Type-I–Type-II Transition in GaAs/AlAs Short Period Superlattices Studied under Pulsed High Magnetic Fields and High Pressures

We have observed type-I–type-II transition in photoluminescence spectra of GaAs/AlAs short period superlattices under pulsed high magnetic fields up to 150 T and hydrostatic pressures up to 30 kbar. In magneto-photoluminescence spectra, the luminescence intensity showed an abrupt decrease at some critical magnetic field due to a Γ- X crossover in the conduction band, and also a remarkable hysteresis when the pulsed fields were swept up and down. The hysteresis arises from the fast sweep of the field pulse in the similar time scale to the lifetime of the type-II exciton, as shown by a rate equation analysis based on a two-level model. The controversial electron effective mass of the AlAs X -point was estimated as m X =0.16±0.07 m 0 .