  Prototypes for hot-carrier solar cells based on type-II InAs/AlAsSb multiple
quantum wells are examined for AC photoconductivity as a function of lattice
temperature and photoexcitation energy to determine the photoexcited charge
carrier transport. These samples previously exhibit an excitation energy onset
of a metastable regime in their short time charge carrier dynamics that
potentially improves their applicability for hot-carrier photovoltaic
applications. The transport results illustrate that the AC photoconductivity is
larger in the dynamic regime corresponding to the metastability as a result of
higher excitation photocarrier densities. In this excitation regime, the AC
photoconductivity is accompanied by slightly lower carrier mobility, arising
from the plasma-like nature of carriers scattered by Auger recombination.
Outside of this regime, higher mobility is observed as a result of a lower
excitation density that is more readily achievable by solar concentration.
Additionally, at ambient temperatures, more scattering events are accompanied
by slightly lower mobility, but the excitation dependence indicates that this
is accompanied by an ambipolar diffusion length that is greater than half a
micron. These transport properties are consistent with good quality inorganic
elemental and III-V semiconductor solar cells and far exceed those of novel
materials. The transport results complement the dynamics observed in type-II
InAs/AlAsSb and can guide the design of hot-carrier solar cells based on these
and related materials.
