Effects of hydrogenation and doping on the conductivity and density of defect states in amorphous silicon

The temperature dependence of the dc conductivity σ has been measured in the temperature range T=100–500 K for a series of a‐SiHx: B thin‐film specimens prepared by magnetron reactive sputtering. Two groups of specimens were measured: (a) undoped specimens containing hydrogen concentration varying from zero to about 30 at. %, and (b) doped specimens containing 10 at. % hydrogen and boron concentration in the range 0.1–10 at. %. Activated band conduction (log σ∼T−1) was observed at high temperatures in undoped specimens containing about 5–10 at. % hydrogen. For all other specimens there is an extended temperature range of log σ∼T−1/4 consistent with charge transport by Mott’s variable range hopping mechanism. The density of states N(EF) at the Fermi level undergoes appreciable changes with increasing concentrations of hydrogen and boron. These changes are interpreted as evidence of substantial structural disorder in hydrogen‐rich and heavily doped a‐SiHx:B films.

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