纳米β-SiC薄膜过剩载流子衰减特性分析

利用微波吸收技术对Si衬底上微晶及纳米β-SiC薄膜的过剩载流子瞬态行为进行了分析.所用样品采用PECVD技术制备,微波吸收测量采用脉宽35 ps,波长355 nm脉冲激光.所测得的载流子浓度衰减分为快、慢2个过程,微波吸收瞬态特性满足双指数衰减规律.该结果表明,样品光生载流子衰减过程主要决定于2种陷阱作用,其中快过程与SiC薄膜中浅能级陷阱的载流子弛豫效应相关,而慢过程则是深能级陷阱的载流子弛豫行为占优势的结果.纳米碳化硅晶粒界面较高的缺陷态密度导致载流子俘获几率增加,非辐射复合几率减小,纳米β-SiC薄膜表现较长的载流子衰减时间.

Excess Carriers Decay Behavior of Nanocrystalline β-SiC Thin Film

The excess carrier decay behavior of microcrystalline and nanocrystalline β-SiC films grown by helicon wave plasma-enhanced chemical vapor deposition process is measured by microwave absorption technique.The third harmonic output of a pulsed YAG laser with wavelength of 355 nm and pulse of 35 ps is used to excite the carriers of SiC films.The decay of the excess carriers concentration includes a fast and a slow processes.The measured transient decay curve of microwave absorption signal can be fitted fairly with a sum of two exponential decay functions,which indicates that the decay process is governed by two different kind of traps.The fast decay is related to the traps with shallow level and the slow one concerns with the traps with deep level.The shallow traps are mainly responsible for the initial carrier decay and the deep ones are dominated ultimately.The longer decay time of nanocrystalline β-SiC films is attributed to the higher defect state density in the gain interface when the size of β-SiC grain in nanometer size,which will increase the trapping rates of excess carriers and decrease the nonradiative probabilities.