Metamorphic InAs1-xSbx/InAs1-ySby superlattices with ultra-low bandgap as a Dirac material.

Metamorphic InAs1-xSbx/InAs1-ySby superlattices with ultra-low bandgap as a Dirac material.

Hard Condensed Matter Seminar


August 24, 2017 - 3:00pm to 4:00pm






Stony Brook University

Recently proposed short period metamorphic InSbxAs1-x/InSbyAs1-y superlattices (SLs) [1, 2] manifest a new class of quasi 3D materials with ultra-low bandgap. Application of the virtual substrate approach relieves strong limitations dictated by the substrate lattice constant and makes it possible to grow materials with high crystalline quality in the entire range of the alloy compositions.

We present experimental and theoretical analysis of the carrier energy spectrum and band structure parameters of short period metamorphic InSbxAs1-x/InSbyAs1-y SLs with different periods and layer thicknesses. We demonstrate that the SL bandgap measured with the interband magneto-absorption technique can be varied in the range from 120 to 0meV by changing the SL period. The spectral position of the photoluminescence line correlates with the bandgap energy Eg. Cyclotron resonance peak energy in SLs with the E_g≈0 shows square root dependence on the magnetic field in the range from 0 to 16T. This manifests a linear character of the electron dispersion, so the SLs belong to a new class of Dirac semimetals. The calculated energy spectrum in the SL with a zero bandgap is linear in a wide energy range. The Dirac velocity is determined by the material parameters of SL layers and SL design. We present a picture of the modification of the energy spectrum caused by variation of the layer thicknesses in short period SLs. The impacts of dimensional quantization, tunneling and band interaction on the SL band structure as well as vertical hole transport in metamorphic InSbxAs1-x/InSbyAs1-y superlattices will be discussed.

A number of spectacular physical phenomena predicted in Dirac semimetals stimulated an active search of materials with the linear carrier dispersion. It was shown that Hg1-xCdxTe alloy with x=0.17 behaves as a Dirac semimetal with 3D conical bands [3]. The important advantages of metamorphic InSbxAs1-x/InSbyAs1-y superlattices are high design flexibility and the opportunity to control the carrier spectrum by varying the SL period rather than the material composition. The new materials can be easily integrated into more complex semiconductor structures and devices such as p-n junctions, semiconductor-semimetal heterostructures, etc. This opens a new prospect for both fundamental research and applications in areas including nonlinear optics and quantum computing.

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