ABSTRACT:

C60 uniformly doped GaAs and C60, Si codoped GaAs layers are grown by a migration enhanced epitaxy method. C60 doped GaAs layers show a single and sharp diffraction peak in x-ray diffraction and only an LO phonon peak is confirmed, indicating that the crystalline quality is fairly good. All of the C60 doped GaAs layers have highly resistive characteristics, and C60, Si codoped GaAs layers show n-type conductivity only when the Si concentration is of the same order or greater than the total carbon concentrations. At low temperatures the conductivity of the C60, Si codoped GaAs layers increases with exposure to light whose energy is below the GaAs bandgap energy. The electron concentrations and mobilities of the layers are confirmed to be increased under illumination by wavelengths between 900 and 1100 nm. These results imply that the electron transitions from the valence band to the trap levels and from the trap levels to the conduction band occur simultaneously as if the traps act as intralevels. As a result, the carrier concentrations are enhanced in the same way they would be if the excitation was above the GaAs bandgap energy.