Suboxide-mediated growth and etching in the metalorganic vapor phase epitaxy of GeO2

Abstract— Rutile GeO₂ is a promising ultra-wide bandgap semiconductor for power electronics. In this work we demonstrate that in metalorganic vapor phase epitaxy (MOVPE) the partial desorption of the volatile intermediate GeO species can limit its growth window. A reaction pathway for GeO₂ deposition in MOVPE using isobutylgermane (iBuGe) and O₂ precursors is proposed. Moreover, the possibility to desorb GeO from a deposited GeO2 layer in the MOVPE reactor is demonstrated, obtaining a controlled etching as a function of the provided flow of the iBuGe precursor. Keywords— GeO2 epitaxy, in-situ etching, growth kinetics Rutile germanium dioxide (r-GeO2) is arising as a promising material in the field of ultra-wide bandgap semiconductors for power electronics applications.1 Its epitaxial growth faces two major challenges: (1) the strong competition between the amorphous material and the rutile phase stabilization and (2) the two-step growth kinetics involving the preliminary formation of the volatile GeO suboxide. Due to point (1), the r-GeO2 heteroepitaxy is strongly affected by the substrate-epilayer misfit2 and might result in the non-homogeneous nucleation of 3-dimensional faceted islands.3 As of point (2), the GeO desorption during GeO2 growth might limit the growth window, particularly in high vacuum based growth techniques like Molecular Beam Epitaxy (MBE),4 where it has been also demonstrated the possibility to etch a GeO2 layer with a Ge flux.6 The higher pressure regimes of the metalorganic vapor phase epitaxy (MOVPE) deposition process allow for a wider deposition window of GeO2, but the GeO desorption might still play a role. In this contribution we investigate the growth kinetics of GeO2 thin films deposited by MOVPE using isobutylgermane (iBuGe) and O2 precursors. In particular, we suggest a plausible reaction pathway and demonstrate that indeed at sufficiently high deposition temperatures a partial GeO desorption can limit its growth rate (Figure 1). Moreover, we demonstrate the possibility to in-situ etch a previously deposited GeO2 layer by solely providing an iBuGe flow (Figure 2). In this direction, we show evidence that the etching rate can be controlled by the provided iBuGe flow. These results offer new insights for optimizing the growth of GeO2 layers by MOVPE and offer a technological route to etch the deposited material inside the deposition reactor. (1) Chae, S.; Lee, J.; Mengle, K. A.; Heron, J. T.; Kioupakis, E. Rutile GeO2: An Ultrawide-Band-Gap Semiconductor with Ambipolar Doping. Appl. Phys. Lett. 2019, 114 (10), 102104. https://doi.org/10.1063/1.5088370. (2) Shimazoe, K.; Ogawa, T.; Nishinaka, H. Growth of Water-Insoluble Rutile GeO2 Thin Films on (001) TiO2 Substrates with Graded Gex Sn1−x O2 Buffer Layers. Appl. Phys. Express 2024, 17 (10), 105501. https://doi.org/10.35848/1882-0786/ad838e. (3) Cicconi, G.; Bosi, M.; Mezzadri, F.; Ugolotti, A.; Cora, I.; Seravalli, L.; Tornatzky, H.; Lähnemann, J.; Wagner, M. R.; Bhatt, P.; Thakur, P. K.; Lee, T.-L.; Regoutz, A.; Baraldi, A.; Bersani, D.; Cademartiri, L.; Parisini, A.; Pécz, B.; Miglio, L.; Fornari, R.; Mazzolini, P. Nucleation and Faceting in (001) r-GeO2 Heteroepitaxy on r-TiO2 by Metalorganic Vapor Phase Epitaxy. Appl. Surf. Sci. 2026, 725, 165788. https://doi.org/10.1016/j.apsusc.2025.165788. (4) Chae, S.; Paik, H.; Vu, N. M.; Kioupakis, E.; Heron, J. T. Epitaxial Stabilization of Rutile Germanium Oxide Thin Film by Molecular Beam Epitaxy. Appl. Phys. Lett. 2020, 117 (7), 072105. https://doi.org/10.1063/5.0018031. (6) Chen, W.; Egbo, K.; Zhang, H.; Ardenghi, A.; Bierwagen, O. Etching of Elemental Layers in Oxide Molecular Beam Epitaxy by O2-Assisted Formation and Evaporation of Their Volatile (Sub)Oxide: The Examples of Ga and Ge. J. Vac. Sci. Technol. A 2024, 42 (3), 032708. https://doi.org/10.1116/6.0003453.