We have studied persistent photoconductivity in 80 Å strained GaAs/In0.26Ga0.74As/GaAs quantum wells grown by molecular beam epitaxy at 480 °C by measuring the Shubnikov de Haas and Hall effects at 4.2 K. Each quantum well was δ doped with Si to 2×1012 cm−2 either (i) at the center of the quantum well, (ii) at the lower interface, or (iii) the bottom barrier. The free-carrier density after exposure to 654 nm red light with above-band-gap energy did not exceed significantly the intended δ-doping level, but the Hall mobility increased dramatically and was accompanied by stronger Shubnikov de Haas oscillations. We attribute this to electron–hole pair generation and separation and/or the photoionization of deep states, which create a positive space charge in the surface depletion region. This leads to electrostatic bandbending, which converts the quantum well from being asymmetric in the dark to square-like after illumination and shifts the charge distribution away from the δ layer, improving the mobility. This hypothesis is corroborated by the light insensitivity of both an identical heterostructure δ doped to 2×1012 cm−2 in the top barrier and an equivalent set of heterostructures δ doped with Si to 4.5×1012 cm−2.

Zervos, M., Elliott, M., & Westwood, D. I. (1999). Light-induced mobility enhancement in delta-doped GaAs/In0.26Ga0.74As/GaAs quantum wells grown by molecular beam epitaxy on GaAs(001). Applied Physics Letters, 74(14), 2026–2028.