Layer-resolved ultrafast extreme ultraviolet measurement of hole transport in a Ni-TiO<sub>2</sub>-Si photoanode.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 32284972.
- Also identified by DOI 10.1126/sciadv.aay6650 and PMC identifier 7124930.
- Licence recorded as CC BY-NC.
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Abstract
Metal oxide semiconductor junctions are central to most electronic and optoelectronic devices, but ultrafast measurements of carrier transport have been limited to device-average measurements. Here, charge transport and recombination kinetics in each layer of a Ni-TiO<sub>2</sub>-Si junction is measured using the element specificity of broadband extreme ultraviolet (XUV) ultrafast pulses. After silicon photoexcitation, holes are inferred to transport from Si to Ni ballistically in ~100 fs, resulting in characteristic spectral shifts in the XUV edges. Meanwhile, the electrons remain on Si. After picoseconds, the transient hole population on Ni is observed to back-diffuse through the TiO<sub>2</sub>, shifting the Ti spectrum to a higher oxidation state, followed by electron-hole recombination at the Si-TiO<sub>2</sub> interface and in the Si bulk. Electrical properties, such as the hole diffusion constant in TiO<sub>2</sub> and the initial hole mobility in Si, are fit from these transient spectra and match well with values reported previously.