Angular dependence of defects introduced in GaAs by alpha-particle bombardment

It is commonly assumed that ion beams used for channelling experiments create little damage when moving along a principal axial channel of a crystal. We have employed deep level transient spectroscopy (DLTS) to characterise the defects induced by 300 keV He-ions in 3 GaAs crystal when entering it along the [100] axis (hyperchannelling: alpha(i) = 0 degrees) as well as at small angles with respect to this axis (alpha(i) less than or equal to 1.2 degrees). The results we obtained indicate that the commonly observed alpha-particle induced defects in Si-doped GaAs (AsvIAs pairs, isolated As-V and a Si-related metastable defect) were introduced at all angles of incidence investigated. The concentration of these defects was a minimum for alpha(i) = 0 and increased with increasing angle of incidence. Finally, we observed a difference between the relative concentrations of defects introduced during hyperchannelling and during bombardment off the channel axis.