Anomalous damaging behaviour of AlAs during ion implantation at 15 K

AlAs is implanted with 125 keV Na and 660 keV Xe ions at a temperature of 1 5 K. Defect analysis is done in situ by Rutherford backscattering spectrome try in channelling configuration without temperature change. An ion-beam-in duced interfacial amorphisation of AlAs is observed at the interface to the GaAs cap layer, which is related to the energy deposition into collision p rocesses, yielding an amorphisation rate of 0.44 nm/dpa (displacements per lattice atom). Over a wide range of ion fluences only point defects and poi nt defect complexes exist in the implanted layer, pointing to a balance bet ween defect formation and recombination during the irradiation. In this dep th region amorphisation occurs if the volume introduced by the implanted io ns exceeds some critical value. We assume that this causes the breaking of bonds in the AlAs lattice and the nucleation of amorphous seeds which grow rapidly during further irradiation. (C) 2001 Elsevier Science B.V. All righ ts reserved.