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Title: Layer-resolved ultrafast extreme ultraviolet measurement of hole transport in a Ni-TiO2-Si photoanode

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-TiO2-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 TiO2, shifting the Ti spectrum to a higher oxidation state, followed by electron-hole recombination at the Si-TiO2 interface and in the Si bulk. Electrical properties, such as the hole diffusion constant in TiO2 and the initial hole mobility in Si, are fit from these transient spectra and match well with values reported previously.

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [3]; ORCiD logo [3];  [1]; ORCiD logo [4]; ORCiD logo [2]
  1. California Institute of Technology (CalTech), Pasadena, CA (United States)
  2. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  3. Univ. of California, Berkeley, CA (United States)
  4. Univ. of California, Berkeley, CA (United States); Univ. of Central Florida, Orlando, FL (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division; USDOE Office of Energy Efficiency and Renewable Energy (EERE); U.S. Air Force Office of Scientific Research
OSTI Identifier:
1631652
Grant/Contract Number:  
AC02-05CH11231; USAF- FA9550-14-1-0154; FA9550-19-1-0314
Resource Type:
Accepted Manuscript
Journal Name:
Science Advances
Additional Journal Information:
Journal Volume: 6; Journal Issue: 14; Journal ID: ISSN 2375-2548
Publisher:
AAAS
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY

Citation Formats

Cushing, Scott K., Porter, Ilana J., de Roulet, Bethany R., Lee, Angela, Marsh, Brett M., Szoke, Szilard, Vaida, Mihai E., and Leone, Stephen R. Layer-resolved ultrafast extreme ultraviolet measurement of hole transport in a Ni-TiO2-Si photoanode. United States: N. p., 2020. Web. doi:10.1126/sciadv.aay6650.
Cushing, Scott K., Porter, Ilana J., de Roulet, Bethany R., Lee, Angela, Marsh, Brett M., Szoke, Szilard, Vaida, Mihai E., & Leone, Stephen R. Layer-resolved ultrafast extreme ultraviolet measurement of hole transport in a Ni-TiO2-Si photoanode. United States. https://doi.org/10.1126/sciadv.aay6650
Cushing, Scott K., Porter, Ilana J., de Roulet, Bethany R., Lee, Angela, Marsh, Brett M., Szoke, Szilard, Vaida, Mihai E., and Leone, Stephen R. Fri . "Layer-resolved ultrafast extreme ultraviolet measurement of hole transport in a Ni-TiO2-Si photoanode". United States. https://doi.org/10.1126/sciadv.aay6650. https://www.osti.gov/servlets/purl/1631652.
@article{osti_1631652,
title = {Layer-resolved ultrafast extreme ultraviolet measurement of hole transport in a Ni-TiO2-Si photoanode},
author = {Cushing, Scott K. and Porter, Ilana J. and de Roulet, Bethany R. and Lee, Angela and Marsh, Brett M. and Szoke, Szilard and Vaida, Mihai E. and Leone, Stephen R.},
abstractNote = {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-TiO2-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 TiO2, shifting the Ti spectrum to a higher oxidation state, followed by electron-hole recombination at the Si-TiO2 interface and in the Si bulk. Electrical properties, such as the hole diffusion constant in TiO2 and the initial hole mobility in Si, are fit from these transient spectra and match well with values reported previously.},
doi = {10.1126/sciadv.aay6650},
journal = {Science Advances},
number = 14,
volume = 6,
place = {United States},
year = {2020},
month = {4}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Figures / Tables:

Fig. 1 Fig. 1: Characterization and measurement of the Ni-TiO2-Si junction. (A) The energy level alignment for the metal, oxide, and semiconductor is shown, along with the expected photoexcited hole transfer in the p-type MOS junction. The Si is p-type–doped by boron at 1015 per cm3. The presence of oxygen defect levelsmore » (n-type) in the TiO2 layer was previously confirmed by photoemission spectroscopy of a Si-TiO2 junction. The band bending is calculated using the drift-diffusion equation. (B) A TEM measurement of the thickness of the TiO2 and Ni, which are 19 ± 0.6 nm and 5.6 ± 0.6 nm, respectively. The TiO2 is amorphous, and an ~1-nm SiO2 interface is measured where the TiO2 and Si contact. (C) The black line overlay is the ground-state XUV absorption. The regions that correspond to the Ti M2,3 edge, the Ni M2,3 edge, and the Si L2,3 edge are indicated by the colored boxes. The differential XUV absorption that results from photoexcitation is shown as the background color map, with the scale on the right of the graph. Each peak is observed to have a unique response to the photoinitiated charge transfer, which will be discussed in the main text.« less

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