Modulation-doped Cd1−xMnxTe/Cd1−yMgyTe quantum well structures with spatial in-plane profiling of the well width and the doping intensity

We report on the design and growth by molecular beam epitaxy of two types of graded ${\mathrm{Cd}}_{\text{1−x}}{\mathrm{Mn}}_x{\mathrm{Te/Cd}}_{\text{1−y}}{\mathrm{Mg}}_y\mathrm{Te}$ quantum well structures having a precisely controlled spatial profile of either the quantum well width and/or of the number of donors in one of the directions perpendicular to the growth axis. The existence of a spatially varying quantum well width was demonstrated by different wavelengths of the photoluminesce emitted from different regions of the sample. The presence of two-dimensional electron gas with a spatially varying concentration produced by graded modulation doping was evidenced by magneto-optical studies which revealed signatures of either excitons, or negatively charged exciton–electron complexes ${\mathrm{(X}}^{-}\mathrm{),}$ or Fermi-edge singularity, all in a single sample grown in one molecular beam epitaxy process. Such structures may be very useful for tunable wavelength radiation sources as well as in detailed studies of various physical characteristics of the quantum wells.