The positron annihilation method was used to investigate DX centers in Te-doped material that had been prepared by metalorganic vapor-phase epitaxy. Vacancy defects were found in all of the layers. The vacancy signal disappeared when the center was optically or thermally ionized. After optical ionization, the signal reappeared when the temperature was increased to more than 50K. An optical cross-section of 4 x 10-17cm2 was determined for the removal of positron trapping at a vacancy. Because the properties of the vacancy signal correlated exactly with those determined earlier for the DX(Te) center, it was concluded that the vacancy which was detected by positrons belonged to the atomic structure of the DX(Te) center. This was in agreement with the vacancy-interstitial model. The latter predicted that, in the case of group-VI(Te) doping, the DX center was formed by the displacement of the Ga atom towards the interstitial position. The positron results also indicated that the open volume of the vacancy which was related to the DX(Te) center was smaller than that for an isolated mono-vacancy in GaAs or for a vacancy in the DX(Si) center in AlGaAs. This indicated that the distortion in the vacancy-interstitial configuration was smaller in the case of the DX(Te) center than in the case of the DX(Si) center.

T.Laine, J.Mäkinen, K.Saarinen, P.Hautojärvi, C.Corbel, M.L.Fille, P.Gibart: Physical Review B, 1996, 53[16], 11025-33