Size-dependent electroluminescence from Si quantum dots embedded in amorphous SiC matrix

Si quantum dots (QDs) were formed by thermal annealing the hydrogenated amorphous silicon carbide films (a-SiC(x):H) with different C/Si ratio x, which were controlled by using a different gas ratio R of methane to silane during the deposition process. By adjusting x and post annealing temperature, the QD size can be changed from 1.4 to 4.2 nm accordingly, which was verified by the Raman spectra and transmission electron microscopy images. Size-dependent electroluminescence (EL) was observed, and the EL intensity was higher for the sample containing small-sized Si QDs due to the quantum confinement effect (QCE). The EL peak energy as a function of the Si QDs size was in good agreement with a modified effective mass approximation (EMA) model. The calculated finite barrier potential of the Si QDs embedded in SiC matrix is 0.4 and 0.8 eV for conduction and valence band, respectively. Moreover, the current-voltage properties and the linear relationship between the integrated EL intensity and injection current indicate that the carrier transport is dominated by Fowler-Nordheim tunneling and the EL mechanism is originated from the bipolar recombination of electron-hole pairs at Si QDs. Our results demonstrate Si QDs embedded in amorphous SiC matrix has the potential application in Si-based light emitting devices and the third-generation solar cells. (C) 2011 American Institute of Physics. [doi:10.1063/1.3641989