Top gating of epitaxial (Bi1−xSbx)2Te3 topological insulator thin films

Abstract

The tunability of the chemical potential for a wide range encompassing the Dirac point is important for many future devices based on topological insulators. Here we report a method to fabricate highly efficient top gates on epitaxially grown (Bi1−xSbx)2Te3 topological insulator thin films without degrading the film quality. By combining an in situ deposited Al2O3 capping layer and a SiNx dielectric layer deposited at low temperature, we were able to protect the films from degradation during the fabrication processes. We demonstrate that by using this top gate, the carriers in the top surface can be efficiently tuned from n-to p-type. We also show that magnetotransport properties give evidence for decoupled transport through top and bottom surfaces for the entire range of gate voltage, which is only possible in truly bulk-insulating samples.Topological insulators (TIs) are a class of insulators possessing an energy gap in the bulk and helically spinpolarized gapless states on the surface. [1][2][3] In the last few years, great efforts and progress have been made to synthesize high-quality, bulk-insulating TI materials in various ways. [4][5][6][7][8][9][10][11][12][13] . As the materials issues being solved, the focus and interest of experimentalists start to shift to the realization of the theoretically proposed TI devices for applications ranging from spintronics to quantum computing. 1-3 For such devices, an efficient gate control to tune the Fermi level in a wide range is usually essential, and already many gating experiments have been done on TI materials by using different gating techniques. [12][13][14][15][16][17][18][19][20] Among the various gating techniques, top gating has an advantage to provide local control of the chemical potential, which is favorable in many applications. However, a damage-free method to fabricate efficient top gates on TIs has not yet been fully developed.To achieve efficient top-gate controls of TI materials, there are two main difficulties. One is to obtain bulkinsulating samples, because the unwanted bulk carriers bring the Fermi level far away from the Dirac point and screen the electric field. This difficulty is being solved by means of chemical doping, in both single crystals 4-10,12,13 and thin films. 11 The other difficulty is the degradations of the sample surface during the fabrication processes, especially during the deposition of the dielectric material. It has been shown that the usual methods to deposit dielectric materials such as atomic layer deposition (ALD) can cause heavy damage to the TI surface; 15 such a damage would lower the surface mobility and also introduce a large number of impurity states to pin the surface chemical potential, making its gate tuning to be difficult. 15 It is thus important to develop a method to fabricate top gates with minimal damage to the TI surface.In this Letter, we report our top-gating results on (Bi 1−x Sb x ) 2 Te 3 topological-insulator thin films grown by molecular beam epitaxy (MBE). Following Ref. 11, the composition of ...

Large linear magnetoresistance in the Dirac semimetal TlBiSSe

“…This is in contrast to the case of 2D Dirac systems like graphene [32] and 3D TIs [33], where µ t shows an enhancement only when the Fermi level is tuned very close to the Dirac point.…”

Large anomalous Hall effect in ferromagnetic insulator-topological insulator heterostructures

“…26 This model nicely fits the data [see fits plotted in Fig. 3(c)], and implies a high mobility, low density (HMLD) channel and a low mobility, high density (LMHD) channel of the same sign (n-type) in all samples.…”

“…14,25,26 The CGT bulk is insulating at low temperatures, so any conduction channels lie in the Bi 2 Te 3 bulk or at the CGT-BT interface. In the two-band model, the measured Hall resistance depends on the magnetic field as…”

In situspectroscopy of intrinsicBi2Te3topological insulator thin films and impact of extrinsic defects

“…For Bi 2 Te 3 films, though, a systematic study is needed in order to determine a suitable capping layer that can preserve the surface states and avoid unintentional doping induced by ambient conditions. An insulating layer would be appropriate since it will allow the fabrication of nearly damage-free top gate structures, so that the carriers in the top surface can be efficiently tuned [55] V. CONCLUSION In summary, we have systematically investigated the effect of in situ exposure to pure oxygen at atmospheric pressure and of ex situ contamination on high quality intrinsic Bi 2 Te 3 films grown sapphire and STO. The XPS studies show narrow and symmetric Te and Bi peaks highlighting the absence of Te or Bi excess in our films.…”