使用MOCVD技术制备的高性能InGaN/GaN MQW LED与Al-doped ZnO透明导电层
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"这篇研究论文探讨了使用金属有机化学气相沉积(MOCVD)技术，以水(H2O)作为氧化剂在n+型InGaN接触层上生长Al掺杂ZnO (Al-doped ZnO, AZO)透明导电层，用于制造高性能的InGaN/GaN多量子阱发光二极管(LEDs)。通过在400°C低温下进行沉积，无需后续退火处理，就能实现高透明度(98%)、低电阻率(5×10^-4 Ω·cm)和类似外延的良好性能的AZO-TCL。这种优化的工艺提升了LED的性能，对于未来LED技术的发展具有重要意义。"
在这篇研究中，科研团队关注的是如何提高InGaN/GaN多量子阱LED的性能，特别是通过改进透明导电层的设计。InGaN/GaN MQW LED是一种重要的固态光源，广泛应用于照明、显示和通信等领域。透明导电层在LED中起着至关重要的作用，因为它不仅需要允许光线透过，还需要提供一个低电阻的电极来有效地传输电流。
传统的透明导电材料如ITO（氧化铟锡）在某些情况下可能会限制LED的性能，例如因为高温生长条件可能导致底层材料的损伤，或者由于ITO的柔性较差而影响器件的集成和可挠性。因此，研究人员选择了Al-doped ZnO (AZO)作为替代材料。AZO具有良好的透明性、较低的电阻率和对半导体材料更好的兼容性，尤其是可以在相对较低的温度下生长，这有助于保护底层的InGaN量子阱结构不受热损伤。
实验结果显示，采用H2O作为氧化剂在400°C下生长的AZO TCL展现了优异的性能：高达98%的透明度意味着大部分光能够穿过该层，这对于提高LED的出光效率至关重要；而低至5×10^-4 Ω·cm的电阻率则确保了电流的高效传播，降低了欧姆损耗，从而提高了器件的电光转换效率。此外，AZO TCL的外延状性能意味着其与InGaN层的界面质量良好，减少了界面缺陷，进一步增强了LED的性能。
这一创新方法简化了制程，避免了额外的退火步骤，这降低了生产成本，同时也为实现大面积和柔性LED提供了可能。该研究为LED技术的进步开辟了新的路径，特别是在寻找更高效、更经济、更适应未来应用需求的透明导电材料方面。
Chin. Phys. B Vol. 25, No. 11 (2016) 118506
High-performance InGaN/GaN MQW LEDs with Al-doped ZnO
transparent conductive layers grown by MOCVD
using H
2
O as an oxidizer
∗
Jia-Yong Lin(林家勇)
1
, Yan-Li Pei(裴艳丽)
1, †
, Yi Zhuo(卓毅)
1
, Zi-Min Chen(陈梓敏)
2
,
Rui-Qin Hu(胡锐钦)
1
, Guang-Shuo Cai(蔡广烁)
1
, and Gang Wang(王钢)
1, ‡
1
State Key Lab of Optoelectronics Materials & Technologies, School of Electronics and Information Technology,
Sun Yat-Sen University, Guangzhou 510006, China
2
School of Materials Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China
(Received 19 April 2016; revised manuscript received 12 August 2016; published online 30 September 2016)
In this study, the high performance of InGaN/GaN multiple quantum well light-emitting diodes (LEDs) with Al-
doped ZnO (AZO) transparent conductive layers (TCLs) has been demonstrated. The AZO-TCLs were fabricated on the
n
+
-InGaN contact layer by metal organic chemical vapor deposition (MOCVD) using H
2
O as an oxidizer at temperatures
as low as 400
◦
C without any post-deposition annealing. It shows a high transparency (98%), low resistivity (510
−4
Ω·cm),
and an epitaxial-like excellent interface on p-GaN with an n
+
-InGaN contact layer. A forward voltage of 2.82 V @ 20 mA
was obtained. Most importantly, the power efficiencies can be markedly improved by 53.8%@20 mA current injection
and 39.6%@350 mA current injection compared with conventional LEDs with indium tin oxide TCL (LED-III), and by
28.8%@20 mA current injection and 4.92%@350 mA current injection compared with LEDs with AZO-TCL prepared by
MOCVD using O
2
as an oxidizer (LED-II), respectively. The results indicate that the AZO-TCL grown by MOCVD using
H
2
O as an oxidizer is a promising TCL for a low-cost and high-efficiency GaN-based LED application.
Keywords: transparent conductive layers, Al-doped ZnO, light-emitting diodes, MOCVD
PACS: 85.60.Jb, 77.55.hf, 81.15.Gh DOI: 10.1088/1674-1056/25/11/118506
1. Introduction
ZnO-based transparent conductive layers (TCLs) have
been widely investigated to replace indium tin oxide (ITO) in
high-efficiency GaN-based light-emitting diodes (LEDs).
[1–5]
In our previous work,
[6]
metal organic chemical vapor depo-
sition (MOCVD) proved to be a good method to grow ZnO-
based TCLs for GaN-based LEDs application. As reported
in literature,
[6]
the GaN-based LEDs with the MOCVD grow-
ing Al-doped ZnO (AZO)-TCL showed an ultra-low forward
voltage of 2.86 V (@20 mA) and an epitaxial-like excel-
lent interface between the AZO-TCL and n
+
-InGaN contact
layer. However, these ZnO-TCLs were grown by MOCVD
using high-purity O
2
as an oxidizer at temperatures as high as
550
◦
C. In addition, to obtain high transparency ZnO-TCL, the
O
2
was overflowed with a diethyl zinc (DEZn) precursor with
a molar ratio of 458:1. This would eventually lead to the high
cost of GaN-based LEDs. To solve these problems, water is
proposed as a cost free oxidizer to replace the high-purity O
2
.
Generally, the film growth temperature of MOCVD is mainly
determined by the cracking efficiency of reactors. Because the
cracking efficiency of water (H
2
O) with the low energy bond
of H–O (464 kJ/mol) is higher than that of oxygen (O–O bond
energy of 498 kJ/mol), using H
2
O instead of O
2
as an oxidizer
is expected to reduce the ZnO-TCL growth temperature.
[7,8]
This would eventually also reduce the cost of the GaN-based
LEDs. In previous studies, as the front or back contacts of
a solar cell, low-cost boron doped zinc oxide (ZnO:B) films
have been prepared by low-pressure chemical vapor deposition
(LPCVD) using H
2
O as an oxidizer with typical resistivity of
1.0 × 10
−3
–2.0 × 10
−3
Ω·cm.
[9–11]
As far as we know, ZnO-
based TCLs grown by MOCVD using H
2
O as an oxidizer have
not been explored for GaN-based LED applications.
In this study, AZO-TCLs were grown on p-GaN with an
n
+
-InGaN contact layer by MOCVD at 400
◦
C using H
2
O
as an oxidizer. The low-cost and high-efficiency GaN-based
LEDs with these AZO-TCLs are demonstrated.
2. Experimental details
In this study, InGaN/GaN multiple quantum well (MQW)
LED structures were grown on c-plane sapphire substrate
by MOCVD. The InGaN/GaN MQW LED structure with an
emission wavelength of 450 nm consists of a Si-doped n-GaN
layer, fifteen pairs of In
0.3
Ga
0.7
N/GaN MQW active layers
(with a well of 6.5–6.8 nm and a barrier of 4.7–5.1 nm), a
Mg-doped p-GaN layer, and a 3-nm-thick Si-doped n
+
-InGaN
contact layer with a carrier concentration of 3 × 10
20
cm
−3
.
∗
Project supported by the National Natural Science Foundation of China (Grant Nos. 61204091, 61404177, 51402366, and U1201254) and the Science and
Technology Planning Project of Guangdong Province, China (Grant No. 2015B010132006).
†
Corresponding author. E-mail: peiyanli@mail.sysu.edu.cn
‡
Corresponding author. E-mail: stswangg@mail.sysu.edu.cn
© 2016 Chinese Physical Society and IOP Publishing Ltd http://iopscience.iop.org/cpb http://cpb.iphy.ac.cn
118506-1
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