Metalorganic chemical vapor deposition of β-(AlxGa1-x)2O3 thin films on (001) β-Ga2O3 substrates

Phase pure beta-(AlxGa(1-x))(2)O-3 thin films are grown on (001) oriented beta-Ga2O3 substrates via metalorganic chemical vapor deposition. By systematically tuning the precursor molar flow rates, the epitaxial growth of coherently strained beta-(AlxGa(1-x))(2)O-3 films is demonstrated with up to 25% Al compositions as evaluated by high resolution x-ray diffraction. The asymmetrical reciprocal space mapping confirms the growth of coherent beta-(AlxGa(1-x))(2)O-3 films (x < 25%) on (001) beta-Ga2O3 substrates. However, the alloy inhomogeneity with local segregation of Al along the (201) plane is observed from atomic resolution STEM imaging, resulting in wavy and inhomogeneous interfaces in the beta-(AlxGa(1-x))(2)O-3/beta-Ga2O3 superlattice structure. Room temperature Raman spectra of beta-(AlxGa(1-x))(2)O-3 films show similar characteristics peaks as the (001) beta-Ga2O3 substrate without obvious Raman shifts for films with different Al compositions. Atom probe tomography was used to investigate the atomic level structural chemistry with increasing Al content in the beta-(AlxGa(1-x))(2)O-3 films. A monotonous increase in chemical heterogeneity is observed from the in-plane Al/Ga distributions, which was further confirmed via statistical frequency distribution analysis. Although the films exhibit alloy fluctuations, n-type doping demonstrates good electrical properties for films with various Al compositions. The determined valence and conduction band offsets at beta-(AlxGa(1-x))(2)O-3/beta-Ga2O3 heterojunctions using x-ray photoelectron spectroscopy reveal the formation of type-II (staggered) band alignment. (c) 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).