Anomalous electrical transport in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>SnSe</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:math> nanosheets: Role of thickness and surface defect states

This work examines the influence of thickness on the electrical transport properties of mechanically exfoliated two-dimensional ${\mathrm{SnSe}}_{2}$ nanosheets, derived from the bulk single crystal. Contrary to the conventional trend observed in two-dimensional systems, we find a semiconducting to metallic resistivity behavior with decreasing thickness. The analysis of low-temperature conduction indicates an increased density of states at the Fermi level with decreasing thickness, which is further corroborated by gate bias-dependent conductance measurement. The enhanced conductivity in thinner flake is attributed to the $n$-type doping arising from surface defect states. The presence and evolution of these defect states with thickness are probed by thickness-dependent room-temperature Raman spectroscopy. Our study provides insights into the thickness-dependent electronic transport mechanism of ${\mathrm{SnSe}}_{2}$ and the crucial role of defect states in governing the observed conductivity behavior.