A two-colour heterojunction unipolar nanowire light-emitting diode by tunnel injection

TL;DR

This paper introduces a novel two-colour heterojunction nanowire LED that uses tunnel injection to produce ultraviolet, visible, or infrared light depending on voltage polarity, enabling dual-wavelength emission from a single device.

Contribution

It presents a new nanowire heterostructure device that allows selective two-colour electroluminescence controlled by voltage polarity, with a proposed tunnelling-based model explaining the emission mechanisms.

Findings

Ultraviolet and visible light emitted from GaN nanowire.

Infrared light emitted from silicon substrate.

Voltage polarity controls emission wavelength.

Abstract

We present a systematic study of the current-voltage characteristics and electroluminescence of gallium nitride (GaN) nanowire on silicon (Si) substrate heterostructures where both semiconductors are n-type. A novel feature of this device is that by reversing the polarity of the applied voltage the luminescence can be selectively obtained from either the nanowire or the substrate. For one polarity of the applied voltage, ultraviolet (and visible) light is generated in the GaN nanowire, while for the opposite polarity infrared light is emitted from the Si substrate. We propose a model, which explains the key features of the data, based on electron tunnelling from the valence band of one semiconductor into the conduction band of the other semiconductor. For example, for one polarity of the applied voltage, given a sufficient potential energy difference between the two semiconductors, electrons can tunnel from the valence band of GaN into the Si conduction band. This process results in the creation of holes in GaN, which can recombine with conduction band electrons generating GaN band-to-band luminescence. A similar process applies under the opposite polarity for Si light emission. This device structure affords an additional experimental handle to the study of electroluminescence in single nanowires and, furthermore, could be used as a novel approach to two-colour light-emitting devices.