CROSSOVER FROM A 2-DIMENSIONAL TO 3-DIMENSIONAL ELECTRONIC-STRUCTURE IN SI SPIKE DOPED GAAS SUPERLATTICES

Periodically Si spike doped GaAs with the doping period in the range 100-830 angstrom was studied by magnetoresistance measurements in tilted fields and by photoconductivity. The angular dependence of the Shubnikov-de Haas oscillations, in conjunction with a self-consistent calculation of the miniband structure is used to construct the Fermi surface. When the doping period decreases, the superlattice potential weakens, and the magnetic breakdown of the superlattice Bragg reflection can be detected. Photoconductivity spectra are described by an absorption threshold at the Fermi energy, which is pushed upwards when the superlattice period decreases.