Uneven AlGaN multiple quantum well for deep-ultraviolet LEDs grown on macrosteps and impact on electroluminescence spectral output

Abstract

AlGaN-based LEDs (λ < 300 nm) fabricated on n-AlGaN templates with a threading dislocation density larger than 5 × 108/cm2, which were grown on (0001) sapphire with a 1.0° miscut relative to the m-plane, showed external quantum efficiencies (EQEs) of 3.5, 3.9, 6.1, and 6.0% at 266, 271, 283, and 298 nm, respectively. These EQE values reveal significantly high internal quantum efficiencies (IQEs). This performance was obtained using an uneven multiple quantum well (MQW) grown on the AlGaN template with macrosteps having height larger than the well thickness. The electroluminescence spectra of the fabricated LEDs using this MQW structure shifts to a longer wavelength compared with those on sapphire with a miscut angle of 0.3° relative to the m-plane. Furthermore, the LEDs with this MQW show no deleterious effect on the lifetime, broader electroluminescence spectral widths, and higher output powers when using sapphire with a miscut of 1.0°.

AlxGa1−xN‐Based Quantum Wells Fabricated on Macrosteps Effectively Suppressing Nonradiative Recombination

“…However, the angle dependence of the optical properties is an interesting subject for future studies. It has been reported that Al x Ga 1− x N‐based UV LED on vicinal sapphire (0001) surfaces show high EQEs . The present study suggests that the high EQE originates due to the suppression of nonradiative recombination processes in the QWs grown on macrosteps.…”

The Impact of AlN Templates on Strain Relaxation Mechanisms during the MOVPE Growth of UVB‐LED Structures

“…The near‐surface region of the AlN template, the homoepitaxial AlN, the AlN/GaN SL, and the bottom of the Al 0.75 Ga 0.25 N buffer layer are visible. This ADF STEM image was obtained in the [11–20] AlN viewing direction and shows all dislocation types formed in the sample.…”

“…Exemplary cross‐sectional images of lower part of UVB‐LED structure on AlN template with TDD of (4 ± 0.2) × 10 9 cm −2 : a) ADF STEM showing formation of horizontal dislocation lines in AlN/GaN superlattice and strong TD inclination in subsequently grown AlGaN (viewed in [11‐20]AlN projection). b,c) Dark‐field diffraction contrast images of the same specimen area visualizing different types of defects (white arrows indicate the same specimen positions).…”

“…In this study we will discuss the influence of AlN templates on the relaxation mechanisms during nonpseudomorphic growth of Al 0.5 Ga 0.5 N layers for UVB LEDs. Basing on the recent approaches for improvement of structural quality of AlGaN‐based LEDs [ 6,11,12 ] and the observation of typical, different growth behavior depending on the used AlN/sapphire template, three templates were chosen: AlN/sapphire templates grown on sapphire with an offcut of 0.2° and 0.5° to the sapphire m‐plane and an HTA‐treated AlN/sapphire template. Our analysis suggests that for decreasing Al content in AlGaN even small differences in TDDs as well as the strain state of the underlying AlN templates can have a strong influence on the relaxation mechanisms of the AlGaN layers.…”

Study on the Main‐Chain Structure of Amorphous Fluorine Resins for Encapsulating AlGaN‐Based DUV‐LEDs

“…AlGaN‐based deep‐ultraviolet (DUV) ( λ < 300 nm) LEDs are expected to be useful for applications such as sterilization, deodorization, and UV curing. The high external quantum efficiencies (EQEs) of 6.1 and 6.0% at 283 and 291 nm without encapsulation and with thick p‐GaN (0.5 μm) show that internal quantum efficiency (IQE) is greater than 60% with a forward voltage ( V f ) of less than 6 V, meaning that bare die's performance has reached the level of practical application. A trial encapsulation showed EQE of 12% and a wall‐plug efficiency (WPE) of 5.5% with V f of 8.4 V at 278 nm using a transparent p‐cladding layer and p‐reflective electrode.…”