STUDY OF ANNEALING-INDUCED LATTICE-DEFECTS IN P-DOPED CDTE BY TRANSMISSION ELECTRON-MICROSCOPY

Lattice defects in P-doped CdTe single crystals grown from melt by horizontal Bridgman technique have been investigated by transmission electron microscopy following various postgrowth annealing treatments at 700°C under well-defined Cd partial pressures for different levels of P-doping. The major defect in the as-grown crystals was a dispersion of fine precipitates of a second phase the volume fraction of which was found to decrease with decreasing P content of the crystal. This phase has been tentatively identified as Cd3P2. Crystals annealed at very low Cd partial pressures (viz. 2.4 X 10-5 and 2 x 10-3 atm), on the other hand, revealed the presence of microvoids that were partially filled with a precipitate phase at all P-doping levels. The size and density of the voids decreased as pCd was increased. For a given pea. higher density of voids were observed in crystals with higher P content. In contrast to this, crystals annealed at higher Pcd's in general showed the presence of a finely distributed second phase precipitate and no voids, while those annealed at intermediate pCd's contained neither types of lattice defects. The pcd and P concentration dependences of the observed lattice defects have been analyzed in the light of previously published defect models for CdTe:P system. The formation of the partially filled voids observed at low pcd's has been attributed to the condensation of Cd vacancies (VCd) which is in excess of Te vacancies (Vte) while the precipitates observed at high pcd's have been identified as those due to clustering of P or Cd interstitials. © 1979, The Electrochemical Society, Inc. All rights reserved.