arXiv subjects

Rajeswari Kolagani

Publications and source records attributed to Rajeswari Kolagani.

3 recordsLinked to original sources

arXiv2026

Emergence of quantum transport in SnTe films upon structural refinement

Topological crystalline insulators are distinguished from the conventional Z2 topological insulators by crystalline symmetry protection of the surface states. Quantitative characterization of these states requires magneto-transport measurements from which the phase coherence length and number of independent coherent channels can be extracted. Here we report such measurements on textured thin films of SnTe grown on Bi2Te3 buffered c-plane sapphire (Al2O3) by pulsed laser ablation. A post deposition annealing protocol was implemented to control the crystallographic texture, which reveals improved crystallinity and enhanced epitaxial alignment along the [111] direction in films annealed at elevated temperatures. The higher carrier density and lower resistivity seen in films annealed at 100 oC are suggestive of Sn vacancies which act as native acceptor defects, while films annealed at 200 oC approach the 1:1 stoichiometry. The magnetoresistance of all samples at T < 10 K characterized by a cusp centered around zero-field is suggestive of weak antilocalization and interpreted in the framework of the Hikami-Larkin-Nagaoka theory in the strong spin-orbit coupling limit. At T > 20 K, the MR is small and positive, and deviates from conventional Kohler scaling. An approximate collapse of the MR curves between 50 and 250 K is obtained using an empirical temperature-dependent scaling factor, indicating that changes in the Hall-derived carrier density alone cannot account for the observed scaling behavior. These results demonstrate that post growth annealing strongly influences the interplay between stoichiometry, crystallinity, and coherent transport in SnTe thin films.

cond-mat.mtrl-sci↗

arXiv2026

Enabling the Ambient Pressure Growth of ScB2 Crystals for AlGaN Power Electronics

Here we report the growth of single crystalline ScB2, an ultrahigh-temperature ceramic, at ambient pressure in a laser-heated Optical Floating Zone via the travelling solvent method. Crystals have been grown from both Sc-rich (55-65 at% Sc) and B-rich self-flux (80-83 at% B) at growth rates in the range of 0.2-2 mm/hr. The structure of grown crystals is in good agreement with an AlB2-type layered hexagonal phase, space group P6/mmm, with lattice constants a = 3.1423(2) Å (resp. 3.1502(3) Å) and c = 3.5084(3) Å (resp. 3.5041(3) Å) for crystals grown under Sc-rich (resp. B-rich) conditions. Crystals natively grow along the in-plane [100] direction. Electron backscattered diffraction shows that Sc-flux growth results in boules with multiple domains containing Sc inclusions, with the domains highly aligned. In contrast, B-flux boules are single domain after the initial nucleation region. Rocking-curve measurements of B-flux crystals for the (h000) and (000l) reflections show single peaks, establishing that the crystals are free from grain boundaries; the asymmetry in the scattered-intensity tails suggests the presence of point defects. Surface X-ray photoemission spectroscopy shows that the electronic environment in B-flux crystals is superior to that of Sc-flux crystals and produces highly resolved binding-energy peaks for B 1s and Sc 2p. Work-function measurements for the (11-20) plane give a value of approximately 5 eV, consistent with the highly electrically conductive nature of ScB2. These results demonstrate the viable ambient-pressure growth of ScB2, establish it as a lattice-matched substrate candidate for Al-rich AlGaN power microelectronics, and show that this growth route enables scalable manufacturing of ScB2 substrates.

cond-mat.mtrl-sci↗

arXiv2026

Scandium diboride: a semi-metallic, lattice, thermally matched substrate for vertical AlGaN power electronics

We report the properties of hexagonal (space group P6/mmm) scandium diboride ($\mathrm{ScB}_2$) single crystals grown by a laser diode floating zone method at growth rates of ~1mm/hr under B-rich conditions with (002) rocking curve widths $Δω$=38'' approaching the quality of commercial SiC/GaN substrates. Lattice expansion measurements reveal matching to $\mathrm{Al_{0.55}Ga_{0.45}N}$ with a coefficient of thermal expansion ~5ppm/K at typical AlGaN growth temperatures, enabling thick AlGaN layers for ultra-wide bandgap (UWBG) power electronics >1kV. We measure semi-metallic room temperature resistivity ~15$μΩ$ cm, climbing to ~93$μΩ$ cm at 773K with a $T^2$ dependence effectively eliminating substrate parasitic resistance, the limiting factor in exploiting the full potential of UWBG. The Debye temperature $θ_{D,ScB_2}$ from heat capacity and lattice expansion is ~850K well matched to $θ_{D,ScB_2}$, but lower than the 1100K measured for Sc-rich growth conditions. We discuss Debye matching as a key substrate codesign criterion providing significant overlap in phonon modes for heat removal and thermal matching during AlGaN growth. The competitive thermal conductivity at room temperature 53W/mK is half that from full first principles calculations, a discrepancy we attribute to the presence of Sc-vacancies generated by B-rich growth. while the resistivity is ~2x the theoretical value, indicating that both electrons and phonons play equal role in thermal transport. The smooth ~2.5nm rms roughness surface enables advanced heat removal modalities through engineered phonon bridges and phonon polaritons in $\mathrm{ScB}_2$/AlGaN interfacial heterostructures, potentially allowing ~10-100x increase in power handling over state-of-the-art GaN/SiC.

cond-mat.mtrl-sci↗