The surface of sulfur (S)-implanted gallium arsenide (GaAs) was covered with hydrogenated amorphous silicon (a-Si:H) film acid subsequently heated to 1000 degrees C. Silicon amounts larger than the implanted dose of S+ ions diffuse from the a-Si:H film into GaAs during annealing. The GaAs had sheet carrier concentrations smaller than that of doped Si atoms. The carrier concentrations decreased with increasing time on cooling from the annealing temperature of 1000 to 50 degrees C, whereas the S and Si atom concentrations were independent of the cooling time.