Miniband structures and effective masses of GaAs/AlAs superlattices with ultra-thin AlAs layers

We report the photoreflectance study of miniband structures of (GaAs)(10)/(AlAs)(m) (A1As), superlattices with m = 1, 2 and 4 monolayers. We clearly observe the optical transitions at the mini-Brillouin-zone center (Gamma point) and the edge (pi point). The observed transition energies are well explained by the calculation in the framework of an effective-mass approximation even in the m = 1 superlattice. Moreover, we detect Franz-Keldysh oscillations originating from the transitions at the Gamma and pi points in the m = 1 superlattice and discuss the miniband masses estimated from the oscillation profiles, comparing with those theoretically derived from the miniband structures. (C) 1997 Elsevier Science Ltd.