Erbium doped hydrogenated amorphous silicon

Abstract

Ever since the demonstration by H. Ennen et al. that erbium-doped silicon shows luminescence near 1.54 ㎛ due to the intra-4f transition ($^4I_{13/2}$ → $^4I_{15/2}$) of $Er^{3+}$, erbium-doping of silicon has been the subject of intense research since it promises the possibility of establishing a silicon-based optoelectronic technology. In this thesis, we have investigated erbium-doping of hydrogenated amorphous silicon (a-Si:H), which is a promising alternative to crystalline silicon (c-Si) for erbium-doping. We have prepared erbium-doped a-Si:H thin films using electron cyclotron resonance plasma enhanced chemical vapor deposition of $SiH_4$ with concurrent sputtering of erbium, which enables to deposit device-quality films with good optical activity of erbium and with low structural disorder, avoiding excessive contamination. Erbium-doping introduces defect states, and that above a concentration of 0.27 at. %. induces strong structural disorder. And also, erbium-doping introduces non-radiative decay paths for carriers in a-Si:H, leading to decrease in both the $Er^{3+}$ and intrinsic a-Si:H luminescence intensity when the Er concentration is increased to more than 0.04 at. %. $Er^{3+}$ luminescence intensity shows a little temperature quenching, and its temperature dependence shows a different behavior from both the intrinsic a-Si:H and the defect luminescence. Considering all results, we argue that luminescent mechanisms relevant to erbum-doped c-Si should be considered in case of erbium-doped a-Si:H as well. And based on the analysis of the temperature dependence of the $Er^{3+}$ luminescence decay time, we identify interaction with the defect state near the mid-gap as the possible back-transfer channel.