Oxygen Plasma Surface Activation of Electron‐Depleted ZnO Nanoparticle Films for Performance‐Enhanced Ultraviolet Photodetectors

Abstract

Zinc oxide (ZnO) nanoparticles (NPs) with uniform particle radius comparable to the desired Debye length provide a low-cost and a scalable scheme to achieve optimized electron depletion effect, which is the key to high performance ultraviolet (UV) photodetection. Here, a simple and improved sol-gel method for in situ synthesis of highly crystalline constituent ZnO-NP mesoporous thin films is reported. In combination with optimal oxygen plasma treatment to activate the ZnO-NP surface, the UV-detection performance is enhanced remarkably with a reduced dark current by one order of magnitude and an increased UV detectivity by over 300%. Moreover, such UV photodetector s exhibit extraordinary performance with high responsivity of up to 0.8 A W À1 V À1 at 340 nm UV power of 0.003 mW cm À2 , detectivity of 1.4 Â 10 11 Jones, and rise/decay time of 3.4 s/5.0 s. These results illustrate that the sol-gel ZnO-NP films provide a promising template for highperformance UV detectors to take full advantages of the electron depletion effect.

Oxygen plasma assisted enhanced photoresponse of ZnO nanowires fabricated by catalyst-free chemical vapor deposition

“…2c) were observed with the oxygen plasma treatment aer 10 minutes, indicating a clear increased concentration of the zinc chemical state on the ZnO NWs surface, because the oxygen plasma treatment primarily improves the surface quality of ZnO NWs and more O 2 À ions forming the Zn-O bonding. 17 The O 1s spectrum revealed details of oxygen associated with various oxygen species, such as surface lattice oxygen and organic molecules. The O 1s peaks ( Fig.…”

Effects of Grain Size on the UV‐Photoresponse of Zinc Oxide Thin Films Grown by Spray‐Pyrolysis

“…However, significant differences in relative intensities of certain peaks with respect to the mentioned file are evident. Specifically, the high intensity of the diffraction peak corresponding to the (0002) plane with respect to planes (10-10) and (10)(11) in samples ZO20 and ZO30 is consistent with an enhanced anisotropic crystal growth in the a-and b-directions, perpendicular to the [0001] direction (c axis). Then, as far as the usual morphologies observed for ZnO nanostructures, [19,20] ZO20 and ZO30 films would be built up of hexagonal platelet-like grains, exhibiting mainly {0001} faces, rather than elongated structures or rods of hexagonal cross section.…”

“…Then, as far as the usual morphologies observed for ZnO nanostructures, [19,20] ZO20 and ZO30 films would be built up of hexagonal platelet-like grains, exhibiting mainly {0001} faces, rather than elongated structures or rods of hexagonal cross section. On the other hand, the changes observed in the relative intensities of planes (10-10), (10)(11), and (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) with respect to plane (0002) in the XRD pattern of film ZO40, show a different crystal morphology revealing an inversion in the anisotropy of grains. It seems that growing in the equatorial a and b directions is overtaken by a preferential growth in the c direction.…”

“…However, by decreasing the electrical resistivity by means of extrinsic defects generated by donor doping, ZnO films turn into transparent conductive oxides (TCO) with applications of increasing technological interest such as transparent electrodes, solar cell anodes, light emitting diodes, liquid crystal displays, and touch‐screens, among others . Another interesting application that has gained attention is the use of ZnO in UV photodetectors for safety devices, flame detection, optical communication, industrial packaging/sealing lines and monitoring of artificially illuminated working environments …”

“…[3][4][5] Another interesting application that has gained attention is the use of ZnO in UV photodetectors for safety devices, flame detection, optical communication, industrial packaging/sealing lines and monitoring of artificially illuminated working environments. [6][7][8][9][10] Transparent ZnO films and coatings may be deposited onto different types of substrates by physical or chemical methods. Among the chemical approaches, dipcoating, spin-coating, flame-spray pyrolysis, and spray-pyrolysis lead to good quality dense transparent films.…”