OPTICAL AND ELECTRICAL-PROPERTIES OF RARE-EARTH (YB,ER) DOPED GAAS GROWN BY MOLECULAR-BEAM EPITAXY

Electrical and optical properties of erbium-doped and ytterbium-doped GaAs are reported in this article. The studied samples are semi-insulating and have been grown by molecular beam epitaxy. The Yb and Er concentrations in the GaAs epitaxial layers measured by secondary ion mass spectroscopy are 2-3 X 10(17) cm-3. The photoluminescence of Yb intra-4f shell has not been observed, while that of Er has been widely reported. Photoinduced current transient spectroscopy measurements (PICTS) reveal that the Yb doping (Er doping) creates a level in the pp with an activation energy of 0.65 eV (0.67 eV). The depth of such levels may be responsible for the absence of Yb 4f photoluminescence in GaAs:Yb. Moreover, photoconductivity experiments show the presence of rare earth related traps. The energies of these traps correspond exactly to the difference between the gap energy and the corresponding activation energy found by PICTS. These observations confirm the excitation model based on the energy transfer from recombination to the rare earth transitions.