Combinatorial Hardware and Software for Accelerated Discovery of Multianion Optoelectronic Thin Films
Eugène Bertin
National Center for Nanofabrication and Characterization – DTU Orbit, Lyngby, Denmark
Abstract
Multi-anion semiconductors—compounds that combine two or more anion species, such as S, P, N, or Se—offer a remarkable degree of chemical and structural diversity for optoelectronics, yet studies on their thin-film synthesis remain scarce. We address this with a glove-box-integrated combinatorial platform: a reactive sputtering chamber (PH3, H2S, NH3, N2 and a S cracking source), a rapid thermal annealing furnace that uses the same reactive gases, and an evaporator for volatile metals. Two-dimensional compositional gradients on a single substrate enable rapid mapping of unexplored composition space, while an IA-ready data infrastructure built on NOMAD captures the structural and optoelectronic property data of the entire sample libraries. Across more than 20,000 samples in exotic ternary systems, including Zr-S-N, Ba-Cd-P, Cu-P-S, Ag-P-S, Sn-P-S, Sb-P-S, Ba-P-S, Ba-Zr-S, and Ba-P-Te, we highlight the defect-tolerant Zintl phase BaCd2P2 BaP, synthesized for the first time as a thin film,4Te2 with unusual P-Te bonds and novel SnPS3 and Cu3P.S.4, two vacuum-processed phosphosulfides with photoluminescence.
We also report the first Zr sulfonitride2SN2 thin film, a member of the unexplored (Hf,Zr)2(S,Se)N2 a family of chalcogenides that defy the usual trade-off between refractive index, transparency, and free-carrier conductivity. Hybrid density functional theory predicts low effective masses, UV absorption edges, and sub-bandgap refractive indices of up to 2.84, exceeding those of TiO2 and SiC, but no method for synthesizing thin films existed. Reactive sputtering followed by rapid thermal annealing yields the first chalconitride thin film, Zr2SN2, which confirms the predictions: refractive index n > 2.7, absorption edge at 2.9 eV, and degenerate n-type conductivity (carrier concentration >1020 cm-3, in-grain mobility > 8 cm2V-1s-1). The theory attributes this unusual combination to a decoupled band structure with forbidden optical transitions at the direct bandgap, a very large density of states in the UV, and low effective masses at the indirect bandgap. A transparent conductor that is also a high-index dielectric could serve simultaneously as an antireflection, index-matching, and charge-extraction layer in thin-film photovoltaics and opens up a new design space for photonics more broadly. Zr2SN2 illustrates what combinatorial exploration of multi-anion chemistry can achieve.
Contact: Léo Choubrac (MIOPS)
