纳米硅薄膜的低温电输运机制

THE TRANSPORT MECHANISM IN NANOCRYSTALLINE SILICON FILMS AT LOW TEMPERATURE

在很宽的温度范围 (5 0 0— 2 0K)研究了本征和不同掺磷浓度的纳米硅薄膜的电输运现象 .发现原先的异质结量子点隧穿 (HQD)模型能很好地解释薄膜在高温下 (5 0 0— 2 0 0K)的电导曲线 ,但明显偏离低温下的实验值 .低温电导 (10 0— 2 0K)具有单一的激活能W ,并与kBT值大小相当 (W～ 1— 3kBT) ,呈现出Hopping电导的特征 .对HQD模型做了修正 ,认为纳米硅同时存在两种输运机制 :热激发辅助的电子隧穿和费米能级附近定域态之间的Hopping电导 .高温时 (T >2 0 0K)以电子隧穿为主 ,低温时 (T <10 0K)则以Hopping电导为主 .在此基础上给出了纳米硅完整的电导解析表达式 ,该表达式能很好地解释在 5 0 0— 2 0K的温度范围 ,本征和不同掺磷浓度纳米硅薄膜的电导率 .

In a wide temperature range (500—20 K), we studied the electrical transport mechanism in intrinsic and P doped nanocrystalline silicon films. We find that the HQD model successfully explains the conductivity at high temperatures (500—200K), but fails at temperature below 200K. Single activation energy W was found in the low temperature range (100—20K), which is approximately equal to the value ofk BTW～1—3k BT).It is in good agreement with the characteristics of hopping conduction in amorphous semiconductor, In this paper we modified the HQD model. We consider two distinct transport mechanisms, thermal assisted tunneling and electrons hopping through the local states near the Fermi level exist simultaneously. At high temperature tunneling transport is the main process. At low temperature transport is governed by electron hopping. On this basis, a complete analytic function of the conductivity is proposed. The function successfully explains the conductivity of intrinsic and P doped nanocrystalline silicon films in the whole temperature range.