Energy position of near-band-edge emission spectra of InN epitaxial layers with different doping levels

Abstract

We studied the shape and energy position of near-band-edge photoluminescence spectra of InN epitaxial layers with different doping levels. We found that the experimental spectra of InN layers with moderate doping level can be nicely interpreted in the frames of the ``free-to-bound'' recombination model in degenerate semiconductors. For carrier concentrations above $n>5\ifmmode\times\else\texttimes\fi{}{10}^{18}{\mathrm{cm}}^{\ensuremath{-}3}$ the emission spectra can also be modeled satisfactorily, but a contribution due to a pushing up of nonequilibrium holes over the thermal delocalization level in the valence band tails should be considered in the model. The emission spectra of samples with low doping level were instead explained as a recombination from the bottom of the conduction band to a shallow acceptor assuming the same value of the acceptor binding energy estimated from the spectra of highly doped samples. Analyzing the shape and energy position of the free-electron recombination spectra we determined the carrier concentrations responsible for the emissions and found that the fundamental band gap energy of InN is ${E}_{g}=692\ifmmode\pm\else\textpm\fi{}2\mathrm{meV}$ for an effective mass at the conduction-band minimum ${m}_{n0}{=0.042m}_{0}.$