Optical properties of GaAs/AlGaAs near a surface quantum well

We have investigated the photo-modulated reflection spectra of GaAs quantum wells where the top barrier is confined by thin Al0.3Ga0.7As layers. The optical transitions spectra of the first heavy hole hh1 and the first light hole lh1 states to the first electron sublevel e1 are observed. Due to the increase of the confinement potential in the near-surface quantum well by varying the Al0.3Ga0.7As top barrier thickness, we observe a significant blue-shift of the transition lines (hh1 to e1 and lh1 to e1) compared to the transition lines of the quantum well with a thick semiconductor barrier. The experimental observation on the energy shift and the variation of the strength ratio between the transitions e1-hh1 and e1-lh1 can be modeled by a rectangular well combined with a vacuum potential and built-in field.