Growth of <i>a</i> -plane BaTiO3 on <i>a</i> -plane <i>β</i> -Ga2O3 by molecular-beam epitaxy

We demonstrate the epitaxial growth of single-phase (100) BaTiO3 films on (100) β-Ga2O3 substrates at substrate temperatures ranging from 600 to 700 °C using molecular-beam epitaxy. Characterization of a 47 nm thick BaTiO3 film by atomic force microscopy reveals a step-and-terrace morphology with unit-cell-high BaTiO3 steps and an rms surface roughness of 0.26 nm. Scanning transmission electron microscopy (STEM) images show that in some regions the β-Ga2O3 substrate terminates with a (100)A plane as it transitions to BaTiO3 and in other regions with a (100)B plane. The (100) BaTiO3 films are fully relaxed and consist of a mixture of two types of a-axis domains: a1 and a2. The orientation relationship determined by X-ray diffraction and confirmed by STEM is (100) BaTiO3 || (100) β-Ga2O3 and [011] BaTiO3||[010] β-Ga2O3. Despite the average linear lattice mismatch of 3.8%, BaTiO3 films with rocking curve full width at half maximum widths as narrow as 28 arc sec are achieved. From capacitance–voltage measurements on a metal–oxide–semiconductor capacitor structure with a-axis BaTiO3 as the oxide layer and Si-doped β-Ga2O3 as the semiconducting layer, we extract a dielectric constant of K11 = 670 for the BaTiO3 epitaxially integrated with (100) β-Ga2O3. We anticipate that this high-K epitaxial dielectric will be useful for electric-field management in β-Ga2O3-based device structures.