Both Er-doped Si-rich silicon nitride (Er:Si 3ð1þxÞ N 4 ) films and electroluminescence (EL) devices with structure of indium tin oxide/Er:Si 3ð1þxÞ N 4 /p-Si with varying Si and Er contents have been fabricated by reactive magnetron sputtering technique. We have investigated the effects of the excess Si content in a wide range (x from 0 to 2.1) on the Er 3þ 1.54 μm photoluminescence (PL), EL and the electrical transport of the Er:Si 3ð1þxÞ N 4 films. It is found that the Er 3þ 1.54 μm PL intensity of the Er:Si 3ð1þxÞ N 4 films and the EL power efficiency of the Er:Si 3ð1þxÞ N 4 devices exhibit strong dependences on x and are enhanced by one to two orders of magnitude around x ¼ 0:27 and x ¼ 0:53, respectively. The Er concentration also has a great influence on both Er 3þ 1.54 μm PL and EL of the Er:Si 3ð1þxÞ N 4 films. The optimum Er concentrations for PL and EL in the Er:Si 3ð1þxÞ N 4 films with x ¼ 0:53 are both $3 at.%.Keywords: Si-rich silicon nitride; luminescence; Er 3þ 1.54 μm emission; energy transfer; electrical transport.The exigent demand of monolithic integration of electronic and optical components on mass-produced Si chips for optical interconnection has motivated enormous efforts to searching for cost-effective and efficient light sources compatible with the existing Si technology. 1 Among these efforts, Si-rich SiO 2 or Er-doped Si-rich SiO 2 has been studied for visible or Er 3þ 1.54 μm electroluminescence (EL) as one possible selection. 2 À 5 However, the difficulty in carrier injection due to the large band offset between Si and SiO 2 limits the applications of (Er-doped) Si-rich SiO 2 in stable and efficient light-emitting devices. Recently, Si-rich silicon nitride (SRN) and Er-doped Si-rich silicon nitride (Er: SRN) have been proposed for the development of Si-based emitters as another possible selection. 6 À 16 Compared to Si-rich SiO 2 hosts, SRN hosts have several advantages such as large refractive index which enables integration of high quality photonic crystals resonant structures, 13 nanosecond luminescence lifetime and energy transfer which are able to achieve faster modulation, 6 , 8 and much lower electron/hole injection barriers at the Si/Er:SRN interfaces which can result in stable and low-voltage EL. 9 , 12 In this paper, the Si and Er contents in our sputtered Er: SRN films are varied in a wide range. We demonstrate that the Si and Er contents strongly affect the electrical transport and luminescent properties of the Er:SRN films. Meanwhile, we find out the optimum contents of Si and Er, which are significant to realize efficient light-emitting devices based on Er:SRN active layers.Er:SRN films with a thickness of about 150 nm were deposited onto p-type Si (100) substrates (8À12 Ωcm) by reactive radio frequency (RF) magnetron sputtering in Ar and N 2 mixed gas using a pure Si wafer clipped with an Er chip as the target. The Si and Er contents in the Er:SRN films were controlled by varying the N 2 :Ar ratio and the size of the Er chip, respectively. For convenience, we denote ...