CONTRIBUTION OF FLOATING BONDS TO LIGHT-INDUCED DEGRADATION OF HYDROGENATED AMORPHOUS SILICON

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Relation between the randomeness of amorphous network and the creation of defects was first investigated in an amorphous system of a-Ge_<1-x> C_x : H films which contains constituent atoms with largely different covalent radii, and compared the results with those in a-Ge_<1-x>Si_x, : H films which contains constituent atoms with close covalent radii. It. was found that the addition of C atoms makes the films stricture more random and increase the Ge dangling bonds per Ge atoms.Next we measured the spin-lattice relaxation time T_1 of Si dangling bonds and its dependence on the light-soaking time in a-Si : H.It was found that T_1 has a fairly good correlation with the randomness of the amorphous network estimated from the Urbach energy. It was also found that T_1's for the broad and narrow component signals of the light-induced ESR decreases by light-soaking, in contrast to that for the dark component. This might be an important clue to judge whether the origin of the broad component of the light-induced ESR comes from the floating bonds.Finally we tried to explain the defect creation processes by the light-soaking and electron-beam irradiation, using rate equations based on a model in which the floating bonds contribute to create dangling bonds.