Hall-effect measurements in Cd-implanted GaAs

Cadmium ions were implanted in GaAs crystals at 135 keV to doses ranging from 10 to 10 ion/cm at room temperature. Sheet-resistivity and Hall-effect measurements were carried out as a function of temperature, 4.2-300°K, after annealings at 700, 800, or 900°C in an Ar ambient. The sample surfaces were protected with pyrolytically deposited SiN. Significant p-type conduction was observed when samples with doses ≳10 cm were annealed at ≳700°C. For doses below 10 cm nearly complete electrical activity was attained after an 800-900°C anneal. The Cd profiles were determined by differential Hall-effect measurements in conjunction with the acid-etch layer-removal technique. Above about 800°C diffusion becomes important and significantly flattens the implantation profile.