INVESTIGATION OF THE VGASNGA COMPLEX IN GAAS BY THE POLARIZATION PHOTOLUMINESCENCE AND PIEZOSPECTROSCOPIC METHODS .1. STRUCTURE OF THE COMPLEX AND ITS REORIENTATION UNDER LOW UNIAXIAL PRESSURES

A wide photoluminescence band with a maximum near the photon energy of 1.2 eV exhibited by n-type GaAs:Sn has been studied. This band is ass ociated with the V(Ga)Sn(Ga) complex. The polarization diagrams and pi ezospectroscopic dependences of the photoluminescence in the pressure range 0-4 kbar were found to be similar to those previously obtained i n the case of the V(Ga)Te(As) complex. They indicate that the test cen ters have a triclinic symmetry, and that they become aligned as a resu lt of pressure applied along the [111] or [110] axis. The computations of the above-mentioned characteristics have been carried out in a mod el which describes distortions of the lattice T(d) symmetry at the pos ition of the complex as a superposition of distortions along different crystallographic directions. Qualitative agreement with the experimen tal data is obtained when one of the distortion components coincides w ith the axis of the V(Ga)-Sn(Ga) pair (the direction of the [110] type ), and when the distortion component, which reorients itself at low te mperatures, is directed along the [111] axis which is perpendicular to the axis of the pair. An alignment of the complexes under uniaxial pr essure is attributable to the alignment of the reorientable components of the complex distortions.