Zn_(1-x)Cd_xS合金薄膜的结构和光学性质

Structural and Optical Properties of Zn_(1-x)Cd_xS Alloys

采用低压金属有机化学气相沉积(LP MOCVD)技术,在普通石英衬底上制备出不同Cd组分(0.02,0.44,0.59,0.83,0.91)的Zn1-xCdxS合金薄膜材料。X射线测量表明样品为单一取向的纤锌矿结构,并且随着x的增加衍射峰位基本成线性地从ZnS衍射峰向CdS衍射峰移动。此外,在PL谱中还可以看出随着样品中Cd含量的增加,发光峰从3.66eV红移到2.43eV。根据发光峰位与Zn1-xCdxS中x的变化关系,推导出它们之间的关系近似为Eg(Zn1-xCdxS)=3.61-1.56x+0.38x2。还探讨了不同Cd组分薄膜材料的X射线衍射峰半峰全宽以及发光峰半峰全宽的变化。

Both CdS and ZnS crystals are Ⅱ-Ⅵ semiconductors and photonic materials having the direct band gaps. Since the wavelength corresponding to the band-gap of CdS is green 500 nm that is very sensitive for human eyes, the CdS thin film is useful for the sensor and the light source. For the CdS thin film produced by pulsed laser deposition (PLD), we first demonstrated the laser oscillation at room temperature excited with He-Cd laser. On the other hand, ZnS has been used for the fluorescence materials with the various doped elements. The band-gap of ZnS is so large (3.6 eV) that has been applied for the quantum well, the blue LED and the optical waveguide. Zn_(1-x)Cd_xS alloy thin films were prepared on quartz substrate by low-pressure metalorganic chemical vapor deposition (MOCVD). The x values of Zn_(1-x)Cd_xS are 0, 0.02, 0.44, 0.59, 0.83, 0.91 and 1. X-ray diffraction (XRD) spectra indicate that all the as-grown alloys with hexagonal wurzite structure was obtained. As the Cd content increases, the luminescence peaks of the samples redshift from 3.66 eV to 2.43 eV in the photoluminescence (PL) spectra. Based on the PL peak position of the alloy with different Cd composition, the relation of Zn_(1-x)Cd_xS emission peak with x was obtained as E_g(Zn_(1-x)Cd_xS)=3.61-1.56x+0.38x^2. The dependence of the PL peak position and the full width at half maximum(FWHM) of the diffraction peak and PL peak on Cd composition were also discussed. It is found that when x increases from 0 to 1, the PL peak position changes from 3.66 eV to 2.43 eV; but the FWHM increases and reaches a maximum when x=0.83, then it decreases sharply.