Photodiodes with thin (∼0.2 &mgr;m) InGaAs light absorbing layers placed inside much wider (∼2 &mgr;m)InP depletion regions were studied to understand the interaction of hole trapping at the InGaAs/InP heterojunction interface and carrier transit effects. In the three devices studied, the absorbing region was located (i) near then+side, (ii) in the center, and (iii) near thep+side of the depletion region. The optical impulse response of these devices consists of a short pulse and a long exponential tail with a bias‐dependent time constant. The relative charge in the fast and slow components could be measured and it was shown that the charge ratios correspond to the fraction of the depletion region transited before and after trapping. These studies show that electron trapping times are much shorter than hole trapping times, and that fast photodetection can occur even in the presence of a severe hole trapping problem if the distance between the trap and thep+side of the depletion region is much smaller than the total depletion width.