Thermally and Optically Induced Nanocrystallites in Amorphous ZnSe Thin Films

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We have investigated the characteristics of thermally and optically induced nanocrystallites in amorphous ZnSe thin films. Although as-deposited ZnSe films prepared by thermal evaporation appear to have uniformly distributed nanocrystallites, it is evaluated to be an amorphous phase on the basis of the lack of peaks in the X-ray diffraction (XRD) pattern. Illumination by a HeCd laser at 300 K induces an increase (about four times) in the size of crystallites and the creation of small two peaks in the XRD pattern. However, no change in size is observed for the illumination at 10 K. Therefore, the thermal effect appear to be the primary factor for the size increase of nanocrystallites. The glass transition temperature ($T_{\text{g}}$) and crystallization temperature ($T_{\text{C}}$) of the ZnSe bulk sample are approximately 320°C and 575°C, respectively. The size of nanocrystallites and the intensity of XRD peaks exhibit a tendency to increase after an initial decrease with increasing annealing temperature. In particular, their maximum values are observed at an annealing temperature of approximately $(T_{\text{g}}+T_{\text{C}})/2$. With increasing annealing temperature, the optical transmittance ($T_{\text{OP}}$) increases and the near-band-edge photoluminescence intensity ($I_{\text{NB}}$) is enhanced. For example, $\Delta T_{\text{OP}}$ (at $\lambda=525$ nm) and $\Delta I_{\text{NB}}$ for 500°C-annealed ZnSe films are approximately $+13$% and $+2.6$ times, respectively. In addition, while $I_{\text{NB}}$ of as-deposited ZnSe is centered at 3.0 eV, that of 500°C-annealed ZnSe is observed at 2.73 eV (energy redshift of $-70$ meV).
INSTITUTE OF PURE AND APPLIED PHYSICSの論文
2003-01-15

Thermally and Optically Induced Nanocrystallites in Amorphous ZnSe Thin Films

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