PROBLEM TO BE SOLVED: To obtain a gain-switched semiconductor laser, which is directly driven by a signal current and used for converting electrical signals into ultra-short light pulses, wherein the semiconductor laser is used in an optical communication system in which light signals are transmitted through a long distance at a high speed. ;SOLUTION: A gain-switched semiconductor laser is a semiconductor layer where an asymmetrical double quantum well structure 1 composed of a narrow quantum well on a p-side electrode across a barrier wall and a wide quantum well on an n-side electrode is made to serve as an active region. In this case, the thickness of the quantum well and the composition of waveguide layers 2 which sandwich in the asymmetrical double quantum well structure 1 between them are properly selected, so as to enable only a lowest order sub-band to be present in the conduction band of the asymmetrical double quantum well structure 1. A composite structure where a multi-quantum well structure 7 in which a barrier layer or a barrier layer and a well layer are doped with an acceptor to be increased in confinement coefficient is arranged on a p-side electrode side and the asymmetrical double quantum well structure 1 is arranged on an n-side electrode coming into contact with the multi-quantum well structure 7 is made to serve as an active region.;COPYRIGHT: (C)1999,JPO
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