a-Si:H掺杂机理的研究

A STUDY ON MECHANISM OF DOPPING IN a-Si:H

本文利用CNDO/2量子化学理论方法,对P和B原子在四面体配位的Si)(46)和Sl_(46)H_(60)H_4~*原子集团中置换S_1原子前后的原子集团能量和能态分布变化进行了计算.计算结果表明:1)在Si_(46)H_(60)H_4~*原子集团中用P(或B)置换引Si原子后在能隙中明显地出现施主(或受主)态子带,同样在Si_(46)中进行置换前后没有这一特性;2)在Si_(46)原子集团中引入P(或B)置换S1原子所需要的能量明显小于在Si_(46)H_(60)H_4~*原子集团中进行相应置换所需要的能量.因此,纯的a-si材料不显示有效的掺杂特性,而a-Si:H具有明显的四面体代位式掺杂效应.此结论可解释大量实验结果.

We have calculated the electronic states and the total energies of a variety of tetrahedrally co-ordinated atomic clusters using the molecular orbital theory CNDO of quantum chemistry. All models in the calculations are based on the cluster Si46 with a single vacancy in the center. We find that for the cluster of Si46 H69 H*, in which all dangling bonds are saturated with hydrogen, the donor or acceptor levels in the gap clearly appear when the phosphorus or the boron is introduced substitutionally into the cluster, whereas no clear impurity levels is found for that without hydrogenation. In addition, the increase in total energy resulting from introducing phosphorus (or boron) into the hydrogenated cluster Si46 H60H* is evidently more than that of the cluster without hydrogenation. Our results have been explain d theoretically by the '8-N' rule. The specific role of hydrogen in doping mechanism and some recent experiments are discussed for a-Si:H films.