Amorphous samples were prepared by the glow discharge of silane, and the kinetics of hydrogen exodiffusion were studied using conductivity, electron paramagnetic resonance, nuclear activation, and infrared absorption methods. The results revealed the existence of two main stages of exodiffusion. At below 500C, H evolution was controlled by a diffusion process with a diffusion coefficient described by:

D(cm2/s) = 4.7 x 10-3exp[-1.5(eV)/kT]

Hydrogen evolution at above 500C was controlled by a first-order process. The activation enthalpy and entropy were 3.4eV and 7.8k, respectively. The observations that the electron paramagnetic resonance signal appeared during the second stage, and that the activation enthalpy was equal to the Si-H binding energy, represented direct evidence that the signal was associated with the breaking of this bond. A model was developed for exodiffusion in which it was assumed that hydrogen atoms could be bound into two types of center.

Possible Configurational Model for Hydrogen in Amorphous Si:H. An Exodiffusion Study. K.Zellama, P.Germain, S.Squelard, B.Bourdon, J.Fontenille, R.Danielou: Physical Review B, 1981, 23[12], 6648-67

Table 49

Diffusivity of H in Si