Abstract
In this paper, the influence of annealing temperature on the structure and optical properties of silicon films was systemically investigated. Silicon films were deposited by electron beam evaporation and then annealed in N2 atmosphere within a temperature range from 200 to 500 °C. The films were characterized by X-ray diffraction (XRD), Raman spectroscopy, electronic-spin resonance (ESR) and optical transmittance measurement, respectively. With annealing temperature increased, the amorphous network order of silicon films was improved on the short and medium range and the defect density decreased remarkably. When sample being annealed at 400°C, the extinction coefficient k decreased from 6.14×1
The optical constants of optical thin films, like refractive index and extinction coefficient, are important factors that directly affect the design and preparation of optical thin films. In the Fabry-Perot (F-P) filters, at a given membrane structure, increasing the ratio of the high and low refractive index, can narrow the passband width and expand the cut-off band widt
Some papers concerned the influence of annealing on optical properties and structure of a-Si:H film
In this paper, the influence of annealing temperature on the structure and optical properties of silicon films was systemically investigated. Silicon films were deposited by electron beam evaporation and then annealed in N2 ambience within 200 ~ 500 °C. The films were characterized by XRD, Raman spectroscopy, ESR and optical transmittance measurement, respectively.
Silicon films were deposited by electron beam evaporation on sapphire substrates under identical conditions. Before deposition, the specimens with dimensions of Φ10×1 mm were cleaned with ethyl ether alcohol solution. During silicon films growth, the temperature of substrates was keeping 250°C. The silicon films were deposited by the evaporation rate of 0.4 nm/s at a base pressure of 1×1
The X-ray diffractometer (XRD) was wielded to investigate the structure of silicon films by Cu-target Kα radiation at 40 kV in the scanning angular from 10° to 80° at 2°/min. The Raman spectra were acquired to estimate the evolution of network structure through Micro Raman Spectrometer with the HeCd laser beam at 532 nm. The ESR measurement was performed by a double-cavities BRUKER ESP4105 spectrometer operated by X-band microwave radiation with a power of 20 mW at 80 K. Via a Lambda 900 spectrophotometer, the transmission spectrum of silicon films were measured and the measurement error was within 0.08%. From transmittance spectra, the refractive index (n) and extinction coefficient (k) of silicon films were calculated by using the Cauchy Exponential Model. In the dispersion model, the absorption coefficient varied exponentially with frequency. This allowed the Cauchy Exponential to model a large variation in the value of k versus wavelength. The following formulas were used to define the optical constant
, | (1) |
, | (2) |
where λ is wavelength, An, Bn, and Cn are material coefficients, Ak is amplitude, Bk is the exponent factor and Ck is the band edge.
As shown in

图1 硅薄膜经过不同温度退火后的XRD谱图
Fig.1 XRD patterns of silicon films annealed at different temperatures.
The widespread usage of Raman scattering into the research of microstructure materials lied in the fact that its intensity was susceptible to the order degree of solid structure. The Raman spectra of as-deposited and annealed silicon films were shown in

图2 (a) 沉积态和退火后的硅薄膜拉曼光谱;(b) 400°C退火后的硅薄膜拉曼光谱分峰谱图
Fig.2 (a) Raman spectra of the as-deposited and annealed silicon films; (b) The Gauss-deconvolution of Raman spectrum for silicon film annealed at 400 °C.
Annealing temperature (°C) | ГTO(c | ILA/ITO | ILO/ITO | ITA/ITO |
---|---|---|---|---|
as-deposited | 68.4 | 1.02 | 0.358 | 0.670 |
200 | 67.4 | 0.718 | 0.352 | 0.592 |
300 | 66.7 | 0.711 | 0.334 | 0.524 |
400 | 66.4 | 0.678 | 0.331 | 0.481 |
500 | 65.9 | 0.690 | 0.350 | 0.478 |
ESR was among few experiments offered defects information in structur

图3 沉积态和退火后的硅薄膜ESR谱图
Fig.3 Derivative ESR spectra of the as-deposited and annealed silicon films
2.2 Optical properties of silicon films

图4 沉积态硅薄膜和经过不同温度退火后的硅薄膜透射光谱
Fig.4 Optical transmittance spectra of as-deposited silicon film and the silicon films annealed at different temperatures.

图5 硅薄膜光学厚度和物理厚度随退火温度的变化
Fig.5 Variation of film optical thickness and physical thickness with annealing temperatures.
The optical constants of silicon films were fitted by using the FilmWizard software from SCI. During fitting process, the Cauchy Exponential Model was used as the dispersion model of material to fit the transmission spectrum.
Annealing temperature (°C) | An | Bn | Cn | Ak | Bk | Ck |
---|---|---|---|---|---|---|
as-deposited | 3.322 | 0.143 | 0.059 |
4.088×1 | 4.858 | 0.228 |
200 | 3.304 | 0.124 | 0.068 |
1.349×1 | 5.680 | 0.229 |
300 | 3.293 | 0.112 | 0.073 |
1.328×1 | 7.117 | 0.232 |
400 | 3.302 | 0.111 | 0.074 |
4.136×1 | 7.861 | 0.245 |
500 | 3.386 | 0.119 | 0.076 |
8.843×1 | 7.509 | 0.271 |

图6 (a)沉积态和退火后硅薄膜的折射率 (b)消光系数的色散曲线
Fig.6 Dispersion of (a) refractive index,(b) extinction coefficient of the as-deposited and annealed silicon films
The silicon films were deposited on sapphire wafer by electron beam evaporation and then annealed in N2 atmosphere in a temperature range from 200 to 500 °C. It was concluded that all silicon films maintained amorphous in microstructure, but with annealing temperature increased, the amorphous network order was improved on the short and medium range. Meanwhile, the defect concentration from ESR measurement decreased distinctly. When sample being annealed at 400°C, the defect density declined to the minimum, about one fifth of the as-deposited sample. With annealing temperature increased, transmittance spectra of silicon films shifted to the shorter wavelength direction, owing to the decrease of film thickness and the change of refractive index. When sample being annealed at 400°C, extinction coefficient also cut down to the minimum, and then mounted up by rising annealing temperature further. According to these results, annealing at an appropriate temperature could effectively reduce the optical absorption of silicon films in the near infrared region, which were very critical for the application in optical thin film coating devices.
Acknowledgements
This work was supported by the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 61605229); Innovation Program of Shanghai Institute of Technical Physics, Chinese Academy of Sciences (Grant No. CX-129).
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