  A type-II InAs/AlAs$_{0.16}$Sb$_{0.84}$ multiple-quantum well sample is
investigated for the photoexcited carrier dynamics as a function of excitation
photon energy and lattice temperature. Time-resolved measurements are performed
using a near-infrared pump pulse, with photon energies near to and above the
band gap, probed with a terahertz probe pulse. The transient terahertz
absorption is characterized by a multi-rise, multi-decay function that captures
long-lived decay times and a metastable state of for an excess-photon energy of
$>100$ meV. For sufficient excess-photon energy, excitation of the metastable
state is followed by a transition to the long-lived states. Excitation
dependence of the long-lived states map onto a near-direct band gap ($E{_g}$)
density of states with an Urbach tail below $E{_g}$. As temperature increases,
the long-lived decay times increase $<E{_g}$, due to the increased phonon
interaction of the unintentional defect states, and by phonon stabilization of
the hot carriers $>E{_g}$. Additionally, Auger (and/or trap-assisted Auger)
scattering above the onset of the plateau may also contribute to longer
hot-carrier lifetimes. Meanwhile, the initial decay component shows strong
dependence on excitation energy and temperature, reflecting the complicated
initial transfer of energy between valence-band and defect states, indicating
methods to further prolong hot carriers for technological applications.
