Kinetics of Dopant Metastability in a-Si:H

Abstract

ABSTRACTSmall temperature-induced perturbations from thermodynamic equilibrium of doped hydrogenated amorphous silicon (a-Si:H) are explored by dark conductivity measurements. The equilibration kinetics reveal significant differences between phosphorus and boron doping. Raising the temperature leads to an increase of electron/hole densities which are related to the activation of additional dopants, while a decrease of temperature causes the opposite effect of dopant passivation. The creation kinetics of P doped a-Si:H is stretched exponential with a temperature independent β value of 0.85 whereas dopant passivation in the same temperature range is also stretched exponential decay, but with values for β < 0.8. In contrast, the kinetics of boron activation and passivation are stretched exponential with equal β values. The time constant τ to achieve thermodynamic equilibrium for both activation and passivation is thermally activated with energies ≃ 1.1 eV for P and B doped a-Si:H. τ depends weakly on the degree of perturbation. A discussion and interpretation of the data based on hydrogen migration in a-Si:H is given.