Two-dimensionalD−centers

Far-infrared magnetotransmission and magnetophotoconductivity measurements on selectively doped GaAs-GaAlAs multiple-quantum-well structures reveal photoionization transitions from two-dimensional ${\mathit{D}}^{\mathrm{-}}$ centers to successive Landau levels. Selective doping of the quantum-well structure favors the formation of ${\mathit{D}}^{\mathrm{-}}$ centers in the well. The two-dimensional nature of this center results in a dramatic enhancement of its binding energy with respect to the three-dimensional case.