BIAS-ENHANCED CONDUCTANCE IN HYDROGENATED AMORPHOUS-SILICON FILMS

Bias-induced metastability has been observed in hydrogenated amorphous silicon (a-Si:H) films deposited under various conditions on soda glass substrates. The transition from the original low-conductance state to a high-conductance metastable state proceeds even at room temperature and with applied electric fields as low as 100 V cm-1. The increase in the film conductance reaches several orders of magnitude. The kinetics of the process depend on both temperature and applied bias. The activation energy of the enhanced conductance decreases by about 0.3-0.35 eV compared with the values characteristic for the original state. The transition to the metastable state is accompanied by the appearance of an internal polarization field. The experimental results have suggested that the increase in conductance is associated with a field-induced increase in the doping efficiency of sodium penetrating into a-Si:H during film deposition. The mechanism is based on the reaction between the neutral alkali atoms and neutral dangling bonds, which results in the formation of negatively charged dangling bonds and positive sodium ions. The applied electric field reduces the reversibility of the reaction because of the drift of sodium ions.