Investigation of electronic structure and electron conduction mechanism of InN

研究了InN电阻率随载流子密度的温度依赖性。Si掺杂使载流子密度由n_e=1.8x10^<18>cm^<-3>变为1.5x10^<19>cm^<-3>。所研究的InN在20k以上显示出金属导电。在较低温度下，a-b平面上的载流子局部化导致了电阻率异常，0.5 K时的磁电阻证实了这一点。Shubnikov - de-Haas振荡表明，当n_e<5 × 10^<18>cm^<-3>时，其半径随ne的增大而增大。此外，在垂直于a-b平面的电场中观测到载流子密度为4.5x10^<12>cm^<-2>的振荡。这种振荡表现出对磁场的反常角度依赖。考虑到这个密度，我们确定Mott跃迁的临界载流子密度为2x10^<17>cm^<-3>。在a-b平面内观察到局域化的各向异性，这表明电子在a-b平面内的分布并不均匀。根据这些结果，给出了在蓝宝石（0001）上生长的InN的基本吸收边的电子结构。另一方面，当载流子密度n_e低至4x10^<17>cm^<-3>时，样品表现出超导性，T_c= 0.47 K（中点）。与层状高Tc铜超导体一样，InN涡旋固体在热波动和外加磁场作用下熔化。临界电流J_c的场依赖性在较宽的磁场范围内呈指数衰减，这是由于电流在微约瑟夫森结中隧穿所致。我们提出了J_c的各向异性与ab平面上有限长度的in - in链的存在有关的机制。

Temperature dependence of the resistivity of InN was investigated as a function of carrier density. The carrier density was changed from n_e=1.8x10^<18>cm^<-3> to 1.5x10^<19>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 n_e<5x10^<18>cm^<-3>. In addition an oscillation corresponding to the constant carrier density of 4.5x10^<12>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 2x10^<17>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. From these results, an electronic structure at the fundamental absorption edge of InN grown on sapphire (0001) was presented.On the other hand, samples with carrier densities n_e as low as 4x10^<17>cm^<-3> show superconductivity with T_c= 0.47 K (midpoint). As in the layered cuprate high Tc superconductors, the vortex solid of InN is melted by thermal fluctuation and by the external magnetic field. The field dependence of the critical current J_c exhibits an exponential decay over a wide range of magnetic field, which is ascribed to the current tunneling through micro Josephson-junctions. We propose a mechanism where the anisotropy of J_c is related to the presence of In-In chains of finite length in the ab plane.