Observation of a Bound Exciton Transition in Ion-Beam Synthesized $\beta $-FeSi$_{2}$

Photoreflectance studies of $\beta $-FeSi$_{2}$ have revealed the presences of strong (direct) optical transitions together with several interesting lower-energy spectral features, including indirect gap excitonic transitions. In this presentation, we focus on one of these features made observable at low temperatures and located a few meV below the first direct gap. We attribute the origin of this feature to a transition that takes place on a bound exciton-ionized acceptor complex. Our observations of this transition together with results of our previous photoreflectance analysis lead us to identify it as the fundamental mechanism for the 1.5 $\mu $m light emission in $\beta $-FeSi$_{2}$. This result provides deeper insight into the light emission properties of $\beta $-FeSi$_{2}$.