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We report on the carrier dynamics in n-type double-barrier quantum well structures in an electric field. Both the intersubband and interband photocurrents, excited by long-wavelength (4μm) and short-wavelength (0.5μm) radiation, respectively, show a photovoltaic asymmetry with respect to the applied field. This asymmetry arises from an internal field due to an asymmetric dopant distribution with respect to the well centers. Time-dependent photoluminescence measurements allow us to determine the field dependence of the electron and hole capture times.

The authors demonstrate p-type modulation-doped strainedlayer In0.35 Ga0.65As/GaAs multiquantum well lasers which achieve a 3dB direct modulation bandwidth of 20 GHz at a low CW drive current of 50mA in a simple 3 × 200 μm2 mesa structure. For the same device dimensions, a modulation bandwidth of 30 GHz was measured at a CW drive current of 114mA. This is the highest direct modulation bandwidth reported for any semiconductor laser.

Highly localised carbon doping is demonstrated within the active region of strained InGaAs/GaAs MQW lasers. As predicted by numerical beam propagation simulations, the smaller linewidth enhancement factor arising from the combination of strain and p-doping leads to reduced filamentation in tapered laser structures, as compared to devices fabricated from otherwise identical epilayer structures containing undoped active regions.