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Register a new userOn the impact of strain on the electronic properties of InAs/GaSb quantum well systems
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Electron-hole hybridization in InAs/GaSb double quantum well structures leads to the formation of a mini band gap. We experimentally and theoretically studied the impact of strain on the transport properties of this material system. Thinned samples were mounted to piezo electric elements to exert strain along the [011] and [001] crystal directions. When the Fermi energy is tuned through the mini gap, a dramatic impact on the resistivity at the charge neutrality point is found which depends on the amount of applied external strain. In the electron and hole regimes, strain influences the Landau level structure. By analyzing the intrinsic strain from the epitaxial growth, the external strain from the piezo elements and combining our experimental results with numerical simulations of strained and unstrained quantum wells, we compellingly illustrate why the InAs/GaSb material system is regularly found to be semimetallic.
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We study the influence of epitaxial strain on the electronic properties of InAs/GaSb composite quantum wells (CQWs), host structures for quantum spin Hall insulators, by transport measurements and eight-band $mathbf{kcdot p}$ calculations. Using different substrates and buffer layer structures for crystal growth, we prepare two types of samples with vastly different strain conditions. CQWs with a nearly strain-free GaSb layer exhibit a resistance peak at the charge neutrality point that reflects the opening of a topological gap in the band-inverted regime. In contrast, for CQWs with 0.50% biaxial tensile strain in the GaSb layer, semimetallic behavior indicating a gap closure is found for the same degree of band inversion. Additionally, with the tensile strain, the boundary between the topological and nontopological regimes is located at a larger InAs thickness. Eight-band $mathbf{kcdot p}$ calculations reveal that tensile strain in GaSb not only shifts the phase boundary but also significantly modifies the band structure, which can result in the closure of an indirect gap and make the system semimetallic even in the topological regime. Our results thus provide a global picture of the topological-nontopological phase diagram as a function of layer thicknesses and strain.
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