A detailed analysis of the electrical and optical properties of GaSb–AlSb quantum well infrared photodetector structures is presented. Hall effect measurements were performed, and a two‐band conduction model was employed to extract the electron concentration in theLsubband, indicating that at typical detector operating temperaturesT=80 K there are at least 1012cm−2carriers in theLsubband. Temperature‐dependent dark current measurements indicate that the dark current mechanism in detector structures consists of a tunneling regime forT<100 K, and a thermionic regime forT≳100 K. An activation energy of 170 meV is extracted from the temperature dependence of the thermionic dark current. Photoluminescence and absorption measurements were also used to obtain information on the subband levels relative to the bottom of the well, and to investigate the effect of doping on the quality of the GaSb quantum wells. We also report on a method to push the intersubband transition to longer wavelengths by growing center‐loaded structures in which a thin layer of AlSb is deposited in the center of the well in order to raise the energy ofonlythe ground state in the well.