nc-Si:H/α-SiC:H多层膜的结构与光吸收特性

Structure and optical absorption of nc-Si:H/α-SiC:H multilayers

利用等离子体增强化学气相沉积工艺制备了α-Si:H/α-SiC:H多层膜结构,并在900—1000?C下进行了高温退火处理,获得了尺寸可控的nc-Si:H/α-SiC:H多层膜样品.Raman测量表明,900?C以上的退火温度可以使α-Si:H层发生限制晶化.透射电子显微镜照片显示出α-Si:H层中形成的Si纳米晶粒的纵向尺寸被α-SiC:H层所限制,而与α-Si:H层的厚度相当,晶粒的择优取向是?111?晶向.傅里叶变换红外吸收谱则清楚地显示出,高温退火导致多层膜中的H原子大量逸出,以及α-SiC:H层中有更多的Si-C形成.对nc-Si:H/α-SiC:H多层膜吸收系数的测量证明,多层膜的吸收主要由nc-Si:H层支配,随着Si晶粒尺寸减小,多层膜的光学带隙增大,吸收系数降低.而当nc-Si:H层厚度不变时,α-SiC:H层厚度变化则不会引起多层膜吸收系数以及光学带隙的改变.

Nanocrystalline silicon nc-Si：H/SiC：H multilayers were fabricated by thermal annealing of the hydrogenated amor-phous Si α-Si：H/hydrogenated amorphous silicon carbide α-SiC：H stacked structures prepared by plasma enhanced chemical vapor deposition （PECVD） system at 900—1000℃. The microstructures of annealed samples were investigat-ed by Raman scattering, cross-section transmission electron microscopy （TEM）, and Fourier transform infrared （FTIR） spectroscopy. Results demonstrate that the size of Si grains formed can be controlled by theα-Si：H layer thickness and annealing temperature. Optical absorption measurements show that the optical bandgap of the multilayered structures increases and the absorption coe？cient decreases with diminishing Si grain size. However, the absorption coe？cient and the optical bandgap of the multilayers are not influenced by the α-SiC：H layer thickness when the size of Si grains is kept constant.