Different Er centres in Si and their use for electroluminescent devices

At low temperatures, Er in Si produces a big variety of spectra in the 1.5 μm region which can be identified by high-resolution spectroscopy as being due to either interstitial Er or different complexes of Er with oxygen, intrinsic defects and other light impurities. Although the luminescence yield can be improved by codoping with light elements (C, N, O, F, etc.) all of these centres show strong thermal quenching of the luminescence above 150–200 K. There is, however, one type of rather broad spectrum in heavily Er- and O- doped Si, which is seen up to temperatures of 400 K and above. This spectrum can be excited in Si by hot electrons generated in a reverse biased diode. The same spectrum appears also in other Si related materials like porous Si and in silica with the same temperature dependence. In these materials, excitation spectroscopy is possible and it shows also close agreement of the excitation spectra. From these findings we infer that Er is incorporated in another surrounding and we propose Si–Er–O nano-precipitates since the spectra of other candidates, like Er₂O₃, are clearly different. We review recent work on the excitation and quenching mechanisms and we discuss consequences for technology.