Nature of gallium deep centres in lead telluride based semiconductors

Doped with Ga lead telluride was taken as a model object to explain the nature of group-III deep levels in IV-VI semiconductors and to elucidate the vapour phase doping mechanism. For this goal, interaction of various gallium-containing molecules with defect-free crystal as well as with native defects in PbTe was considered. Formation energies for different point defects created in PbTe as a result of interaction the Ga 2 Te molecules, Ga 2 dimers and single Ga atoms with a host crystal were calculated using density functional theory. Particularly Ga Pb and Ga i together with formation of accompanied self interstitials Pb i in various charge states were examined. In addition we propose the new type of defects - the impurity complex (2Ga) Pb which looks like -oriented gallium dumbbell. Calculations suggest the double donor behaviour and DX-like properties of this defect together with extremely low formation energy values. Namely, (2Ga) Pb centres are preferably formed under Ga 2 Te doping while (Ga 2 ) Pb +Pb i ones are formed under Ga 2 or Ga doping. In all cases, formation energies are negative and resulting defect concentration is determined by reaction kinetics only. Mechanisms of the lead vacancy compensation with the vapour phase doping are considered as well.