Optical Properties of Periodically δ-Doped GaAs

Abstract

We have grown and studied the optical properties of a series of periodically 5-doped Si:GaAs structures. The sheet densities of Si range from l×10¹¹ to 5×l0¹² cm^-2, and the periods from 5 to 50 nm. Within this range of parameters, the electronic structure can exhibit a variety of behaviors, from planar-confined subbands through minibands to three dimensional freedom. Even in a given sample, we may hope to find such a variety of electrons.

Short-period and strongly doped samples give spectra, both in photoluminescence and in resonant electronic Raman scattering, which are similar to those of uniformly doped material. This implies not surprisingly, that the electronic overlap has triumphed over the Coulomb attraction of the donor layers. We are thus in the metallic portion of the metal-insulator (one-dimensional) phase diagram. At the other extreme, with the layers well separated, we expect insulating behavior in the direction of the axis perpendicular to the doping layers, and the electronic structure should be that of a collection of isolated 6-doping layers. Correspondingly, in the Raman spectra of longer-period structures we find new lines, which arise from intersubband or interminiband transitions. Small differences between spectra in different polarizations are taken to indicate collective effects such as resonant screening.

Future work in this area involves attempts to observe and interpret a variety of collective interactions arising from the variety of electron behaviors that are predicted to occur, and to observe Raman scattering from short-wavelength phonons made possible by the periodic electric fields.