| Abstract | This Chapter discusses the phenomena associated with germanium (Ge) nanocrystals emitting near infrared radiation under optical excitation. We describe how the emission properties are influenced by various effects, including those of strain and particle confinement, as well as excitation mechanisms. Two example systems are discussed, namely one of isolated Ge quantum dots and another of Ge nanocrystals coherently imbedded in SiGe alloy layers, where both systems were grown by molecular beam epitaxy (MBE) on Si substrates. For the Ge dot ensembles, we show how particle size information can be derived from the emission spectrum. For the Ge nanocrystals, the emission spectra are analyzed for the effects of strain and particle confinement over a wide range of Ge fractions in the surrounding SiGe medium. This analysis provided significant insight into the properties of the Ge nanocrystals, including their size and shape, which were a 1.4 nm thickness in the MBE growth direction and a 7 nm lateral dimension. We also discuss the mechanisms leading to the high quantum efficiency observed for emission from the Ge nanocrystals at low temperatures. |
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