Abstract
We examined the influence of O2 plasma treatment for the ZnO seed layer (SL) crystallites on the material characteristics of ZnO nanorods (NRs) synthesized by the hydrothermal method. Diode photocurrent and photo-response transient characteristics of the p-Si/n-ZnO-NR heterojunction-based ultraviolet (UV) photodetectors were also examined according to the plasma treatment for the SLs. The superior optical properties of NRs were measured from the photoluminescence by exhibiting 4.6 times greater near-band edge emission when grown on the O2-plasma-treated SL. The degree of (002) orientation of the NR crystals was improved from 0.67 to 0.95, as revealed by X-ray diffraction analysis, and a higher NR surface density of ~80 rods/μm2 with a smaller mean diameter of 65 nm were also observed by the SL modification using plasma-treatment. It was shown by X-ray photo-electron spectroscopy that this improvement of NR crystalline quality was due to the recovery of stoichiometric oxygen with significant reduction of oxygenated impurities in the SL crystals and the subsequent low-energy growth mode for the NRs. UV PDs fabricated by the proposed SL plasma treatment technique showed significantly enhanced UV-to-dark current ratio from 2.0 to 83.7 at a forward bias of +5 V and faster photo-response characteristics showing the reduction in recovery time from 16 s to 9 s.
Highlights
Nanostructures using oxide semiconductors such as Zinc oxide (ZnO), NiOx, SnO2, TiO2, and CuO have been highlighted recently for various applications such as chemical sensors, photo-electrode materials of dye-sensitized solar cells, non-enzymatic glucose sensors, and ultraviolet (UV) photodetectors (PDs) [1,2,3,4,5]
Results andWDe ciasrcriuedssoiuotnPsL analysis for the ZnO NRs grown on O2-plasma-treated seed layer (SL) at various treatment We catNirmRrseieeidnxtheoirbuviattelsPdoLsfim3a,ni6laa, r9ly,p1sa2itstaenfrodnsr1i5tnhmaeilnlZcanassOdese,pNwicRhteesdreginrtwoFwoigcunlreeoar2nas.pOLe2uc-tmrpaillnabessamcnednasc-eotrfsepUaeVtcetredamoSifsLstihoaentavcse-agnrrtieoorweudns treatment time interavta3l.s31oefV3,(367,49n,m12waanvedle1n5gthm) ianndasvidsiebpleiecmteidssiionnFceigntuerreed2aat.2L.0u3 meVin(6e0s8cnemnc) ewsepreeschtorwa no.fTthhee as-grown NRs exhibUiVteedmsisimsioinlairs kpnaotwtenrntosbiencaaullsecdasbeyst,hwe hbaenrde-ttow-boancdleeaxrcitsopneicctrreacolmbbainadtisonofwUhiVcheims hiisgshiloyn centered at 3.31 eVpr(o3n7o4unncemd wwheanvtehleednegntshity) oafnddefevctissicbaulesinegmthiessiniotrna-bcaenndtterraensditiaont s2is.0s3upepVres(s6ed0.8Thnemvi)sibwleere shown
It was shown that the improvement of ZnO SL material quality was achieved in every aspect of structural, optical, and electrical property examined in this study by the surface post-treatment method utilizing O2 plasma
Summary
Nanostructures using oxide semiconductors such as ZnO, NiOx, SnO2, TiO2, and CuO have been highlighted recently for various applications such as chemical sensors, photo-electrode materials of dye-sensitized solar cells, non-enzymatic glucose sensors, and ultraviolet (UV) photodetectors (PDs) [1,2,3,4,5]. A variety of synthesis methods have been reported to date for the growth of ZnO NRs, which includes vapor-liquid-solid process [5,11], chemical vapor deposition (CVD) [7], pulse laser deposition [13], and hydrothermal method [5,9,12,14] Among all these methods to grow ZnO one-dimensional NSs, an aqueous solution-based hydrothermal method is known to be attractive due to its low cost, low thermal budget, and simple process architecture for the material synthesis on large-scale substrates [9,12,14]
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