Sn掺杂ZnO薄膜的室温气敏性能及其气敏机理

采用化学气相沉积方法在预制好电极的玻璃基底上制备出Sn掺杂ZnO薄膜和纯ZnO薄膜. 两种样品典型的形貌为四足状ZnO晶须, 其直径约为150-400 nm, 呈疏松状结构. 气敏测试结果显示Sn掺杂ZnO薄膜具有优良的室温气敏性, 并对乙醇具有良好的气敏选择性, 而纯ZnO薄膜在室温条件下对乙醇和丙酮均没有气敏响应. X射线衍射结果表明两种样品均为六方纤锌矿结构. Sn掺杂ZnO样品中没有出现Sn及其氧化物的衍射峰, 其衍射结果与纯ZnO样品对比, 衍射峰向小角度偏移. 光致发光结果表明, Sn掺杂ZnO薄膜与纯ZnO薄膜均出现紫外发光峰和缺陷发光峰, 但是Sn的掺杂使得ZnO的缺陷发光峰明显增强. 将Sn掺杂ZnO样品在空气中退火后, 其室温气敏性消失, 说明Sn掺杂ZnO样品的室温气敏性可能与其缺陷含量高有关. 采用自由电子散射模型解释了Sn掺杂ZnO薄膜的室温气敏机理.

Room temperature gas sensing property and sensing mechanism of Sn-doped ZnO thin film

Sn-doped ZnO and pure ZnO thin films are deposited on glass substrates with prepared electrode by the chemical vapor deposition method. The gas sensing performances of Sn-doped ZnO and pure ZnO thin films are investigated by our home-made system at room temperature, and the gas sensing test results reveal that Sn-doped ZnO thin film exhibits high gas response to ethanol and acetone, while no response is detected for pure ZnO to ethanol or acetone at room temperature. Sn-doped ZnO thin film also has high selectivity that the response to ethanol is higher than that to acetone in the same measurement conditions, and the response of Sn-doped ZnO thin film sample to ethanol is almost the third largest when the concentration is 320 ppm. The typical scanning electron microscopy images reveal that these two samples are tetrapod-shaped ZnO whiskers with diameters in a range of about 150-400 nm. X-ray diffraction results indicate that all the samples are of wurtzite structure. Neither trace of Sn, nor that of Sn alloy nor that of Sn oxide is detected in the Sn-doped ZnO film, while its diffraction peak shifts towards the left compared with that of pure ZnO sample, which suggests that Sn atoms exist in the form of interstitial atoms in the ZnO crystal. The energy dispersive spectrum shows that the Sn-doped ZnO thin film is composed of Zn and O elements, and no Sn signal is defected. Photoluminescence spectra reveal that both Sn-doped ZnO and pure ZnO films have ultraviolet light emission peaks and green emission peaks, while the intensities of the defect emissions are significantly enhanced by doping of Sn. In addition, no gas response to ethanol is detected after Sn-doped ZnO thin film has been annealed in the air, which indicates that the room temperature gas sensitivity of the Sn-doped ZnO thin film may be related to its high defect concentration. The working mechanism of Sn-doped ZnO thin film is explained by a free electron random scattering model. As is well known, ZnO semiconductor gas-sensor is of surface-controlled type. In this work, upon exposure to ethanol vapor, the physical absorbed ethanol molecules acting as scattering centers can reduce the mean free path of the electrons in the surface of the film, changing the mean free time τ_n, which would increase the resistance of Sn-doped ZnO thin film at room temperature. This work provides a simple method of fabricating the highly sensitive ethanol gas sensor operating at room temperature, which has great potential applications in gas sensor field.