WEB Bandgap engineering of hydrogenated amorphous silicon carbide thin films for photoelectrochemical water splittingWednesday (01.01.2020) 00:45 - 01:00 Part of:
Bandgap engineering of undoped and Al doped sputtered amorphous hydrogenated silicon carbide (a-SiC:H) thin films was carried out to assess light absorption properties of the material by maintaining the silicon to carbon stoichiometry without compromising its photoelectrochemical water splitting capabilities. Properties tailoring was achieved by varying the hydrogen concentration in the semiconductor during the deposition process and trough post-deposition thermal treatments. Optical constants were retrieved by suitable methods for the accurate determination of the fundamental absorption of dielectric thin films from optical absorption measurements. Bandgap values were obtained by fitting the fundamental absorption using three different models, namely iso-absorption, Tauc and Band-fluctuations. Variations in the structure and hydrogen composition were tracked by Infrared and Raman spectroscopy techniques. Differences among bandgap values extracted by distinct methods and their correlation to a-SiC:H structural features demonstrated that a structural disorder, rather than a hydrogen rearrangement or depletion, would be responsible for the observed annealing induced optical bandgap enhancement. The tuning of the optical bandgap of a p-doped a-SiC:H sample, with low hydrogen dilution conditions, showed a gradual increase of the bandgap from 2.59 to 2.76 eV. The latter increase was induced after annealing steps from 200 °C till 600 °C. At this temperature the electric performance was strongly improved and required ohmic contacts were obtained. These bandgap values are close to the reported minimum bandgap necessary for water splitting taking into account overpotentials. We believe that these results will contribute to the design of monolithic tandem solar cells for water splitting applications.