Atomically thin materials can be used to build novel forms of conventional semiconductor heterostructure devices. One such device is a resonant tunnelling diode, which can exhibit negative differential resistance and usually consists of a quantum-well structure between two barrier layers. Here, we show that a twisted black phosphorus homostructure can be used to create a resonant tunnelling diode. The devices have a trilayer structure in which a thin non-degenerate black phosphorus layer is sandwiched between two thicker degenerate black phosphorus layers. The interlayer coupling strength depends sensitively on the twist angle between the layers, and thus the twist angle can be used to control the vertical transport behaviour, from ohmic to tunnelling. Because resonant tunnelling through quantum-well states occurs without the need for a physical tunnelling barrier, our devices exhibit a higher tunnelling conductance and negative differential resistance peak-to-valley current ratio than resonant tunnelling diodes based on van der Waals heterostructures.
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