一种纳米硅薄膜的传导机制

ON THE CONDUCTION MECHANISM OF HYDROGENATED NANOCRYSTALLINE SILICON FILMS

基于对实验和理论的分析，提出一种异质结量子点隧穿（ＨＱＤ）模型，并导出了纳米硅薄膜电导率完整的表达式．其主要思想是，纳米硅薄膜中的微晶粒（几个纳米大小）具有量子点特征，在微晶粒与界面之间由于两者能隙的差异构成晶间势垒，这类似于多晶硅中经常使用的晶间势垒模型（ＧＢＴ）．考虑到量子点中的单电子隧穿特征，认为纳米硅薄膜中的电传导是由微晶粒中电子弹道式输运与单电子越过势垒的隧穿构成的．这就是ＨＱＤ模型的主要内容。

A hetero quantum dots (HQD) model for hydrogenated nanocystalline silicon films (nc Si∶H) is proposed. The main contents of our model are: (i) the nanocrystalline grains and their amorphous conterparts have very different band gap and band structures. As a result, they form heterojunction like structures in the interface regions, where the band offset effects dramatically reduce the activation energy and the grains act like quantum dots; (ii) in the presence of an external field, the activated electrons in the quantum dots conduct via quantum tunneling through the interface barriers. By means of the HQD model, we have identified the conduction of nc Si∶H as thermal assisted tunneling process. Our results show that there are two distinctive regimes for the conductivity of nc Si∶H:(1) low temperature regime,where there is a simple activation energy Δ E; (2) high temperature regime, where Δ E is enhanced by the temperature effect of the electronic tunneling in the nanoscale particales. The theory is in good agreement with the experiments. Finally, we propose a perfect conductivity formula for nc Si∶H films.