  TaON and Ta3N5 are considered promising materials for photocatalytic and
photoelectrochemical water splitting. But their counterpart Ta2O5 does not have
good photocatalytic performance. This may cause by the different charge carrier
transport mechanism in Ta2O5, TaON and Ta3N5 which are not well understood yet.
Here, we investigated the charge transport mechanism in Ta2O5, TaON, and Ta3N5
by polaron and bandlike models. We find the charge transfer mechanism is small
polaron hopping in Ta2O5. In TaON and Ta3N5, small polaron may not occur, and
the charge may transfer through bandlike mechanism. The calculated mobility
using effective mass approximation are not consistent with experimental
observation. This study sets a foundation understanding of charge transport in
oxynitrides and nitrides. A more accuracy model or understanding is needed to
rationalize the calculated results and experimental observations in the future.
