ON THE REASONS LEADING TO AN APPEARANCE OF CORRELATED AND ANTICORRELATED DEPENDENCES OF THE MINORITY-CARRIER LIFETIME ON THE DISLOCATION DENSITY IN UNDOPED SEMIINSULATING STOICHIOMETRIC GAAS CRYSTALS

It is shown that in undoped semi-insulating GaAs crystals grown under the stoichiometric conditions both correlated and anticorrelated depen dences of the minority carrier lifetime tau on the dislocation density N-d could be observed. The above-pointed effect is connected with a s light excess of Ga atoms (then the correlated dependence tau vs N-d ap pears) or of As atoms (then the anticorrelated dependence tau vs N-d a ppears) which inevitably exists even in ''stoichiometric'' GaAs crysta ls (i.e. in GaAs crystals of ''stoichiometric'' composition).