Exciton states and photoluminescence in Ge quantum dots.

We have studied, both theoretically and experimentally, the mechanism of photoluminescence (PL) of Ge nanocrystals in SiO2 and GeO2 matrices. Ge quantum dots (QDs) have been created by pulsed laser deposition (PLD). Time-resolved PL spectra in the photon energy range of 1.4- 3.2 eV have been measured within the time range 50 ns-20 μs. We have calculated the exciton binding and radiative transition energies accounting for both finite potential barriers and heterointerface polarization in the system. PL spectra have been calculated and compared with experimental results accounting for quantum-mesoscopic fluctuations and possible oscillations in exciton radiative lifetime occurring as QD size decreases. Good agreement between calculated and experimental PL spectra supports an assumption on the excitonic character of PL in Ge QDs and enables the parameters of the PL model to be determined. [ABSTRACT FROM AUTHOR]