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

The temperature dependence of the resistivity of InN was investigated as a function of carrier density. The carrier density was changed from ne =1.8× 1018 cm-3 to 1.5× 1019 cm-3 by Si doping. The InN investigated showed metallic conduction above 20 K. At lower temperatures there was a resistivity anomaly originating from carrier localization in the a-b plane, which was confirmed by the magnetoresistance at 0.5 K. The Shubnikov-de Haas oscillation showed that InN had a spherical Fermi surface and its radius increased according to the increase of ne when ne <5× 1018 cm-3. In addition, an oscillation corresponding to the constant carrier density of 4.5× 1012 cm-2 was observed in the field applied perpendicular to the a-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× 1017 cm-3. Anisotropy of localization was observed within the a-b plane, which indicates that the distribution of the electrons was not uniform in the a-b plane. The ne dependence of the magnetoresistance revealed an electronic structure change around 5× 1018 cm-3. From these results, an electronic structure at the fundamental absorption edge of InN grown on sapphire (0001) was presented.