Correlations among hydrogen bonding configuration, structural order and optical coefficients in hydrogenated amorphous germanium obtained by X-ray - Chemical Vapor 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 Eopt 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.