Milliwatt power UV-A LEDs developed by using n-AlGaN superlattice buffer layers grown on AlN templates

Abstract

Ultraviolet (UV)-A light-emitting diode (LED) light sources are strongly demanded for both medical and photochemical applications. In our previous report, we investigated the conventional n-AlGaN buffer layer (BL)-based UV-A LED devices and a very low output power was achieved. In this work, we aim for the suppression of vertically propagating threading dislocation densities (TDDs) in the n-AlGaN BL including the current spreading layer (CSL) by introducing Si-doped n-Al 0.37 Ga 0.63 N/n-Al 0.27 Ga 0.73 N superlattices (SLs) between the AlN template and n-AlGaN BL for the demonstration of 341 nm UV-A LEDs. When the conventional n-AlGaN BLs were replaced with n-AlGaN SL-based BLs (with a suitable number of periods up to ~70) in the UV-A multi-quantum wells, then the full width at half maximum of the x-ray rocking curves in the n-AlGaN CSL for the (0 0 0 2) and (10-12) planes, respectively, were reduced to 346 and 431 arcsec and the total TDDs were suppressed to approximately ~1 × 10 9 cm −2 . Finally, when the conventional Ni (20 nm)/Au (150 nm) p-electrodes were replaced with new Ni (1 nm)/Mg (200 nm) p-electrodes in the n-AlGaN SL-based UV-A LEDs, the maximum output power was improved from 2.1 to 2.5 mW.

Influence of Undoped‐AlGaN Final Barrier of MQWs on the Performance of Lateral‐Type UVB LEDs

“…The crystal quality of AlN template grown on c‐(0001) sapphire substrates was reasonably improved (total‐TDDs ≈5×10 8 cm −2 ) by our group, using a well‐known technique of “ammonia (NH 3 ) pulsed‐flow multilayer (ML) growth.” But still the epitaxial growth of AlGaN on an AlN template can have a lattice mismatch as large as ≈4%, depending on the molar ratio of the Al‐contents in the grown layer. However, the performances of AlGaN‐based UVA and UVB LED devices grown on AlN template on sapphire substrates are still very low, due to the UVB emissions in the challenging wavelength ranges under 340 nm . Engineering of UVB light emission based on the Al composition around 40% in AlGaN is quite challenging due to the complex growth issues in MOCVD.…”

“…Engineering of UVB light emission based on the Al composition around 40% in AlGaN is quite challenging due to the complex growth issues in MOCVD. Such complex growth of AlGaN might be caused either by kinetic separation as well as 3D growth‐mode, which is further associated with the Ga‐rich localized energy states or due to the existence of vertically propagating TDDs in the n‐AlGaN electron injection layer (EIL) underneath the multi‐quantum‐wells (MQWs) …”

“…However, the performances of AlGaN-based UVA and UVB LED devices grown on AlN template on sapphire substrates are still very low, due to the UVB emissions in the challenging wavelength ranges under 340 nm. [19][20][21][22] Engineering of UVB light emission based on the Al composition around 40% in AlGaN is quite challenging due to the complex growth issues in MOCVD. Such complex growth of AlGaN might be caused either by kinetic separation as well as 3D growth-mode, which is further associated with the Ga-rich localized energy states or due to the existence of vertically propagating TDDs in the n-AlGaN electron injection layer (EIL) underneath the multiquantum-wells (MQWs).…”

“…Such complex growth of AlGaN might be caused either by kinetic separation as well as 3D growth-mode, which is further associated with the Ga-rich localized energy states or due to the existence of vertically propagating TDDs in the n-AlGaN electron injection layer (EIL) underneath the multiquantum-wells (MQWs). [19][20][21][22][23][24][25] Some research groups reported about the AlGaN-based UVB LED devices, either grown on an AlN template or on HTAsputtered AlN template, where the maximum light output power remains restricted to the range of 2.9 mW at 250 mA and 18 mW at 500 mA, respectively, with a maximum external quantum efficiency (EQE) of 1.8% at emission band of 290-310 nm (excluding the data from company catalog, where we cannot access to their device structure's information as well as growth conditions). [26][27][28] After the reduction of TDDs (total-TDDs %1 Â 10 9 cm À2 ) in the n-AlGaN EIL underneath the MQWs region leads us to a significant increase in the internal quantum efficiency (IQE) up to 47% from the AlGaN MQWs of UVB LED, which is measured by the method given in previous study.…”

Хлорид-гидридная газофазная эпитаксия полуполярного слоя AlN(1012) на наноструктурированной подложке Si(100)

“…Нитрид алюминия (AlN) является привлекательным материалом для создания датчиков на основе поверхностных акустических волн, светодиодов для ультрафиолетовой области спектра [1], а также в качестве буферного слоя для синтеза нитрида галлия. Приборы электроники на основе III-нитридных полупроводников создаются в основном на базе гексагональных кристаллов, синтезированных в направлении оси c. Однако использование плоскости (0001) в III-нитридных оптоэлектронных приборах приводит к появлению эффекта Штарка из-за сильной пьезоэлектрической поляризации.…”