We report the optimization of barrier thickness and well doping density for GaAs/AlGaAs p-type quantum well infrared photodetectors covering the 3-5 mu m wavelength region. We investigated a series of samples with barrier widths varying from 10 to 50 nm and found that the optimum barrier thickness is about 20 nm. For devices operating at about 100 K, the optimum two-dimensional doping density is found to be in the range 1-2x10(12)cm(-2), which maximizes the background limited infrared performance temperature and dark current limited detectivity.