Terahertz intersubband absorption in GaN/AlGaN step quantum wells

We demonstrate terahertz intersubband absorptions at frequencies of 2.1 THz (λ≈143 μm) and 4.2 THz (λ≈70 μm) in nitride-based semiconductor quantum wells. The structures consist of a 3 nm thick GaN well, an Al0.05Ga0.95N step barrier, and a 3 nm thick Al0.1Ga0.9N barrier. The absorption is detected at 4.7 K. The structure design has been optimized to approach a flat-band potential in the wells to allow for an intersubband absorption in the terahertz frequency range and to maximize the optical dipole moments.