Excitation and De-Excitation Processes in Er Implanted Light Emitting Si Devices

In this paper we show that room temperature electroluminescence at 1.54 μm can be obtained in Er and O co-doped Si diodes, fabricated by ion implantation, under both forward and reverse bias conditions. This electroluminescence is particularly strong under reverse bias at the breakdown, when Er is excited through impact with hot carriers. This last mechanism is shown to occur with a cross section of 6×10-17 cm2. The measured decay lifetime of Er ions during pumping is 100 μs at room temperature and this allows to obtain a high internal quantum efficiency. However, when the diode is shut off, the decay lifetime becomes shorter and in particular it is less than 1.2 μs (that is the time response of our system). These results can be explained by the presence of Auger nonradiative de-excitation processes that are inhibited within the depletion region during pumping and set in when, at the shut off, the Er ions are immediately embedded within the heavily doped region (∼1019/cm3) of the device. The long lifetime (100 μs) during pumping and the very fast decay time (≤ 12 μs) at the diode shut off allow us to obtain, in our diode and under reverse bias, both a high efficiency (> 10-4) and a fast modulation (≥ 80 kHz) of the 1.54 μm emission.