Abstract for 1999 American Vacuum Society National Symposium
Seattle, WA  October 1999

Title:  Vacancy Mediated Growth of Ga2Se3 Thin Films

Authors: Z. (Sherry) Qian, Dept. of Mat. Sci. & Eng., Univ. of Washington
	 Zurong Dai, Dept. of Mat. Sci. & Eng., Univ. of Washington 
         Fumio S. Ohuchi, Dept. of Mat. Sci. & Eng., Univ. of Washington
	 Keichi Ueno, Dept. of Chemistry, Univ. of Tokyo, Japan
	 Atsuko Koma, Dept. of Chemistry, Univ. of Tokyo, Japan
	 Shuang Meng, Dept. of Physics, Univ. of Washington
	 Marjorie A. Olmstead, Dept. of Physics, Univ. of Washington 

Abstract:

Ga2Se3 thin films were grown on GaAs(100) and Si(111) substrates by
molecular beam epitaxy (MBE). In spite of large differences in lattice and
symmetry found in GaAs(100) and Si(111), reflection high energy electron
diffraction (RHEED) showed that the Ga2Se3 thin films were epitaxially
grown on both surfaces. Electronic structures were determined by
ultraviolet photoelectron spectroscopy (UPS) and electron energy loss
spectroscopy (EELS). For the Ga2Se3 thin films growth on GaAs(100)
substrate, transmission electron microscopy (TEM) revealed that vacancies
were distributed on one set of the [111] crystal planes of alpha-Ga2Se3
structure by forming a root-3xroot-3 configuration, resulting in the
formation of vacancy ordered beta-Ga2Se3 structure. In this structure,
modulation periodicity along [110] crystal directions was three times
larger than that of ?-Ga2Se3, and the crystal structure was consistent to
the model proposed by LŸbbers and Leute for bulk material (J. Solid State
Chem., 43 (1982) 339). Very different nature of the growth habit was
observed on the Si(111). High population of planer defects observed in the
thin film was regarded as the result of Ga vacancy ordering in the crystal
structure of Ga2Se3. We claim that the vacancies play an important role in
determining the thin film structure in addition to lattice and symmetry
matching conditions in the heteroepitaxy.