In 1.35 μm‐InGaAsP/InP DHS mesastructure diodes with differently spaced p‐n and heterojunctions the electron‐beam induced current and cathodoluminescence, the C–U characteristics, the DLTS, and the photoresponse as well as the injection luminescence as functions of the wavelength, temperature, and time are measured. The InP‐interlayer lying between p‐n and heterojunction supresses the collection of the photogenerated holes by means of the valence‐band offset induced pile‐up effect at low illumination levels and low temperatures, delays the motion of the holes during the collection at high illumination levels and reduces the hole injection into the n‐type quaternary active layer at low temperatures. Probably due to the separation of the p‐n junction from the active layer the content of nonradiative recombination centres in the active layer is reduced.