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

Abstract

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.

The influence of hydrogen on the chemical, mechanical, optical/electronic, and electrical transport properties of amorphous hydrogenated boron carbide

“…range as for the films characterized here. The Tauc slope parameter for a-B x C:H y is further comparable to those found in a-Si:H, 86,89,90 a-Ge:H, 86,91 and a-SiC:H, 92,93 which range anywhere from 100 to 1200 cm À1/2 eV À1/2 . The authors are not aware of any reports of E U values for B x C or a-B x C:H y films.…”

“…Although both E U and B 1/2 can be taken as measures of disorder, they do not necessarily represent identical effects, and the precise type of disorder probed by the individual parameters is not fully understood. In many cases, the two parameters exhibit an inverse linear relationship, 91,121 implying that they do in fact probe a similar underlying disorder feature. Zanatta et al 86,128 highlight some of the more subtle differences between the two, such as sensitivity to substitutional (electronic) disorder vs. structural disorder.…”

On the mechanisms of hydrogen-induced blistering in RF-sputtered amorphous Ge

“…On the contrary, the break of the GeGe bonds, when annealing is applied, produces new Ge dangling bonds where H atoms can attach to instead of remaining free. Moreover, the GeGe enthalpy in a-Ge is much greater than the measured E a as it varies in the range 2.68-2.81 eV [3,38]. suggest that the mechanism for blister formation and growth implies the simultaneous rupture of two GeH bonds and creation of the H 2 molecule.…”

A catalyst-free synthesis of germanium nanowires obtained by combined X-ray chemical vapour deposition of GeH4 and low-temperature thermal treatment techniques

“…In this study, an innovative catalyst-free synthesis in quantitative extents of Ge-NWs featured with high purity and quality, obtained by a combined application of CVD activated by X-ray irradiation (X-ray CVD) [32,33] and of thermal treatment technique of the deposition substrate, is reported. The X-ray radiolytic CVD technique, which has never been applied since so far to Ge-NW synthesis, provides an high amount of energy, to promote the chemical dissociation of gaseous precursors and the formation of highly reactive species (i.e., ions and radicals) [34] that enhance the deposition process on thermal-activated surfaces [35].…”