External Quantum Efficiency of 6.5% at 300 nm Emission and 4.7% at 310 nm Emission on Bare Wafer of AlGaN-Based UVB LEDs

Abstract

As per the Minamata Convention on Mercury, regulation on mercury use will be stricter from the year of 2020, and safe AlGaNbased ultraviolet (UV) light sources are urgently needed for killing SARS-CoV-2 (corona virus). AlGaN-based ultraviolet-B (UVB) light-emitting diodes (LEDs) and UVB laser diodes (LDs) have the potential to replace toxic mercury UV lamps. Previously, the internal-quantum-efficiency (η int ) was enhanced from 47 to 54% in AlGaN UVB multiquantum wells (MQWs). However, some nonlinear behaviors in both light output power (L) and external quantum efficiency (η ext ) in the 310 nm band UVB LEDs were observed, and later on, such nonlinearities were overcome by reducing the thicknesses of quantum well barriers (T QWB ) in MQWs. After relaxing the n-AlGaN electron injection layer up to 50% underneath the MQWs and using a highly reflective Ni/Al p-electrode, L and η ext of the 310 nm band UVB LED were greatly improved from 12 mW and 2.3% to record values of 29 mW and 4.7%, respectively. Similarly, for the 294 nm band UVB LED, η ext and L values, respectively, were also remarkably improved up to 6.5% and 32 mW at room temperature under bare wafer conditions using a better carrier confinement scheme in the MQWs as well as using a moderately Mgdoped p-type multiquantum-barrier electron-blocking layer (p-MQB EBL). The moderately doped p-MQB EBL was used to achieve better hole transport to enhance the hole injection toward the MQWs as well as to block the high-energy electron from overshooting. Possible explanations and recommendations for the improvements in the performances of 294−310 nm UVB LEDs are broadly discussed. Most importantly, such controllable multi-UVB-wavelength emitters may extend nitride-based LEDs to previously inaccessible areas, for example, electrically pumped AlGaN-based UVB LDs.

Sec‐Eliminating the SARS‐CoV‐2 by AlGaN Based High Power Deep Ultraviolet Light Source

“…[ 43 ] It has been verified that the strain relaxation of n ‐AlGaN is crucial to the IQE of emission from quantum wells by modulating the density of dislocations, furthermore contributing to the performance of LED, for example, in UVA and UVB device. [ 44,45 ] For various kinds of AlGaN‐based LEDs with different Al compositions, a relatively low strain relaxation is preferred to achieve low TDDs. Herein, the low relaxation ratio of ≈4.2% promises a high quality of n ‐Al 0.64 Ga 0.36 N layer, which is the prerequisite to achieve the satisfied IQE as high as 60%.…”

Enhancing Efficiency of AlGaN Ultraviolet‐B Light‐Emitting Diodes with Graded p‐AlGaN Hole Injection Layer

“…The moderately doped p‐MQB EBL was used to achieve better hole transport to enhance the hole injection toward the MQWs as well as prevent the high‐energy electron from overshooting. [ 16 ] The influence of excimer laser annealing (ELA) on the activation of Mg dopants and on the suppression of unwanted impurities such as H, C, and O as well as on the annihilation of the localized energy state in the p‐ALGaN hole source layer (HSL) was reported. After ELA treatment, the GaN bonding ratio is reduced and GaO, as well as GaGa bonding ratios in the p‐AlGaN HSL, are increased.…”

Sheet Charge Engineering Towards an Efficient Hole Injection in 290 nm Deep Ultraviolet Light-Emitting Diodes

“…The theory has been proved to be effective in both blue and DUV LEDs with graded p-type AlGaN layer [19]- [23]. In addition, some researchers found that by taking advantage of the tunneling process, the conventional thermionic emission process limited by the potential barrier can be bypassed and thus the hole injection efficiency can be boosted effectively [12], [24], [25]. Furthermore, we reported that the hole injection of blue LEDs can be boosted by introducing a series of shallow wells in the valence band with an InGaN/GaN superlattice layer [26].…”