Ion implantation doping for optoelectronic applications

We show that the major problems hampering efficient performances of Si in optoelectronic applications, i.e. the achievement of efficient light emission and fast modulation, can be successfully approached by a proper engineering of its optical properties. In particular, the incorporation of a high Er concentration, if concomitant with codoping with other impurities such as O and F, allows to achieve efficient 1.54 mu m light emission at room temperature. This emission arises from an electrically excitable, atomically sharp, intra 4f transition of the Er ions. The formation of impurity-rare earth ion complexes is shown to enhance the effective solubility of Er in Si and optimize its electrical properties thus providing a higher excitation efficiency and a reduction of the temperature quenching of the luminescence yield. Furthermore we show that the proper design of a Si light emitting diode, allowing the incorporation of Er ions within the depletion layer region of a p(+)-n(+) junction, allows to achieve simultaneously high efficiency and fast modulation of the electroluminescence signal. In fact, under reverse bias, Er ions are pumped with a cross section of 6 x 10(-17) cm(2) and decay with a lifetime of 100 mu s, which guarantees an internal quantum efficiency > 10(-4) and an emitted power of similar to 30 mu W at room temperature. On the other hand, at the diode turn-off, the onset of fast, non-radiative, Auger-type decay processes of the excited ions allow a very fast turn off of the electroluminescence signal.