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Enhanced photoresponse of Cu2O/ZnO heterojunction
with piezo-modulated interface engineering Pei Lin1, §, Xiaoqin Yan1, §, Xiang Chen1 , Zheng Zhang1, Haoge Yuan1, Peifeng Li1, Yanguang Zhao1, Yue Zhang1,2 ()
Nano Res., Just Accepted Manuscript • DOI: 10.1007/s12274-014-0447-6 http://www.thenanoresearch.com on March 7, 2014 © Tsinghua University Press 2014
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Nano Research DOI 10.1007/s12274‐014‐0447‐6
Enhanced Photoresponse of Cu2O/ZnO
heterojunction with Piezo-modulated Interface
Pei Lin1, Xiaoqin Yan1, Xiang Chen1, Zheng Zhang1,
Haoge Yuan1, Yanguang Zhao1, Peifeng Li1, Yue
1 State Key Laboratory for Advanced Metals and Materials, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China. 2 Key Laboratory of New Energy Materials and
Technologies, University of Science and Technology
Beijing, Beijing 100083, People’s Republic of China.
Piezo-modulated interface engineering to enhance the photoresponse of
all-oxide Cu2O/ZnO heterojunction was firstly reported. Under the
illumination of 17.2 mw/cm2, a photoresponse increase of 18.6% has
been obtained when applying a -0.88% compressive strain.
Enhanced Photoresponse of Cu2O/ZnO heterojunction with Piezo-modulated Interface Engineering
Pei Lin1, §, Xiaoqin Yan1, §, Xiang Chen1 , Zheng Zhang1, Haoge Yuan1, Peifeng Li1, Yanguang Zhao1, Yue Zhang1,2 () 1 State Key Laboratory for Advanced Metals and Materials, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China. 2 Key Laboratory of New Energy Materials and Technologies, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China. § These two authors contributed equally to this work. Received: day month year / Revised: day month year / Accepted: day month year (automatically inserted by the publisher) © Tsinghua University Press and Springer-Verlag Berlin Heidelberg 2011
ABSTRACT The ability to arbitrarily regulate semiconductor interface provides the most effective way to modulate performance of optoelectronic devices. However, relatively less work were reported on piezo‐modulated interface engineering in all‐oxide system. In this paper, an enhanced photoresponse of all‐oxide Cu2O/ZnO heterojunction was obtained by taking advantage of the piezotronic effect. The illumination density‐dependent piezoelectric modulation ability was also comprehensively investigated. An 18.6% enhancement of photoresponse has been achieved when applying a ‐0.88% compressive strain. Comparative experiment confirmed that this enhancement could be interpreted from the band modification induced by interfacial piezoelectric polarization. Positive piezopotential generated at ZnO side produces an augment of space charge region in Cu2O, thus providing an extra driving force to separate the excitons apart more efficiently under illumination. Our research provides a promising method to boost the performance of optoelectronics without altering the interface structure and could be extended to other metal oxide devices. KEYWORDS all‐oxide device, piezotronic effect, interface modulation, enhanced photoresponse
Exploitation of interface phenomena has always been a focus in fundamental semiconductor research. As we all know, performance of semiconductor devices depends more on the properties of interface than the bulk material which is away from the interface [1‐2]. The rational design of customized homo or
heterojunctions could give rise to a multitude of fascinating discoveries, such as interface superconductivity, p‐n switching and quantum Hall effect, enabling novel electronics or photonics with remarkable functional behaviors [3‐6]. In recent years, intensive efforts have been made to realize the precise tailoring of interfacial energetics. Among of which, morphological control of materials and
Nano Res DOI (automatically inserted by the publisher) Research Article
———————————— Address correspondence to Yue Zhang, email@example.com
surface modification are the most common approaches. In the case of catalysis, enhanced catalytic activity could be achieved through shape‐controlled synthesis of metal crystals with exposed more active facets . For quantum dot (QD) solar cells, a larger photocurrent is procurable through moderate energy level alignment of QDs using molecular dipoles modification .
Recently, all‐oxide semiconductor devices have attracted much attention with potential applications in optoelectronics in virtue of their natural abundance, excellent chemical stability, nontoxicity and facile low‐cost manufacturing methods [9‐10]. So far, two of the promising candidates for such devices are Cu2O and one‐dimensional (1‐D) ZnO nanomaterials [11‐15]. As a p‐type direct band gap semiconductor, Cu2O exhibits favorable solar spectral absorption in the visible range, while 1‐D ZnO provides a direct pathway for efficient electron charge transport. Besides, the unique piezoelectric property of ZnO could be used to optimize the heterointerface with the appearance of piezoelectric polarization [16‐20].
Many techniques have been implemented with the focus of improving photoresponse of Cu2O/ZnO, such as optimization of material property, novel device structure design and improved fabrication method [21‐24]. However, to the best of our knowledge, relatively less work have been directed to piezo‐modulated interface engineering in the Cu2O/ZnO system. In this paper, piezotronic effect on the photoresponse performance of Cu2O/ZnO devices is systematically investigated and an interface energy band theory is proposed to explain these phenomena. The photoresponse current at zero bias was enhanced 18.6% when applying a ‐0.88% compressive strain with the response time in the range of millisecond (ms). The illumination‐density‐dependent piezoelectric modulation ability was also comprehensively studied. The well‐designed control experiment confirmed that such enhancement originates from the polar piezotronic effect rather than other nonpolar factors, such as piezoresistive effect, change of contact resistance or the defect states. This
exploitation of oxide interfaces holds promise as a new route to boost the all‐oxide optoelectronic devices performance, such as photovoltaics or photosensors.
1 Experimental section
Both of the p‐type Cu2O and n‐type ZnO were synthesized with low‐temperature solution methods . In the first step, Cu2O layer was cathodically deposited on a fluorine‐doped tin oxide (FTO) substrate using an aqueous solution containing 0.02 M copper sulfate and 0.4 M lactic acid that was adjusted to pH 12.5 with 1 M sodium hydroxide . The electrochemical deposition was carried out potentiostatically at ‐0.45 V with the temperature kept at 313 K, the deposition time w