Abstract

We have performed femtosecond pump and probe experiments using a white- light continuum on a series of symmetrically strained InGaAs/GaAsP multiple quantum well (MQW) samples. By changing the In-concentration, the compressive strain in the (Galn)As layers and thus the energetic splitting between light- hole (lh) and heavy-hole (hh) states can be varied. To maintain overall strain-balance in the structure, the P-concentration must be adjusted for any given In-concentration to have the same absolute values for the tensile strain in the Ga(PAs) barrier and the compressive strain in the InGaAs well. Figure 1 shows low-temperature absorption spectra of 11 (Galn)As/Ga(PAs) MQW samples with In-concentrations between 3% and 16.9%. The energy of the lh-hh splitting varies between 18 meV and 85 meV, respectively. The horizontal solid curve in Fig. 1 separates the samples for which the lh- hh splitting is less (top) and more (bottom) than the optical phonon energies.

© 1996 Optical Society of America