Correlations among hydrogen bonding configuration, structural order and optical coefficients in hydrogenated amorphous germanium obtained by x-ray-activated chemical vapour deposition

Hydrogenated nonstoichiometric germanium materials have been produced by x-ray-activated chemical vapour deposition from germane, GeH4. The optical gap, Tauc slope and Urbach energy have been obtained from UV-Vis spectra and correlated with structural parameters, considered as a measure of short and intermediate order, calculated by Raman spectra. The results show that the structural disorder increases with the irradiation time. Investigation of the hydrogen local bonding configuration demonstrates a correlation between the variation of the relative abundances of GeH, GeH2 and GeH3 groups and both structural parameters and E-opt value. Moreover, evidence of the crucial role played by the increase in the GeH3 group abundance in the determination of the Eopt value was revealed.