Photon-stimulated desorption of positive and negative hydrogen ions from hydrogenated diamond film and Di͑100͒ surfaces and amorphized diamond surface has been studied for incident photon energies in the 280-340 eV range. From comparison between the H ϩ yield as a function of photon energy and the near-edge x-ray absorption fine structure recorded by detecting secondary electrons of selected kinetic energies the processes leading to photodesorption are assessed. It is shown that desorption of H ϩ occurs through two different processes: an indirect process involving secondary electrons from the bulk and a surface process. The surface process is characterized by a resonance at 287.5 eV photon energy, which reveals the presence of C-H bonds on the diamond surface. Stimulated desorption of H Ϫ is mainly the result of indirect processes that involve secondary electrons. H ϩ photodesorption from an amorphized diamond surface can be also induced by C (1s) ionization. However, no H Ϫ desorption from the amorphized surface could be detected. We suggest that this effect is associated with the reduced secondary electron emission yield of the amorphized diamond surface. Our results demonstrate that ion photodesorption may be used as a sensitive probe for hydrogen on diamond surfaces. ͓S0163-1829͑99͒05603-9͔
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.
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