F. Plazaola et al., Characterization of defects in (ZnMg)Se compounds by positron annihilationand photoluminescence, J APPL PHYS, 88(3), 2000, pp. 1325-1332
Defect characterization of as-grown Zn1-xMgxSe mixed crystals (0 less than
or equal to x < 0.6) and the effect of Zn vapor annealing has been studied
by positron lifetime and photoluminescence measurements. We obtain both exp
erimental and theoretical evidence that the bulk lifetime of free positrons
increases linearly with Mg alloying. The average positron lifetime increas
es with temperature indicating that both vacancies and negative ions trap p
ositrons. The decompositions of the lifetime spectra show that the vacancy
has the characteristic positron lifetime of 325 ps. The comparison with the
oretical calculations indicate that the lifetime 325 ps corresponds either
to divacancies relaxed inwards or to monovacancies strongly relaxed outward
s. We consider the latter identification more likely and attribute the posi
tron lifetime 325 ps to Zn vacancy or a complex involving V-Zn. The vacancy
concentration is almost independent of Mg content above x=0.2 but decrease
s strongly at x=0.56. The Zn vapor annealing decreases the concentration of
Zn vacancies. The intensity of the green photoluminescence correlates with
the concentration of V-Zn both as a function of Mg alloying and Zn vapor a
nnealing. We thus conclude that the electron levels of the Zn vacancy are i
nvolved in the optical transition leading to the green photoluminescence. (
C) 2000 American Institute of Physics. [S0021-8979(00)01015-X].