Deep-Ultraviolet (DUV) light emitting diodes (LEDs) show great potential in a wide range of applications, but suffer from poor external quantum efficiencies (EQEs) when compared to visible LEDs, due to their exceptionally poor light extraction efficiency (ηEXT). One successful method of improving the ηEXT of DUV LEDs is the use of micropillar and nanowire arrays. Our previous works have reported the development of an "inverse taper" profile in AlGaN micropillars during wet etching in heated hydroxyl-based chemistries. Here, we study the effects of inverse tapering on the ηEXT of AlGaN microstructures and nanostructures at 270 nm using finite-difference time-domain simulations, in accordance with our experimental results. Results show that ηEXT can be increased from ~45% to more than 95% for TM-polarized emission in microstructures with diameters of 1 µm and heights >1 µm, and from ~35% to more than 85% for TE-polarized emission by an inverse taper angle of 5°. Results for nanostructures also indicate significant ηEXT improvements through tuning of the inverse taper angle. These findings, along with our demonstration of inverse tapered high Al-content AlGaN micro and nanostructures, could enable the development of record-high EQE DUV LEDs based on arrays of high aspect ratio structures with high ηEXT.
<p>Metal–semiconductor–metal (MSM) configuration UV photodiodes (PD’s) were designed and fabricated on an AlGaN/GaN–based substrate for efficient and ultrafast UV detection. The purpose was to investigate the feasibility of obtaining efficient and ultrafast temporal response from these devices in the UV given the challenges associated with the formation of Schottky contacts on laterally oriented AlGaN/GaN thin films. Two sets of devices were implemented using Pt and Au as metal contacts with 5-<em>m</em>m finger width, 5-<em>m</em>m finger spacing, and a 50-<em>m</em>m ´ 50-<em>m</em>m active area. Spectral and voltage bias studies were done to establish the spectral profile and the effect of bias voltage on the responsivity of the detectors at 265 nm. The best vertical MSM PD’s produced 0.6-A/W responsivity under 10-V bias voltage at 265 nm. Peak spectral responsivities were recorded as 1.35 A/W and 1.25 A/W at 240 nm for Pt and Au PD’s respectively.</p>
<p>Metal–semiconductor–metal (MSM) configuration UV photodiodes (PD’s) were designed and fabricated on an AlGaN/GaN–based substrate for efficient and ultrafast UV detection. The purpose was to investigate the feasibility of obtaining efficient and ultrafast temporal response from these devices in the UV given the challenges associated with the formation of Schottky contacts on laterally oriented AlGaN/GaN thin films. Two sets of devices were implemented using Pt and Au as metal contacts with 5-<em>m</em>m finger width, 5-<em>m</em>m finger spacing, and a 50-<em>m</em>m ´ 50-<em>m</em>m active area. Spectral and voltage bias studies were done to establish the spectral profile and the effect of bias voltage on the responsivity of the detectors at 265 nm. The best vertical MSM PD’s produced 0.6-A/W responsivity under 10-V bias voltage at 265 nm. Peak spectral responsivities were recorded as 1.35 A/W and 1.25 A/W at 240 nm for Pt and Au PD’s respectively.</p>
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