arXiv subjects

Ashlee M. García

Publications and source records attributed to Ashlee M. García.

3 recordsLinked to original sources

arXiv2026

Highly Lattice-Mismatched Selective Area Epitaxy and Coalescence of PbSe Nanostructures on GaAs

Selective area growth of PbSe has the potential to realize deterministic placement of high-density, defect-tolerant nanostructure networks toward a scalable quantum platform. PbSe is a narrow bandgap semiconductor with advantageous (opto)electronic properties that has been shown to have a desirable defect-tolerance, enabling bright emission even when grown on highly-dissimilar platforms, and could be leveraged in combination with selective growth for site-selective quantum emitters and low-disorder hybrid nanowire networks. In this work, we achieve site-selective growth of well-faceted and ordered PbSe nanostructures, despite a large 8% lattice mismatch. Structural and morphological characterization reveal that $>$99% of selectively grown islands within 100 nm opening are single-orientation and cube-on-cube oriented with sub-nm root-mean-square surface roughness. Defect analysis showed that 74% of the islands and 86% of the coalesced regions between different mask openings were free of threading dislocations. These PbSe islands achieved equivalent emission in the mid-infrared despite having a higher surface-to-volume ratio than the planar control. Further, we present a gate-tunable two-terminal Josephson junction fabricated from the PbSe nanowires grown with conditions identified in this study. The combination of the accessible selective growth regime, morphological control of island growth and demonstrations of optical and electrical transport properties indicates promise for PbSe SAG as a defect-tolerant scalable quantum platform.

cond-mat.mtrl-sci↗

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

Surface Modification for III-V Selective Area Molecular Beam Epitaxy of Non-Selective Mask Materials

Selective-area embedded regrowth of III-V semiconductors by molecular beam epitaxy enables the seamless integration of metals and dielectrics into crystalline material for novel design of optoelectronic devices. However, traditional masks like $SiO_2$ and $Si_{3}N_{4}$ limit the design of high-contrast photonics in the infrared due to their high extinction coefficients at technologically relevant wavelengths. Consequently, there is a need to explore alternative mask materials to expand the selective area molecular beam epitaxy capabilities beyond those traditionally used. This study evaluates the deposition selectivity of the alternative materials $Al_{2}O_{3}$, $TiO_2$, and $HfO_2$, films with preferable spectral responses but higher surface reactivity. It was found that $Al_{2}O_{3}$ exhibits promising selective growth characteristics within typical GaAs growth temperatures, $HfO_2$ demonstrated a high non-selectivity dominated by Ga adsorption on the mask at temperatures up to 650 $^\circ$C, and $TiO_2$ proved reactive during deposition. To achieve selective growth of highly non-selective and even reactive mask materials, a surface modification technique was employed to improve the selective growth characteristics of any given film. Selective growth of $Si_{3}N_{4}$ and $TiO_2$ films was achieved with the application of a thin $SiO_2$ capping layer utilizing growth conditions typical of the GaAs/$SiO_2$ system. The relationship between the thickness of $SiO_2$ caps and growth selectivity was examined, revealing that sub-1 nm capping layers can significantly influence the mask surface chemistry, indicating that by depositing a thin layer of $SiO_2$, $SiO_2$-like selectivity for any mask material can be realized without degrading its optical response.

cond-mat.mtrl-sci↗