GAP STATES DUE TO INTRINSIC DEFECTS IN a-Si:H
a-Si:H中本征缺陷引起的赝隙态

Calculations of electronic structures for Si29 and Si47 clusters, which are cut from continuous random networks of a-Si, and those of simple ones Si8H18,Si17, have been performed by using CNDO LCAO MO method. The origin and nature of the gap states due to intrinsic defects such as weak bond, bent bond and charged configurations are examined in a-Si:H. The results show that two weak bond states situated in both sides of band gap have been contracted and shifted to the center of the gap as the weak bond is stretched. These weak bond levels have been shifted to some location near the top of valence band or near the bottom of conduction band due to extra charges. The bent bond states mainly appear near the top of valence band. When the bond is bent severely,the bond level shifted upwards, close to the center of band gap from below. The structural lopological disorder may induce the gap states at any position within the band gap. It is suggested that all the weak bond and bent bond as well as charged configuration are the principal forms of intrinsic defects in a-Si:H. Various experimental results of gap states are explained according to these theoretical calculations.