Defects in GaAs on Si studied with the positron-beam technique.

Positron-beam experiments have been carried out to characterize defects in metal-organic vapor-phase-epitaxially grown GaAs layers on (100)GaAs and (100)Si substrates. The Te-doped GaAs/GaAs layer (n=2×10 15 cm -3 ) appears to be free of vacancies which are present in similarly doped bulk n-type GaAs crystals. The heteroepitaxial GaAs/Si layer with the low (<10 7 cm 2 ) dislocation density is also free of positron trapping. At ahigher dislocation density of 10 7 -10 8 cm -2 positrons detect Si cluters.