2018 Volume 43 Issue 5 Pages 311-317
The optical and electronic transport properties of bismuth telluride (Bi2Te3) nanoplates were determined using infrared spectroscopy measurements combined with first-principles calculations. The Bi2Te3 nanoplates were prepared by solvothermal synthesis and consisted of single-crystalline particles of hexagonal shape, with edge lengths of approximately 1.2 μm and a thickness of less than 30 nm. To determine the optical and electronic transport properties, the nanoplates were aligned on a glass substrate by using a drop-casting method. We prepared two types of nanoplates: a non-annealed sample with high resistance (due to the presence of isolated nanoplates) and an annealed sample with relatively low resistance, due to its connected nanoplates. The bandgap of the nanoplates, evaluated using infrared spectroscopy, was not significantly affected by the connecting process. The direct and indirect bandgaps were estimated to be approximately 0.14 and 0.06 eV, respectively, and were different from the values previously reported for single-crystalline bulk materials. Although the exact reason for this difference is not clear, we suggest that the structure of the nanoplates might influence the electronic band structure. The electronic transport properties were estimated by infrared spectroscopy using the Drude model, with the effective mass determined from the band structure obtained from first-principles calculations based on density functional theory. The electronic transport properties of the non-annealed nanoplates were essentially the same as those of their annealed counterparts. Therefore, we conclude that the electronic transport properties of nanoplates can be estimated through a combined analysis of different samples, in which the nanoplates are tightly connected or isolated from each other.
