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Journal of Crystal Growth
journal homepage: www.elsevier.com/locate/jcrysgro
Deep-UV emission at 260 nm from MBE-grown AlGaN/AlN quantum-well
structures
Wenxian Yang
a,b
, Yukun Zhao
b
, Yuanyuan Wu
b
, Xuefei Li
b
, Zhiwei Xing
a,b
, Lifeng Bian
b
,
Shulong Lu
b,
⁎
, Muchang Luo
c
a
School of Nano Technology and Nano Bionics, University of Science and Technology of China, Hefei 230026, China
b
Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, China
c
Chongqing Institute of Optoelectronics Technology, Chongqing 400060, China
ARTICLE INFO
Communicated by C. Charles W. Tu
Keywords:
A3. Molecular beam epitaxy
B1. Nitrides
B2. Semiconducting III-V materials
A1. Growth models
ABSTRACT
Deep ultraviolet (UV) emission at 260 nm has been obtained from high Al content AlGaN/AlN multi-quantum
well (MQW) structures by plasma-assisted molecular beam epitaxy (PA-MBE) on AlN template on sapphire
substrates. The effect of III/V ratio and growth temperature on structural and optical properties of AlGaN was
studied. It was observed that Al content in AlGaN material increased with increasing Al flux ratio or growth
temperature. By altering growth conditions, AlGaN with high Al content of 47–80% was obtained. Further
studies indicate that AlGaN layers have excellent surface morphology and optical properties grown in slightly
metal-rich condition. As for AlGaN/AlN MQW, the emission wavelength was tuned by controlling the thickness
of AlGaN quantum well, and deep ultraviolet emission below up to 260 nm was obtained from AlGaN (2.4 nm)/
AlN(6.9 nm) MQW at room temperature.
1. Introduction
AlGaN films with high Al content of over 40% and hetero-structures
are greatly promising in application of ultraviolet light emitting diodes
(LED) and lasers diodes (LD), solar-blind avalanche photodiodes (APD)
and other UV optoelectronic devices [1–4]. Several deep LED used
AlGaN MQW as active regime has been reported [5–10]. Nevertheless,
AlGaN-based LEDs with wavelength of 210–280 nm still have low the
external quantum efficiencies (EQE) of less than 10% [6] until now,
which mainly attributed to the poor material quality with high
threading dislocation densities [11] and other limiting factors including
the difficulties of the p- and n-type doping of high-Al-content AlGaN
layers [12–14] and severe valence band-mixing effect in AlGaN-based
QW structures [15–17]. So it is very important and challenging to ob-
tain high quality AlGaN material with high Al content. In addition,
many researchers in the past decade have devoted to improve the
quality of high Al content AlGaN material by optimizing buff er layers
[18] to reducing threading dislocation densities and proposing new
growth techniques [19–22] including epitaxial lateral overgrowth,
metal modulated epitaxy, pulsed and migration enhanced epitaxy, and
droplet elimination by thermal annealing.
Metal-organic chemical vapor deposition (MOVCD) is most
commonly used to perform the growth of high Al content AlGaN. But
parasitic reactions [23] between Al-metal organic precursors and the
nitrogen gas source (NH3) often restricts the material growth process,
which is di fficult to obtain smooth surface, instead of forming easily
islands, step bunching and hillocks [24]. Due to unique advantages,
plasma-assisted MBE has great potential for growing high-quality
AlGaN epilayers and hetero-structures. First, high vacuum growth en-
vironment and high-purity elemental material can protect effectively
epitaxial layers from impurity (carbon, oxygen) incorporation. Second,
stoichiometric conditions are easily altered to control the growth mode
and the alloy content of AlGaN films. Finally, the low growth tem-
perature and the ability of the ultimately fast change of the group-III
atoms are good to obtain sharp interfaces inAlGaN QW hetero-
structures.
The investigated on the MBE-growth kinetics of AlGaN layers was
reported that Al atoms incorporate completely into the epitaxial ma-
terial, while Ga atoms act as a surfactant and its incorporation is con-
trolled by that unconsumed activated nitrogen atoms [13,25]. Collins
et al. [26] demonstrated for the first time a double hetero-structure UV-
LED with emitting at 324 nm grown by PA-MBE. And then Jmerik et al.
[18] reported the growth of high-Al-content AlGaN-based QW struc-
tures by PA-MBE and determined the bowing parameter of 1.1 eV for
https://doi.org/10.1016/j.jcrysgro.2019.02.037
⁎
Corresponding author.
E-mail address: sllu2008@sinano.ac.cn (S. Lu).
Journal of Crystal Growth 512 (2019) 213–218
Available online 16 February 2019
0022-0248/ © 2019 Elsevier B.V. All rights reserved.
T