DENSITY OF STATES STUDY IN SPUTTERED a-Si : H : EFFECT OF IMPURITIES AND H RELATED DEFECTS

Abstract

We observe two regimes in the variation of qap size (Eo4) and den- sity of states (DOS) as a function of H-content (c?) in sputtered a-Si:H. In the first regime, an increase in cH from 5 to 17% 1s accompanied by an exponen- tial functional decrease of the DOS near midgap, which varies a lso directly with E04 over a wide range of p reparation c onditions. In the second regime, additional incorporation of H beyond 17% fails to further decrease the DOS (with CH and EO4), which shows a saturation with scatter. This behavior is interpreted in terms of H-induced and residual impurity related defects. Vari- ation of the DOS in the lower half of the gap, responsible for hole t rapping, is observed via the hole mobility-lifetime product, which exhibits a dramatic drop with impurity incorporation (P,O) and deteriorates for increasing cH in the second regime.