脉冲功率对含硅量子点SiC<sub><em>x</em></sub>薄膜物相结构及光谱特性的影响

doi:10.3964/j.issn.1000-0593(2019)02-0529-06

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Abstract All-silicon tandem solar cells based on silicon quantum dots (Si-QDs) are considered to be one of the most promising high efficiency solar cells. In recent years, Si-QDs films with low Si-QDs density and many defects were reported. Thence, the photoelectric conversion efficiency of Si-QDs solar cells waslimited. Microwave Annealing (MWA) is considered to be a useful method to prepare nanostructured materials. The non-thermal effect of MWA can reduce energy for nucleation and improve the microstructure and photoelectric properties of the films. In this paper, SiC_x thin films containing Si quantum dots were prepared via magnetron co-sputtering technique and MWA with different pulse power.The phase structure and spectral properties of Si-QDs films were characterized by grazing incidence X-ray diffraction (GIXRD), Raman, photoluminescence (PL) and spectrophotometer. The influence of different pulse power on the Si-QDs density and performance was studied systematically.Thin films with highdensity and good performance weredeposited by improving the magnetron sputtering process.The GIXRD and Raman spectra all showed that the Si-QDs existed in the samples, and their intensities first increased and then decreased. By Scherrer’s formula, it was estimated that the size of Si-QDs increased initially and then decreased, and the maximum size of Si-QDs (7.98 nm) wasobtained when the sputtering power was 80 W. The centers of Raman peaks areat 511 cm^-1. This is ascribed to Si-Si lateral optical vibration modeand its intensity is also increased first and then decreased. The optimum Gauss peak fitting was used for the Raman spectra. It showed that the crystalline fraction was higher than 62.58%, and the highest crystallinefraction (79.29%) was gained when the power was 80 W. The above analysis showed that Si-QDs formed in the films and the size of Si-QDs first increases and then decreases. The maximum number of Si-QDs was acquiredwith the power of 80 W. The optical bandgap was estimated by Tauc formula. These bandgaps were going to decrease and then increase with the increase of power. The bandgap reachedminimum value (17.2 eV) with the power of 80 W. The Si-QDs size was inversely proportional to the band gap, indicating that the Si-QDs in the films had good quantum confinement effect. The luminescence properties of the samples were analyzed by the PL spectra, the optimum Gauss peak fitting was used. It was found that there were 6 luminescence peaks. Combine with the results of Raman spectrum, the luminescence peaks between 463~624 nm were derived from the role of the Si-QDs. The luminescence peaks between 408 and 430 nm originated from the defect state inside the films withoutthe shift of peak position, while the intensity varies. The distribution of the energy band gap were calculated according to the wavelength of the luminescence peak. Thus, the types of the defect state were determined, the luminescence peak at 408 nm is attributed to the electron radiation transition of ≡Si°→E_v, and the luminescence peak at 430 nm is attributed to ≡Si°→≡Si—Si≡ defect state luminescence. The Si-QDs size on the luminescence peak shift was also studied. The results show that blueshift (redshift) of luminescence peak occurred with the size of Si-QDs becoming smaller (larger). In conclusion, SiC_x films with Si-QDs prepared at the sputtering power of 80 W exhibited the best performance. The research results laid the foundation for the follow-up study of Si-QDs solar cells.

Key words：Pulse power; MWA; Si-QDs; Si-rich silicon carbide thin films; Spectral properties

Received: 2018-01-20 Accepted: 2018-05-15

ZTFLH:

O484.5

Corresponding Authors: YANG Wen E-mail: wenyang1972@hotmail.com

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https://www.gpxygpfx.com/EN/10.3964/j.issn.1000-0593(2019)02-0529-06 OR https://www.gpxygpfx.com/EN/Y2019/V39/I02/529