ELECTRON-STRUCTURAL METASTABILITY OF CATIONIC DONOR CENTERS IN GAAS

The reconstruction of shallow donors in GaAs-Ga1-xAlxAs crystals, whic h is accompanied by the formation of deep cationic DX centers, is stud ied for the first time in a cluster approximation using the self-consi stent, scattered-wave method. It is demonstrated that the formation of a C-3 nu DX- state could be due to the difference in the electronic s tructure of a shallow donor from the structure of a lattice atom. This difference is the reason why an impurity atom transfers into the near est tetrahedral interstice. The model proposed for cationic DX centers is based on the fundamental possibility of localization of two antibo nding electrons on an antobonding orbital of one of the four tetrahedr al bonds of an impurity center with arsenic ligands. This greatly weak ens the bond and results in a corresponding formation of a trigonal DX - state. (C) 1997 American Institute of Physics. [S1063-7826(97)00411- 0].