We have studied the near-infrared photoluminescence properties of free-standing germanium nano-crystals (20 nm on average) and micro-crystals (60 µm on average) at 80–300 K. Two peaks were observed at ~1.0 and ~1.4 eV from both the nano- and micro-crystals. The integrated PL (IPL) intensity of the nano-crystals is about an order of magnitude stronger than that of the micro-crystals and the IPL is also enhanced by ageing in air for both crystals. The ~1.0 eV peak position does not change with either the crystal size or temperature. We suggest that the deep traps located at the interfacial region between the surface GeO2 layer and the bulk crystal Ge is responsible for the near-infrared PL.
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