Compensational boron doping and the determination of the mobility gap of hydrogenated amorphous Ge

Abstract

The n-type character of nominally undoped hydrogenated amorphous Ge (a-Ge: H) films is clearly demonstrated by the effect of the addition of trimethylborane (CH₃)₃B to the gas atmosphere of the sputtering preparation process. The minimum conductivity of the fully compensated material was investigated as a function of the H content and used to determine the mobility gap. The mobility gap obtained for sputtered boron−and−carbon−doped a-Ge : H films, which is always smaller than the optical gap (E _T or E ₀₄), increases with increasing H content and saturates at 0·95 eV, whereas for glow−discharge films a value of 1·03 eV was found.