Ion-induced changes in semiconductor properties of hydrogenated amorphous silicon

Undoped, phosphorus doped (n-type), and boron doped (p-type) hydrogenated amorphous silicon (a-Si:H) thin films are irradiated with 3.0 MeV protons, 100 keV protons, and 2.8 MeV silicon ions, and the electric conductivity variations as a function of ion fluence are investigated. The Seebeck coefficient variations as a function of ion fluence are also investigated and are compared to the electric conductivity variations. As a result, a systematic interpretation of radiation effects on a-Si:H semiconductors is obtained. In the fluence regime of below 10−6 dpa, the increase in electric conductivity and the emergence of negative Seebeck effect are observed in the undoped a-Si:H because of donor-center generation. In the fluence regime from 10−6 dpa to 10−4 dpa, the decrease in electric conductivity and the decrease in absolute value of Seebeck coefficient are observed in the doped a-Si:H, since the carrier removal effect is caused by radiation defects, which are thought to be mainly dangling bonds. In the fluence regime of above 10−4 dpa, the increase in electric conductivity caused by the enhancement of hopping transport via localized states is observed. The absolute value of Seebeck coefficient of doped a-Si:H decreases in this fluence regime, whereas no Seebeck effect is observed in the undoped a-Si:H.