OPTICAL-PROPERTIES OF GAAS ALGAAS NEAR A SURFACE QUANTUM-WELL/

We have investigated the photo-modulated reflection spectra of GaAs qu antum wells where the top barrier is confined by thin Al0.3Ga0.7As lay ers. The optical transitions spectra of the first heavy hole hh1 and t he first light hole lh1 states to the first electron sublevel e1 are o bserved. 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 t he energy shift and the variation of the strength ratio between the tr ansitions e1-hh1 and e1-lh1 can be modeled by a rectangular well combi ned with a vacuum potential and built-in field.