[Granted] An ion source includes an arc chamber having an extraction aperture, and a plasma sheath modulator positioned in the arc chamber. The plasma sheath modulator is configured to control a shape of a boundary between a plasma and a plasma sheath proximate the extraction aperture, wherein the plasma sheath modulator includes a semiconductor. A well focused ion beam having a high current density can be generated by the ion source. A high current density ion beam can improve the throughput of an associated process. The emittance of the ion beam can also be controlled.