8–12 &mgr;m InGaAs/GaAs quantum well infrared photodetectors with two different well doping concentrations have been studied. The devices with and without surface gratings are compared for normal incident operation. It is found that the TE to TM absorption ratio depends on the doping density in the quantum wells. A higher doping density increases TE absorption. A detectivity about1×1010 cm Hz1/2/Wand a peak responsivity of 0.23 A/W at 9 &mgr;m have been obtained for the grating-free devices. ©1997 American Institute of Physics.