Ultrafast hole tunneling in GaInAs/AlInAs asymmetric double quantum wells

Absorption and refractive index nonlinearities in semiconductor heterostructures due to real carrier generation are large, but the relatively long recovery time (~1ns) represents a major problem for fast device applications. There have been many attempts to reduce the recovery time by optimizing the design of heterostructures. For example, in structures such as asymmetric double quantum wells (ADCWs) which consist of different size quantum wells coupled by a thin barrier, the recovery time of the narrow well excitonic absorption is controlled by carrier tunneling from the narrow well to the wide well. It was demonstrated that tunneling of electrons indeed results in fast absorption recovery, however slow heavy hole tunneling makes it incomplete [1]. Fast electron tunneling is controlled by longitudinal optical (LO) phonon scattering when the energy separation between the lowest electronic subbands in the narrow and wide well is larger than the LO phonon energy. Hole tunneling is slow because the separation between the hole subbands is usually smaller than the LO phonon energy and the heavy hole wavefunctions are more localized due to their larger effective mass. However, resonances between hole subbands efficiently accelerate hole tunneling [2].