Effect of erbium fluoride doping on the photoluminescence of SiO$_x$ films

The photoluminescence of SiO$_x$ films deposited on $c$-Si wafers by the thermal evaporation of SiO in a vacuum and, for the first time, doped with ErF$_3$ by coevaporation is studied. It is shown that, like undoped SiO$_x$ films, the unannealed SiO$_x$ :ErF$_3$ films passivate the surface of the Si wafers and, thus, increase their edge photoluminescence intensity almost fivefold. A similar increase is observed after annealing of the doped films in air at 750$^\circ$C. Doping with ErF$_3$ suppresses the photoluminescence of Si nanoclusters, if the films have been subjected to high-temperature annealing (at 750$^\circ$C). In this case, the PL intensity of the band with a peak at $\sim$890 nm decreases as well. The $\sim$890 nm band is observed for the first time and, due to its features, is attributed to transitions in SiO$_x$ matrix defects. The experimentally observed effect of ErF$_3$ doping on SiO$_x$ film photoluminescence is interpreted. An intense photoluminescence signal from Er$^{3+}$ ions in the nearinfrared spectral region (the $^4I_{11/2}\to^4I_{15/2}$ и $^4I_{13/2}\to^4I_{15/2}$ transitions) is observed in the SiO$_x$ :ErF$_3$ films annealed in air at 750$^\circ$C. This finding shows that 1.54 $\mu$m luminescent emitters, which are currently in popular demand, can be produced by a simple low-cost method.