Figure 3. BP thickness dependences of Al-contacted devices.

(a) Optical image of the BP flake (before processing) used for testing layer dependences of transport properties with Al contacts. Yellow shaded region shows locations of electrodes (Supplementary Fig. 3). Scale bar, 3 μm. (b) R_s (open points) and μ_FE (solid lines) from 4-terminal measurements at 300 K. (c) μ_FE at 300 K and V_bg=50 V fit to Matthiessen's rule. From fitting, μ_Bulk=2.6 × 10³ cm² V⁻¹ s⁻¹ and estimated monolayer surface scattering is limited to 94 cm² V⁻¹ s⁻¹. (d) R_s (open points) and μ_FE (solid lines) from 4-terminal measurements at 80 K. The n-type to ambipolar conversion is observed as the flake thickness increases. Mobility increases with increasing thickness, with n- and p-type μ_FE∼9.5 × 10² cm² V⁻¹ s⁻¹ at 80 K for 13 nm thick region (V_1,2 in a).