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C3.4 MBE growth, phase formation, and relaxation mechanisms in

binary and ternary group III-sesquioxides



Overview of the research project:

Gallium oxide is a promising semiconducting material for various applications in devices. It is transparent even to the UV light due to its wide optical band gap of around 4.9 eV, which gives it the potential of application in UV devices, high power field emission transistors (FET), and also transparent contacts when doped. Under ambient conditions, monoclinic β-phase is thermodynamically more stable than the other four phases. In the plasma-assisted MBE growth of gallium oxide, rotational domains of β-phase are observed on c-plane sapphire substrates with a thin (3 ML) α-phase in between. To make use of either α- and/or β-phase gallium oxide in devices, a detailed study of the underlying growth mechanisms is necessary. An in-situ x-ray diffraction study will be performed during the epitaxial growth of the gallium oxide on different substrates. With this setup, installed at BESSYII (Helmholtz-Zentrum Berlin), we are able to monitor the growth layer-by-layer and probe the structural evolution and strain dynamics in thin film. This integral method strongly requires a high structural quality of the layers as provided by MBE. To get started we ex-situ probe (optimized) epitaxial oxide layers grown at PDI’s MBE lab. All these investigations are accompanied by kinematic scattering simulations.

Major accomplishments expected:

  • Establishing MBE growth experiment at BESSY (based on attainments developed at PDI)
  • Comprehensive understanding of growth mechanisms of gallium oxide on different substrates and/or surface orientations by in-situ x-ray diffraction
  • Direct observation of phase transition from α- to β-phase during growth, exploring/identifying the effect of strain
  • Development of x-ray scattering formalism within a kinematic approach


Collaboration with partners in the project:

  • Transmission electron microscopy directly provides crystal structure and extended defects, which will complementary accompany XRD results.
  • SEM and AFM resolves surface morphology of the epitaxial layers. EDX might serve as a powerful tool to provide the chemical composition of the sample.

The Research Team


Zongzhe Cheng

Zongzhe Cheng
PhD student

Zongzhe Cheng joins GraFOx from China. After his bachelor study, he came to Ulm, Germany, and finished his master study on the topic of semi-polar GaN. At PDI, he works with the in-situ and operando synchrotron based xrd study of group III sesquioxides MBE growth.


Project lead

If you have queries about the project, please contact the PI:
Michael Hanke, Paul-Drude-Institut


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The Leibniz ScienceCampus GraFOx is a network of two Leibniz Institutes, two universities and one institute of the Max Planck Society. It is based in Berlin, Germany.


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Kai Hablizel

Paul-Drude Institut für Festkörperelektronik (PDI)
Leibniz-Institut im Forschungsverbund Berlin e.V.
Tel.: +49 30 20377-342




Prof. Dr. Henning Riechert, PDI

Scientific Coordinator:

Dr. Oliver Bierwagen, PDI
Dr. Martin Albrecht, IKZ