CPB Online In-PressCPB Online In-Press
Chin. Phys. B Vol. 23, No. 8 (2014) 087307
Forward and reverse electron transport properties across
a CdS/Si multi-interface nanoheterojunction
∗
Li Yong(李 勇)
a)b)
, Wang Ling-Li(王伶俐)
a)
, Wang Xiao-Bo(王小波)
a)
, Yan Ling-Ling(闫玲玲)
a)
,
Su Li-Xia(苏丽霞)
a)
, Tian Yong-Tao(田永涛)
a)
, and Li Xin-Jian(李新建)
a)†
a)
Department of Physics and Laboratory of Materials Physics, Zhengzhou University, Zhengzhou 450052, China
b)
Department of Physics and Solar Energy Research Center, Pingdingshan University, Pingdingshan 467000, China
(Received 13 January 2014; revised manuscript received 21 April 2014; published online 10 June 2014)
The electron transport behavior across the interface plays an important role in determining the performance of op-
toelectronic devices based on heterojunctions. Here through growing CdS thin film on silicon nanoporous pillar array, an
untraditional, nonplanar, and multi-interface CdS/Si nanoheterojunction is prepared. The current density versus voltage
curve is measured and an obvious rectification effect is observed. Based on the fitting results and model analyses on the
forward and reverse conduction characteristics, the electron transport mechanism under low forward bias, high forward
bias, and reverse bias are attributed to the Ohmic regime, space-charge-limited current regime, and modified Poole–Frenkel
regime, respectively. The forward and reverse electrical behaviors are found to be highly related to the distribution of inter-
facial trap states and the existence of localized electric field, respectively. These results might be helpful for optimizing the
preparing procedures to realize high-performance silicon-based CdS optoelectronic devices.
Keywords: heterojunction, multi-interface nanoheterojunction, electron transport, silicon nanoporous pillar
array (Si-NPA), CdS/Si-NPA
PACS: 73.63.–b, 81.07.–b, 73.63.Bd, 73.63.Rt DOI: 10.1088/1674-1056/23/8/087307
1. Introduction
In the past decade, mainly aimed at the application of cad-
mium sulfide (CdS) thin films in fabricating solar cells,
[1,2]
light emitting diodes,
[3]
laser diodes,
[4,5]
and other optoelec-
tronic devices,
[6]
the study of the electron transport proper-
ties across the interface formed between CdS thin film and
the nether semiconductor has attracted considerable atten-
tion. Generally, the conduction behavior across a semiconduc-
tor heterojunction could heavily influence the device perfor-
mances, such as efficiency and stability. So a clear understand-
ing of the electron transport mechanism would be very impor-
tant for the optimization of device producing process. Tech-
nically, the conduction mechanism of a typical semiconductor
heterojunction could be clarified by measuring and analyzing
its current density–voltage (J–V ) curves.
[7]
Nevertheless, if
the CdS thin film is grown on a nanostructured semiconduc-
tor surface, an untraditional, nonplanar, and multi-interface
nanoheterojunction would be formed. In the case, the clari-
fication of the electron transport mechanism would be a much
more complicated and difficult work.
In the previous study, we reported the preparation and
characterization of a CdS/Si nanoheterojunction based on a
micron-nanometer hierarchical silicon substrate,
[8,9]
the sili-
con nanoporous pillar array (Si-NPA).
[10]
Through construct-
ing an ITO/CdS/Si-NPA/Si/Ag structure, a prototype solar
cell was prepared and an obvious photovoltaic effect was
observed.
[9]
In the device, a relatively big open circuit voltage
was obtained, which indicated the realization of high separa-
tion efficiency for photo-generated carriers. Although the big
series resistance of the nanosystem leads to a small short cir-
cuit current and therefore low energy conversion efficiency, the
obtaining of a CdS/Si-based solar cell with higher conversion
efficiency is still hopeful. This might be realized through im-
proving the CdS–Si interface status by optimizing the prepar-
ing processes. Considering the roles played by the conducting
behavior in promoting the device performances, a deep and
systemic study of the electron transport mechanism across the
complex interface of CdS/Si-NPA is both important and nec-
essary.
In this paper, we report that utilizing Si-NPA as a func-
tional substrate, an n-CdS/p-Si multi-interface nanohetero-
junction is prepared by a chemical bath deposition (CBD)
method. The J–V curve is measured and the electron transport
mechanisms both under forward and reverse biases are ana-
lyzed. An analysis based on the fitting results discloses that
the electron transports under low forward bias, high forward
bias, and reverse bias obey the Ohmic, space-charge-limited
current (SCLC), and modified Poole–Frenkel (PF) models, re-
∗
Project supported by the National Natural Science Foundation of China (Grant Nos. 61176044 and 11074224), the Science and Technology Project for
Innovative Scientist of Henan Province, China (Grant No. 1142002510017), and the Science and Technology Project on Key Problems of Henan Province,
China (Grant No. 082101510007).
†
Corresponding author. E-mail: lixj@zzu.edu.cn
© 2014 Chinese Physical Society and IOP Publishing Ltd http://iopscience.iop.org/cpb http://cpb.iphy.ac.cn
087307-1