SEMICONDUCTOR MATERIALS

Phase transformation from cubic ZnS to hexagonal ZnO by thermal annealing

K. Mahmood1, M. Asghar2, N. Amin1 and Adnan Ali1

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 Corresponding author: K. Mahmood, E-mail: Khalid_mahmood856@yahoo.com

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Abstract: We have investigated the mechanism of phase transformation from ZnS to hexagonal ZnO by high-temperature thermal annealing. The ZnS thin films were grown on Si (001) substrate by thermal evaporation system using ZnS powder as source material. The grown films were annealed at different temperatures and characterized by X-ray diffraction (XRD), photoluminescence (PL), four-point probe, scanning electron microscope (SEM) and energy dispersive X-ray diffraction (EDX). The results demonstrated that as-deposited ZnS film has mixed phases but high-temperature annealing leads to transition from ZnS to ZnO. The observed result can be explained as a two-step process: (1) high-energy O atoms replaced S atoms in lattice during annealing process, and (2) S atoms diffused into substrate and/or diffused out of the sample. The dissociation energy of ZnS calculated from the Arrhenius plot of 1000/T versus log (resistivity) was found to be 3.1 eV. PL spectra of as-grown sample exhibits a characteristic green emission at 2.4 eV of ZnS but annealed samples consist of band-to-band and defect emission of ZnO at 3.29 eV and 2.5 eV respectively. SEM and EDX measurements were additionally performed to strengthen the argument.

Key words: ZnSphase transformationEDXXRDPL



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Fig. 1.  (Color online) X-ray diffraction pattern of as-grown and annealed thin films grown on Si (001) by thermal evaporation system.

Fig. 2.  Arrhenius plot of ln (resistivity) versus 1000 / $T$ of annealed thin films. The plot yielded dissociation energy of Zn-S bond 2.1 eV.

Fig. 3.  PL spectra of annealed samples consisted of band-to-band and defect emission of ZnO at 3.29 eV and 2.5 eV respectively. The inset consists of only characteristic green emission peak of ZnS.

Fig. 4.  EDX measurements of as-grown and annealed thin films grown by thermal evaporation. The concentration of S atoms decreases as annealing temperature increases.

Fig. 5.  SEM images of as-grown and annealed ZnS thin films at different temperatures. The crack formation indicates the O diffusion.

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    Received: 11 September 2014 Revised: Online: Published: 01 March 2015

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      K. Mahmood, M. Asghar, N. Amin, Adnan Ali. Phase transformation from cubic ZnS to hexagonal ZnO by thermal annealing[J]. Journal of Semiconductors, 2015, 36(3): 033001. doi: 10.1088/1674-4926/36/3/033001 K. Mahmood, M. Asghar, N. Amin, A Ali. Phase transformation from cubic ZnS to hexagonal ZnO by thermal annealing[J]. J. Semicond., 2015, 36(3): 033001. doi: 10.1088/1674-4926/36/3/033001.Export: BibTex EndNote
      Citation:
      K. Mahmood, M. Asghar, N. Amin, Adnan Ali. Phase transformation from cubic ZnS to hexagonal ZnO by thermal annealing[J]. Journal of Semiconductors, 2015, 36(3): 033001. doi: 10.1088/1674-4926/36/3/033001

      K. Mahmood, M. Asghar, N. Amin, A Ali. Phase transformation from cubic ZnS to hexagonal ZnO by thermal annealing[J]. J. Semicond., 2015, 36(3): 033001. doi: 10.1088/1674-4926/36/3/033001.
      Export: BibTex EndNote

      Phase transformation from cubic ZnS to hexagonal ZnO by thermal annealing

      doi: 10.1088/1674-4926/36/3/033001
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      • Corresponding author: E-mail: Khalid_mahmood856@yahoo.com
      • Received Date: 2014-09-11
      • Accepted Date: 2014-10-16
      • Published Date: 2015-01-25

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