  This paper assesses nonpolar m- and a-plane GaN/Al(Ga)N multi-quantum-wells
grown on bulk GaN for intersubband optoelectronics in the short- and
mid-wavelength infrared ranges. The characterization results are compared to
those for reference samples grown on the polar c-plane, and are verified by
self-consistent Schr\"odinger-Poisson calculations. The best results in terms
of mosaicity, surface roughness, photoluminescence linewidth and intensity, as
well as intersubband absorption are obtained from m-plane structures, which
display room-temperature intersubband absorption in the range from 1.5 to 2.9
um. Based on these results, a series of m-plane GaN/AlGaN multi-quantum-wells
were designed to determine the accessible spectral range in the mid-infrared.
These samples exhibit tunable room-temperature intersubband absorption from 4.0
to 5.8 um, the long-wavelength limit being set by the absorption associated
with the second order of the Reststrahlen band in the GaN substrates.
