An experimental and theoretical study of the carrier capture time into a semiconductor quantum well is presented. Oscillations of the phonon emission induced capture time are experimentally observed and good agreement with theory is found. The calculations show that not only the LO‐phonon emission induced capture time (ph‐capture) oscillates as a function of well width, but also the carrier–carrier scattering induced capture time (c‐c capture) oscillates by more than one order of magnitude as a function of the active layer design. Recently it has been shown that the carrier capture time is directly related to the modulation band width in a quantum well laser. As a result, it might be possible to tailor the modulation band width by optimizing the capture efficiency using a proper design of the active layer in a quantum well laser.