| dc.description.abstract | By applying Raman spectroscopy, we have analyzed the phonon properties and crystal structure of different diameters of Ge quantum dot. When the germanium bulk transformed into quantum dot, we can observe that the Raman peak frequency increases as the diameter decreases via the Raman spectra. The reference indicates that the Ge-Ge mode frequency of Ge nanocrystals can be changed by quantum confinement and strain effect. And, Strain tensor in the Ge quantum dots can be further calculated by the Raman shift, and by comparing the different structures of the two samples, their strain sources would be found.The Raman spectra from various sizes of Ge quantum dot shows changes in peak position and linewidth with temperature. These temperature-dependent changes can attribute to the anharmoicity in the vibrational potential. Whether we calculcated the strain tensor from the Raman shift at 300K or intrinsic frequency, we can get the same result. Compared with the anharmonic coefficients, we find that Ge quantum dots were indeed influenced by quantum confinement effect. Quantum confinement effect plays a role in anharmonic oscillations, even though there is no significant change in the phonon frequency.The lifetime of the phonons can be obtained through the result from the temperature-dependent Raman peak, which is divided into the intrinsic lifetime and the decay lifetime. The former lifetime corresponds to the crystal quality, and it is the main contribution to the lifetime of the phonons at low temperature. The latter lifetime will be close to the value of the former lifetime with the rising temperature. Therefore, we conclude that as the temperature rises, the anharmonic effect would be raised.
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