Optical and Terahertz Characterization of Be-Doped GaAs/AlAs Multiple Quantum Wells

We report on optical, photoreflectance and surface photovoltage, as well as terahertz photocurrent investigation of Be-doped GaAs/AlAs multiple quantum wells at room and liquid helium temperatures, respectively. From the Franz-Keldysh oscillations observed in photoreflectance spectra we determine built-in electric fields within the structure. Interband transition energies calculated by the transfer matrix method are in qualitative agreement with experimentally determined values for the samples having various, from 2×10$\text{}^{10}$ up to 2.5×10$\text{}^{12}$ cm$\text{}^{-2}$, Be doping densities. The photocurrent observed in the range of 5.4-7.3 THz we associate with photoionization of Be-acceptor states.