  By considering the changes in the interface charge-carrier densities of a
single-carrier device as a function of injection-barrier heights and comparing
these to the equilibrium, background charge-carrier density of a device with
Ohmic contacts, we calculate simple conditions for when these barriers are
expected to limit injection and therefore significantly affect
space-charge-limited currents in the device. We show that these conditions
depend on the device temperature, semiconductor relative permittivity, and
effective density of states, but most importantly the thickness of the
semiconducting film being probed. This is in accordance with previous
observations and similar derived expressions for when defects influence
single-carrier devices. The conditions described herein can be used to aid the
design of single-carrier devices for space-charge-limited current measurements
that are not limited by injection.
