Comparison of light- and heavy-ion-irradiated quantum-wells for use as ultrafast saturable absorbers

We have compared light- and heavy-ion irradiation of InGaAs/InAlAs multiple-quantum wells for ultrafast saturable absorption applications. Under heavy-ion impacts, defect clusters were produced, as observed via transmission electronic microscopy. By contrast, in proton-irradiated samples, only point defects were formed. Nonlinear absorption measurements were performed with excitonic resonance pumping. The relaxation time of absorption saturation (minimum value 2 ps) did not depend on the irradiating ion, and was practically independent of the pulse repetition rate (up to 10 GHz) and optical excitation fluence (0.1 mJ/cm(2)). We conclude that irradiating multiple-quantum wells with light ions is as effective as using heavy ions, when fabricating ultrafast saturable absorber devices operating at high bit rate and near bandedge wavelength. (C) 2001 American Institute of Physics.