Efeito metaestavel induzido por luz em a-Ge:H

AUTOR(ES)
DATA DE PUBLICAÇÃO

1991

RESUMO

This work reports on light induced metastable defect creation and annealing in a-Ge:H thin films of electronic quality. The films were deposited by the RF sputtering method in an Ar-Hz o atmosphere onto substratum?s held at 180 ºC. The samples are photo-conductive, with apc/ad = 1.5 to 2 under AM1 conditions (100 mW/cm2) at room temperature. Both, the dark-and the photo-conductivity of the samples decrease after light soaking. The effect is attributed to light induced defect formation. At T = 310 K the dark conductivity decreases to 86% of its initial value after a few minutes of AM1 soaking. The changes are metastable and both, apc and ad, return to their original values after some hours in the dark. In order to establish the kinetics of defect formation and annealing a differential setup was used to measure conductivity transients at different temperatures and under different illumination conditions. Both, the defect formation and the annealing processes. Were found to be temperature activated. The temporal evolution of the annealing process is best explained by a stretched exponential law: Da exp ?(t/t)b , with b = 0.8 ± 0.1. The characteristic inverse decay time 1/t has an activation energy of 0.45 eV. As in the case of a-Si:H, this kind of process kinetics may be associated with hydrogen diffusion in the material. Hydrogen diffusion measurements are being carried on our samples by thermal annealing at different temperatures and annealing times. The hydrogen detection techniques used are IR spectroscopy and ERDA (Elastic Recoil Detection Analysis). A dispersive type of diffusion was found with a diffusion coefficient of @ 10-15 cm2/s at 300 °C .Results obtained up to now do not give a clear role to the hydrogen diffusion on the metastable effects observed in a-Ge:H

ASSUNTO(S)

teoria eletromagnetica filmes finos

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