Simple tuning of carrier type in topological insulator Bi2Se3 by Mn doping

Abstract

Bi2Te3 is a well-known thermoelectric material for room-temperature operations because it has a high Seebeck coefficient, and the charge carrier type is easily tunable. However, the carrier type of Bi2Se3 is not tunable, which is one of the weaknesses for the thermoelectric applications, in spite of its high Seebeck coefficient. Here, we report the tuning of charge carriers in Bi2Te3 from n type to p type by doping Mn into the Bi sites. The carrier type is n type up to the Mn doping level of 5% and changes to p type above 5% Mn doping. The temperature-dependent resistivity of Bi2−xMnxSe3 shows a metallic behavior for x < 0.05, while for x ≥ 0.05, it shows an upturn at low temperatures. This provides evidence that by Mn doping, the Fermi level is continuously tuned from the bulk conduction band to the bulk valence band. The Seebeck coefficient increases monotonically with increasing temperature, and the absolute values are same for both n- and p-type samples. This implies that Bi2Se3 is another candidate of high-temperature thermoelectric materials, like Bi2Te3, simply by Mn doping.

X-ray magnetic spectroscopy of MBE-grown Mn-doped Bi2Se3 thin films

“…The sample reaches 80% of the saturation magnetization at an applied field of 0.2 T. It then exhibits more paramagnetic-like behavior, not reaching full saturation until 4 T, consistent with previous studies. 25 A similar effect has been seen in other dilute magnetically doped TIs and is attributed to the continuous reorientation of domains in the field. 16 The sample is found to have a saturation magnetization of (5.1 ± 0.5) µ B /Mn.…”

“…Films were deposited at a constant substrate temperature of 200 • C, then cooled under a residual Se background to room temperature (25 • C) for the deposition of an amorphous Se capping layer to protect the surface against oxidation. The low growth temperature and residual background whilst cooling inhibit defect formation in the film.…”

Experimental study of the valence band ofBi2Se3

“…Note that an earlier paper from the Cava group (Ref. [9]) also showed thermopower smaller than the predictions of Ref.…”

“…While the other two plots have a subsidiary valence- With regards to calculated dispersions and band masses, in Table 2 we present Γ-Z-point valence band masses inferred from the calculations published in Refs. [9,19,20,24]. Note that for two of these calculations -the work of Zhang et al Ref.…”

“…The band structure features and strong spin-orbit interactions of Bi 2 Se 3 are favorable for the development of topologically protected surface states, which has been the basis behind recent efforts to make intrinsic and/or doped p-type Bi 2 Se 3 . Several new acceptor impurities have been discovered for Bi 2 Se 3 , including Ca, 8 Mn, 9 Mg, 10 and Pb (this work). Yet, it is suspected that the native defects of Bi 2 Se 3 still exist even in the presence of these chemical acceptors, and we do not know if the ptype material is compensated, or if the acceptor impurities alleviate the donor action of the native defects.…”