Reliable passivation of black phosphorus by thin hybrid coating

Black phosphorus (BP) possesses several extraordinary physical properties, which include in-plane anisotropy, thickness dependent direct bandgap and high carrier mobility. These physical properties make BP highly desirable from the point of view of fundamental science and modern optoelectronics applications. The excitement about this material has always been accompanied by unreserved skepticism due to its extraordinary degradation under ambient conditions. Here we show ambient degradation of exfoliated BP can be effectively suppressed using thin layer of hybrid metal organic chemical vapor deposition coating of boron nitride (BN) followed by atomic layer deposition coating of Al₂O₃. We have extensively studied the time dependent surface, optical and electrical properties of BP encapsulated by BN and/or Al₂O₃ using nanoscale infrared imaging and I-V characterizations. Our results show hybrid thin layer (∼5 nm) BN/Al₂O₃ coated BP exfoliated on SiO₂ substrate is protected from degradation in ambient for over 6 months, much longer than those coated only by BN or Al₂O₃ layers. Our theoretical modeling of the experimental degradation growth pattern shows that the influence of neighboring elements on the degradation of a given element is minimal for BP flakes with hybrid coating. Electrical characterization further confirms the effectiveness of BN/Al₂O₃ as encapsulation layer and gate dielectrics with minor changes after several weeks.