Electron density dependence of the electronic structure of InN epitaxial layers grown on sapphire (0001)

Abstract

The temperature dependence of the resistivity of InN was investigated as a function of carrier density. The carrier density was changed from ${n}_{e}=1.8\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1.5\ifmmode\times\else\texttimes\fi{}{10}^{19}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ by Si doping. The InN investigated showed metallic conduction above $20\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. At lower temperatures there was a resistivity anomaly originating from carrier localization in the $a\text{\ensuremath{-}}b$ plane, which was confirmed by the magnetoresistance at $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The Shubnikov--de Haas oscillation showed that InN had a spherical Fermi surface and its radius increased according to the increase of ${n}_{e}$ when ${n}_{e}<5\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. In addition, an oscillation corresponding to the constant carrier density of $4.5\ifmmode\times\else\texttimes\fi{}{10}^{12}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ was observed in the field applied perpendicular to the $a\text{\ensuremath{-}}b$ plane. This oscillation showed an anomalous angle dependence on the magnetic field. Taking into account this density, we determined the critical carrier density of the Mott transition to be $2\ifmmode\times\else\texttimes\fi{}{10}^{17}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. Anisotropy of localization was observed within the $a\text{\ensuremath{-}}b$ plane, which indicates that the distribution of the electrons was not uniform in the $a\text{\ensuremath{-}}b$ plane. The ${n}_{e}$ dependence of the magnetoresistance revealed an electronic structure change around $5\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. From these results, an electronic structure at the fundamental absorption edge of InN grown on sapphire (0001) was presented.