Anomalous sharp dip of large field-induced refractive index change in GaAs/AlGaAs five-layer asymmetric coupled quantum well

The five-layer asymmetric coupled quantum well (FACQW) is a new potential-t ailored quantum well for ultrafast and low-voltage optical modulators and s witches. Almost linear and large electrorefractive index change can be obta ined in the transparency wavelength regions. In the GaAs/AlGaAs FACQW, an a brupt change in refractive index change an due to an applied electric field F occurs at a cel-tain electric field range, which results in an anomalous sharp dip of ar Deltan versus F. The physical origin and the elimination o f the dip are discussed in detail. The abrupt change of refractive index is caused by significant changes of the wavefunction overlap integrals (and e xciton binding energies) of transitions between the ground states for an el ectron (el) and a heavy hole (hh1), and transitions between el and the firs t excited state for a heavy hole (hh2). The overlap changes are mainly due to shifts of the wavefunction distribution of hh1 and hh2, respectively. Th e dip can be eliminated by changing the position or Al content of the AlGaA s barrier layer in the FACQW. In addition, the larger negative index change in a modified FACQW structure is demonstrated.