紫外线透明纹理氧化铟锡薄膜在发光二极管的应用

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"这篇研究论文探讨了高度紫外线透明的纹理化氧化铟锡(ITO)薄膜及其在发光二极管(LED)中的应用。实验发现，纹理化的ITO在紫外线波长下的透明度显著提高，平均在UVA（315nm-400nm）和UVB（280nm-315nm）范围内的透射率分别高达94%和74%。" 在半导体光电子设备中，透明导电材料扮演着至关重要的角色。尽管已经发展出多种此类材料，但它们在紫外线（UV）波长下的透明度下降一直是制约其商业应用的一个瓶颈问题。这篇来自中山大学国家重点实验室的研究论文，针对这一挑战提出了新的解决方案：采用纹理化的氧化铟锡（ITO）薄膜。纹理化的ITO薄膜通过一种称为Burstein-Moss效应的现象，成功拓宽了其光学带隙至4.7电子伏特(eV)。这种效应是由于载流子浓度增加导致能带结构的改变，使得材料能够吸收更短的波长，从而在紫外线范围内保持较高的透明度。在实际应用中，这种改进的ITO薄膜在UVA和UVB波段表现出优异的光学性能，透射率分别达到了94%和74%，这极大地满足了紫外线器件对透明导电材料的需求。纹理化的ITO薄膜的独特结构是其优秀光学特性的重要原因。与传统的平滑ITO薄膜相比，纹理化表面增加了光的散射，增强了在特定波长下的光透过率。这不仅提高了材料的紫外线透明性，而且可能对LED的效率和稳定性产生积极影响，特别是在紫外LED领域，如紫外固化、杀菌消毒和光通信等应用。此外，高透明度的纹理化ITO薄膜还可能促进新型太阳能电池、显示器和其他光学组件的创新设计。例如，在太阳能电池中，它可以允许更多的紫外线光子通过，从而提高能量转换效率。而在显示器技术中，这种材料可以提供更好的屏幕亮度和对比度，特别是在户外环境下。这篇研究论文揭示了纹理化ITO薄膜在提升紫外线透明度方面的重要性，并展示了其在光电子领域的潜在应用价值。这项工作为开发更适合紫外线环境的透明导电材料开辟了新途径，对于推动相关技术的发展具有重要意义。

Highly ultraviolet transparent textured indium tin oxide thin films and the

application in light emitting diodes

Zimin Chen, Yi Zhuo, Wenbin Tu, Xuejin Ma, Yanli Pei, Chengxin Wang, and Gang Wang

State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-Sen University, HEMC,

Guangzhou 510275, China

(Received 1 March 2017; accepted 4 June 2017; published online 15 June 2017)

Various kinds of materials have been developed as transparent conductors for applications in

semiconductor optoelectronic devices. However, there is a bottleneck that transparent conductive

materials lose their transparency at ultraviolet (UV) wavelengths and could not meet the demands for

commercial UV device applications. In this work, textured indium tin oxide (ITO) is grown and its

potential to be used at UV wavelengths is explored. It is observed that the pronounced Burstein-Moss

effect could widen the optical bandgap of the textured ITO to 4.7 eV. The average transmittance in

UVA (315 nm–400 nm) and UVB (280 nm–315 nm) ranges is as high as 94% and 74%, respectively.

The excellent optical property of textured ITO is attributed to its unique structural property. The com-

patibility of textured ITO thin ﬁlms to the device fabrication is demonstrated on 368-nm nitride-based

light emitting diodes, and the enhancement of light output power by 14.8% is observed compared to

sputtered ITO. Published by AIP Publishing. [http://dx.doi.org/10.1063/1.4986452]

Ultraviolet (UV) optoelectronic semiconductor devices

have drawn more and more attention for the growing demands

on water puriﬁcation, biological detection, medical diagnostics,

UV curing, and so on. Therefore, development of transparent

conductive materials that could work at UV wavelengths is of

great importance. Indium oxide andzincoxidearewidelyused

as transparent conductive electrodes (TCEs) at the wavelength

of visible light. However, the optical bandgaps of these materi-

als are smaller than 3.8 eV, which is considered to be unsuitable

for applications in UV areas. Some oxides such as Ga

:Sn,

(Ga

1x

)

:Sn, and Mg

1x

O:Al possess wide enough

bandgap. However, the resistivity of these materials is in the

order of 10

1

–10

3

X cm, which is unacceptable for practical

device use.

1–4

New designs and strategies, such as correlated

metals, carbon nanotubes, graphene, and silver nanowires, are

developed as TCE materials for the replacement of commercial

indium tin oxide (ITO) thin ﬁlms.

5–13

However, these materials

still face problems when used in UV devices. For example, sil-

ver nanowires absorb UV light of 350 nm due to electron

plasma oscillation.

For ITO, a possible strategy to solve the UV bottleneck is

by the use of the Burstein-Moss effect, which is usually

reported to be able to widen the optical bandgap.

14,15

However,

because of the difference in preparing methods and conditions,

the reported optical bandgap of ITO thin ﬁlms conﬂicts seri-

ously even for samples with similar electron concentrations and

conductivities. The bandgap widening is typically 0.1–0.5 eV

and could not be used for UV applications.

15–23

In this work,

textured crystalline ITO thin ﬁlms are prepared and investi-

gated. It is found that the grain structure could protect the ﬁlms

from optical degradation, which ensures the optical bandgap to

be effectively widened by the Burstein-Moss effect.

The ITO thin ﬁlms were grown c-plane sapphire sub-

strates by metal organic chemical vapor deposition (MOCVD)

using a Veeco Emcore400 system. Trimethyl indium (TMIn),

Tetrakis-dimethylamino tin (TDMASn), oxygen, and argon

were used as the precursors of In, Sn, O, and carrier gas.

Samples were grown at a temperature of 500



Cwitha

thickness of 90 nm. The ﬂow rate of TMIn was kept constant.

The ﬂow rates of the Tin source were 0, 6, 18, 54, 150, 250,

350, and 380 sccm, corresponding to a maximum Sn/In mole

ﬂow ratio of 1:5. The room temperature Hall effect was mea-

sured with van der Pauw geometry. The optical transmittance

of the ITO thin ﬁlms was measured with the reﬂection of the

substrate subtracted. Structural properties were characterized

by X-ray diffraction (XRD) and scanning electron microscopy

(SEM). The contact resistance is measured by using a

circular-transmission line model. Electroluminescence (EL) is

measured at a dc current of 50 mA.

The UV light emitting diodes (LEDs) were grown on c-

plane sapphire with a 2–lm-thick AlGaN template, a

2.5–lm-thick Si-doped n-AlGaN layer, a multiple quantum

well consisting of 9 pairs of AlGaInN/AlGaN layers, a 40-

nm-thick electron blocking layer, a 100-nm-thick Mg-doped

p-AlGaN layer, and a 3-nm-thick p-GaN contact layer. The

magneto sputtering-ITO was deposited on LEDs and sap-

phire at room temperature, followed by annealing in nitrogen

at 550



C for 5 min. The target is the mixture of 10% SnO

and 90% In

by weight. The sputtering power was opti-

mized to suppress the plasma damage and form Ohmic con-

tact. When used as TCEs, the MOCVD-ITO was deposited

with a Sn ﬂow rate of 250 sccm. During the device fabrica-

tion, the thickness of both sputtering- and MOCVD-ITO

ﬁlms was increased to 120 nm in order to improve the current

spreading. Cr/Pd/Au were used as the metal pads, and the

LED chip size is 1143  1143 lm

For ITO grown with different Sn ﬂow rates, the thin

ﬁlms are characterized by grain structures with the width

ranging from 40 nm to 80 nm. Two kinds of grains are

observed in the SEM images shown in Figs. 1(a) and 1(b).

Grains with a pyramid-like shape are (100) grains, while

Author to whom correspondence should be addressed:

stswangg@mail.sysu.edu.cn.

0003-6951/2017/110(24)/242101/4/$30.00 Published by AIP Publishing.110, 242101-1

APPLIED PHYSICS LETTERS 110, 242101 (2017)

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