Modeling and in situ probing of surface reactions in atomic layer deposition

Summary¶

The work combines ReaxFF reactive molecular dynamics with in situ real-time spectroscopic ellipsometry (and complementary ex situ AFM and XPS) to interpret atomic layer deposition (ALD) of Al\(_2\)O\(_3\) from trimethylaluminum and water on hydrogen-terminated and oxidized Ge(100). The goal is molecular-level insight into how surface preparation changes nucleation, intermixing, and electrical interface quality. Ge channel devices motivate high-κ Al\(_2\)O\(_3\) gate stacks, but ALD nucleation on Ge is sensitive to native oxide versus H-terminated starting surfaces; linking atomistic chemistry to in situ optical thickness tracks helps separate interfacial oxidation from dielectric growth transients.

Methods¶

Molecular dynamics (reactive). ReaxFF molecular dynamics resolves trimethylaluminum (TMA) and water half-reactions during the first ALD cycles on H-terminated Ge(100) versus oxidized Ge(100) slabs, tracking adsorption, ligand elimination, and oxygen insertion that couple to GeO_x formation at the temperature (K) setpoints listed in ACS AMI Methods. Periodic supercells with explicit atom inventories, timestep (fs), thermostat/barostat choices, NVT/NPT staging, and equilibration/production duration (ps/ns) are given in ACS Appl. Mater. Interfaces 2017, 9, 15848–15856 (pdf_path). Electric fields and metadynamics/umbrella enhanced sampling are not highlighted in the abstract-level summary used here.

Experiments (integrated diagnostics). In situ spectroscopic ellipsometry follows film thickness and optical constants during TMA/H₂O exposure; AFM, XPS, and impedance spectroscopy provide ex situ morphology, chemical state, and interface trap metrics tied to the simulated intermixing trends.

Force-field fitting. N/A — the manuscript employs a published Al/Ge/O/H ReaxFF parameterization suited to ALD on Ge; no new training loop is summarized in the excerpted abstract.

Static QM / DFT. N/A — the coupled workflow centers on ReaxFF MD plus laboratory probes, not on-the-fly DFT dynamics.

Review scope. N/A — primary experiment-integrated research article (sibling ingests: [[2017zheng-venue-research]], [[2017zheng-venue-research-2]]).

Findings¶

Outcomes and mechanisms. Reactive trajectories rationalize a nucleation delay on H–Ge(100) while oxidized templates undergo a self-cleaning response that builds an Al₂O₃/GeO_x intermixed layer, suppressing oxygen diffusion into Ge relative to the hydrogen-terminated case in the modeled chemistry.

Comparisons. In situ ellipsometry, AFM, and XPS benchmarks align with the simulated early-cycle trends, and impedance data argue the intermixed layer is critical for low interface trap density and well-behaved dielectric/Ge contacts.

Sensitivity / design levers. Contrasting hydrogen-terminated versus oxidized starting surfaces is the primary experimental/computational lever controlling nucleation timing and suboxide interdiffusion.

Limitations / outlook. The combined workflow is positioned as extensible to other ALD precursors, but each new chemistry requires refreshed simulation targets and optical modeling assumptions.

Corpus honesty. Duplicate PDF ingests exist for ASAP/proof variants; this slug uses the AMI article PDF named in front matter—confirm figure numbering against siblings before external citation.

Limitations¶

Full numerical protocol for ReaxFF runs (supercell sizes, temperatures, cycle definitions) is not summarized on this page; use the article and SI.

Relevance to group¶

Co-authored by Adri C. T. van Duin; demonstrates ReaxFF paired with in situ optics for semiconductor dielectric deposition.

Related corpus entries for the same study under alternate PDFs: 2017zheng-venue-research, 2017zheng-venue-research-2.

Citations and evidence anchors¶

DOI: 10.1021/acsami.7b01618.