arXiv subjects

Pooja D. Reddy

Publications and source records attributed to Pooja D. Reddy.

4 recordsLinked to original sources

arXiv2026

Monolithic integration of optically anisotropic GeSe-based films on GaAs by templated solid-phase epitaxy

Layered IV-VI semiconductors such as GeSe exhibit strong in-plane optical anisotropy, making them promising candidates for polarization-sensitive photonic devices. However, realizing these properties in scalable platforms requires heteroepitaxial integration on technologically relevant substrates like GaAs. Direct growth of GeSe is complicated by its glass formation at low temperatures and high vapor pressure at elevated temperatures. To overcome this, we develop a method for ex-situ solid-phase epitaxy utilizing a SnSe buffer and offcut GaAs substrate to enable single-orientation crystalline GeSe films. Using polarized reflection measurements, we find that stabilizing a single-in-plane-orientation results in a 2x increase in anisotropic response between the armchair and zigzag directions. This work provides a new integration route to harness the anisotropic optical properties of GeSe and its alloys for polarization-sensitive technologies.

cond-mat.mtrl-sci↗

arXiv2026

Epitaxial Growth of Anisotropic SnSe on GaAs(001) via Step-Edge Orientation Control

Epitaxial growth of orthorhombic SnSe on cubic substrates is challenging due to lattice-symmetry mismatch and anisotropic bonding. Here we demonstrate that epitaxial films with sharp interfaces can be achieved for layered SnSe grown directly on on-axis and 4 degree miscut GaAs(001) substrates. The substrate miscut strongly influences the growth morphology, evolving from spirals on on-axis GaAs to a terraced structure on miscut GaAs. X-ray diffraction reveals that on-axis GaAs supports SnSe with two in-plane orientation variants, whereas the miscut substrate stabilizes a single orientation and introduces a small out-of-plane tilt. Accordingly, in-plane optical anisotropy is enhanced in the single variant film compared to the double variant, as determined by cross-polar reflectance. High-resolution TEM shows that the SnSe/GaAs interface is atomically abrupt and incoherent, characteristic of quasi-van der Waals epitaxy. We find a pronounced tendency for the zigzag edges of SnSe to align parallel to step edges on both substrates, and we show that step-skipping nucleation and layer growth on the miscut substrate leads to the additional tilt. These results establish direct SnSe/GaAs heteroepitaxy as a route to integrate anisotropic layered semiconductors with cubic platforms, and show that miscut substrates provide additional control over in-plane anisotropy.

cond-mat.mtrl-sci↗

arXiv2025

Heteroepitaxial growth of highly anisotropic $Sb_{2}Se_{3}$ films on GaAs

The epitaxial integration of anisotropic materials with mainstream cubic semiconductors opens new routes to advanced electronic and photonic devices with directional properties. In this work, we synthesize heteroepitaxial thin films of orthorhombic "quasi-1D" $Sb_{2}Se_{3}$ on cubic GaAs(001) using molecular beam epitaxy. Traditionally, the synthesis of anisotropic films with low symmetry materials is challenging due to multiple grain orientations that form. On a macroscopic scale, such a film tends towards isotropic properties, even if individual grains possess anisotropic responses. We achieve epitaxial $Sb_{2}Se_{3}$ grains on pristine homoepitaxial GaAs templates at low temperatures of 180-200 °C. With the $Sb_{2}Se_{3}$ 1D axis aligned in-plane to GaAs [110] and the primary van der Waals direction lying out-of-plane, we find a birefringence of 0.2 between in-plane orthogonal directions and a giant out-of-plane birefringence greater than 1 at telecom wavelengths. Growth at higher temperatures up to 265 °C yields $Sb_{2}Se_{3}$ of an unusual in-plane rotated texture that further enhances the in-plane optical index anisotropy to 0.3.

cond-mat.mtrl-sci↗

arXiv2024

Expanded stability of layered SnSe-PbSe alloys and evidence of displacive phase transformation from rocksalt in heteroepitaxial thin films

Bulk PbSnSe has a two-phase region or miscibility gap as the crystal changes from a Van der Waals-bonded orthorhombic 2D layered structure in SnSe-rich compositions to the related 3D-bonded rocksalt structure in PbSe-rich compositions with large contrast in the electrical, optical, and thermal properties across this transition. With an aim to understand and harness this transition in thin films devices, we epitaxially integrate PbSnSe on GaAs by molecular beam epitaxy using an in-situ PbSe surface treatment and show a significantly reduced two-phase region by stabilizing the Pnma layered structure out to Pb$_{0.45}$Sn$_{0.55}$Se, beyond the bulk-limit of Pb$_{0.25}$Sn$_{0.75}$Se. Pushing further, we directly access metastable two-phase epitaxial films of layered and rocksalt grains that are nearly identical in composition around Pb$_{0.5}$Sn$_{0.5}$Se and entirely circumvent the miscibility gap. We present microstructural evidence for an incomplete displacive transformation from rocksalt to layered structure in these films that we speculate occurs during the sample cool down to room temperature after synthesis. In situ temperature-cycling experiments on a Pb$_{0.58}$Sn$_{0.42}$Se rocksalt film reproduce characteristic attributes of a displacive transition and show a modulation in electronic properties. We find well-defined orientation relationships between the phases formed and reveal unconventional strain relief mechanisms involved in the crystal structure transformation, using transmission electron microscopy. Overall, our work adds a scalable thin film integration route to harnessing the dramatic contrast in material properties in PbSnSe across a potentially ultrafast structural transition.

cond-mat.mtrl-sci↗