Transient Evolution of Built-In Field at Junctions of GaAs Photoelectrodes

Xihan Chen, Ryan Pekarek, Jing Gu, Andriy Zakutayev, Katherine Hurst, Nathan Neale, Ye Yang, Matthew Beard

Research output: Contribution to journalArticlepeer-review

12 Scopus Citations


Built-in electric fields at semiconductor junctions are vital for optoelectronic and photocatalytic applications since they govern the movement of photogenerated charge carriers near critical surfaces and interfaces. Here, we exploit transient photoreflectance (TPR) spectroscopy to probe the dynamical evolution of the built-in field for n-GaAs photoelectrodes upon photoexcitation. The transient fields are modeled in order to quantitatively describe the surface carrier dynamics that influence those fields. The photoinduced surface field at different types of junctions between n-GaAs and n-TiO2, Pt, electrolyte and p-NiO are examined, and the results reveal that surface Fermi-level pinning, ubiquitous for many GaAs surfaces, can have beneficial consequences that impact photoelectrochemical applications. That is, Fermi-level pinning results in the primary surface carrier dynamics being invariant to the contacting layer and promotes beneficial carrier separation. For example, when p-NiO is deposited there is no Fermi-level equilibration that modifies the surface field, but photogenerated holes are promoted to the n-GaAs/p-NiO interface and can transfer into defect midgap states within the p-NiO resulting in an elongated charge separation time and those transferred holes can participate in chemical reactions. In contrast, when the Fermi-level is unpinned via molecular surface functionalization on p-GaAs, the carriers undergo surface recombination faster due to a smaller built-in field, thus potentially degrading their photochemical performance.

Original languageAmerican English
Pages (from-to)40339-40346
Number of pages8
JournalACS Applied Materials and Interfaces
Issue number36
StatePublished - 9 Sep 2020

Bibliographical note

Publisher Copyright:
© 2020 American Chemical Society.

NREL Publication Number

  • NREL/JA-5900-76807


  • carrier dynamics
  • photoelectrochemical cell
  • semiconductor photoelectrode
  • solar energy conversion
  • ultrafast spectroscopy


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