Topological insulator (TI) materials such as Bi 2 Te 3 and Bi 2 Se 3 have attracted strong recent interests. Large scale, high quality TI thin films are important for developing TI-based device applications. In this work, structural and electronic properties of Bi 2 Te 3 thin films deposited by metal organic chemical vapor deposition (MOCVD) on GaAs (001) substrates were characterized via X-ray diffraction (XRD), Raman spectroscopy, angle-resolved photoemission spectroscopy (ARPES), and electronic transport measurements. The characteristic topological surface states (SS) with a single Dirac cone have been clearly revealed in the electronic band structure measured by ARPES, confirming the TI nature of the MOCVD Bi 2 Te 3 films. Resistivityand Hall effect measurements have demonstrated relatively high bulk carrier mobility of ~350 cm 2 /Vs at 300K and ~7,400 cm 2 /Vs at 15 K. We have also measured the Seebeck coefficient of the films. Our demonstration of high quality topological insulator films grown by a simple and scalable method is of interests for both fundamental research and practical applications of thermoelectric and TI materials.

Femtosecond laser pulses are used to excite coherent optical phonons in single crystal Bi 2 Te 3 thin films. Oscillations from low-and high-frequency A 1g phonon modes are observed. A perturbation model based on molecular dynamics reveals various possibilities of phonon generation due to complex interactions among different phonon modes. In order to elucidate the process of phonon generation, measurements on thin films with thicknesses below the optical absorption depth are carried out, showing that a gradient force is necessary to excite the observed A 1g phonon modes, which provides a refined picture of displacive excitation of coherent phonon.

To obtain reduced specific contact resistivity, iodine donors and silver acceptors were ion-implanted into n-type and p-type (Bi,Sb)2(Se,Te)3 materials, respectively, to achieve >10 times higher doping at the surface. Implantation into n-type materials caused the specific contact resistivity to decrease from 1.7 × 10−6 Ω cm2 to 4.5 × 10−7 Ω cm2. Implantation into p-type materials caused specific contact resistivity to decrease from 7.7 × 10−7 Ω cm2 to 2.7 × 10−7 Ω cm2. For implanted thin-film superlattices, the non-implanted values of 1.4 × 10−7 Ω cm2 and 5.3 × 10−8 Ω cm2 precipitously dropped below the detection limit after implantation, ≤10−8 Ω cm2. These reductions in specific contact resistivity are consistent with an increase in tunneling across the contact.