p-i-nphotodiodes with integrated optical waveguides were successfully fabricated in the GaInAsP/InP material system. This integration leads to optoelectronical integrated circuits of significantly increased functionality, and it also offers the possibility to build high-speed detectors with high quantum efficiency. Butt-joint coupling between waveguide and photodiode was used allowing smallest detector sizes. Selective embedded growth of the photodiode layer stack was accomplished by metal-organic vapor-phase epitaxy on partially masked substrates. This technique was proven to be suitable for device fabrication. To study the influence of the lateral growth interface between waveguide and the photoabsorbing GaInAs material, the spacingdbetween interface andpregion of the photodiode was varied between 0 and 4 &mgr;m. The detector bandwidth is not limited by the electricalRCtime constant up to frequencies of 50 GHz for devices with an active area of 10×11 &mgr;m2. Best values for the quantum efficiency and the electrical 3 dB cutoff frequency of 65&percent; and 8 GHz are obtained. Both decrease strongly with increased spacingddue to an enhanced diffusion component and an increase of carriers trapping and recombination effects at the growth interface. This interpretation of the experimental data was well confirmed by a detailed analysis of the dynamic device behavior based on analytical calculations of the physical transport mechanisms. Consequently, for a redesigned photodiode the distancedhas to be minimized as far as possible. ©1997 American Institute of Physics.