Broadening factors ofE1(LO)phonon-plasmon coupled modes of hexagonal InN investigated by infrared reflectance measurements

Abstract

The LO phonon-plasmon coupling of InN for the ${E}_{1}(\mathrm{LO})$ mode has been found; however, the decoupling for the ${A}_{1}(\mathrm{LO})$ mode has been reported in many issues. Several reports have discussed the electron- and phonon-scattering mechanisms, while there is no detailed investigation on the broadening factors of mode energies even for ${E}_{1}(\mathrm{LO})$ phonon-plasmon coupled scheme. In this issue, the studied InN layers grown by the molecular-beam epitaxy method have residual electron density obtained by Hall measurements in a range from $8\ifmmode\times\else\texttimes\fi{}{10}^{17}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1\ifmmode\times\else\texttimes\fi{}{10}^{19}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. The electron density measured by infrared reflectance measurements is almost constant with a temperature variation from $5\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The dependence of the observed broadening factors of the ${E}_{1}(\mathrm{LO})$ phonon-plasmon coupled modes on the electron density is found to show the characteristic properties of the level anticrossing, in particular, for the increase of these broadening factors around the level anticrossing region with the temperature increase from $5\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Compared to the recent report on the $\mathrm{LO}$ phonon-plasmon coupled modes for ${A}_{1}(\mathrm{LO})$, smaller broadening for ${E}_{1}(\mathrm{LO})$ is observed here.