability. This model elucidates the mysterious nonmonotonic doping as a function of oxygen content in ZnSnN2, a promising photovoltaic material. The key lies in the formation of a dual sublattice mixed solid solution.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Binary III-N nitride semiconductors with wurtzite crystal structure such as GaN and AlN have been long used in many practical applications ranging from optoelectronics to telecommunication. The ...structurally related ZnGeN2 or ZnSnN2 derived from the parent binary compounds by cation mutation (elemental substitution) have recently attracted attention, but such ternary nitride materials are mostly limited to II-IV-N2 compositions. This paper demonstrates synthesis and characterization of zinc niobium nitride (Zn2NbN3) - a previously unreported II2-V-N3 ternary nitride semiconductor. The Zn2NbN3 thin films are synthesized using a one-step adsorption-controlled growth, and a two-step deposition/annealing method that suppresses the loss of Zn and N. Measurements indicate that this sputtered Zn2NbN3 crystalizes in cation-disordered wurtzite-derived structure, in contrast to chemically related rocksalt-derived Mg2NbN3 compound, also synthesized here for comparison using the two-step method. The estimated wurtzite lattice parameter ratio of Zn2NbN3 is 1.55, and the optical absorption onset is at 2.1 eV. Both of these values are lower compared to published Zn2NbN3 computational values of c/a = 1.62 and Eg = 3.5 - 3.6 eV. Additional theoretical calculations indicate that this difference is due to cation disorder in experimental samples, suggesting a way to tune the structural parameters and the resulting properties of heterovalent ternary nitride materials. Overall, this work expands the wurtzite family of nitride semiconductors to include Zn2NbN3, and suggests that related II2-V-N3 and other ternary nitrides should be possible to synthesize.
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