DOI: http://dx.doi.org/10.1590/1516-1439.310714
Materials Research. 2015; 18(3): 519-524
© 2015
*e-mail: csuxjw@126.com
1. Introduction
Tin-doped indium oxide (ITO) lms with high conductivity
and transparency have been extensively served as transparent
and conductive electrodes in optoelectronic devices
1
.
There are some techniques to deposit the ITO lms, such
as magnetron sputtering, pulsed laser deposition, electron
beam (EB) evaporation, chemical vapor deposition, sol-gel,
spray pyrolysis
2-7
. Among these different methods, the EB
evaporation technique is one of the most frequently used
methods for producing ITO lms having better electrical and
optical properties, which is easy to be applied to commercial
production
8
. Some investigative works have reported the
relationship between the EB evaporation process and the
properties of the ITO lms
4,8-12
, such as oxygen, post-
annealing, substrate temperature, ingredient ratio. One of
the most important applications of the ITO lms deposited
by EB evaporation is served as the p-type electrodes of
GaN-based light emitting diodes (LEDs). The utilization of
the ITO lms substituting for metal lms can enhance the
output of light from GaN-based LEDs
13,14
, which is due to
its low direct current resistivity and high transmittance in
the visible light range.
To the best of our knowledge, the high density ITO
targets used for magnetron sputtering were served as the
raw material of EB evaporation process. However, the ITO
tablets designed for the source of EB evaporation were rarely
investigated. In general, the low density of ITO tablets with
about 62% relative density were designed to resist thermal
shock of high energy electron beam. The surface needles
or the internal cracks of the low density ITO tablets may
be formed during EB evaporation process. Obviously, the
formation of these needles or cracks are likely to change
the scattering angel of the oxide vapor during evaporation
process. These slight uctuations would deteriorate the
structural, electrical and optical properties of the deposited
ITO lms, such as resistivity, transmittance and uniformity.
These deteriorated ITO lms used for GaN-based LEDs
would inuence its electrical and optical properties.
In this work, the formation mechanism of the needles
and cracks in the low density ITO tablets were investigated,
and the corresponding solutions were proposed.
2. Experiments
The conventional ITO tablets were fabricated by using
the sintered-ITO powders. The modied ITO tablets were
fabricated by using the nano- and sintered-ITO powders.
The sintered-ITO powders were obtained by pressing and
sintering the nano-ITO powders at 1200 °C. Then, the
nano-and sintered-ITO powders, organic agents and water
were grinded, dried and granulated. Finally, the conventional
and modied ITO tablets with dimension of Φ25×10 mm
were sintered at 1350 °C under oxygen atmosphere. The ITO
tablets were evaporated by electron beam to analyze the
needles and cracks.
The microstructure and ingredients of the needles and
tablets were analyzed by scanning electron microscope (SEM)
using JSM-5610LV (JEOL) and F50 (FEI Inspect). Thermal
conductivity was measured by laser ash thermal constant
analyzer (TC-7000, ULVAC-RIKO). Three-point bending
strength of the ITO tablets were measured by electronic
universal testing machine (Shimadzu, AG-X). The optical
Study on Needles and Cracks of Tin-doped Indium Oxide Tablets for
Electron Beam Evaporation Process
Jiwen Xu
a,b
*, Zupei Yang
b
, Xiaowen Zhang
a
, Ling Yang
c
, Huarui Xu
b
, Hua Wang
a
a
Guangxi Key Laboratory of Information Materials, Guilin University of Electronic Technology,
Guilin 541004, P.R. China
b
School of Material Science and Engineering, Shaanxi Normal University, Xi’an 710062, P.R. China
c
Guangxi Experiment Center of Information Science, Guilin University of Electronic Technology,
Guilin 541004, P.R. China
Received: July 20, 2014; Revised: June 12, 2015
Tin-doped indium oxide (ITO) tablets were used to deposit ITO lms on p-GaN layer of light-
emitting diodes. Needles and cracks in ITO tablets generated during electron beam evaporation process
were deeply investigated. The formation of needles is predominantly resulted from the scanning trace,
which is controlled by x and y axes scanning singles. The needles can be eliminated by controlling
electron beam scanning trace. The loose microstructure with uniform grains and pores in the ITO
tablets results in weak bonding strength, which leads to cracks under the thermal shock of high energy
electron beam. A three-dimensional reticulated skeleton structure with strong bonding strength can
restrain these cracks.
Keywords: needle, crack, ITO, electron beam evaporation