Photoluminescence and transport in selectively doped p-GaAs/AlGaAs   quantum wells: manifestation of the upper Hubbard band
  By selective doping (Be) of the well and barrier regions of p-GaAs/AlGaAs structures we have realized the situation where the upper Hubbard band (A+ centers) has been occupied by holes in the equilibrium. We studied temperature behavior of the Hall effect, variable range hopping conductivity and the photoluminescence spectra of the corresponding structures. The experimental data demonstrated that the binding energy of the A+ states significantly increases with respect to 3D case and strongly depends on well width (9nm,15nm). The localization radii of the A+ states are of the order of well widths. 
N.V.Agrinskaya, Yu.L.Ivanov, P.V.Petrov, V.M.Ustinov