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Emission dynamics of InGaAs-InGaAsP dot and wire DFB lasers were systematically investigated and compared with quantum-well lasers. Accordingly, the effective carrier capture times, which limit the maximum modulation bandwidth of low-dimensional semiconductor lasers, were determined and compared for these lasers. A quite large effective capture time of about 350 ps was found for the dot laser in contrast to about 56 ps for the quantum-well laser. This is attributed to a dramatically reduced volume of active region which induces a large scaled-up quantum capture time in the dot lasers. The systematic comparison of the quantum-well, -wire and -dot lasers reveal the dominant limitation of geometry effect on the high-speed modulation of quantum-wire and -dot lasers except when the packing density of the dots or wires is increased.