Recent progress in GaN-based superlattices for near-infrared intersubband transitions

A review of the recent progress in intersubband transitions in GaN-based superlattice structures grown by plasma-assisted molecular beam epitaxy (MBE) is presented. Careful control of the growth parameters resulted in reduced threading dislocation density as well as optimized interfaces for the superlattices. Intersubband absorption has been observed from a variety of configurations involving GaN single or asymmetric double quantum wells with either thick AlxGa1-xN barriers or short-period GaN/AlxGa1-xN superlattice barriers. The peak wavelength of absorption can be varied between 1.4 - 4.2 mm by changing the quantum well thickness. Electron scattering times were measured by the pump-probe technique and were found to be 240-330 fs at 1.55 mm. In addition, intersubband transitions have also been observed for GaN/AlN superlattices grown with a non-polar (1120) orientation.