RECOMBINATION PROCESSES IN ERBIUM-DOPED MBE SILICON

The incorporation of erbium from a solid source into molecular beam epitaxy (MBE) Si and Si/Ge alloys grown at substrate temperatures of 500-degrees-C and 700-degrees-C has been studied by photoluminescence, electrical measurements, secondary-ion mass spectrometry (SIMS), Rutherford backscattering (RBS) and transmission electron microscopy (TEM). Erbium concentrations between 10(18) and 10(22) cm-3 were obtained but the maximum photoluminescence intensity was from samples with an erbium concentration of 2 x 10(18) cm-3. Above this concentration the onset of erbium precipitation could just be observed by TEM. We found no shallow donors or acceptors attributable to erbium but we observed a high concentration of deep acceptors with an activation energy of 360 meV; these may be due to impurities in the erbium source rather than being directly related to the rare earth. Implantation with oxygen is found to enhance the Er3+-related photoluminescence signal when measured at temperatures greater than 77 K but to have little effect on the low-temperature luminescence. A detailed study of the temperature dependence of the luminescence reveals three quenching mechanisms with average activation energies of approximately 5, 20 and 130 meV. We attribute the first two to de-excitation effects in the matrix, and the last to processes competing with the internal 4f transition.