A combined scanning tunneling microscopy and electron energy loss spectroscopy study on the formation of thin, well-ordered β-Ga2O3 films on CoGa(001)

Abstract

The formation of thin, well-ordered β-Ga2O3 films on CoGa(001) was studied by means of high resolution electron energy loss spectroscopy (EELS), scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and Auger electron spectroscopy. The crystalline β-Ga2O3 films on CoGa(001) are prepared upon adsorption of O2 at 300 K and subsequent annealing at 700 K or by oxidation of the sample directly at 700 K, respectively. EEL spectra of these films exhibit Fuchs–Kliewer modes at 305, 455, 645, and 785 cm−1 in good agreement with calculated spectra using the IR parameters of Ga2O3. The band gap was determined to be 4.5±0.2 eV. In addition, a gap state at 3.3 eV was found. The observed LEED pattern of β-Ga2O3/CoGa(001) can be explained by a (2×1) structure in two perpendicularly oriented domains. STM images exhibit atomically flat and large oxide terraces (up to 2500×700 Å2) mainly of rectangular shape. STM pictures with atomic resolution confirm the (2×1) structure. In addition, a square substructure can be observed which is related to the closed-packed oxygen lattice of β-Ga2O3.