  We describe studies on the nanoscale transport dynamics of carriers in
strained AlN/GaN/AlN quantum wells: an electron-hole bilayer charge system with
large difference in transport properties between the two charge layers. From
electronic band diagram analysis, the presence of spatially separated
two-dimensional electron and hole charge layers is predicted at opposite
interfaces. Since these charge layers exhibit distinct spectral signatures at
terahertz frequencies, a combination of terahertz and far-infrared spectroscopy
enables us to extract (a) individual contributions to the total conductivity,
as well as (b) effective scattering rates for charge-carriers in each layer.
Furthermore, by comparing direct-current and terahertz extracted conductivity
levels, we are able to determine the extent to which structural defects affect
charge transport. Our results evidence that (i) a non-unity Hall-factor and
(ii) the considerable contribution of holes to the overall conductivity, lead
to a lower apparent mobility in Hall-effect measurements. Overall, our work
demonstrates that terahertz spectroscopy is a suitable technique for the study
of bilayer charge systems with large differences in transport properties
between layers, such as quantum wells in III-Nitride semiconductors.
