Fig. 2: Height-dependent electronic properties of BP flakes at room temperature.

a Representative four-point field-effect characteristic of a BP flake showing unipolar p-type behaviour and weak on/off switch. The hole mobility was extracted from the linear part of the subthreshold slope (denoted in the graph by a dashed grey line). b Charge carrier mobility values are estimated based on the field-effect characterisation. The mobility values do not show a height-dependent trend and show a few variations around 200 cm²/Vs, which fall within the range of the weakly developed in-plane anisotropy in charge transport at room temperature¹¹. c Electrical conductivity and d charge carrier density show a steep increase for flakes with a height below ca. 20 nm (dashed lines as a guide to the eye), whereas, in thicker flakes, the values remain approximately constant. Inset d Linear dependence between conductivity and carrier density implies a height-independent average charge carrier mobility of ca. 215 cm²/Vs. Error bars result from data acquisition and error propagation in data evaluation.