多孔硅的微结构及其冷阴极的电子发射特性研究

采用电化学腐蚀法在n型单晶Si基底上制备多孔硅(PS)膜,利用场发射扫描电子显微镜(FE-SEM)分析其微结构特征,研究了硅基底材料、腐蚀电流密度和腐蚀时间等制备条件和工艺参数对PS微结构的影响。实验结果表明,轻掺杂n型Si基底上形成的PS膜(n--PS)中的孔较深且孔径较大,而重掺杂n型Si基底上的PS膜(n+-PS)中的孔分布较为密集,而且呈多分枝结构;腐蚀电流密度相同时,PS的膜厚和腐蚀时间成正比,而在较高的腐蚀电流密度下制备得到的PS膜在结构上更为疏松。制作了基于n+型硅基底的PS阴极,此阴极的阈值电压约为14 V,高于该电压后发射电流随着二极管电压提高而呈指数性增加趋势,而且发射电流对环境气压不敏感,即使在0.1 Pa的低真空中也没有明显的衰减。

Microstructures and Emission Characteristics of Porous Silicon Films

The microstructures of the porous silicon(PS) film,fabricated on n-type silicon wafer by electrochemical etching,were characterized with field emission scanning electron microscopy(FE-SEM).The impacts of the etching conditions,including the doping levels of the Si wafer,etching current density and time,on the porous Si films were studied.The results show that the doping levels of Si wafer strongly affect the film’s porosity.For the lightly-doped(n——type) Si,deepand wide pores were observed;in contrast,for the heavily-doped(n+-type) Si,high density of dendritic-structured pores was found.At a fixed etching current density,the PS film thickness was proportional to the etching time;and large etching current reduced its compactness.The emission threshold-voltage of the prototyped cold cathode,made of the PS films,was found to be 14 V.Moreover,low pressure little affected the emission current,even at 0.1 Pa.