2, Université de Liège, CESAM/Q-MAT, SPIN, Liège, , Belgium
3, Université Grenoble-Alpes, CNRS, Grenoble INP, SIMAP, Grenoble, , France
4, Université de Lyon, Institut des Nanotechnologies de Lyon INL - UMR5270, CNRS, INSA Lyon, Villeurbanne, , France
5, Optoelectronics Group, Cavendish Laboratory, J.J. Thomson Avenue, University of Cambridge, Cambridge, , United Kingdom
ZnO nanowire (NWs) based core-shell heterostructures have been attracting considerable attention for optoelectronic devices owing to efficient light trapping and charge carrier management.1 These type-II heterostructures have recently been integrated into novel self-powered nanoscale UV photodetectors2 by combining wide band gap p-type semiconducting shells, such as CuSCN3, with ZnO NWs. These devices benefit from the photovoltaic effect in the UV region to operate at 0 V bias. Among the delafossite group, CuCrO2 is a promising direct wide band gap p-type semiconductor4,5 (2.95-3.30 eV) reaching conductivities as high as 217 S.cm-1 through Mg doping.5 It has previously been integrated into p-n diodes with ZnO thin films, but with relatively low rectifying behavior.6
In this work, we present the fabrication of an original ZnO / CuCrO2 core-shell NW heterostructure and its integration into efficient self-powered UV photodetectors, using scalable chemical approaches. In particular, the ZnO NW arrays are grown by the low-cost, low temperature chemical bath deposition technique on commercial ITO/glass substrates, while the CuCrO2 shell is deposited by aerosol-assisted chemical vapor deposition at 400°C.
A 35 nm-thick CuCrO2 shell with high conformity and uniformity has been deposited on the ZnO NWs. The structural morphology of the CuCrO2 grains and their composition have been characterized by automated crystal phase and orientation mapping with precession (ASTAR) in a transmission electron microscope as well as by energy-dispersive x-ray spectroscopy, revealing a columnar grain growth at the top of the ZnO NWs, while smaller nano-grains are located on their vertical sidewalls.
The ZnO / CuCrO2 core-shell NW heterostructure device shows a high rectification ratio up to 5500 at ±1 V, and high absorption above 85% in the UV region. The attractive responsivity, response (rise/decay) times and photovoltaic performances of the device, performing as a UV photodetector at 0 V bias, are also measured. The fabrication of devices using ZnO NWs covered with a semiconducting copper-based compound as a shell with low-cost surface scalable chemical fabrication routes at moderate temperatures establishes the ZnO / CuCrO2 core-shell NW heterostructures as a promising cost-efficient, all oxide self-powered UV photodetector.
1E.C. Garnett et al. Annual Review of Materials Research 41 (2011), 269-295
2L. Su et al. Small DOI: 10.1002/smll.201701687 (2017), 1701687
3J. Garnier et al. ACS Appl. Mater. Interfaces 7 (2015), 5820−5829
4D.O. Scanlon and G.W. Watson J. Mater. Chem. 21 (2011), 3655
5T.S. Tripathi and M. Karppinen, Adv. Electron. Mater. 3 (2017), 1600341
6L. F. Chen et al. Jpn. J. Appl. Phys. 52 (2013), 05EC02