Grouped and Multistep Nanoheteroepitaxy: Toward High-Quality
GaN on Quasi-Periodic Nano-Mask
Xiaohui Feng,
†
Tongjun Yu,*
,†
Yang Wei,*
,‡
Cheng Ji,
†
Yutian Cheng,
†
Hua Zong,
†
Kun Wang,
†
Zhijian Yang,
†
Xiangning Kang,
†
Guoyi Zhang,
†
and Shoushan Fan
‡
†
State Key Laboratory for Artificial Microstructures and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, P.
R. China
‡
Department of Physics and Tsinghua-Foxconn Nanotechnology Research Center, Tsinghua University, Beijing 100084, P. R. China
*
S
Supporting Information
ABSTRACT: A novel nanoheteroepitaxy method, namely, the
grouped and multistep nanoheteroepitaxy (GM-NHE), is
proposed to attain a high-quality gallium nitride (GaN)
epilayer by metal−organic vapor phase epitaxy. This method
combines the effects of sub-100 nm nucleation and multistep
lateral growth by using a low-cost but unique carbon nanotube
mask, which consists of nanoscale growth windows with a
quasi-periodic 2D fill factor. It is found that GM-NHE can
facilely reduce threading dislocation density (TDD) and
modulate residual stress on foreign substrate without any
regrowth. As a result, high-quality GaN epilayer is produced
with homogeneously low TDD of 4.51 × 10
7
cm
−2
and 2D-modulated stress, and the performance of the subsequent 410 nm
near-ultraviolet light-emitting diode is greatly boosted. In this way, with the facile fabrication of nanomask and the one-off epitaxy
procedure, GaN epilayer is prominently improved with the assistance of nanotechnology, which demonstrates great application
potential for high-efficiency TDD-sensitive optoelectronic and electronic devices.
KEYWORDS: GaN, nanoheteroepitaxy, quasi-periodic nanomask, carbon nanotubes, near-UV LED
1. INTRODUCTION
Gallium nitride (GaN) has aroused considerable interest for its
broad applications.
1,2
However, due to the inaccessibility of
native substrate, heteroepitaxial GaN remains dominant with
high threading dislocation density (TDD) (10
9
−10
11
cm
−2
).
Consequently, micron-selective area growth (micron-SAG)
methods are proposed to reduce TDD, indicating that lateral
growth is an eff ective way.
3,4
The well-applied method,
patterned sapphire substrate (PSS), can reduce TDD to mid-
10
8
cm
−2
that is adequate for high-efficiency blue light-emitting
diode (LED).
5
However, PSS fails to meet higher demands of
TDD-sensitive devices with less indium-related carrier local-
ization. It is reported that the efficiency of short-wavelength
light-emitting devices can be dramatically increased to high
levels and the lifetime greatly prolonged, provided that TDD is
below the possible critical point of around 1 × 10
8
cm
−2
.
6−9
Low TDD of sub-10
8
cm
−2
also benefits high-performance and
high-stability electronic devices as well.
10,11
Therefore, complex
methods with low TDD are utilized for high-end applications,
though these methods involve native substrate or complicated
mask plus regrowth, which lead to a dramatic increase in cost
and limitation in application.
4,12,13
With technical progress, nano-SAG methods, known as
nanoheteroepitaxy (NHE),
14,15
have emerged to pro vide
another way to achieve both TDD reduction and strain release
at the initial growth stage on the condition of small nucleus size
(10−100 nm).
16−21
However, the current TDD level of NHE
(rarely less than 1 × 10
8
cm
−2
without complex methods) is
roughly equivalent to that of PSS.
22−24
Presumably, NHE effect
is compromised with the prevailing feature size of 200−500 nm,
while one can hardly obtain large-area sub-100 nm patterns at
low cost so far. Besides, threading dislocations (TDs) formed
after the initial growth cannot be terminated effectively, since
lateral growth is confined in nanoscale narrow space. It is
believed that sub-100 nm nucleation is an essential requirement
for significant NHE effects, and further improvement can be
expected if additional lateral growth is incorporated. Therefore,
it is desirable to achieve TDD of sub-10
8
cm
−2
by facile
integration of sub-100 nm nucleation and sufficient lateral
growth, i.e., a novel combination of nano- and micron-SAG.
In 2012, we first reported GaN on carbon nanotube (CNT)
patterned sapphire substrate (CPSS) at low cost.
25,26
In this
work, a novel NHE method, namely, the grouped and multistep
NHE (GM-NHE), is proposed to achieve the combination of
nano- and micron-SAG by using a unique CNT mask with
nanoscale growth windows and a quasi-periodic 2D fill factor.
Received: May 11, 2016
Accepted: June 28, 2016
Published: June 28, 2016
Research Article
www.acsami.org
© 2016 American Chemical Society 18208 DOI: 10.1021/acsami.6b05636
ACS Appl. Mater. Interfaces 2016, 8, 18208−18214