Time resolved screening of the piezoelectric field in InGaAs/GaAs V-shaped quantum wires of variable profile

InGaAs/GaAs V-shaped quantum wires grown in grooves with either(111) or (411) sidewalls have been studied by ps-transient photoluminescence as a function of the excitation intensity. The optical nonlinearity associated with the screening of the internal piezoelectric field is temporally monitored by the blue-shift of the spectrally resolved photoluminescence, occurring in the first 150 ps after the laser pulse, followed by the recovery of the unperturbed energy resonance at longer delays. Such an energy shift strongly depends on the photoexcited carrier density and reaches a maximum value of about 14 meV in the (411) wires. Despite their larger piezoelectric field, we observe a smaller energy shift in wires with (111) sidewalls, due to the enhanced confinement which localizes the wire wave-function at the bottom of the groove. The observed energy shifts are consistent with the theoretical calculation of the polarization charge density induced by the strain via the piezoelectric effect.