Sensitive, Fast, Solution‐Processed Ultraviolet Detectors Based on Passivated Zinc Oxide Nanorods

Abstract

Solution-processed ultraviolet photodetectors based on passivated and unpassivated zinc oxide (ZnO) nanorods, in which the ZnO nanoparticles are synthesized by a hydrothermal method, are demonstrated and characterized. Photoconductive photodetectors fabricated using simple solution processing have recently been shown to exhibit high gains and outstanding sensitivities. One ostensible disadvantage of exploiting photoconductive gain is that the temporal response is limited by the release of carriers from trap states. Herein, specific chemical species are introduced onto the surfaces of ZnO nanoparticles to produce desired trap states with a carefully selected lifetime. Compared with conventional photodetectors based on ZnO nanoparticles, the proposed UV photodetectors have much higher photoresponses and faster response times in the UV region. The photoconductive gain of the fabricated photodetectors varies from 26.83 to 2.32×10(2) for passivated samples, which indicates high gain. The best temporal response for the fabricated detectors is 34 ms rise time and 132 ms decay time for ZnO nanoparticles passivated by hexamethylenetetramine.

Metal-Semiconductor-Metal Near-Ultraviolet (~380 nm) Photodetectors by Selective Area Growth of ZnO Nanorods and SiO2 Passivation

“…At the bias of 5 V, for all devices, the R λ exhibited relatively high values below 390 nm while it was gradually decreased above 400 nm, which exhibits similar tendency with typical absorption spectra of ZnO NRs. Though the passivation on ZnO NRs with dielectric or organic materials enables enhanced photoconduction and efficiency by reducing the probability of surface recombination [ 29 – 31 ], for the ZnO NR-based NUV PDs, the R λ was dramatically dropped down with increasing the SiO 2 deposition time for passivation. This is mainly attributed to the high resistivity of SiO 2 [ 31 ].…”

Recent advances in solution-processed inorganic nanofilm photodetectors

“…Benefiting from a large surface-to-volume ratio and a Debye length comparable to a small size, 1D semiconductor nanostructures are considered as the most promising building blocks for photodetectors with superior sensitivity, high quantum efficiency, and fast response. A wide range of semiconductor nanowires/belts, including Ge, 216 CdS, 5 Bi 2 S 3 , 6 CdSe, 10 Cu 2 O, 11 ZnO, 217,218 SnO 2 , 43 Zn 2 GeO 4 , and In 2 Ge 2 O 7 , 9 have been used for fabrication of nanofilm photodetectors. In this section, we highlight recent progress with respect to CdSe, ZnO-SnO 2 based film photodetectors, and describe their performance.…”

Toward Understanding the Role of VZn Defect on the Photoconductivity of Surface-Passivated ZnO NRs

“…One-dimensional (1D) nanostructures are the most promising materials for various optoelectronic applications ranging from sensing devices to LEDs to solar cells. − The nanorods (NRs) array films offer the most appropriate design which can effectively modulate the optical and electronic characteristics due to availability of their high surface area. One-dimensional nanostructure of different morphologies of ZnO is one of the most studied wide band gap semiconductors ( E gap = 3.36 eV at 300 K) owing to its outstanding physicochemical properties controlled by the surface defects as a result of their high surface to bulk ratio whereas the role of the bulk properties is comparatively negligible. − One such example is very high ultraviolet (UV) response properties of ZnO NRs due to its low photoexcited electron–hole recombinations controlled by its large surface defects. − The photoresponse of ZnO can also be tuned within the visible spectral region by controlling the intrinsic surface defect levels, which makes it an excellent photodetector in the sub-UV regime. Therefore, understanding the behavior of surface defects is essential to the successful application of ZnO as UV and visible photodetector since the surface defects often capture the electron–hole pairs and make the response slow.…”