Intersubband absorption in GaN/AlGaN multiple quantum wells in the wavelength range of λ∼1.75-4.2 μm

Intersubband optical absorption in narrow, 15-30 Angstrom wide, GaN/AlGaN quantum wells has been measured. The samples were grown by molecular-beam epitaxy on sapphire substrate and the barrier AlN mole fraction was varied from 0.45 to 0.8. Peak absorption wavelengths ranged from 4.2 mu m for 30 Angstrom wide wells to 1.77 mu m for a 15 Angstrom wide well. Modeling shows that a large contribution to the considerable spectral width of the absorption of similar to 150 meV likely results from monolayer fluctuations. In addition to the composition dependent band offset, the intrinsic electric fields in the wells and barriers are the determining factors for the shortest possible wavelength. (C) 2000 American Institute of Physics. [S0003-6951(00)05029-4].