Electrically Injected GHz-Class GaN/InGaN Core–Shell Nanowire-Based μLEDs: Carrier Dynamics and Nanoscale Homogeneity

Abstract

We present the first demonstration of RF characteristics of electrically injected GaN/InGaN core−shell nanowire-based micro light-emitting diodes (μLEDs) for μLED displays and visible-light communication. A record −3 dB modulation bandwidth ∼1.2 GHz at 1 kA/cm 2 (higher than any LED grown on c-plane GaN), and a lowleakage current−voltage characteristic with excellent rectifying behavior are achieved. Analysis using a small-signal equivalent electrical circuit for the μLEDs indicates a significantly longer differential recombination lifetime (∼330 ps) compared to the measured RC time constant (∼30 ps) at 1 kA/cm 2 , confirming negligible effects from RC parasitic delay on the modulation speed. The bandwidth versus current density (J) characteristic shows a different trend compared to planar c-plane and m-plane reference μLEDs, even though the nanowires are composed of both polar cplane and nonpolar m-plane sidewalls. The anomalous behavior of the bandwidth versus J characteristic is explained by nonuniform carrier injection, coupled with nonuniform quantum well thickness and indium composition, across the nanowire. The interpretation of the RF behavior of the nanowire-based μLEDs is supported by scanning transmission electron microscopy images, a significant blue shift (∼55 nm) of the electroluminescence spectra with applied bias, and nonuniform injection revealed by COMSOL simulations.

Role of Underlayer for Efficient Core–Shell InGaN QWs Grown on m-plane GaN Wire Sidewalls

“…14 Such core-shell wires can also be used to develop flexible devices (LEDs and photodetectors) 15,16,17,18 and GHzrange µ-LEDs for VLC applications due to the reduced carrier lifetimes of m-plane non-polar InGaN QWs. 19 However, despite the expected QCSE mitigation and dislocation-free crystal quality, the internal quantum efficiency (IQE) measured by temperature-dependence photoluminescence is generally found in the range of 5-20% for m-plane core-shell InGaN multiple quantum wells (MQWs) emitting blue light. 20,14 These efficiencies still remain low in comparison of standard planar LEDs.…”

“…23 A further optimized core-shell LED structure including AlGaN UL and electron blocking barrier (EBL) exhibiting an IQE as high as 62% have been reported by the group of Feezell with the demonstration wire-LED having an EQE equal to 8.3%. 19,24 Also, the group of Waag and the company Osram report coreshell wire-LED with high IQE (about 60%) and high EQE (maximum of 10% at current density of 40 A/cm 2 . 25 Therefore, achieving high efficiency with wire-based LED remains a significant challenge till date to be able to compete against the present planar technology.…”

Controlling Defect Formation of Nanoscale AlN: Toward Efficient Current Conduction of Ultrawide‐Bandgap Semiconductors

“…Ultrawide‐bandgap semiconductors, including AlN, BN, and diamond, are critical for applications in next‐generation high‐power, high‐frequency electronics, ultraviolet (UV) optoelectronics, high‐power photonics, and quantum devices and systems. [ 1–10 ] Progress in these fields, however, has been severely limited by the lack of scalable substrate, the presence of large densities of defects, and the extremely poor current conduction. [ 3,11,12 ] Moreover, it has remained challenging to achieve a precise control of impurity incorporation and defect formation in these ultrawide‐bandgap semiconductors, severely limiting their structural, electronic, optical, and quantum properties.…”

Effect of Different Bonding Materials on Flip-Chip LED Filament Properties

“…As a new generation of light source, the light-emitting diode (LED) has many advantages, such as energy saving, environmental protection, and no radiation emission [1][2][3]. With the growing demand of LEDs, the white LED has been industrialized [4,5].…”