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Transient Evolution of the Built-in Field at Junctions of GaAs
journal contribution
posted on 2020-08-29, 00:13 authored by Xihan Chen, Ryan T. Pekarek, Jing Gu, Andriy Zakutayev, Katherine E. Hurst, Nathan R. Neale, Ye Yang, Matthew C. BeardBuilt-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.
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thus potentially degradingphotocatalytic applications sinceimpact photoelectrochemical applicationssurface carrier dynamicsexploit transient photoreflectancemany gaas surfacesphotoinduced surface fieldlevel pinning resultssurface fieldresults reveallevel pinningtransient evolutiontransient fieldstransferred holessurface fermiquantitatively describephotogenerated holesphotochemical performancelevel equilibrationdynamical evolutiondifferent typescontacting layerchemical reactionsbeneficial consequences
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