Intersubband spectroscopy probing higher order interminiband transitions in AlN-GaN-based superlattices

We investigate midinfrared intersubband photodetectors based on short-period AlN/GaN superlattices with different quantum well thicknesses. Band structure calculations, as well as optical transmission and photovoltage measurements, underline the importance of higher order interminiband transitions. In particular, it was found that optical transitions between the second and third minibands benefit from much larger electron displacements and oscillator strengths than those between the first and second minibands. Our results suggest that optical rectification is therefore much more efficient for devices based on a higher order interminiband transition.