Multivalley electron conduction at the indirect-direct crossover point in highly tensile-strained germanium

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Clavel, M. B.
Murphy-Armando, Felipe
Xie, Y.
Henry, K. T.
Kuhn, M.
Bodnar, R. J.
Khodaparast, G. A.
Smirnov, D.
Heremans, J. J.
Hudait, M. K.
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As forward-looking electron devices increasingly adopt high-mobility low-band-gap materials, such as germanium (Ge), questions remain regarding the feasibility of strain engineering in low-band-gap systems. Particularly, the Ge L-Γ valley separation (∼150 meV) can be overcome by introducing a high degree of tensile strain (ε ≥ 1.5%). It is therefore essential to understand the nature of highly strained Ge transport, wherein multivalley electron conduction becomes a possibility. Here, we report on the competitiveness between L- and Γ-valley transport in highly tensile-strained (ε ∼ 1.6%) Ge/In0.24Ga0.76 Asheterostructures. Temperature-dependent magnetotransport analysis reveals two contributing carrier populations, identified as lower- and higher-mobility L- and Γ-valley electrons (in Ge), using temperature-dependent Boltzmann transport modeling. Coupling this interpretation with electron-cyclotron-resonance studies, the effective mass (m*) of the higher-mobility Γ-valley electrons is probed, revealing m* = (0.049 ± 0.007)me. Moreover, a comparison of empirical and theoretical m* indicates that these electrons reside primarily in the first-two quantum sublevels of the Ge Γ valley. Consequently, our results provide an insight into the strain-dependent carrier dynamics of Ge, offering alternative pathways toward efficacious strain engineering.
Straintronics , Transport phenomena , Elemental semiconductors , Narrow band , Gap systems , Boltzmann theory , Cyclotron resonance , Density functional theory development
Clavel, M. B., Murphy-Armando, F., Xie, Y., Henry, K. T., Kuhn, M., Bodnar, R. J., Khodaparast, G. A., Smirnov, D., Heremans, J. J. and Hudait, M. K. (2022) 'Multivalley electron conduction at the indirect-direct crossover point in highly tensile-strained germanium', Physical Review Applied, 18(6), 064083 (13pp). doi: 10.1103/PhysRevApplied.18.064083
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