Conditions under which heterogeneous charge-transfer rate constants can be extracted from transient photoluminescence decay data of semiconductor/liquid contacts as determined by two-dimensional transport modeling

Samir J. Anz, Olaf Krüger, Nathan S Lewis, Herbert Gajewski

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

An extensive series of digital simulations of the decay dynamics of photoexcited charge carriers at a semiconductor/liquid interface has been performed using the two-dimensional simulation code ToSCA. ToSCA treats majority and minority carrier capture processes separately and incorporates field-dependent carrier mobility terms. These features produce dramatic differences in the output parameters obtained when fitting experimental data with ToSCA relative to those obtained by fitting such data with prior, less complete, simulations. The simulations revealed that for a typical (n-type in our example) InP electrode in contact with outer-sphere redox reagents dissolved in the liquid phase the photoluminescence decays were generally insensitive to the value of the minority carrier charge-transfer rate constant, kht. Instead, diffusion and drift-induced separation of photogenerated carriers in the space-charge layer of the semiconductor dominated the time decay of the observed luminescence signal under most experimentally accessible conditions. Values of kht and of the minority carrier low-level surface recombination velocity, Sp, could be obtained from an analysis of the photoluminescence decays only when the following restricted sets of conditions were satisfied simultaneously: 101 cm s-1 ≤ Sp ≤ 105 cm s-1, 1018 cm4 s-1 ≤ kht ≤ 10-15 cm4 s-1, and the electrode potential, E, was in the region 0 <E <+0.15 V relative to the flat-band potential of the n-type semiconductor/ liquid interface. The simulations demonstrated that it was not possible to extract a "field dependence" of the charge-transfer rate constant when the semiconductor/liquid contact was maintained in reverse bias (E ≥ +0.15 V vs the flat-band potential) and was subjected to light pulses that produced low or moderate carrier injection levels. Under such conditions, the photoluminescence decay dynamics were dominated by drift-induced charge separation in the space-charge layer of the semiconductor. Under high-level injection conditions, no "field dependence" could be observed because the majority of the photoluminescence decay dynamics occurred near the flat-band condition, so the value of the band bending in the semiconductor under dark, equilibrium conditions had negligible influence on the luminescence transients produced by a high-intensity laser pulse. Additionally, comparison between one-dimensional and two-dimensional simulations showed that use of one-dimensional simulation routines to extract Sp and kht values from experimental data obtained using focused laser beam excitation can lead to severe overestimates of interfacial charge-transfer rates.

Original languageEnglish
Pages (from-to)5625-5640
Number of pages16
JournalJournal of Physical Chemistry B
Volume102
Issue number29
Publication statusPublished - Jul 16 1998

Fingerprint

Contacts (fluid mechanics)
Charge transfer
Rate constants
Photoluminescence
charge transfer
Semiconductor materials
photoluminescence
Liquids
decay
liquids
minority carriers
simulation
Electric space charge
Luminescence
space charge
luminescence
digital simulation
Electrodes
n-type semiconductors
majority carriers

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

@article{371cb3f5a0e54f3ab00347bfb0787112,
title = "Conditions under which heterogeneous charge-transfer rate constants can be extracted from transient photoluminescence decay data of semiconductor/liquid contacts as determined by two-dimensional transport modeling",
abstract = "An extensive series of digital simulations of the decay dynamics of photoexcited charge carriers at a semiconductor/liquid interface has been performed using the two-dimensional simulation code ToSCA. ToSCA treats majority and minority carrier capture processes separately and incorporates field-dependent carrier mobility terms. These features produce dramatic differences in the output parameters obtained when fitting experimental data with ToSCA relative to those obtained by fitting such data with prior, less complete, simulations. The simulations revealed that for a typical (n-type in our example) InP electrode in contact with outer-sphere redox reagents dissolved in the liquid phase the photoluminescence decays were generally insensitive to the value of the minority carrier charge-transfer rate constant, kht. Instead, diffusion and drift-induced separation of photogenerated carriers in the space-charge layer of the semiconductor dominated the time decay of the observed luminescence signal under most experimentally accessible conditions. Values of kht and of the minority carrier low-level surface recombination velocity, Sp, could be obtained from an analysis of the photoluminescence decays only when the following restricted sets of conditions were satisfied simultaneously: 101 cm s-1 ≤ Sp ≤ 105 cm s-1, 1018 cm4 s-1 ≤ kht ≤ 10-15 cm4 s-1, and the electrode potential, E, was in the region 0 <E <+0.15 V relative to the flat-band potential of the n-type semiconductor/ liquid interface. The simulations demonstrated that it was not possible to extract a {"}field dependence{"} of the charge-transfer rate constant when the semiconductor/liquid contact was maintained in reverse bias (E ≥ +0.15 V vs the flat-band potential) and was subjected to light pulses that produced low or moderate carrier injection levels. Under such conditions, the photoluminescence decay dynamics were dominated by drift-induced charge separation in the space-charge layer of the semiconductor. Under high-level injection conditions, no {"}field dependence{"} could be observed because the majority of the photoluminescence decay dynamics occurred near the flat-band condition, so the value of the band bending in the semiconductor under dark, equilibrium conditions had negligible influence on the luminescence transients produced by a high-intensity laser pulse. Additionally, comparison between one-dimensional and two-dimensional simulations showed that use of one-dimensional simulation routines to extract Sp and kht values from experimental data obtained using focused laser beam excitation can lead to severe overestimates of interfacial charge-transfer rates.",
author = "Anz, {Samir J.} and Olaf Kr{\"u}ger and Lewis, {Nathan S} and Herbert Gajewski",
year = "1998",
month = "7",
day = "16",
language = "English",
volume = "102",
pages = "5625--5640",
journal = "Journal of Physical Chemistry B Materials",
issn = "1520-6106",
publisher = "American Chemical Society",
number = "29",

}

TY - JOUR

T1 - Conditions under which heterogeneous charge-transfer rate constants can be extracted from transient photoluminescence decay data of semiconductor/liquid contacts as determined by two-dimensional transport modeling

AU - Anz, Samir J.

AU - Krüger, Olaf

AU - Lewis, Nathan S

AU - Gajewski, Herbert

PY - 1998/7/16

Y1 - 1998/7/16

N2 - An extensive series of digital simulations of the decay dynamics of photoexcited charge carriers at a semiconductor/liquid interface has been performed using the two-dimensional simulation code ToSCA. ToSCA treats majority and minority carrier capture processes separately and incorporates field-dependent carrier mobility terms. These features produce dramatic differences in the output parameters obtained when fitting experimental data with ToSCA relative to those obtained by fitting such data with prior, less complete, simulations. The simulations revealed that for a typical (n-type in our example) InP electrode in contact with outer-sphere redox reagents dissolved in the liquid phase the photoluminescence decays were generally insensitive to the value of the minority carrier charge-transfer rate constant, kht. Instead, diffusion and drift-induced separation of photogenerated carriers in the space-charge layer of the semiconductor dominated the time decay of the observed luminescence signal under most experimentally accessible conditions. Values of kht and of the minority carrier low-level surface recombination velocity, Sp, could be obtained from an analysis of the photoluminescence decays only when the following restricted sets of conditions were satisfied simultaneously: 101 cm s-1 ≤ Sp ≤ 105 cm s-1, 1018 cm4 s-1 ≤ kht ≤ 10-15 cm4 s-1, and the electrode potential, E, was in the region 0 <E <+0.15 V relative to the flat-band potential of the n-type semiconductor/ liquid interface. The simulations demonstrated that it was not possible to extract a "field dependence" of the charge-transfer rate constant when the semiconductor/liquid contact was maintained in reverse bias (E ≥ +0.15 V vs the flat-band potential) and was subjected to light pulses that produced low or moderate carrier injection levels. Under such conditions, the photoluminescence decay dynamics were dominated by drift-induced charge separation in the space-charge layer of the semiconductor. Under high-level injection conditions, no "field dependence" could be observed because the majority of the photoluminescence decay dynamics occurred near the flat-band condition, so the value of the band bending in the semiconductor under dark, equilibrium conditions had negligible influence on the luminescence transients produced by a high-intensity laser pulse. Additionally, comparison between one-dimensional and two-dimensional simulations showed that use of one-dimensional simulation routines to extract Sp and kht values from experimental data obtained using focused laser beam excitation can lead to severe overestimates of interfacial charge-transfer rates.

AB - An extensive series of digital simulations of the decay dynamics of photoexcited charge carriers at a semiconductor/liquid interface has been performed using the two-dimensional simulation code ToSCA. ToSCA treats majority and minority carrier capture processes separately and incorporates field-dependent carrier mobility terms. These features produce dramatic differences in the output parameters obtained when fitting experimental data with ToSCA relative to those obtained by fitting such data with prior, less complete, simulations. The simulations revealed that for a typical (n-type in our example) InP electrode in contact with outer-sphere redox reagents dissolved in the liquid phase the photoluminescence decays were generally insensitive to the value of the minority carrier charge-transfer rate constant, kht. Instead, diffusion and drift-induced separation of photogenerated carriers in the space-charge layer of the semiconductor dominated the time decay of the observed luminescence signal under most experimentally accessible conditions. Values of kht and of the minority carrier low-level surface recombination velocity, Sp, could be obtained from an analysis of the photoluminescence decays only when the following restricted sets of conditions were satisfied simultaneously: 101 cm s-1 ≤ Sp ≤ 105 cm s-1, 1018 cm4 s-1 ≤ kht ≤ 10-15 cm4 s-1, and the electrode potential, E, was in the region 0 <E <+0.15 V relative to the flat-band potential of the n-type semiconductor/ liquid interface. The simulations demonstrated that it was not possible to extract a "field dependence" of the charge-transfer rate constant when the semiconductor/liquid contact was maintained in reverse bias (E ≥ +0.15 V vs the flat-band potential) and was subjected to light pulses that produced low or moderate carrier injection levels. Under such conditions, the photoluminescence decay dynamics were dominated by drift-induced charge separation in the space-charge layer of the semiconductor. Under high-level injection conditions, no "field dependence" could be observed because the majority of the photoluminescence decay dynamics occurred near the flat-band condition, so the value of the band bending in the semiconductor under dark, equilibrium conditions had negligible influence on the luminescence transients produced by a high-intensity laser pulse. Additionally, comparison between one-dimensional and two-dimensional simulations showed that use of one-dimensional simulation routines to extract Sp and kht values from experimental data obtained using focused laser beam excitation can lead to severe overestimates of interfacial charge-transfer rates.

UR - http://www.scopus.com/inward/record.url?scp=0001168247&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0001168247&partnerID=8YFLogxK

M3 - Article

VL - 102

SP - 5625

EP - 5640

JO - Journal of Physical Chemistry B Materials

JF - Journal of Physical Chemistry B Materials

SN - 1520-6106

IS - 29

ER -