Unintentionally degenerately doped $n$-type hexagonal wurtzite InN samples were studied by using Fourier-transform photoluminescence spectroscopy and reflectivity measurements. We found in luminescence overlapping band acceptor $\left(e,A^0\right)$ transitions related to two different acceptors with a strong enhancement of their intensities close to the Fermi energy of the electrons recombining with the localized holes. Our explanation is in terms of a Fermi-edge singularity of the electrons due to strongly increased electron-hole scattering. Electron-hole pairs with such resonantly enhanced oscillator strengths have been referred to as Mahan excitons. Temperature-dependent reflectivity measurements confirm this interpretation.

• Received 11 February 2008

DOI:https://doi.org/10.1103/PhysRevB.77.245207