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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.

A quantum well design for controlling of the carrier relaxation process and reducing of the gain damping effect was investigated for improvement of high speed direct modulation semiconductor lasers. The proposed Well-in-Well structure decreases the carrier relaxation time into an active well by carefully designed wave function which relates to the LO phonon scattering rate. The decrease of relaxation time and the increase of modulation bandwidth was analyzed numerically. The reduction of damping factor γ was also demonstrated by experimental measurement of the relative intensity noise spectrum.

A quantum-well design for controlling carrier dynamics was investigated for high-speed direct-modulation semiconductor lasers. The proposed well-in-well (WWell) structure decreases the carrier relaxation time into an active well by designing the wave function that is related to longitudinal optical phonon scattering rate. The electron relaxation time was analyzed numerically and was estimated to become 1/2–1/10 times smaller than that of a conventional quantum-well structure. This reduction of the relaxation time is effective for reducing the optical gain damping. The advantage of an asymmetrical WWell structure is also shown.