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

Abstract

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.