STRUCTURAL-PROPERTIES OF LI-DOPED HYDROGENATED AMORPHOUS-SILICON

Interstitially doped a-Si:H films were prepared by in-diffusion of lithium at T(D) = 230-degrees-C and 320-degrees-C, respectively, and characterized by infrared and Raman spectroscopy, ellipsometry measurements as well as SIMS analysis and thermal effusion. Two new infrared modes at frequencies of about 1600 cm-1 and 1400 cm-1 are observed which we attribute to LiOH and LiH in the near surface region. The decrease of the SiH infrared-absorption peaks and the observation of a new mode in the Raman spectra at 620 cm-1 which we attribute to a SiLi alloy suggest an exchange reaction between Li and bonded hydrogen. Changes of the dielectric function in the visible spectral region show that this material contains Li precipitations which give rise to an enhanced Raman scattering cross-section. The results also suggest that lower diffusion temperatures lead to more pronounced Li clustering.