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Elemental 2D pnictogens (group 15) are an interesting class of materials with tunable band structures and high carrier mobilities. Heavier pnictogens (Sb and Bi) are stable under ambient conditions compared to lighter members (P and As) and are emerging as interesting candidates for various electronic and optoelectronic applications. The reactivity of these materials is due to the presence of a lone pair which can be effectively utilized to tune material properties

Antimonene and bismuthene are promising members of the 2D pnictogen family with their tunable band gaps, high electronic conductivity, and ambient stability, making them suitable for electronic and optoelectronic applications. However, semi-metal to semiconductor transition occurs only in the mono/bilayer regime, limiting their applications. Covalent functionalization is a versatile method for tuning materials' chemical, electronic, and optical properties and can be explored for tuning the properties of pnictogens. In this work, emissions in liquid exfoliated antimonene and bismuthene are observed at ≈2.23 and ≈2.33 eV, respectively. Covalent functionalization of antimonene and bismuthene with p-nitrobenzene diazonium salt proceeds with the transfer of lone pairs from Sb/Bi to the diazonium salt, introducing organic moieties on the surface attached predominantly via Sb/BiC bonds. Consequently, Sb/Bi signatures in Raman and X-ray photoelectron spectra are blue-shifted, implying lattice distortion and charge transfer. Interestingly, emission can be tailored upon functionalization to 2.18 and 2.27 eV for antimonene and bismuthene respectively, and this opens the possibility of tuning the properties of pnictogens and related materials. This is the first report on covalent functionalization of antimonene and bismuthene. It sheds light on the reaction mechanism on pnictogen surfaces and demonstrates tunability of optical property and surface passivation.

The interaction of light with collective charge oscillations, called plasmon-polariton, and with polar lattice vibrations, called phonon-polariton, are essential for confining light at deep subwavelength dimensions and achieving strong resonances. Traditionally, doped-semiconductors and conducting metal oxides (CMO) are used to achieve plasmon-polaritons in the near-to-mid infrared (IR), while polar dielectrics are utilized for realizing phonon-polaritons in the long-wavelength IR (LWIR) spectral regions. However, demonstrating low-loss plasmon- and phonon-polaritons in one host material will make it attractive for practical applications. Here, we demonstrate high-quality tunable short-wavelength IR (SWIR) plasmon-polariton and LWIR phonon-polariton in complementary metal-oxide-semiconductor compatible group III-V polar semiconducting scandium nitride (ScN) thin films. We achieve both resonances by utilizing

Integrating silicon and III-nitride technologies for high-speed and large bandwidth communication demands optically interconnected active components that detect, process, and emit photons and electrons. It is imperative that multifunctional materials can enhance the performance and simplify fabrication of such devices. Spontaneously grown GaN in the nanowall network (NwN) architecture simultaneously displays unprecedented optical and electrical properties. A two-order increase in band-edge emission makes it suitable for high-brightness light-emitting diodes and laser applications. Decorating this NwN with silver nanoparticles further enhances emission through plasmonic interactions and renders it an excellent surface-enhanced Raman spectroscopy substrate for biomolecular detection. The observation of very high electron mobility (approximately 104 cm2/Vs) and large phase-coherence length (60 μm) is a consequence of two-dimensional (2D) electron gas formation applicable for high electron mobility transistors. Detecting ballistic transport in the nanowalls confirms proximity-induced superconductivity (

Interaction of light with collective charge oscillations termed as plasmon-polariton and with polar lattice vibrations termed phonon-polariton is a new frontier in nano-photonics. Traditionally doped-semiconductors and conducting metal oxides (CMO) are used to achieve plasmon-polaritons in the near-to-mid infrared (IR), while polar dielectrics are utilized for realizing phonon-polaritons in the long-wavelength IR (LWIR) spectral regions. However, demonstrating plasmon- and phonon-polariton in one host material with low-loss is challenging due to the mutually conflicting physical property requirements. In this article, we demonstrate high-quality tunable short-wavelength IR (SWIR) plasmon-polariton and LWIR phonon-polariton in complementary metal-oxide-semiconductor (CMOS) compatible group III-V polar semiconducting scandium nitride (ScN) thin films. We achieve both resonances by utilizing n-type (oxygen) and p-type (magnesium) doping in ScN that allows modulation of carrier concentration from 5 × 1018 to 1.6 × 1021 cm-3. Our work enables infrared nano-photonics with an epitaxial group-III semiconducting nitride, opening the possibility for practical applications.

Chromium nitride (CrN) is a well-known hard coating material that has found applications in abrasion and wear-resistant cutting tools, bearings, and tribology applications due to its high hardness, high-temperature stability, and corrosion-resistant properties. In recent years, CrN has also attracted significant interest due to its high thermoelectric power factor, and for its unique and intriguing metal-insulator phase transition. While CrN bulk single-crystals exhibit the characteristic metal-insulator transition accompanied with structural (orthorhombic-to-rocksalt) and magnetic (antiferromagnetic-to-paramagnetic) transition at ~260-280K, observation of such phase transition in thin-film CrN has been scarce and highly debated. In this work, the formation of the secondary metallic Cr2N phase during the growth is demonstrated to inhibit the observation of metal-insulator phase transition in CrN thin films. When the Cr-flux during deposition is reduced below a critical limit, epitaxial and stoichiometric CrN thin film is obtained that reproducibly exhibits the phase transition. Annealing of the mixed-phase film inside reducing NH3 environment converts the Cr2N into CrN, and a discontinuity in the electrical resistivity at ~ 277 K appears which supports the underlying hypothesis. A clear demonstration of the origin behind the controversy of the metal-insulator transition in CrN thin films marks significant progress and would enable its nanoscale device realization.

Scandium nitride (ScN) is an emerging group III-B transition metal pnictide and has been studied extensively for its thermoelectric properties, as interlayers for defect-free GaN growth, in epitaxial metal/semiconductor superlattices, and recently for its polaritonic and optoelectronic synaptic functionalities. However, to realize the full potential of its semiconducting properties in electronic, thermionic, and optoelectronic device applications, it is necessary to develop Schottky diodes of ScN that are missing thus far. Here we show Schottky diodes of ScN with elemental metals such as silver (Ag) and gold (Au). As-deposited ScN thin films exhibit a high electron concentration in the (1–4) × 1020 cm−3 range due to unintentional oxygen doping. These excess electrons are compensated by Mg hole doping, leading to a wider depletion region at the metal/ScN interface for activated electronic transport. Current–voltage (I–V) characteristics show the rectification nature in ScN/Ag and ScN/Au diodes, and the barrier heights of 0.55 ± 0.05 eV and 0.53 ± 0.06 eV, respectively, are obtained. Interface annealing with time and temperature results in a slight increase in the forward junction potential. The capacitance–voltage (C–V) measurements also revealed the presence of interface trap states. The demonstration of Schottky diodes marks an important step in realizing the full potential of ScN in electronic, thermionic, and optoelectronic devices.

Wurtzite–Al1−xScxN thin films deposited by solid-state alloying of AlN with ScN exhibit high piezoelectric coefficient and large band gap that makes it a promising material for a variety of applications in piezo-electronics, electronic, acoustoelectric devices, etc. Research on epitaxial Al1−xScxN growth in wurtzite crystal structure is still at an early stage and achieving high scandium (Sc) concentrations in epitaxial films without any phase separation or secondary phase formation is still a critical challenge. Moreover, as most of the reports of wurtzite–Al1−xScxN growth thus far relies on low-vacuum growth techniques, such as magnetron sputtering that are prone to large impurities and contaminants detrimental for device applications, high-vacuum deposition techniques, such as molecular beam epitaxy method needs to be developed. In this paper, we report the epitaxial growth of wurtzite–Al1−xScxN on sapphire (Al2O3) substrates under different Sc fluxes using ultra-high vacuum plasma-assisted molecular beam epitaxy. To prevent ScN phase separation, a 30 nm AlN buffer layer is deposited in situ on GaN epilayers as well as Al2O3 substrates that result in phase-pure wurtzite–Al1−xScxN thin films without any phase separation or secondary phase formation. The structural and compositional analyses performed with high-resolution X-ray diffraction (HRXRD) and secondary ion mass spectroscopy (SIMS), reveal epitaxial wurtzite–Al1−xScxN growth with 0001 orientations on (0001) Al2O3 substrates and the presence of cubic ScN. Demonstration of phase-pure Al1−xScxN on AlN buffer layers will enable the development of devices with improved efficiencies.

Scandium nitride (ScN) has attracted significant interest in recent years for diverse electronic and thermoelectric applications. Most ScN growth utilizes MgO and Al2O3 as substrates that lead to extended defects such as dislocations and grain boundaries. (0001) GaN exhibits less than 0.1% lattice mismatch with (111) ScN, and therefore, should result in single-crystalline ScN film growth. However, not much attention is devoted to understanding the microstructure of ScN on GaN substrates. In this work, we present (111) oriented lattice matched ScN film growth on (0001) GaN substrates. X-ray pole figure exhibited six spots for the (002) ScN superimposed on that of (101) GaN separated by 60° corresponding to twin domains of threefold symmetry for (111) ScN, which are furthermore directly imaged by lattice resolved microscopy images. The presence of twins is attributed to vertical dislocations originating at the GaN/Al2O3 interface and extending throughout the GaN film to its interface with ScN.

This work reports on fabrication using vacuum evaporation and characterization of n-CdSe/p-ZnTe heterojunctions. Before forming the junction, CdSe and ZnTe layers were characterized for crystal structure and chemical composition to account for observed electrical properties. The heterojunction was characterized by current–voltage (I–V) measurements, temperature dependence of reverse saturation current, admittance, and capacitance–voltage (C–V) measurements. I–V characteristics of the heterojunction exhibited clear diode nature with rectification ratio of 9.05 at ±0.5 V and ideality factor n = 3.34. From the temperature dependence of the I–V characteristic, a barrier height ϕ b of 0.36 eV was determined for the CdSe–ZnTe junction. Conduction mechanism analysis revealed contributions from both thermionic and space-charge-limited conduction. Furthermore, the shunt leakage current was found to be space-charge limited, showing symmetry in current near V = 0 V. The dependence of capacitance on frequency and bias voltage has been analyzed to identify the bulk and interface defects. These measurements indicate the presence of bulk defects and high series resistance, severely affecting current transport.

Scandium nitride (ScN) is an emerging rock salt indirect bandgap semiconductor and has attracted significant interest in recent years for thermoelectric energy conversion, as a substrate for defect-free GaN growth, as a semiconducting component in single-crystalline metal/semiconductor superlattices for thermionic energy conversion, as well as for Al1−xScxN-based bulk and surface acoustic devices for 5G technologies. Most ScN film growth traditionally utilizes physical vapor deposition techniques such as magnetron sputtering and molecular beam epitaxy, which results in stoichiometric films but with varying crystal quality, orientations, microstructures, and physical properties. As epitaxial single-crystalline ScN films with smooth surfaces are essential for device applications, it is important to understand the ScN growth modes and parameters that impact and control their microstructure. In this Letter, we demonstrate that large adatom mobility is essential to overcome the Ehrlich–Schwoebel (E–S) and grain boundary migration barriers and achieve defect (voids, dislocations, stacking faults, etc.)-free single-crystalline ScN films. Using the substrate temperature to tune adatom mobility, we show that nominally single-crystalline ScN films are achieved when the homologous temperature is higher than ∼0.3. For homologous temperatures ranging from 0.23 to 0.30, ScN films are found to exhibit significant structural voids in between pyramidal growth regions with multiple in-plane orientations resulting from additional lateral growth off the facets of the pyramids and broken epitaxy after ∼80 nm of growth. The in-depth discussion of the growth modes of ScN presented here explains its varying electrical and optical properties and will help achieve high-quality ScN for device applications.

We propose a low-cost approach for the synthesis of multifunctional CuSnS3 (CTS) ternary compound thin film via spray pyrolysis technique. By varying Sn and S doping concentrations, a high energy absorber layers of CuSnS3 thin films were deposited on a glass substrate at a substrate temperature of 405 °C. The prepared samples were analysed with respect to their optical, structural and electrical and nonlinear optical properties. X-Ray diffraction (XRD) analysis reveals that the films exhibit a tetragonal crystal structure with a preferential growth orientation along (1 1 2). The surface morphology of the films was explored by atomic force microscopy (AFM) in tapping mode configuration. Variation in the carrier charge density and electrical properties were observed for different Sn and S combination. The analysis of the Raman spectra indicates the presence of multiple phases apart from CuSnS3. The obtained Raman spectra were assigned to phonon mode as per zone centre phonon representation of optical and acoustic modes and identified to dominant “A” symmetry modes. The maximal laser stimulated induced second harmonic generation (SHG) signal was observed for the CTS 3 film and the corresponding second order nonlinear optical susceptibility which was equal to about 0.89 pm/V at 1064 nm and the minimal SHG signal was found for the CTS 2 film (about 0.22 pm/V). This strategic improvement in SHG and third harmonic generation (THG) signal efficiency endorses the role of Sn and S in modulating second and third harmonic generations in CuSnS3 compound.

Approximately 1.5–2.5 μm thick nanocomposite coatings of TiAlCrYN were deposited using a four-cathode reactive unbalanced pulsed direct current magnetron sputtering system from the sputtering of Ti, Al, Cr, and Y targets in Ar + N 2 plasma. The TiAlCrYN nanocomposite coatings were deposited on various substrates such as high speed steel (HSS) drill bits, mild steel and silicon. TiAlCrYN coatings with almost similar mechanical properties but with different Ti, Al, Cr and Y contents were prepared to study their thermal stability and machining performance. The structural and mechanical properties of the coatings were characterized using X-ray diffraction and nanoindentation technique, respectively. The elemental composition, bonding structure, surface morphology and cross-sectional data were studied using energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy and field-emission scanning electron microscopy, respectively. Nanoscratch tests were performed to determine the adhesive strength of the coatings. The corrosion behavior of TiAlCrYN nanocomposite coatings on mild steel substrate was studied using potentiodynamic polarization in a 3.5% NaCl solution. Micro-Raman spectroscopy was used to characterize the structural changes as a result of heating of the nanocomposite coatings in air (600–1000 °C). TiAlCrYN coatings prepared at 17 at.% Ti, 13 at.% Al, 21 at.% Cr and 1 at.% Y exhibited thermal stability as high as 900 °C in air (denoted as Sample 3). For the performance evaluation, the TiAlCrYN coated HSS drill bits were tested under accelerated machining conditions. With a drill speed of 800 rpm and a feed rate of 0.08 mm/rev the TiAlCrYN coated HSS drill bits (Sample 3) averaged 657 holes, while drilling a 12 mm thick 304 stainless steel plate under dry conditions, before failure. Whereas, the uncoated drill bits failed after drilling 50 holes under the same machining conditions. Results indicated that for the HSS drill bits coated with TiAlCrYN, the tool life increased by a factor of more than 12.

In this paper, we report a heterojunction of p-CdTe/n-ZnSe fabricated on a quartz substrate using thermal evaporation technique. The materials have a larger band gap difference in comparison to other II–VI heterojunctions-involving CdTe. The larger band gap difference is expected to increase diffusion potential and photovoltaic conversion efficiency. The electrical conduction mechanism involved, barrier height and band offset at the interface that are crucial to determine device performance are evaluated using electrical characterization of heterojunction. The junction exhibited excellent rectification behavior with an estimated barrier height of 0.9 eV.