  Two-dimensional (2D) materials, such as graphene and transition metal
dichalcogenides have attracted great attention because of the rich physics and
potential applications in next-generation nano-sized electronic devices.
Recently, atomically thin black phosphorus (BP) has become a new member of the
2D materials family with high theoretical mobility and tunable bandgap
structure. However, degradation of properties under atmospheric conditions and
high-density charge traps in BP have largely limited its mobility (~400 cm2/Vs
at room temperature) and thus restricted its future applications. Here, we
report the fabrication of stable BN-BP-BN heterostructures by encapsulating
atomically thin BP between hexagonal boron nitride (BN) layers to realize
ultraclean BN-BP interfaces which allow a record-high field-effect mobility
~1350 cm2/Vs at room temperature and on-off ratios over 10^5. At low
temperatures, the mobility reaches ~2700 cm2/Vs and quantum oscillations in BP
2D hole gas are observed at low magnetic fields. Importantly, the BN-BP-BN
heterostructure can effectively avoid the quality degradation of BP in ambient
condition.
