AN EXAFS STUDY OF THERMAL DISORDER IN GAAS

This paper presents the experimental results of a cumulant analysis of the extended x-ray absorption fine structure amplitude of GaAs at the K edges of Ga and As. The second and fourth cumulants of the distance distributions of the near neighbours of Ga and As have been obtained as a function of temperature in the range 77-450 K. The fourth cumulan t of Ga-As nearest-neighbour distance distributions is zero in the exa mined temperature range; a non-Gaussian distribution of the second and third coordination shell distances of Ga and As has been revealed for the first time. Temperature dependences of mean square relative displ acements (MSRDS) of the first three shells of Ga and As have been comp ared with Einstein and correlated Debye models. The MSRD of the first- shell Ga-As distance is connected to the optical modes at 7.6-8 THz of the phonon spectrum of GaAs.