The first direct measurement is reported of the bulk density of deep states in $n$-type $a$-Si: H. The spectral distribution is considerably different from previous field-effect and $C-V$ measurements and the overall density is much lower than has previously been reported. The states seen in these samples appear to be extrinsic and suggest that the extrapolated total density of deep states in pure $a$-Si: H may be less than ${10}^{15}$ ${\mathrm{cm}}^{-3\mathrm{}}$.

• Received 21 February 1980

DOI:https://doi.org/10.1103/PhysRevLett.45.197