Control of threshold voltage during gallium arsenide (GaAs) Metal Semiconductor Field Effect Transistor (MESFET) processing is critical. Channel formation typically is done using ion implantation of 29Si+ from a SiF4 source. The use of Si+ presents a variety of potential cross-contamination problems. 28Si+ and 30Si+ beams can become contaminated with 28N2
+, 28CO+, and 30NO+. While 29Si+ is relatively pure, the abundance of 29Si+ in the mass spectrum is 4.67%, thus reducing the potential beam current. This study investigates the effects of varying the mass resolving power of an Eaton 6200AV implanter on the electrical parameters and defect formation. The mass resolving power was adjusted by changing the mean path size through the slit of the aperture opening and magnetic separator current. Electrical device characterization measured a small shift in saturated source-drain current (Idss) and break down voltage, while threshold voltage shifts of approximately 80 mV were observed, with the various mass resolution powers. Transmission Electron Microscopy (TEM) showed that there is minimal change in the extended defect density with changes in isotope and aperture opening. Secondary Ion Mass Spectrometry (SIMS) measured the amount of cross contamination and these results correlated well with the observed changes in device electrical properties.