Characterization of Er/O-doped Si-LEDs with low thermal quenching
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Characterization of Er/O-doped Si-LEDs with low thermal quenching A. Karim, W.-X. Ni, A. Elfving, P.O.Å. Persson, and G.V. Hansson Department of Physics and Measurement Technology, Linköping University, SE-58183 Linköping, Sweden.
ABSTRACT Electroluminescence studies of MBE-grown Er/O-doped Si-diodes at reverse bias have been done. For some devices there is much reduced thermal quenching of the emission at 1.54 µm. There are examples where the temperature dependence is abnormal in that the intensity for a constant current even increases with temperature up to e.g. 80 oC. These devices have been studied with cross-sectional transmission electron microscopy to see the microstructure of the Er/O-doped layers as well as the B-doped SiGe-layers that are used as electron emitters during reverse bias. Although there are defects in the layers there is no evidence for large thick precipitates of SiO2. While reduced thermal quenching often is attributed to having the Er-ions within SiO2 layers, this is not the case for our structures as evidenced by our TEM-studies. The origin of the abnormal temperature dependence is attributed to the two mechanisms of breakdown in the reverse-biased diodes. At low temperature the breakdown current is mainly due to avalanche resulting in low-energy electrons and holes that quenches the intensity by Auger deexcitation of the Er-ions. At higher temperature the breakdown current is mainly phonon-assisted tunneling which results in a more efficient pumping with less de-excitation of the Er-ions. Finally at the highest temperatures the thermal quenching sets in corresponding to an activation energy of 125 meV, which is slightly lower than 150 meV that has been reported in other studies.
INTRODUCTION After the observation of light emission at the wavelength of 1.54 µm from the rare earth element erbium inside Si by Ennen and coworkers [1, 2], the interest in incorporation of Er into silicon has been high. The investigation of the emission properties of the material has been stimulated by the prospects of integrating light-emitting silicon into the available silicon technology. This work could lead to a new era of Si-based optoelectronic technology if once the emission at 1.54 µm becomes reasonably efficient. In addition to the prospective of Si based light emitters for monolithic integration of optical and electronic devices, the 1.54 µm wavelength of the intra 4f–shell transition of the Er3+ ions in the Si host material itself is particularly interesting, since it falls in the minimum loss window of silica based fibres. For the realisation of useful optical devices the excitation of Er ions must take place electrically resulting in electroluminescence (EL) and an intense room temperature emission is needed. In general, for the light emitting devices that contain an Er-doped pn-junction the excitation of Er3+ ions is obtained either by forward bias, where electron-hole recombination at an Er related level is responsible for the excitation mechanism, or reverse bias, where hot car
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