Fully Solution-Processed Ultraviolet Photodetector Based on Hydrothermally Grown ZnO Nanorod Array

Patterned nanostructures exhibit interesting optoelectronic characteristics due to light-matter interaction at the comparable dimension of incident light and material. At a comparable dimension, the optoelectronic response of the nanostructure-based devices is modulated by the size and the periodicity of the structure. Numerous techniques based on top-down and bottom-up approaches are used to obtain patterned nanostructure. However, the solution-based technique is considered to be best due to cost-effectiveness as well as large-area processing. Recently patterned structures of metal oxide semiconductors are getting attention for various optoelectronic devices like photodetectors, solar cells, etc. ZnO is an abundantly available metal oxide that has high absorption coefficient and is highly appropriate for low-cost ultraviolet photodetectors. The hydrothermally patterned ZNA was achieved in two steps of deposition starting with ZnO quantum dots (QDs) seed layer followed by hydrothermal reaction. The as-grown ZNA was treated with ZnO QDs to remove any pin-holes or trap sites. P-type polymer PEDOT:PSS was used for making heterojunction with n-type ZNAs. The carbon electrode at the top was deposited by screen printing of carbon paste.<br/>The optical bandgap increases with decreasing the size/periodicity of the ZNA. ZNR based film and heterojunction devices are investigated for different sizes/periodicity using surface morphology and optoelectronic properties. The ZNA based heterojunction photodetectors have shown improved photoresponse under ultraviolet (UV) light. The maximum photoresponsivity of 9.2 A/W and external quantum efficiency of 3144% are achieved for the ZNA obtained by 20 mM precursor solution. The response time is also fast due to the reduction in surface pin-holes/traps.<br/><br/><b>KEYWORDS: </b><i>Hydrothermal deposition; Patterned ZnO; P-N junction, UV photodetector; </i><br/><b>ACKNOWLEDGEMENT: </b>The authors express their gratitude for support from SAIF and IRCC, IIT Bombay, and funding from DST (India); SERI (grant no. DST/TM/SERI/2k10/12/(G)), TMD (grant no. DST/TM/WTI/WIC/2K17/100(C)), and SERB (grant no. EMR/2017/005144).<br/><br/><b>References: </b><br/>Kasani, S., Curtin, K. and Wu, N. (2019), <i>Nanophotonics</i>, 8(12), pp. 2065–2089.<br/>Kumar, C. <i>et al.</i> (2020), <i>IEEE Photonics Technology Letters</i>, 32(6), pp. 337–340.<br/>Kumar, C. <i>et al.</i> (2022), <i>IEEE Electron Device Letters</i>, 43(2), pp. 260–263.<br/>Sørensen, M. W. and Sørensen, A. S. (2008), <i>Physical Review A</i>, 77, p. 013826.