A Liquid Ge(IV) Precursor for Low Temperature Plasma Enhanced Atomic Layer Deposition of Germanium Oxide Thin Films

Germanium oxide thin films are promising for advanced applications such as microelectronics, optoelectronics, high-power electronics, optics, and biomedical uses. However, scalable and controlled low-temperature synthesis of GeO₂ thin films via atomic layer deposition (ALD) is limited by the small range of available Ge precursors. We introduce monomeric tetrakis-3-(N,N-dimethylamino)propyl germanium(IV) [Ge(DMP)₄] as a promising Ge precursor. It is non-pyrophoric, thermally stable, and liquid, and can be obtained in high purity on a multigram scale through an industrially feasible synthesis. Using density functional theory (DFT) and mass spectrometry (MS), we rationalize the coordination environment and identify a feasible chemisorption pathway, indicating a high reactivity of the precursor. Subsequently, [Ge(DMP)₄] was employed in low-temperature plasma-enhanced ALD (PEALD) over a wide temperature range from 40°C to 240°C, yielding smooth, uniform germanium oxide films. Rapid and homogeneous nucleation leads to dense films with sub-nanometer thickness. By adjusting the deposition temperature and plasma duration, the film composition could be readily tuned from GeO₂ to sub-stoichiometric GeO_x. These findings establish [Ge(DMP)₄] as an effective, scalable precursor for low-temperature ALD of GeO₂, emphasizing the critical role of precursor chemistry in ALD process development.