Excitons bound to neutral donors in InP

Four sharp lines in very pure InP vapor-phase epitaxial layers are identified by absorption and luminescence experiments to be due to excitons bound to a shallow neutral donor in the $1S_{\frac{1}{2}}$ ground state. The symmetries of the three lower exciton states are determined by Zeeman spectroscopy to be ${\Gamma }_8$ (ground state), ${\Gamma }_8$, and ${\Gamma }_7$ (excited states). A simple model is proposed in which the excited states consist of a nonrigid rotation of light and heavy holes around the donor. In this model the energy spacings between excited and ground states are well understood.