arXiv subjects

Mohit Raghuwanshi

Publications and source records attributed to Mohit Raghuwanshi.

4 recordsLinked to original sources

arXiv2026

Bonding Signatures of Incipient Electron Localization in Topological Chiral Semimetals Near the Metal-Insulator Transition

How do electronic localization and delocalization compete in solids beyond the traditional limiting cases of metals and iono-covalent insulators? Topological chiral semimetals (TCSMs), characterized by their unique crystal symmetry, offer an intriguing platform to explore this question. Here, we systematically compare TCSMs with covalent compounds, ordinary metals, and metavalent solids (incipient metals), and show that TCSMs occupy a distinct region in a multidimensional property fingerprint. Atom probe tomography reveals an unusual bond-rupture signature, consistent with a bonding regime intermediate between electron localization and delocalization. This interpretation is supported by measurements of optical properties showing a transfer of spectral weight from interband to intraband transitions. For highly conductive TCSMs, this transition is accompanied by the disappearance of the Born effective charge, a measure of chemical bond polarizability, while less conductive TCSMs retain a nonzero value. Together, these results identify a property based bonding perspective on TCSMs that distinguishes them from metals, covalent solids, and metavalent compounds. Although metavalent solids and TCSMs both lie near the metal-insulator transition and exhibit distorted crystal structures, ultrafast coherent phonon spectroscopy reveals fundamentally different lattice-dynamical responses: a phonon-driven Peierls-like instability in metavalent solids versus a robust chiral B20 bonding motif in TCSMs.

cond-mat.mtrl-sci↗

arXiv2024

Structural and electrical properties of fiber textured and epitaxial molybdenum thin films prepared by magnetron sputter epitaxy

Molybdenum (Mo) due to its optimal structural, physical, and acoustic properties find application as electrode material in aluminum scandium nitride (AlScN) and aluminum nitride (AlN) based bulk acoustic wave (BAW) resonators. Epitaxial Mo thin films exhibiting low resistivity can improve the performance of the BAW resonator by enhancing both the electromechanical coupling coefficient and quality factor. In this study, we systematically vary the growth temperature of Mo grown on fiber-textured and epitaxial wurtzite-aluminum nitride (AlN) to study the changes in structural and electrical properties of the Mo films. Results show that Mo grown at 700°C on epitaxial AlN exhibit low surface roughness, large average grain diameter, low resistivity, and high crystal quality. XRD pole figure and phi-scan reveal that irrespective of the growth temperature, Mo is fiber textured on fiber-textured AlN, and has three rotational domains on epitaxial AlN. The study shows that the resistivity of Mo reduces with increasing growth temperature, which we relate to increasing average grain diameter. Additionally, we show that fiber-textured Mo has more high angle grain boundaries resulting in consistently higher resistivity than its epitaxial equivalent.

physics.app-ph↗

arXiv2024

Sputtered Aluminum Nitride Waveguides for the Telecommunication Spectrum with less than 0.16 dB/cm Loss

We report the fabrication and characterization of photonic waveguides from sputtered aluminum nitride (AlN). The AlN films were deposited on 6" silicon substrates with a 3 $μ$m buried silicon oxide layer using reactive DC magnetron sputtering at a temperature of 700°C. The resulting uncladded polycrystalline waveguides exhibit propagation losses of 0.137 $\pm$ 0.005 dB/cm at wavelengths of 1310 nm and 0.154 $\pm$ 0.008 dB/cm at a wavelength of 1550 nm in the TE polarization. These results are the best reported for sputtered AlN waveguides in the C-band and the first report in the O-band. These performances are comparable to those of the best-reported AlN waveguides, which are epitaxially grown by metal-organic chemical vapor deposition (MOCVD) on sapphire substrates. Our findings highlight the potential of sputtered AlN for photonic platforms working in the telecom spectrum.

physics.optics↗

arXiv2021

Intense sulphurization process can lead to superior heterojunction properties in Cu(In,Ga)(S,Se)$_2$ thin-film solar cells

Sulphurization processes in Cu(In,Ga)Se$_2$ thin-film solar cells has been intensively studied in the last decade as a viable alternative to the existing Ga-grading. The main advantage of using S grading is that by substituting Se with S we will achieve not only an upshift of the conduction-band minimum as done by employing Ga grading, but also a downshift of the valence-band maximum. Several existing studies stipulate that S is very often inserted in too high concentrations into Cu(In,Ga)Se$_2$ absorber by sulphurization resulting in a deteriorated device performance instead of the expected beneficial effect. However, we demonstrate here that the intense sulphurization process when accompanied by Ga-grading leads to improved electrical properties of the buffer/absorber heterojunction. More exactly, this double grading at the absorber surface leads to strong reduction of the p-doping and hence to a change in the band diagram. This work also proves that the intense sulphurization process is accompanied by strong structural and chemical changes, i.e., by the formation of a S-rich CuIn(S,Se)$_2$ compound at the absorber surface. Finally, all these experimental findings were complemented by ab-initio calculations of the conduction-band and valence-band offsets between absorber and buffer obtained by using density functional theory. Hence, the present work opens up new possibilities for synthesizing Cu(In,Ga)(Se,S)2 solar cells with superior cell performance when using an intense sulphurization process.

physics.app-ph↗