Enhancement of photoluminescence in Ge nanoparticles by neighboring amorphous C in composite Ge/C thin films

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Abstract
Composite thin films of Ge and C prepared with the pulsed laser deposition method were found to exhibit enhancement of photoluminescence (PL). X-ray diffractometry and atomic force microscopy established that the structure of the as-prepared sample consisted of Ge nanocrystals and amorphous C. A blue PL from the films was found in the wavelength region of 400–550 nm with two distinct humps in its peak. For the as-prepared sample, the PL intensity was found to peak at a certain Ge : C composition ratio. For films with the same Ge : C ratio, the PL intensity was found to increase monotonically with intensity of annealing in the open atmosphere. The origin of the PL is attributed to localized Ge/O-related defects and that of the humps to the two nonbonding electrons of Ge(O). It is argued that the two nonbonding electrons are related to the intermediate Ge oxidation states ( GO x , 0<x<2), one of them being related to x near 0, and the other to x near 2, that is, near the saturated GeO 2 state. The observed enhancement in the PL of the Genanoparticles is attributed to the presence of amorphous C because it enhances the formation of Genanoparticles and the localized Ge/O-related defects at the Ge/C interfacial regions. This phenomenon offers a possible useful way to control the PL intensity of the film by adjusting its Ge : C ratio or its intensity of annealing.