Robust Topological Interfaces and Charge Transfer in Epitaxial Bi₂Se₃/II–VI Semiconductor Superlattices

Abstract

Access to charge transport through Dirac surface states in topological insulators (TIs) can be challenging due to their intermixing with bulk states or nontopological two-dimensional electron gas (2DEG) quantum well states caused by bending of electronic bands near the surface. The band bending arises via charge transfer from surface adatoms or interfaces and, therefore, the choice of layers abutting topological surfaces is critical. Here we report molecular beam epitaxial growth of Bi2Se3/ZnxCd1–xSe superlattices that hold only one topological surface channel per TI layer. The topological nature of conducting channels is supported by π-Berry phase evident from observed Shubnikov de Haas quantum oscillations and by the associated two-dimensional (2D) weak antilocalization quantum interference correction to magnetoresistance. Both density functional theory (DFT) calculations and transport measurements suggest that a single topological Dirac cone per TI layer can be realized by asymmetric interfaces: Se-terminated ZnxCd1–xSe interface with the TI remains “electronically intact”, while charge transfer occurs at the Zn-terminated interface. Our findings indicate that topological transport could be controlled by adjusting charge transfer from nontopological spacers in hybrid structures.

Topological Insulator Film Growth by Molecular Beam Epitaxy: A Review

“…MBE-grown films have a number of advantages over exfoliated films, including large area growth and the ability to controllably dope the materials, resulting in recent observations of the quantum anomalous Hall effect [22][23][24][25][26][27]. Unfortunately, both bulk crystals and thin films tend to exhibit significant conductivity from non-topological electrons, either from bulk states and/or from surface accumulation layers [28,29]. This is a particular problem for electrical measurements and applications, as the electrical signal from the non-topological electrons can overwhelm the signal from the surface states even in very thin films.…”

“…They reported that Zn0.49Cd0.51Se and Zn0.23Cd0.25Mg0.52Se layers had improved quality relative to ZnSe. Another work by the same group reported that in MBE grown Zn0.49Cd0.51Se/Bi2Se3 superlattices, a single topological Dirac cone per TI layer was realized [28]. Leveraging the wide In addition to band insulators, II-VI semiconductor layers have also been grown in combination with TI materials.…”

“…They reported that Zn 0. 49 [28]. Leveraging the wide range of band gaps and band alignments in II-VI materials lattice-matched to TIs opens the door to the creation of multifunctional devices.…”

Spinodal Superlattices of Topological Insulators

“…17,[19][20][21][22] The characteristics of the gapless boundary states are linear dispersion in the bulk band gap, spin-texture, robustness against scattering by nonmagnetic impurities, and symmetry protection. Studies have demonstrated that the formation of heterostructures, [23][24][25][26] alloying, 20,27 and thickness engineering 28 have advantages for controlling the electronic properties of TIs. In addition, recent studies show that it is possible to observe novel properties in TI superlattices, such as both time-reversal and crystal symmetry protected surface states, 29,30 band structure tuning through a topological phase transition, 31 topologically nontrivial surface states in a magnetic-TI/TI superlattice, 32 and the realization of 3D Weyl semimetal phases. 33 To fully exploit TIs in future devices, a detailed exploration of TI heterostructures/superlattices is needed.…”

Lattice-matched heterojunctions between topological and normal insulators: A first-principles study

“…While initial research efforts had mostly been devoted to the vacuum-facing TI surfaces [29][30][31][32][33][34][35] , increasing experimental [36][37][38][39] and theoretical attention [40][41][42][43][44] have recently been paid to the more realistic situation, the interfaces between TIs and normal insulators (NIs). It is motivated by the fact that interfaces are protected from the possible ambient contamination 45,46 and moreover these types of heterojunctions can be integrated into existing semiconductor technology, hence, they are more advantageous for utilizing the topological conducting boundary states.…”