Transition from miniband to Wannier-Stark states in GaAs-AlAs superlattices

摘要

We have studied the field dependence of the absorption coefficient of three GaAs-AlAs superlattices using a new modulation technique, the wavelength modulated photocurrent spectroscopy. At small applied electric fields we observe transitions corresponding to the edges of the joint miniband density of states between electrons and heavy holes as well as light holes. At intermediate fields Franz-Keldysh oscillations appear at the lower and upper band edges of the heavy and light hole joint miniband. With further increasing electric field these oscillations transform gradually into Wannier-Stark ladder transitions. The experimentally observed features are well reproduced by numerical calculations.