【Epitaxy Papers】Defect States in the Electronic Structure of Ga₂O₃ Transparent Conductive Oxide Surfaces

      Researchers from Karlsruhe Institute of Technology (KIT) have published a dissertation titled " Defect States in the Electronic Structure of Ga₂O₃ Transparent Conductive Oxide Surfaces " in The Journal of Physical Chemistry C.

Abstract

      Defect states are crucial in many electronic devices. Oxygen vacancies, for example, are common in transparent conductive oxides and can both be beneficial (e.g., as a dopant to enhance conductivity) as well as detrimental (e.g., leading to reduced device performance by recombination at interfaces). Using soft and hard X-ray photoelectron spectroscopy (PES and HAXPES) with excitation photon energies ranging from 0.1 to 6.3 keV, we study the electronic surface structure of differently processed Ga₂O₃ samples in a depth-resolved fashion. Specifically, we investigate a Ga₂O₃ thin film, as used in Cu(In,Ga)Se₂-based thin-film solar cells, as well as a β-Ga₂O₃ single crystal before and after a defect-inducing Ar⁺-ion treatment. Spectra calculations based on density functional theory (DFT) are used to explain the PES and HAXPES valence band signatures as a function of the excitation photon energy. The β-Ga₂O₃ single crystal spectra can be well described by the DFT calculations. In contrast, the Ga₂O₃ thin film and Ar⁺-ion treated β-Ga₂O₃ show significant spectral broadening of the valence band features and additional spectral intensity close to the valence band maximum, which we assign to defect states. This additional intensity varies as a function of probing depth, suggesting that these defects are mostly localized at the surface. We also discuss the importance of DFT-based spectra calculations to verify the proper determination of valence band maxima using a linear extrapolation.

DOI：

https://doi.org/10.1021/acs.jpcc.6c02301