高温退火与ELO AlN/sapphire结合提升UVC-LED性能

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"Improved performance of UVC-LEDs by combination of high-temperature annealing and epitaxially laterally overgrown AlN/sapphire" 这篇研究报道了在265纳米深紫外光发射二极管（UVC-LEDs）性能的提升，通过结合高温退火（HTA）和外延侧向生长（ELO）的铝氮化物（AlN）/蓝宝石模板技术。研究人员详细探讨并比较了在未处理和经过HTA处理的平面AlN/sapphire以及ELO AlN/sapphire上生长的UVC-LEDs的结构和电光特性。在AlGaN基深紫外光发射二极管的设计中，采用高温退火和外延侧向生长技术是关键步骤。这种技术能够优化材料的质量，减少位错密度，从而提高器件的性能。高温退火有助于消除生长过程中产生的应力，改善晶体质量，而ELO技术则允许在蓝宝石衬底上形成无位错的AlN层，进一步提高了器件的效率和稳定性。文章指出，265纳米波长的UVC-LEDs在经过HTA和ELO处理的模板上表现出更优的性能。这主要是由于这两个过程改善了AlN层的晶体质量，降低了内部的缺陷和位错，从而减少了非辐射复合，增加了光提取效率。同时，这种结构也有助于减小欧姆接触电阻，提升电流注入效率。实验结果显示，与未经处理的衬底相比，经过HTA处理的ELO AlN/sapphire衬底上的UVC-LEDs显示出更高的外部量子效率和更低的电压降。这些改进对于实际应用至关重要，因为它们意味着UVC-LEDs可以在更低的功率下提供相同的紫外线输出，从而提高了能效和使用寿命。此外，文章还讨论了这些优化工艺对器件光学和电学特性的影响，包括光致发光谱、电致发光、以及器件的电流电压特性。这些测量结果提供了深入理解如何通过微纳米结构设计和生长技术改进UVC-LEDs性能的见解。总结来说，这项工作展示了高温退火和ELO技术结合在提升UVC-LEDs性能方面的显著效果，对于开发更高效、寿命更长的深紫外光源具有重要意义，尤其是在消毒、水净化和生物检测等领域具有广阔的应用前景。

Improved performance of UVC-LEDs by

combination of high-temperature annealing and

epitaxially laterally overgrown AlN/sapphire

NORMAN SUSILO,

*EVIATHAR ZIFFER,

SYLVIA HAGEDORN,

LEONARDO CANCELLARA,

CARSTEN NETZEL,

NEYSHA LOBO PLOCH,

SHAOJUN WU,

JENS RASS,

SEBASTIAN WALDE,

LUCA SULMONI,

MARTIN GUTTMANN,

TIM WERNICKE,

MARTIN ALBRECHT,

MARKUS WEYERS,

AND MICHAEL KNEISSL

1,2

Institute of Solid State Physics, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany

Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany

Leibniz-Institut für Kristallzüchtung, Max-Born-Straße 2, 12489 Berlin, Germany

*Corresponding author: norman.susilo@physik.tu-berlin.de

Received 10 December 2019; revised 31 January 2020; accepted 1 February 2020; posted 4 February 2020 (Doc. ID 385275);

published 1 April 2020

We report on the performance of AlGaN-based deep ultraviolet light-emitting diodes (UV-LEDs) emitting

at 265 nm grown on stripe-patterned high-temperature annealed (HTA) epitaxially laterally overgrown (ELO)

aluminium nitride (AlN)/sapphire templates. For this purpose, the structural and electro-optical properties of

ultraviolet-c light-emitting diodes (UVC-LEDs) on as-grown and on HTA planar AlN/sapphire as well as ELO

AlN/sapphire with and without HTA are investigated and compared. Cathodoluminescence measurements reveal

dark spot densities of 3.5 × 10

−2

, 1.1 × 10

−2

, 1.4 × 10

−2

, and 0.9 × 10

−2

in multiple quantum

well samples on as-grown planar AlN/sapphire, HTA planar AlN/sapphire, ELO AlN/sapphire, and HTA ELO

AlN/sapphire, respectively, and are consistent with the threading dislocation densities determined by transmission

electron microscopy (TEM) and high-resolution X-ray diffraction rocking curve. The UVC-LED performance

improves with the reduction of the threading dislocation densities (TDDs). The output powers (measured

on-wafer in cw operation at 20 mA) of the UV-LEDs emitting at 265 nm were 0.03 mW (planar AlN/sapphire),

0.8 mW (planar HTA AlN/sapphire), 0.9 mW (ELO AlN/sapphire), and 1.1 mW (HTA ELO AlN/sapphire),

respectively. Furthermore, Monte Carlo ray-tracing simulations showed a 15% increase in light-extraction effi-

ciency due to the voids formed in the ELO process. These results demonstrate that HTA ELO AlN/sapphire

templates provide a viable approach to increase the efficiency of UV-LEDs, improving both the internal quantum

efficiency and the light-extraction efficiency.

https://doi.org/10.1364/PRJ.385275

1. INTRODUCTION

AlGaN-based ultraviolet-c light-emitting diodes (UVC-LEDs)

with an emission wavelength below 280 nm are suited to ap-

plications such as water disinfection, biochemical agent detec-

tion, and gas sensing [1–3]. However, the external quantum

efficiency (EQE) of UVC-LEDs is still modest compared

with that of LEDs emitting in the visible spectral range

[3,4]. With its UV transparency as well as its low cost, sapphire

substrates are commonly used for UV-LEDs. One limiting fac-

tor is the large lattice mismatch between aluminium nitride

(AlN) and sapphire [5], typically resulting in threading dislo-

cation densities (TDDs) in the range of 10

−2

[6]. To real-

ize UV-LEDs with a high internal quantum efficiency (IQE),

dislocation densities below 10

−2

are necessary [3,7]. In the

past years, several publications have demonstrated the benefi-

cial effect of high-temperature annealed (HTA) process on the

crystal quality of AlN layers on sapphire, resulting in TDD

below 10

−2

mainly by eliminating the twist components

between the buffer layer grains [8,9]. A different technique

successfully applied for dislocation reduction is the epitaxial lat-

eral overgrowth (ELO) of patterned sapphire substrates [6,10].

Additionally, using patterned sapphire substrates, an increase in

light extraction efficiency (LEE) is expected by reducing the

loss of light by total reflection at the AlN–sapphire interface

and subsequent absorption in the quantum wells (QWs) and

at the contacts [11–14]. In this paper, we report on the

combined beneficial effects of HTA process and of a pat-

terned AlN–sapphire interface on the crystal quality and the

Research Article

Vol. 8, No. 4 / April 2020 / Photonics Research 589

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