Study of Be d-doped GaAs/AlAs multiple quantum wells by the surface photovoltage spectroscopy

We report a surface photovoltage and differential surface photovoltage (DSPV) study of Be d-doped GaAs/AlAs multiple quantum wells (QWs) with widths ranging from 3 to 20 nm and sheet doping densities from 2 1010 to 2.5 1012 cm 2 per well aiming to characterize their electronic properties and structural quality. From a line shape analysis of room temperature DSPV spectra the interband excitonic transition energies and broadening parameters for a large number of QW-related subbands have been established. A study of well-width and quantum number dependencies of the excitonic linewidths allowed us to evaluate the various broadening contributions to the spectral line shapes in QWs of different design. It was found that an average half monolayer well-width fluctuations are the dominant broadening mechanism of the excitonic line for QWs thinner than 10 nm. In QWs thicker than 10 nm, the spectral line broadening originates mainly from thermal broadening as well as Stark broadening due to random electric fields of ionized impurities and exciton scattering by free holes.