Photoconductivity and absorption in amorphous Si

TLDR: In this paper, the photoconductivity and absorption of Si specimens were measured at room temperature as a function of photon energy and Td in a spectral range from 0.5 eV to 3 eV and the absorption coefficient was determined for evaporated, sputtered and glow discharge specimens.

Abstract: The paper deals with photoconductivity and absorption in aSi specimens, prepared mainly by the decomposition of silane in a glow discharge. Substrate temperatures, Td, between 300 K and 650 K were used during deposition. The normalised photoresponse was measured at room temperature as a function of photon energy and Td in a spectral range from 0.5 eV to 3 eV. The absorption coefficient was determined for evaporated, sputtered and glow discharge specimens. The main features of the results are in agreement with conclusions drawn from previous electrical transport and field effect measurements and can be interpreted on the basis of the proposed model for the localised state distribution. It is confirmed that ϵc−ϵv is 1.5 to 1.6 eV, and that there is a local density of state maximum at about 1.2 eV below ϵc. At room temperature the steady photocurrent is carried predominantly by electrons in states above ϵc, whether excitation is from localized or extended states. Specimens prepared at Td > 500 K are highly photosensitive, with electron recombination lifetimes, τ, of up to 10−5s. Rise and decay times of the signal lie in the millisecond range. For Td < 500 K there is a drastic decrease in τ, which falls to 10−11 s at Td ⋍ 300 K and is even less for evaporated specimens. These results are discussed in some detail.