arXiv subjects

Rafael Costa-Amaral

Publications and source records attributed to Rafael Costa-Amaral.

3 recordsLinked to original sources

arXiv2026

Oxygen-deficiency-driven phase segregation enables enhanced hole transport in amorphous tellurium oxides

Amorphous oxide semiconductors allow scalable electronics, yet high-mobility p-type counterparts remain rare because O-$2p$ valence bands are typically deep and spatially localized. Motivated by recent reports of unusually high hole mobilities in oxygen-deficient \ce{Se}-doped amorphous tellurium oxides ($a$-\ce{TeO$_x$}), we investigated $a$-\ce{TeO$_x$} with and without \ce{Se} doping using machine-learning-accelerated ab initio molecular dynamics with hybrid-functional defect calculations. We find that oxygen depletion drives nanoscale segregation into interpenetrating $a$-Te and $a$-TeO$_2$ domains with distinct roles: Te vacancies in oxide-like/interfacial environments supply holes, while transport is mediated by percolating Te-$5p$ pathways within the $a$-Te subnetwork. Upon doping, we theoretically verify that Se preferentially incorporates into the $a$-Te domains enhancing connectivity. This preference is nontrivial without explicit modeling given that \ce{Se} shares similar electronic structure with both Te and O. We further find that reducing the oxygen content can likewise enhance hole conductivity. Finally, using amorphous SeO$_x$, we show that domain segregation persists in other amorphous chalcogen oxides, suggesting a transferable route to achieving higher-mobility p-type amorphous oxides.

cond-mat.mtrl-sci↗

arXiv2024

Exploring Intrinsic and Extrinsic $p$-type Dopability of Atomically Thin $β$-TeO$_2$ from First Principles

Two-dimensional (2D) $β$-TeO$_2$ has gained attention as a promising material for optoelectronic and power device applications, thanks to its transparency and high hole mobility. However, the underlying mechanism behind its $p$-type conductivity and dopability remains unclear. In this study, we investigate the intrinsic and extrinsic point defects in monolayer and bilayer $β$-TeO$_2$, the latter of which has been experimentally synthesized, using the HSE+D3 hybrid functional. Our results reveal that most intrinsic defects are unlikely to contribute to $p$-type doping in 2D $β$-TeO$_2$. Moreover, Si contamination could further impair $p$-type conductivity. Since the point defects do not contribute to $p$-type conductivity, we propose two possible mechanisms for hole conduction: hopping conduction via localized impurity states, and substrate effects. We also explored substitutional $p$-type doping in 2D $β$-TeO$_2$ with 10 trivalent elements. Among these, the Bi dopant is found to exhibit a relatively shallow acceptor transition level. However, most dopants tend to introduce deep localized states, where hole polarons become trapped at Te's lone pairs. Interestingly, monolayer $β$-TeO$_2$ shows potential advantages over bilayers due to reduced self-compensation effects for $p$-type dopants. These findings provide valuable insights into defect engineering strategies for future electronic applications involving 2D $β$-TeO$_2$.

cond-mat.mes-hall↗

arXiv2024

Native defects and $p$-type dopability in transparent $β$-TeO$_2$: A first-principles study

Although $β$-TeO$_2$ is a promising $p$-type transparent conducting oxide (TCO) due to the large optical gap ($\sim$ 3.7 eV) and a light effective hole mass, its hole dopability still remains unexplored. In this work, electronic structure of $β$-TeO$_2$ and its point defects are investigated using the HSEsol functional with the band-gap-tuned mixing parameter. Our calculations reveal that $β$-TeO$_2$ exhibits a significant difference between the fundamental and optical band gaps because lower energy optical transitions are dipole forbidden. Additionally, it has a low hole effective mass, especially in-plane. The point defect calculations show that $β$-TeO$_2$ is intrinsically an insulator. From systematic calculations of the trivalent dopants as well as hydrogen, Bi doping is suggested as the best candidate as an acceptor dopant. This work paves the way for the material design of the $p$-type $β$-TeO$_2$.

cond-mat.mtrl-sci↗