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Magnetoresistance in Sputtered Hydrogenated Amorphous Silicon

Magnetoresistance (MR) measurements have been made on sputtered hydrogenated amorphous silicon films for magnetic fields up to 1 T in the temperature range 100-300 K. The effect of a systematic increase of the hydrogen content in the films has been studied. In α-Si films with no hydrogen MR was always negative and it increased with decreasing temperature. In hydrogenated films MR was positive and its magnitude about a decade larger than the negative MR. The positive MR showed a maximum at low fields ∼ 0.2 T. Most of the observed features in the temperature range 200 K < T < 300 K can be explained by a hopping model in which MR is a result of the modification of the spin-flip relaxation time by the external magnetic field. It is concluded that the change of sign in MR with increasing hydrogen content is most probably due merely to the decrease in the density of states in the gap which causes a narrowing in the distribution of the hopping relaxation times. The obtained results support the idea that the variable range hopping mechanism dominates the electrical conduction in sputtered α-Si below room temperature. Further, the results indicate that spin dependent effects have a strong influence on the electrical transport in amorphous semiconductors.