Control of carrier relaxation for suppression of optical gain damping by using Well-in-Well structure

A quantum well design for controlling of the carrier dynamics was investigated for high speed direct modulation semiconductor lasers. The proposed Well-in-Well structure decreases the carrier relaxation time into an active well by designing the wave function which relates to the LO phonon scattering rate. By analyzing the scattering rate of each energy state, the electron relaxation time was estimated to be a few picoseconds which is 2-10 times smaller than that of a conventional quantum well structure. The result is desirable for improving the modulation damping effect which limits the modulation band width. f-3dB is expected above 50GHz. The effect of an asymmetrical Well-in-Well structure was also discussed.