Origin of the anomalous temperature evolution of photoluminescence peak energy in degenerate InN nanocolumns.

Photoluminescence (PL) behaviour in InN nanocolumns reveal decreasing, increasing and near invariant peak energies (E(PL)) as a function of temperature. Samples, having E(PL)~0.730 eV at 20 K, showed temperature invariance of E(PL). Samples possessing E(PL) on the lower and higher energy side of 0.730 eV demonstrate a normal redshift and anomalous blueshift, respectively, with increasing temperature. This temperature evolution can be effectively explained on the basis of a competition between a conventional red shift from lattice dilation, dominant for low carrier density sample, on one hand, and a blue shift of the electron and hole quasi Fermi-level separation, dominant for high carrier density samples, on the other.