Current Crowding in a High-Efficiency Black Phosphorus Light-Emitting Diode Using a Reflective Back Contact
Abstract
We demonstrate a high-performance mid-infrared (MIR) light-emitting diode (LED) based on a black phosphorus (b-P)/n-MoS2 heterojunction. A gold back contact combined with a rhenium-doped n-type MoS2 layer is used to enhance light extraction. The device shows a MIR peak external quantum efficiency (EQE) of (1.6 0.2) % at room temperature and a record (7.0 0.5) % EQE at 77 K, with a maximum radiant power density of (108 8) W/cm2. Finite-element simulations highlight the importance of phonon-assisted band-to-band tunneling under reverse bias and the influence of carrier velocity saturation under forward bias. The simulations also reveal that the high ideality factors extracted from the current-voltage characteristic are due to current crowding at the heterojunction and a consequence of the device geometry. These findings establish a new high-performance b-P LED architecture and provide crucial insights into the physics of MIR sources based on 2D materials.
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