High Efficiency and Fast Modulation of Er-Doped Light Emitting Si Diodes

We demonstrate that the electrical excitation of Er ions incorporated within the depletion layer of a p(+)-n(+) Si diode allows one to simultaneously obtain efficient pumping of rare earth ions and a fast turnoff time of the electroluminescence signal. In fact it is found that during pumping, under reverse bias at the breakdown, a high internal quantum efficiency (10(-4)) can be achieved since the Er ions are excited with a cross section of 6x10(-17) cm(2) and exhibit a decay lifetime of 100 mu s at room temperature. On the other hand, when the diode is turned off, the electroluminescence signal dies off in less than 10 mu s (a limit set by the time response of the adopted detector). These results are explained by observing that fast nonradiative decay of the excited Er ions can occur by Auger transfer of the energy to a free electron or to an electron bound to an Er-related level in the bandgap. These processes are inhibited within the depletion layer and only set in when, at the turnoff, the excited Er ions are suddenly embedded within the heavily doped (similar to 10(19)/cm(3)) neutral region of the diode.