Absorption Saturation Energy Density of InGaAs-InAlAs Multiple Quantum Well under Tensile and Compressive Strain

Optical absorption saturation density Is was measured for InxGa1-xAs-In0.52Al0.48As multiple quantum well structures grown on InP (100) substrates by molecular beam epitaxy. Indium composition x was varied from 0.32 to 0.70 so that the quantum well layer was under tensile strain (x 0.53). Optical measurement was carried out using femtosecond light pulses from the optical parametric amplifier of a mode-locked Ti-sapphire laser amplifier. The density Is in a sample changed as a function of photon energy and exhibited a minimum value at the band-edge exciton energy. This minimum Is showed the smallest value at x=0.46 (under tensile strain) of all the samples with different x. This was in marked contrast to the results reported in the literature. Degenerate pump-probe measurement was also carried out, and the results showed that the relative transmission change ΔT/T measured at zero delay between the pump and probe pulses exhibited the largest value at x=0.46, confirming the result of Is measurement.