Temperature Dependence and Quenching Processes of the Intra-4f Luminescence of Er in Crystalline Si

The luminescence quenching of Er in crystalline Si at temperatures between 77 and 300 K is investigated. Samples were prepared by solid-phase epitaxy of Er-implanted amorphous Si layers with or without O codoping. After epitaxial regrowth at 620-degrees-C, thermal annealing at 900-degrees-C for 30 sec was performed in order to eliminate residual defects in the regrown layer and electrically and optically activate the Er ions. Measurements of photoluminescence intensity and time decay were performed as a function of temperature and pump power. By increasing the temperature from 77 K to room temperature the luminescence intensity decreases by approximately three orders of magnitude in the Er-doped sample without 0 codoping, but only by a factor of 30 in the 0-doped sample. In this sample room-temperature photoluminescence and electroluminescence have been observed. Time-decay curves show a fast initial decay (approximately 100 musec) followed by a slow decay (approximately 1 msec), with the relative intensity of these two components depending on temperature, pump power, and 0 codoping. The decay curves can be fitted by a sum of two exponential functions revealing the existence, in both samples, of two different classes of optically active Er sites. Tle concentration of excitable sites belonging to the slow-decaying class is similar for the samples with or without O codoping and rapidly decreases when temperature is increased. At temperatures above 150 K the Er luminescence is dominated by the fast-decaying centers the concentration of which is greatly increased by the presence of O. It is found that in the absence of oxygen room-temperature luminescence is hampered by the limited amount of excitable Er ions. In contrast, in O-doped samples the nonradiative decay of excited Er is the main quenching mechanism. The main factors determining the temperature quenching of Er luminescence and the crucial role of oxygen are discussed.