Hall-effect measurements in Cd-implanted GaAs

Cadmium ions were implanted in GaAs crystals at 135 keV to doses ranging from 1012 to 1016 ion/cm2 at room temperature. Sheet-resistivity and Hall-effect measurements were carried out as a function of temperature, 4.2 to 300 0K, after annealings at 700, 800, or 9000C in an Ar ambient. The sample surfaces were protected with pyrolytically deposited Si3N4. Significant p-type conduction was observed when samples with doses approximately greater than 1013 cm-2 were annealed at 7000C. For doses below 1014 cm-2 nearly complete electrical activity was attained after an 800 to 9000C anneal. The Cd profiles were determined by differential Hall-effect measurements in conjunction with the acid-etch layer-removal technique. Above about 8000C diffusion becomes important and significantly flattens the implantation profile