Electroreflectance studies of GaAs/AlGaAs multiple quantum well based resonant Bragg structure at excited states

Electroreflectance (ER) Spectroscopy was employed to study the optical properties of GaAs/AlGaAs multiple quantum well (MQW) based resonant Bragg structure (RBS). The sample used in this experiment consists of 60 periods of quantum well structures with GaAs well and AlGaAs barrier layers grown by molecular beam expitaxy on a semi-insulating GaAs substrate. The sample structure was designed to achieve a double resonance condition to coincide the Bragg resonance peak with the exciton transitions at the second quantum state. Bragg peak can significantly be tuned by changing the angle of incidence of the light. Exciton energies can be tuned by changing the temperature and external electric field. The exciton energies are very sensitive to the thickness of the quantum wells. We performed low temperature ER measurements of the RBS samples of different thicknesses by tuning the angle of incidence of the light for double resonance and observed ER features related to the exciton transitions at excited states such x(e2-hh2), x(e2-hh1), x(e2-hh3) x(e2-lh1) and x(e1-hh3) exciton transitions along with the sharp features of x(e1-hh1) and x(e1-lh1) ground state exciton transitions. Details about the origin of the ER features related to the transitions will be presented.