Electroluminescence in amorphous silicon p-i-n junctions

Abstract

Abstract We present a detailed study of EL (electroluminescence) spectra and EL quantum efficiency (ηEL) for well-characterized a-Si p+-i-n+ junctions deposited on stainless-steel substrates. EL spectra were measured under forward bias and the PL (photoluminescence) characteristics of the i region were also probed using laser excitation. The PL spectra are much more strongly modulated by interference fringes, owing to reflection at the steel substrate, and are shifted to higher energies by ∼0·17 eV as compared to the EL spectra. There is good evidence that EL is generated near the p+ contact, at a distance ∼ 100 to 200 nm from the reflecting substrate. We propose that the relative shift in the EL spectra is also due to optical interference effects, which depend on this distance. We conclude that optically and electrically excited pairs have the same luminescence spectrum. Further evidence for this view is provided by the close similarity in the temperature dependence of ηEL and ηPL· ηEL is ∼ 0·03 times smaller than the PL efficiency in the i region at 100 K. Some factors controlling ηEL are discussed, including field quenching and a novel photoenhancement process. We conclude that ηEL depends on the fraction of injected electrons that are captured by holes in the i region at a finite distance from the p+ contact, where the PL efficiency is reasonably high.