Intersubband transition in (GaN)m/(AlN)n superlattices in the wavelength range from 1.08 to 1.61 μm

Intersubband transition (ISBT) in the wavelength range from 1.08 to 1.61 μm was systematically investigated in $(\mathrm{GaN}{)}_m\mathrm{/(}\mathrm{AlN}{)}_n$ superlattices (SLs), grown directly on (0001) sapphire substrates by rf-plasma molecular beam epitaxy. The SLs consisted of 90 periods of GaN wells $\text{(m=2∼10}$ monolayers (ML) in thickness) and AlN barriers $\text{(n∼11\hspace{0.17em}}\mathrm{ML}\mathrm{).}$ One ML corresponds to a thickness of around 2.6 Å. For a 3.3 ML GaN well, the ISBT absorption wavelength reached a minimum of 1.08 μm, close to a theoretically predicted limitation, and it increased monotonically up to 1.61 μm with increasing well thickness to 9.5 ML. We observed absorption spectra as narrow as 61 and 66 meV in linewidth for 1.55 and 1.37 μm samples, respectively.