Current Crowding in a High-Efficiency Black Phosphorus Light-Emitting Diode Using a Reflective Back Contact

TL;DR

This paper reports a high-efficiency black phosphorus-based mid-infrared LED with a reflective back contact, achieving record external quantum efficiency and providing insights into the device physics and current crowding effects.

Contribution

The study introduces a novel high-performance black phosphorus LED architecture with a reflective back contact, enhancing light extraction and revealing the physics of current crowding in 2D material-based MIR sources.

Findings

Achieved record 7.0% EQE at 77 K for black phosphorus LED.

Finite-element simulations highlight phonon-assisted tunneling and carrier velocity saturation effects.

Current crowding at the heterojunction explains high ideality factors.

Abstract

We demonstrate a high-performance mid-infrared (MIR) light-emitting diode (LED) based on a black phosphorus (b-P)/n-MoS$_2$ heterojunction. A gold back contact combined with a rhenium-doped n-type MoS$_2$ layer is used to enhance light extraction. The device shows a MIR peak external quantum efficiency (EQE) of (1.6 $\pm$ 0.2) % at room temperature and a record (7.0 $\pm$ 0.5) % EQE at 77 K, with a maximum radiant power density of (108 $\pm$ 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.