  As the only non-carbon elemental layered allotrope, few-layer black
phosphorus or phosphorene has emerged as a novel two-dimensional (2D)
semiconductor with both high bulk mobility and a band gap. Here we report
fabrication and transport measurements of phosphorene-hexagonal BN (hBN)
heterostructures with one-dimensional (1D) edge contacts. These transistors are
stable in ambient conditions for >300 hours, and display ambipolar behavior, a
gate-dependent metal-insulator transition, and mobility up to 4000 $cm^2$/Vs.
At low temperatures, we observe gate-tunable Shubnikov de Haas (SdH)
magneto-oscillations and Zeeman splitting in magnetic field with an estimated
g-factor ~2. The cyclotron mass of few-layer phosphorene holes is determined to
increase from 0.25 to 0.31 $m_e$ as the Fermi level moves towards the valence
band edge. Our results underscore the potential of few-layer phosphorene (FLP)
as both a platform for novel 2D physics and an electronic material for
semiconductor applications.
