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The roles of amorphous Si nanoparticles in light-emitting diodes (LEDs) based on Er-doped Si(1+x)O(2) films (x representing the degree of Si content, and varying widely from 0 to 4.50) have been investigated. In the aspect of the LEDs' electrical performance, it was found that the incorporation of Si nanoparticles facilitates the electrical conductivity of the films by improving the carrier mobility. With x increasing from 0 to 4.50, the mobility increases monotonically up to 5 times. The efficiency of Er(3+) electroluminescence (EL) at 1.54 µm can be enhanced by as much as 160 times when the degree of Si content x is 2.00, coincident with the value at which the rate of mobility increasing versus x slows down. The fact that the maximum of EL efficiency and the slowing down of the rate of increase of mobility occur at the same x value can be explained by coalescence of Si nanoparticles starting at x = 2.

Phonon modes in spherical GaAs quantum dots (QDs) embedded in spherical AlAs shells with up to 11 855 atoms (about 8.0 nm in diameter) are calculated by using a valence force field model. All the vibration frequencies and vibration amplitudes of these shell QDs are calculated directly from the lattice dynamic matrix by employing the projection operators of the irreducible representations of the group theory. The effects of the size of GaAs cores and the thickness of AlAs shells on the phonon modes are investigated. The quantum confinement effects of both the vibration frequencies and vibration strengths are investigated. The microscopic interface modes, which can only be revealed by the microscopic model, are identified and discussed.