(A) study on the $Er^{3+}$ excitation mechanism using Er-doped $Si/SiO_2$ superlattice

Abstract

The $Er^{3+}$ excitation mechanism was investigated using Er-doped $Si/SiO_2$ or $SiO_x/SiO_2$ superlattice (SL) structure. The Er-doped SL films were deposited by the two-target alternation UHV-ion beam sputtering method (IBSD). The carrier-Er interaction properties was determined using α-$Si/SiO_2$ SL films whose Er-doped $SiO_2$ layer thickness was controlled with sub-nm resolution. The dependence of $Er^{3+}$ photoluminescence intensity on the thickness of the Er-doped $SiO_2$ layer was well-described by carrier-Er interaction that decreases exponentially with a characteristic carrier-$Er^{3+}$ interaction distance to be 0.5±0.1 nm, indicating the likelyhood of an exchange interaction between carriers and $Er^{3+}$ ions. The effects of crystallinity on the $Er^{3+}$ excitation properties were investigated using Er-doped $SiO_x/SiO_2$ SL structure. The stoichiometries of $SiO_x$ layers of SL films were obtained by controlling oxygen partial pressure such that one SL film had $SiO_x$ layers with x=1.6 and the other with x=1.8. Deposited SL films were subsequently annealed at different temperatures up to 1100℃. The formations of well-ordered Si nanocrystals with size of 3-4 nm in film with x=1.6 and size of less than 2 nm in film with x=1.8 were observed after annealing at temperature of higher than 1050℃. The effective excitation cross sections for $Er^{3+}$ excitation were determined experimentally by measuring the rise traces of luminescence at 1.54 ㎛ as a function of excitation power. Based on the comparison both of the measured cross sections and Si contents between films, we conclude that the $Er^{3+}$ excitation is strongly related to the size of nc-Si and thus nc-Si with size of less than 2 nm are more important for achieving the efficient $Er^{3+}$ excitation than both α-Si clusters or nc-Si with size of larger than 2 nm.