This work reports on electronic design, epitaxial growth and characterization of GaN/Al(Ga)N quantum wells which constitute the active region of intersubband (ISB) devices for near-, mid- and far-infrared. The design of the GaN/Al(Ga)N quantum wells to tune the ISB transitions in the infrared spectrum was performed using the 8-band k.p Schrödinger-Poisson Nextnano3 solver. The investigated structures were synthesized using plasma-assisted molecular beam epitaxy (PAMBE). The strain issues arising due to the lattice mismatch during the epitaxial growth of GaN/Al(Ga)N heterostructures are investigated by combination of in-situ and ex-situ techniques. The optimal buffer layer, Al content and relaxation mechanisms during the PAMBE growth are determined. Achieving efficient ISB absorption at longer wavelengths requires heavy silicon doping of the quantum wells, so that the single-particle theory leads to a large discrepancy with the experimental results. Therefore, a study of silicon doping of GaN/Al(Ga)N superlattices for near- and mid-infrared spectral region are presented. This work also contributes to a better understanding of the infrared quantum cascade detector technology. Relevant achievements of room-temperature detection at 1.5 µm and 3-5 µm spectral range are demonstrated. Finally, the first observation of far-infrared (4.2 THz) ISB absorption in III-nitrides is reported.
