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 $500°C$⁠. 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 $500°C$⁠, 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.