Below-band-gap electroluminescence related to doping spikes in boron-implanted siliconpndiodes

Abstract

The origin of two luminescence bands with maxima around 1.05 eV and 0.95 eV is studied in silicon pn diodes prepared by boron implantation. The two peaks are related to the formation of p-type doping spikes on a nanometer scale. These doping spikes are generated by long-time thermal activation of preformed boron clusters. The peak with a larger binding energy stems from spatially indirect excitons bound to doping spikes in a strained environment, while the peak with a lower binding energy is related to doping spikes without strain. The doping spikes are able to capture spatially indirect bound excitons with a low recombination rate, thus effectively suppressing the fast nonradiative recombination at defects. This effect leads to an efficient room temperature electroluminescence in silicon light-emitting diodes prepared by boron implantation.

Efficient silicon based light emitters

“…This correlation indicates that the increase of the band-edge free electron-hole recombination comes from the thermal dissociation of bound excitons with increasing temperature. Our results can be well reproduced with a rate equation model [23], taking into account the excitons bound to the two traps and the free excitons/electron-hole pairs. A fit yields activation energies of 9.5 and 61 meV, respectively, as shown in Fig.…”

“…These results suggest that both peaks are related to the traps created by high-dose B implantation and the subsequent annealing (for details, see Ref. [23]). …”

“…[23]) as well as individual dark spots with a diameter of 10-20 nm at the end of curved dislocation lines close to the pn junction after annealing. Their origin is attributed to high strain in an area of locally high density of Si-B interstitial clusters, Si interstitials or to strain fields around extended defects.…”

“…[25] for a similar behavior) and it corroborates the assumption that the traps are related to boron doping spikes. We then attribute P TO I and P TO II to unstrained and strained boron-rich areas [23], respectively (strain would reduce the effective band gap, thus explaining the relative spectral positions, see also Ref. [26]).…”

Temperature dependence of electroluminescence from silicon p-i-n light-emitting diodes

“…The enhancement of light emission at higher temperature was observed in the samples with dislocation loops, which was attributed to the spatial localization of the radiative carrier population decoupled from nonradiative recombination, 7 or to the binding of electronhole pairs to the boron doping spikes. 10 The enhancement of light emission from other samples was attributed to the reduction of silicon self-absorption. 8,9 In our case, electroluminescence ͑EL͒ from the silicon p-i-n light-emitting diodes was demonstrated and the anomalous blueshift of the peak energy was observed from 50 to 200 K, which cannot be explained with the above mechanisms.…”