Passivation and generation of deep level defects in hydrogenated n-GaAs (Si)

Bulk n-type GaAs wafers (Si doped) have been exposed to a capacitively coupled rf hydrogen plasma at different power densities ranging from 0.01 to 0.2 W/cm2 at 260 °C. The electronic properties of these layers have been investigated by capacitance-voltage experiments and deep level transient spectroscopy. Besides the neutralization of the silicon donors by the in-diffused hydrogen atoms, we observe a modification of the deep level transient spectroscopy (DLTS) spectra after hydrogenation. For rf power densities lower than 0.1 W/cm2, the deep levels present in the region of the starting material explored by DLTS are passivated. The absence of electronic states associated with the silicon-hydrogen complexes in the neutralized donor region indicates that these complexes are either electrically inactive or deeply located in the energy band gap. For rf power densities higher than 0.1 W/cm2, two new deep electronic states appear at 0.41 and 0.55 eV below the conduction band. These levels are the signature of a large amount of defects in the near-surface region of n-GaAs (Si) after exposure to a rf hydrogen plasma at such power densities. Trapping of hydrogen on these defects is probably responsible for the accumulation of hydrogen in the near-surface region observed in the hydrogen diffusion profiles.