Record Surface State Mobility and Quantum Hall Effect in Topological Insulator Thin Films via Interface Engineering

Abstract

Material defects remain as the main bottleneck to the progress of topological insulators (TIs). In particular, efforts to achieve thin TI samples with dominant surface transport have always led to increased defects and degraded mobilities, thus making it difficult to probe the quantum regime of the topological surface states. Here, by utilizing a novel buffer layer scheme composed of an In2Se3/(Bi0.5In0.5)2Se3 heterostructure, we introduce a quantum generation of Bi2Se3 films with an order of magnitude enhanced mobilities than before. This scheme has led to the first observation of the quantum Hall effect in Bi2Se3.

Solution to the Hole-Doping Problem and Tunable Quantum Hall Effect in Bi2Se3 Thin Films

“…When Bi2Se3 films are grown directly on commercial substrates, there exists a high density of defects confined to the interface between the film and the substrate. These interfacial defects lead to high level of n-type carriers with the surface Fermi level located far above the bottom of the conduction band minimum 2,8,32 . Our current study suggests that this interfacial defect density on the commercial substrate is higher than the solubility limit of the compensation dopant so that the film remains ntype up to the maximum counter-doping (Figure 1f).…”

“…Hole (p) doping has been challenging in Bi2Se3 [1][2][3] , one of the most widely studied topological insulators (TIs) [4][5][6][7][8][9][10] . Unlike conventional semiconductor materials, the problem is complicated due to the presence of both surface and bulk states in topological insulators: we have to consider the doping problem of the surface and the bulk states separately.…”

“…Unlike conventional semiconductor materials, the problem is complicated due to the presence of both surface and bulk states in topological insulators: we have to consider the doping problem of the surface and the bulk states separately. Both the surface and bulk states of Bi2Se3 have a strong tendency toward n-type due to its native n-type defects such as selenium vacancies [1][2][3][11][12][13][14][15][16][17] . In bulk crystals compensation dopants such as Ca and Mn can be used to convert the dominant carrier type from n-to p-type [18][19][20][21][22][23][24][25] .…”

Measurement of the topological surface state optical conductance in bulk-insulating Sn-doped Bi1.1Sb0.9Te2S single crystals

“…The older generation film had a large charge density with E F almost 350 meV above the Dirac point which is nearly in the bottom of the conduction band, but still had transport dominated by the TSS 7,23 . The second film is grown with a method that results in a true bulk insulator 23,24 , is more comparable to the present generation of BSTS crystals and has an E F approximately 50 meV above the Dirac point. The optical conductance of Bi 2 Se 3 thin films show smaller scattering rate than that of BSTS single crystals, which is consistent with the fact that the thin films have nominally perfect stoichiometry.…”

Stability of low-carrier-density topological-insulator Bi2Se3 thin films and effect of capping layers

“…The low-carrier-density Bi 2 Se 3 films used for this study were grown on (Bi 1−x In x ) 2 Se 3 buffer layers on sapphire substrate using a custom-designed molecular beam epitaxy (MBE) system by SVT Associates; details will be published elsewhere. 15 As for capping layers, 100 nm amorphous Se and 50 nm amorphous In 2 Se 3 were deposited in situ at room temperature, whereas ∼200 nm PMMA was spin-coated ex situ, followed by baking process at different temperatures. Both capped and uncapped films were measured for over 280 days.…”