Frequency-dependent conductivity in sputtered amorphous phosphorus thin films

The first measurements are reported of frequency-dependent (ac) conductivity in thin films of amorphous phosphorus prepared by rf sputtering. The behavior of the ac conductivity {σ}({ω}) is broadly similar to that which has been observed previously in many other types of amorphous semiconductors, namely a nearly linear frequency dependence but a weak temperature dependence. However, there are subtle but important differences for films treated in different ways. As-deposited films show a relatively large temperature dependence of {σ}({ω}) and of its frequency exponent s: annealing, or hydrogenation during the sputtering deposition, acts to decrease the temperature dependences of both quantities. The results are analyzed with reference to three models of the ac conductivity in amorphous semiconductors. It is shown that the best agreement is with the correlated barrier hopping model of ac conductivity and it is concluded that paramagnetic, neutral dangling-bond defects (D⁰) predominate in the ac loss process in the as-deposited material, whereas diamagnetic, charged defects (D⁺,D^-) predominate in annealed films.