AVS 45th International Symposium
    Thin Films Division Thursday Sessions
       Session TF-ThA

Paper TF-ThA3
TEM Study of Defects, Domains and Vacancy Ordering in Ga@sub 2@Se@sub 3@/GaAs(100) and Ga@sub 2@Se@sub 3@/Si(111) Thin Films

Thursday, November 5, 1998, 2:40 pm, Room 310

Session: Ex-situ Characterization of Thin Films
Presenter: Z.R. Dai, University of Washington
Authors: Z.R. Dai, University of Washington
S.R. Chegwidden, University of Washington
S. Meng, University of Washington
K. Ueno, University of Tokyo, Japan
A. Koma, University of Tokyo, Japan
M.A. Olmstead, University of Washington
F.S. Ohuchi, University of Washington
Correspondent: Click to Email
Ga@sub2@Se@sub3@ belongs to a class of M2(III)X3(VI) compounds (where M=AL, Ga or In and X=S, Se or Te) that is largely unexplored, but which has potential applications in novel optoelectronic devices. The crystal structure of Ga@sub2@Se@sub3@ is based on tetrahedral atomic coordination as in the zinc-blende structure, but in which one third of Ga sites on the average are left as vacancies to preserve charge balance in the crystal. The existence of vacancies complicates the Ga@sub2@Se@sub3@ crystal structure, with their arrangement leading to a variety of polymorphs and possible defect structures, but the arrangement of vacancies also strongly influences the properties of Ga@sub2@Se@sub3@. In particular, the vacancy ordering in the crystal structure likely results in the unique optical and electronic properties of Ga@sub2@Se@sub3@. In this work, the Ga@sub2@Se@sub3@ films were grown on GaAs(100) and Si(111) substrates, respectively, by Molecular Beam Epitaxy (MBE). The microstructure of the Ga@sub2@Se@sub3@ films were characterized by transmission electron microscopy (TEM). For the case of Ga@sub2@Se@sub3@/GaAs(100), a single crystal Ga@sub2@Se@sub3@ film was obtained, in which a number of plane boundaries parallel to [111] crystal planes were observed, as well as some micro-twins. The electron diffraction analysis indicates that the vacancies are ordered to distribute into the domains separated by the boundaries in some equivalent orientations of the zinc-blende structure. For the case of Ga@sub2@Se@sub3@/Si(111), the Ga@sub2@Se@sub3@ film consists of domains forming a twin relationship each other, relative to the [-110] crystal planes of the Si substrate. The vacancy ordering occurs in the [111] crystal planes and the periodicity of atomic stacking along <111> crystal direction is two times of that for the cubic zinc-blende structure. The ordered arrangement of the vacancies is associated with the surface structure of the substrates. The attribute of the boundaries and formation mechanism of the domains and vacancy ordering will be discussed.