Defect-mediated Rashba engineering for optimizing electrical transport in thermoelectric BiTeI

Abstract

The Rashba effect plays a vital role in electronic structures and related functional properties. The strength of the Rashba effect can be measured by the Rashba parameter α R ; it is desirable to manipulate α R to control the functional properties. The current work illustrates how α R can be systematically tuned by doping, taking BiTeI as an example. A five-point-spin-texture method is proposed to efficiently screen doped BiTeI systems with the Rashba effect. Our results show that α R in doped BiTeI can be manipulated within the range of 0-4.05 eV Å by doping different elements. The dopants change α R by affecting both the spin-orbit coupling strength and band gap. Some dopants with low atomic masses give rise to unexpected and sizable α R , mainly due to the local strains. The calculated electrical transport properties reveal an optimal α R range of 2.75-3.55 eV Å for maximizing the thermoelectric power factors. α R thus serves as an effective indicator for high-throughput screening of proper dopants and subsequently reveals a few promising Rashba thermoelectrics. This work demonstrates the feasibility of defect-mediated Rashba engineering for optimizing the thermoelectric properties, as well as for manipulating other spin-related functional properties.

Molybdenum as a versatile dopant in SnTe: a promising material for thermoelectric application

“…The two parabolic branches with opposite spin aligned states occur as a consequence of specific atomic site asymmetries on either side of the Γ point just 0.09 eV above the Fermi level. 18,[38][39][40] We observe its effect on the fourth set of doubly degenerate band (of L CB ) which shows three valleys CV 2 at Γ point 0.02 eV above the Fermi level, CV 3 at Γ+δ′ in Γ→Z direction 0.04 eV above the Fermi level and CV 4 at Γ-δ′′ in Γ→M direction 0.06 eV above the Fermi level. Thus, Mo doping in SnTe provides a new approach for the generation of multiple bands for transport which lie in close vicinity of the Fermi level resulting in the increased 'S' values.…”

Vanadium: A Protean Dopant in SnTe for Augmenting Its Thermoelectric Performance

“…41 The decrease in the carrier mobility caused by the increase in band effective mass due to the resonant states is compensated by the increased number of valleys involved in the transport. 6,43 Such Rashba splitting is not previously observed in n-type resonant dopants like Bi or even in p-type dopants like In and Zn in SnTe, which shows a single maximum in the spin degenerate parabolic band in conduction and valence bands in n and p-type materials, respectively. 16,18,29,41 This feature is very unique to V-doped SnTe, which promotes more band edges to participate in the transport.…”

“…Such a defectmediated Rashba engineering is a consequence of a low-atomicmass V dopant, which induces local strain. 43 Although generation of multiple electronic valleys by band inversion was previously reported in Zn-doped Pb 0.6 Sn 0.4 Te, it was a p-type material with involvement of toxic lead as the major component. 44 The added advantage in the n-type Sn 15 VTe 16 is the proximity of these conduction band valleys and the resonance states to the Fermi level, which eliminates the requirement of an additional dopant to tune the Fermi level.…”

“…41,42 Such a phenomenon is extremely crucial in optimizing the thermoelectric properties as the power factor of the material is highly sensitive to the band structure due to the conflicting traits in electrical conductivity and Seebeck coefficient. 21,43 In pristine SnTe, the second set of eightfold degenerate conduction bands (L CB′ in Figure 1a) lies 0.369 eV above the first set of eightfold degenerate bands (L CB ). In V-doped SnTe, as the first set of conduction band splits off into the resonance level, the second set of eightfold degenerate bands undergo splitting as a consequence of the Rashba effect (Figure 2).…”

Defect Compensation Weakening Induced Mobility Enhancement in Thermoelectric BiTeI by Iodine Deficiency

“…Recently, ternary BiTeI has been reported as a promising TE material, [31–35] which possesses the Rashba‐type spin splitting band structures and strong internal electric fields that contribute to higher Seebeck coefficient and intrinsic low lattice thermal conductivity [34] . However, due to the similar atomic radius of Te 2− and I − (2.07 Å vs. 2.06 Å), [36] high concentration of antisite defects and exist in BiTeI, [37] just like in the case of Bi 2 Te 3 system, where high concentration of and antisite defects exist [38] .…”