Two-Dimensional Square-A(2)B (A = Cu, Ag, Au, and B = S, Se) : Auxetic Semiconductors with High Carrier Mobilities and Unusually Low Lattice Thermal Conductivities

• Using evolutionary structure search combined with ab initio theory, we investigate the electronic, thermal, and mechanical properties of two-dimensional (2D) A(2)B (A = Cu, Ag, Au, and B = S, Se) auxetic semiconductors. Two types of structures are found to have low energy, namely, s(I/II)-A(2)B, which have direct bandgaps in the range 1.09-2.60 eV and high electron mobilities. Among these semiconductors, Cu2B and Ag2B have light holes with 2 orders of magnitude larger mobility than the heavy holes, up to 9.51 X 10(4)cm(2) v(-1) s(-1) , giving the possibility of achieving highly anisotropic hole transport with the application of a uniaxial strain. Due to the ionic bonding nature, s-A(2)B structures have unusually low lattice thermal conductivities down to 1.5 W m(-1) K-1 at 300 K, which are quite promising for new generation thermoelectric devices. Besides, s-A(2)B structures show extraordinary flexibility with ultralow Young's moduli (down to 20 N/m), which are lower than most previously reported 2D materials. Moreover, under strain along the diagonal direction, five of the structures have in-plane negative Poisson's ratios.

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NATURVETENSKAP  -- Fysik -- Den kondenserade materiens fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Condensed Matter Physics (hsv//eng)

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