Universal dopant and defect equilibration kinetics inn-typea-Si:H

Abstract

The time dependences of the reversible decay of the dc conductivity of single-layer doped a-Si:H films following thermal quenching and the reversible increase of the threshold voltage in metal–insulator–a-Si:H structures during voltage biasing were measured to determine the kinetics of dopant and defect equilibration, respectively, in n-type a-Si:H. The equilibration time constants were measured as a function of temperature for different dopant-gas ratios (3×${10}^{\mathrm{-}7}$ to 1×${10}^{\mathrm{-}2}$), different dopant atoms (Li, P, As, and Sb), and different voltage biases (3.5 to 20 V) in the absence of dopants. In all cases, the time constants were thermally activated with activation energies between 0.7 and 1.0 eV, and were inversely proportional to the two-thirds power of the electron concentration. This universal behavior suggests that the rate-limiting step of the two distinct chemical reactions describing dopant deactivation and defect creation in a-Si:H are the same. We propose that this step is the dispersive diffusion of hydrogen from bond-terminating to weak-bond-trapping sites.