AIN/GaN multiple quantum wells were grown by RF plasma-assisted molecular beam epitaxy on (0 0 0 1) sapphire substrates. Intersubband (ISB) absorption in the range of 1.5-1.9 μ m was investigated in these structures as a function of the main quantum well design parameters. It is found that the ISB transition line width does not depend strongly on the degree of strain relaxation in the investigated structures, but rather is sensitive to both the well and barrier widths. This is explained by considering well/barrier thickness fluctuations. A reduction in the ISB absorption line width was achieved by doping the wells in the first 5&ANGS; only as compared to uniformly doping the wells. ISB absorption was also demonstrated for the case in which the AIN barriers only were doped. © 2005 Elsevier B.V. All rights reserved.