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

The formation of thin, well-ordered beta-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 beta-Ga2O3 films on CoGa(001) are prepared upon adsorption of O-2 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 beta-Ga2O3/CoGa(001) can be explained by a (2x1) structure in two perpendicularly oriented domains. STM images exhibit atomically flat and large oxide terraces (up to 2500x700 Angstrom(2)) mainly of rectangular shape. STM pictures with atomic resolution confirm the (2x1) structure. In addition, a square substructure can be observed which is related to the closed-packed oxygen lattice of beta-Ga2O3. (C) 1998 American Institute of Physics.