Focused-ion-beam implantation of Ga in elemental and compound semiconductors

Small-area [∼(50 μm)2], focused-ion-beam implantation of 25 keV Ga+ in Si, Ge, InP, InSb, and ZnSe was investigated by experiments and by computer simulations. Specifically, the Ga concentration was determined for implantation fluences Φ ranging from 1×1014 to 3×1017 Ga+ ions/cm2 by means of secondary-ion mass spectrometry. In all materials the Ga peak concentration exhibits an essentially linear increase with fluence up to some 1016 cm−2; for higher values of Φ the Ga concentration tends to saturate. The saturation content of Ga at the surface c∞ ranges from ∼2 at % for ZnSe to ∼40 at % for Si. These values appear roughly inversely correlated with the specimens’ sputtering yields and agree thus with the predictions of a model of ion retention in the presence of concurrent sputter erosion. The computer simulations with the dynamic binary-collision-approximation code t-dyn produce a fluence-dependent evolution of the Ga concentrations in the examined semiconductors which is in qualitative agreement with the experiments. Furthermore, partial sputtering yields and the most probable ranges for 25 keV Ga+ impact on the different materials have been determined both experimentally and from the simulation output.