基于同步辐射的黑硅红外增强吸收机理研究

Black silicon has excellent properties of full-spectrum light absorption, since it can absorb almost completely the light with wavelength from 250 nm to 2500 nm. When the energy of incident photon is larger than the silicon band gap, the enhanced absorption can be attributed to the multireflection and thus light trapping, induced by the surface microstructures of black silicon; When the energy of the incident photon is smaller than the silicon band gap, it has been well accepted that the strong absorption is due to the hyperdoped chalcogen. However, concerning the detailed mechanisms responsible for the strong infrared absorption, there still exists different opinions. Annealing the black silicon even at 200℃, with which temperature the doped chalcogen can not diffuse thermally, the infrared absorption of black silicon begins to drop, which indicates that the infrared absorption very probably originates from some kinds of unknown Si-chalcogen local configurations. Up to now, however, we still have little informations about this kind of local chalcogen configurations. This research plan aims at exploring the detailed informations about this kind of local chalcogen configurations and the effects of post annealing on it, by using the strong detect tools of synchrotron radiation X-ray absorption fine structure (XAFS) and synchrotron radiation X-ray photoelectron spectroscopy (XPS), together with the change of infrared absorption during annealing, in order to demonstrate clearly the micromechanism of infrared absorption of black silicon. The expected results will be very instructive to improve the performance of the photoelectronic devices based on black silicon at the infrared wavelength band.

黑硅具有优异的全光谱吸收性能，波长从250nm到2500nm其吸收率都接近1。当入射光子能量大于硅禁带宽度时，增强的光吸收主要是由于黑硅表面微结构多次反射带来的陷光效应；当入射光子能量小于硅的禁带宽度时，吸收的增强目前大家都认为是由于硫族元素的过饱和掺杂引起的。但对掺入的硫族元素通过何种机制吸收红外光还存在争议。黑硅在较低温度下（200℃）退火时，掺杂元素还无法热扩散，它在红外波段的强吸收就开始下降，这使人们认为红外吸收很可能是硫族元素与硅形成的一种局域结构的吸收。但目前我们对这种局域结构的详细信息所知甚少。本项目计划应用同步辐射X射线吸收精细结构（XAFS）和同步辐射X射线光电子能谱（XPS），来探测退火前后黑硅内掺杂原子周围的局域结构和化学态的微观变化，结合退火中黑硅红外光吸收的变化，从而阐明黑硅红外吸收的详细机制，这对进一步提高黑硅光电器件在红外波段的性能具有重要指导意义。