The effect of erbium-doping on the electrical, optical, and structural properties of hydrogenated amorphous silicon (a-Si:H) is investigated. The electrical conductivity and thermopower measurements show that erbium acts as an n-type dopant in a-Si:H. The photoluminescence measurements show that an optical activity of Er decreases as the Er concentration increases beyond 0.04 at. %. Raman and optical absorption measurements show that erbium induces structural disorder and subsequent increase in the bandtail states of a-Si:H. From the temperature dependence of Er3+ photoluminescence intensities, we identify competitive carrier capture by these band-tail states as all important factor in determining the overall Er3+ photoluminescence intensity. And carbon co-doping enhances the Er3+ PL intensity and reduces the temperature quenching of the Er3+ PL intensity.