Steve M. Young, Andrew M. Rappe
The photovoltaic effect in ferroelectrics is well known, but despite much
investigation its origins remain poorly understood. The bulk photovoltaic
effect,occurring even in pure, macroscopic samples under uniform unpolarized
light, has been proposed to derive from multiple mechanisms, including
non-linear optical effects such as optical rectification and "shift current."
These mechanisms have not been confirmed, and their contributions to the
overall response are unknown, complicating interpretation of experimental
results. Here, we compute the shift current for the classic ferroelectrics
BaTiO3 and PbTiO3, analyzing in detail the effect of illumination frequency and
polarization, material polarization, and electronic structure. We successfully
reproduce experimental results, identifying the shift current as the dominant
mechanism. We find a large variation in both the intensity and current
generated for particular transitions, and that intensity and cur- rent are not
strongly correlated in general. The photocurrent does not depend strongly on
the magnitude of material polarization, as has been previously assumed; instead
the electronic states involved in covalent bonding can lead to strong shift
current enhancements. The complexity of the response dependence on the material
parameters suggests applications not only in solar energy conversion, but
catalysis and device engineering as well.
View original:
http://arxiv.org/abs/1202.3168
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