Anomalous and normal Hall effect in hydrogenated amorphous Si prepared by plasma enhanced chemical vapor deposition

The double sign anomaly of the Hall coefficient has been studied in p-doped and n-doped hydrogenated amorphous silicon grown by plasma enhanced chemical vapor deposition and annealed up to 500 degrees C. Dark conductivity as a function of temperature has been measured, pointing out a conduction mechanism mostly through the extended states. Anomalous Hall effect has been observed only in the as-deposited n-doped film, disappearing after annealing at 500 degrees C, while p-doped samples exhibit normal Hall effect. When Hall anomaly is present, a larger optical band gap and a greater Raman peak associated with Si-H bond are measured in comparison with the cases of normal Hall effect. The Hall anomaly will be related to the hydrogen content and implication on photovoltaic applications will be discussed.