p-typeBi2Se3for topological insulator and low-temperature thermoelectric applications

Abstract

The growth and elementary properties of p-type Bi 2 Se 3 single crystals are reported. Based on a hypothesis about the defect chemistry of Bi 2 Se 3 , the p-type behavior has been induced through low level substitutions (1% or less) of Ca for Bi. Scanning tunneling microscopy is employed to image the defects and establish their charge. Tunneling and angle resolved photoemission spectra show that the Fermi level has been lowered into the valence band by about 400 meV in Bi 1.98 Ca 0.02 Se 3 relative to the n-type material. p-type single crystals with ab plane Seebeck coefficients of +180 µV/K at room temperature are reported. These crystals show a giant anomalous peak in the Seebeck coefficient at low temperatures, reaching +120 µVK -1 at 7 K, giving them a high thermoelectric power factor at low temperatures. In addition to its interesting thermoelectric properties, p-type Bi 2 Se 3 is of substantial interest for studies of technologies and phenomena proposed for topological insulators.2

Transport properties of topological insulators: Band bending, bulk metal-to-insulator transition, and weak anti-localization

“…[14,[18][19][20][21][22][23][24][25][26][27][28][29]. On the other hand, in the bulk limit shown in (g) at t = 1000 nm, Δ(t) is zero over most of the range of N BD and n SD .…”

Trapping of three-dimensional electrons and transition to two-dimensional transport in the three-dimensional topological insulator Bi2Se3under high pressure

“…In this way they identified the TI surface layer contribution to conductance as a thickness-independent sheet electron density of 1.5×10 13 cm -2 and mobility of the order of 1000 cm 2 /Vs for the thicker samples. For a few QLs the TI electron mobility falls to about 300 cm 2 High-pressure techniques are useful tools in the investigation of semiconductors electronic structure, based on its ability to produce continuous and finely tuned changes in their electronic structure. In this paper we explore the possibility of isolating the 2D electron contribution to charge transport by applying hydrostatic pressure, based on the observed increase of Bi 2 Se 3 bandgap under pressure, which could result in a reduction of the 3D electron mobility or in 3D electrons being trapped by pressure-induced deep levels.…”

Two-dimensional surface charge transport in topological insulators

“…Therefore, in all materials studied to date, residual conduction from the bulk exists due to unintentional doping. One potential way forward was opened by Hor et al, 74 who demonstrated that Ca doping (≈ 1% substituting for Bi) brings the Fermi energy into the valence band, followed by the demonstration by Hsieh et al 54 that Ca doping can be used to tune the Fermi energy so that it lies in the gap. Checkelsky et al 75 performed transport experiments on Ca-doped samples noting an increase in the resistivity, but concluded that surface state conduction alone could not be responsible for the smallness of the resistivities observed at low temperature.…”