Evaluation of metal-Bi2Te3 contacts by electron tunneling spectroscopy

Understanding the states of the metal electrode-semiconductor junctions is important for improving the performance of the thermoelectric devices. Tunneling spectroscopy has been applied to the evaluation of metal-semiconductor Schottky junctions. In this study, tunneling spectroscopy is applied to understanding the states of a metal/Bi/sub 2/Te/sub 3/ or a metal/Bi/sub 2/Se/sub 3/ junction. Bi/sub 2/Te/sub 3/ and Bi/sub 2/Se/sub 3/ single crystals were prepared by Bridgman method. The metal contacts were made on the cleavage surface of Bi/sub 2/Te/sub 3/ or Bi/sub 2/Se/sub 3/ by the thermal evaporation in the vacuum of 10/sup -3/ Pa. All tunnel conductance were measured at 4.2 K. Mg/, Al/ and Ag/Bi/sub 2/Te/sub 3/ junctions exhibit V-shaped tunnel conductance curves which indicate that these contacts ate the Schottky barrier. A Au/Bi/sub 2/Te/sub 3/ junction shows a flat conductance characteristic, so that we expect to be an ohmic contact formed in this junction. It becomes clear that the Schottky barrier is formed on the Mg/, Al/, or Ag/-Bi/sub 2/Te/sub 3/ junction. In the case of Au/ or Al/Bi/sub 2/Se/sub 3/ is also formed the Schottky barrier. Since Bi/sub 2/Te/sub 3/ and Bi/sub 2/Se/sub 3/, which are narrow energy gap semiconductors, form the Schottky barriers with those metals, the characterization of metal-semiconductor contacts is important to improve the performance of thermoelectric devices.