13 - Intersubband transitions in GaN-based heterostructures

Abstract

The application of intersubband (ISB) engineering to III-nitride heterostructures sets the basis for new optoelectronic technologies to cover a wide range of infrared (IR) wavelengths, from the fiber optic telecommunication wavelengths to the terahertz range. Suitable conduction band offsets and sub-picosecond ISB scattering rates make III-nitrides interesting candidates for the implementation of ISB devices, particularly in the near- and mid-IR (from 1.0 to 10μm). ISB transitions in polar GaN/AlGaN quantum wells can be tuned along the near- and mid-IR wavelengths. Decreasing the energy between electronic levels toward longer wavelengths (>20μm) can be achieved either by using nonpolar crystallographic orientations or by band engineering to locally reduce the internal electric fields that are present in III-nitrides. Elaborating on these results, prototypes of GaN-based quantum well IR photodetectors and quantum cascade detectors with peak response in the mid-IR range have been reported. Furthermore, there have been demonstrations of ISB transitions in GaN/AlGaN nanowire heterostructures, paving the way for nanowire-based photodetectors. Finally, mid-IR ISB electroluminescence has been measured on chirped AlGaN/GaN multiquantum wells and in quantum cascade GaN/AlGaN heterostructures. However, challenges related to the optical/electronic design, management of the lattice mismatch, and fabrication methodology are yet to be solved to open the way toward the fabrication of a quantum cascade laser.