Comparative study of optical properties of ZnO films and nanorods grown by atmospheric-pressure CVD and chemical bath deposition

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Abstract

Optical properties of ZnO films and nanorods (NRs) grown by atmospheric-pressure CVD (AP-CVD) and chemical bath deposition (CBD) were studied by photoluminescence (PL), photoluminescence excitation (PLE) and photoacoustic (PA) measurements. Visible emissions from the samples were classified into three groups; a green band (GB) at ∼2.34 eV, an orange band (OB) at ∼1.97 eV and a red band (RB) at ∼1.77 eV. Regardless of precursor, PL spectra of the CBD NRs were dominated by the OB. However, PLE measurements revealed that the difference in precursor resulted in the difference of the excitation process for the OB. The PLE spectrum for the RB exhibited the excitation bands at 2.75-3.18 eV and 1.91-2.48 eV. The former was also observed on the PLE spectrum for the GB, suggesting that the same defect or impurity states contribute to both the GB and RB. The PA spectra of the NRs synthesized by CBD from the mixed aqueous solution of Zn(CH3COO)22H2O and C6H12N4 exhibited the decrease in intra-band-gap-absorption with increasing solution concentration. For the AP-CVD Ga-doped ZnO films, when the carrier concentration (n) increased from 5.2×1017 to 7.2×1019 cm-3, the difference between PLE and PL peak energies (EPLE-EPL) decreased slightly. This is probably due to the broadening of the Ga-related impurity level, followed by merging with the edge of the conduction band. Above n =9.5×1019 cm-3, the EPLE-EPL increased rapidly with increasing n, resulting from the filling of the tail states and lower parts of the conduction band. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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