ZnxCd₁-xSe 박막의 성장과 물리적 특성
Growth and physical properties of ZnxCd₁-xSe thin films
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About 431-nm-thick ZnxCd1-xSe (x = 0.12, 0.33, 0.53, 0.72, and 0.92) thin films were prepared on the ITO-coated glass substrate by evaporation of high purity ZnSe and CdSe mixed tablet in high vacuum. During deposition the substrate temperature was kept to 100 ℃, and the deposition rate was about 40 nm/min. After deposition, the samples were annealed at 200 ℃, 300 ℃, 400 ℃, and 500 ℃ for 10 min in a vacuum furnace. The structural characteristics of the films were investigated by using field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffractometry (XRD). The optical and electronic properties were studied by using X-ray photoelectron spectroscopy (XPS), ultraviolet visible and near infrared (UV-VIS-NIR) spectrophotometer, and photoinduced discharge characteristics (PIDC) measurement. Peaks for CdSe (111), (220), and (311) planes and ZnSe (311) and (331) planes were observed in the XRD spectra of ZnxCd1-xSe films with x = 0.12 and 0.33. Diffraction peaks for CdSe (111), (220), and (311) planes and ZnSe (220) plane were observed in the ZnxCd1-xSe films with x = 0.53. Diffraction peaks for ZnSe (111), (200), and (422) planes and CdSe (311) plane were observed in the ZnxCd1-xSe films with x = 0.72 and 0.92. All XRD peaks were enhanced as the annealing temperature increased. The crystal structures of the ZnxCd1-xSe films were cubic zinc blende with space group . The lattice constant (x) of the ZnxCd1-xSe films increased monotonically with increasing x. The lattice constant was linearly dependent on the fraction x, and was fitted by an empirical equation (x) = 0.001x + 6.032 for CdSe-base cubic zinc blende structure or (x) = 0 for ZnSe-base cubic zinc blende structure. This implies that the cell size of the ZnxCd1-xSe crystal increases from =6.032 Å (lattice constant of ZnSe) to =5.773 Å (that of CdSe) according to the amount of Cd in the ZnxCd1-xSe matrix. The optical transmission spectra for the ZnxCd1-xSe thin films were measured in the wavelength range from 300 nm to 1,200 nm. The plots for the ZnxCd1-xSe films showed that all samples had direct transition band gap. The energy band gap of the ZnxCd1-xSe film increased monotonically from 1.97 eV at x = 0.12 to 2.65 eV at x = 0.92 and the band gap energy Eg with “” can be expressed as . The dynamical behavior of the charge carriers in the ZnxCd1-xSe films was investigated by using PIDC techniques. The sign of the major charge carriers was positive for all samples. The transit time was 16 μs ~ 49 μs. The drift mobility μ and the carrier concentration n were 9.0 × 10-4 cm2/V・s ~ 1.02 × 10-2 cm2/V・s and 2.5 × 1019 /cm3 ~ 2.44 × 1020 /cm3, respectively.