Fotoluminescencia resolvida no tempo em a-Si1-x Cx:H

AUTOR(ES)
DATA DE PUBLICAÇÃO

1997

RESUMO

The low temperature luminescence quantum efficiency h of amorphous hydrogenated silicon-carbon alloys a-Si1-xCx:H decreases with increasing carbon concentration below 25%. For higher carbon concentrations h increases with increasing carbon concentration and is almost temperature independent. The objective of this work is to understand the recombination processes that occur in a-Si1-xCx:H. Time resolved photoluminescence measurements were made over a temperature range from 17K to 300K. Samples were prepared by radio-frequency PECVD (Plasma Enhanced Chemical Vapour Deposition) from mixtures of CH4 and SiH4 in the "low power regime". As happens for a a-Si:H, the PL decay of a a-Si1-xCx:H is not exponential. It can be described by lifetime distribution functions. Samples with small carbon concentrations (<25%) show a peak in the lifetime distribution centered at about 10-4s-10-3s, wich shifts towards shorter lifetimes as the carbon concentration in increased or the temperature raises. Samples with carbon concentration higher than 25% present two peaks in the lifetime distribution. The peak with longer lifetime hehaves qualitatively in the same way as the peak observed in samples with less than 25% carbon. The peak corresponding to shorter lifetimes (~10-8s) is almost temperature independent. In these high content carbon samples the two peaks depend weaklu on the carbon concentration. The behavior of the PL lifetime in samples with less than 25% carbon and of the slow peak in samples with higher carbon concentrations can be described by the model accepted for a-Si:H. The faster peak in the higher carbon concentration samples involves another recombination mechanism. It is probably associated to completely overlapping electron and hole wavefunctions. This overlap can be found when electron and hole states are coincident in space. Such states can be caused by short-range antiparallel potential fluctuations which are enhanced as the carbon concentration increases.

ASSUNTO(S)

fotoluminescencia semicondutores amorfos carboneto de silicio

ACESSO AO ARTIGO

Documentos Relacionados