Luminescence studies of a Si/SiO2 superlattice

Abstract

Photoluminescence and electroluminescence from a Si/SiO2 superlattice have been measured. They show similar characteristics and exhibit an inhomogeneously broadened photoluminescence band peaked at 2.06 eV. The excitation spectrum indicates that excitations occur in the Si layers. The insensitivity of the luminescence spectrum and decay to temperature and excitation wavelength suggests that luminescence originates from transitions between localized defect states. These localized states are most likely defect states residing at the Si/SiO2 interfaces, because there should be a significant concentration of defects at the interface and SiO2 due to the large lattice mismatch and the amorphous state. The close proximity of these states offers a more rapid transition path for the excited electrons. An energy band diagram of the superlattice is constructed based on our results.

Size, oxidation, and strain in smallSi/SiO2nanocrystals

“…The strong fluctuations of the electronic gap with the nanocrystal size could be responsible for the large broadening of the PL spectra that have been observed experimentally, also at low temperatures. 3,5,6,8,9,12,[43][44][45][46][47][48][49] …”

“…4,7,10,12,46,47 Moreover, the presence of other oxygen-bond types is frequently reported in experimental samples, beside the single-bond type discussed here. Several works report the Si-O-Si bridge bond as the most stable configuration, and the Si=O double bond as the less energetically favoured.…”

“…These considerations suggest a final picture in which the gap of small embedded NCs show an oscillating behaviour with size, and not strictly following the QC, as already observed in other works. 34,38 The large broadening of the PL spectra, observed also at low temperatures, 3,5,6,8,9,12,[43][44][45][46][47][48] even for apparently monodispersed multilayered samples, 49 could be a possible consequence of such fluctuations of the electronic gap with the NC size.…”

“…Embedding Si-NCs in wide band gap insulators is one way to obtain a strong quantum confinement (QC). SiNCs embedded in a silica matrix have been obtained with several techniques as ion implantation, 3,4 chemical vapour deposition, [5][6][7][8] laser pyrolysis, 9,10 electron beam lithography, 11 sputtering, 12,13 and some others. Alternative preparation methods produces NCs with different surface terminations (D, F, C, and others) that earned some interest in the last years.…”

Polarity-controlled visible/infrared electroluminescence in Si-nanocrystal/Si light-emitting devices

“…In order to understand the electrical and optical properties of the device, we calculate the distribution of bias voltage across the LED. 5,7,[13][14][15] Figure 4 shows the band diagrams of the LED at a negligible current ͑10 A͒ under forward and reverse biases. Here, we approximate the Si-nc/ SiO 2 matrix as a uniform SiO 2 thin film with a dielectric constant of ϳ5 measured by ellipsometry.…”