  A combined experimental and theoretical study is presented of the band gap of
AlInN, confirming the breakdown of the virtual crystal approximation (VCA) for
the conduction and valence band edges. Composition dependent bowing parameters
for these quantities are extracted. Additionally, composition dependent band
offsets for GaN/AlInN systems are provided. We show that local strain and
built-in fields affect the band edges significantly, leading to optical
polarization switching at much lower In composition than expected from a VCA
approach.
