物理学报2017，Vol.66Issue(19)：259-267,9.DOI:10.7498/aps.66.196801
过渡区p型氢化硅氧薄膜结构和光电特性的研究
Structural and optoelectronic properties of p-type SiO:Hfilms deposited in transition zone
摘要
Abstract
P-type hydrogenated silicon oxide (p-SiOx:H) films are prepared by radio frequency plasma enhanced chemical deposition with various CO2 flow rates. We use gas mixtures of carbon dioxide (CO2), hydrogen (H2), silane (SiH4) and diborane (B2H6) as reaction source gases. For all experiments the substrate temperature, pressure and power density are fixed at 200 ?C, 200 Pa and 200 mW/cm2, respectively. The films are deposited on Corning Eagle 2000 glass substrates for optoelectronic measurements and on crystalline Si wafers for Fourier transform infrared (FTIR) measurement. The structural, optical and electronic properties of the films are systematically studied as a function of CO2 flow rate. The CO2 flow rate is varied from 0 to 1.2 cm3·min?1, with all other parameters kept constant. It is shown that with the CO2 flow rate increasing from 0 to 1.2 cm3·min?1, the Raman peak shifts from 520 cm?1 to 480 cm?1 and corresponding crystalline volume fraction decreases from 70% to 0. In addition, the FTIR spectrum shows that the oxygen content increases from 0 to 17%and the hydrogen bond configuration gradually shifts from mono-hydrogen (Si-H) to di-hydrogen (Si-H2) and (Si-H2)n complexes in the film. What is more, with the incorporation of oxygen, the optical band gap of each of all p-type SiO:H films increases from 1.8 eV to 2.13 eV, while the dark conductivity decreases from 3 S/cm (nc-Si:H phase) to 8.310?6 S/cm (a-SiOx:H phase). Furthermore, the oxygen incorporation tends to disrupt the growth of silicon nanocrystals due to the created dangling bonds that arises from an increased structural disorder. This leads to microstructural evolution of SiO:H film from a single nanocrystalline phase into first a mixed amorphous–nanocrystalline and subsequently into an amorphous phase. At a certain threshold of CO2 flow rate, a transition from nanocrystalline to amorphous growth takes place. The transition from nanocrystalline to amorphous silicon is confirmed by Raman and FTIR spectra. In the transition region or crystalline volume fraction of about 45%, Raman spectrum also reveals that the a mixture of nanocrystalline silicon and amorphous silicon oxide (a-SiOx:H) phase exists in the film. This means that nanocrystalline silicon oxide (nc-SiO:H) is a two-phase structural material consisting of a dispersion of silicon nanocrystals (nc-Si) embedded in the amorphous SiOx network. As is well known, the oxygen-rich amorphous phase can help enhance the optical band gap, while the nc-Si phase contributes to high conductivity. Finally, it is the SiO:H film deposited at phase transition that can realize a relatively high dark conductivity (about S/cm) with a wide optical band gap of 2.01 eV in the film. By using the transition p-layer as the window layer in conjunction with a suitable buffer thickness, we obtain a thin film solar cell with an open-circuit voltage of 890 mV, a short-circuit current density of 12.77 mA·cm?2, fill factor of 0.73, and efficiency of 8.27%without using any back reflector.关键词
射频等离子体增强化学气相沉积/过渡区p层/硅氧薄膜/光学带隙Key words
radio-frequency plasma enhanced chemical vapor deposition/transition p layer/SiO:H films/optical band gap引用本文复制引用
李同锴,徐征,赵谡玲,徐叙瑢,薛俊明..过渡区p型氢化硅氧薄膜结构和光电特性的研究[J].物理学报,2017,66(19):259-267,9.基金项目
国家自然科学基金(批准号: 61575019)资助的课题.Project supported by the National Natural Science Foundation of China (Grant No. 61575019). （批准号: 61575019）
