Oxygen-related radiation-induced defects in SiGe alloys

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Electronic properties of the vacancy–oxygen (V–O) complex and the interstitial oxygen and carbon atompair (Ci–Oi) inunstrained Si1−xGex crystals have been studied by means of capacitance transient techniques. TheSi1−xGex crystals were grown by the Czochralski method and were dopedwith either phosphorus or boron during growth. The V–O andCi–Oi centres were introduced into the crystals by room temperature irradiation with 4 MeV electrons or withγ-raysfrom a 60Co source.The enthalpy of electron ionization for the single acceptorlevel of the V–O centre relative to the conduction band edge,ΔHn, was found toincrease with a rate d (ΔHn)/d x = 0.56 eV upon increase in Ge content. The enthalpy of hole ionization for the single donor level of theCi–Oi centre relative to the valence band edge,ΔHp, was found to decreasewith a rate d (ΔHp)/d x = −0.96 eV. For boththe V–O- and Ci–Oi-relatedlevels no significant changes in the values of the electron (hole) capture cross section orentropy of ionization with the changes in Ge content were observed. The levels are notpinned to the conduction band edge or to the valence band edge. It is argued that the valueof the enthalpy of V–O ionization can be correlated with the lattice parameter or the Si–Sibond length: the larger this parameter, the bigger the enthalpy of the ionization.