  We report time-dependent photocurrent and transport measurements of
sub-bandgap photoexcited carriers in nitrogen-rich (type Ib), single-crystal
diamond. Transient carrier dynamics are characteristic of trapping conduction
with long charge storage lifetimes of ~3 hours. By measuring the photoexcited
Hall effect we confirm that the charge carriers are electrons and by varying
the excitation energy we observe a strong turn-on in the photoconduction at
~1.9 eV. These findings shed new light on sub-bandgap states in nitrogen doped
single-crystal diamond.
