Optical emission fromSiO2-embedded silicon nanocrystals: A high-pressure Raman and photoluminescence study

Abstract

We investigate the optical properties of high-quality Si nanocrystals (NCs)/SiO 2 multilayers under high hydrostatic pressure with Raman scattering and photoluminescence (PL) measurements. The aim of our study is to shed light on the origin of the optical emission of the Si NCs/SiO 2 . The Si NCs were produced by chemical-vapor deposition of Si-rich oxynitride (SRON)/SiO 2 multilayers with 5-and 4-nm SRON layer thicknesses on fused silica substrates and subsequent annealing at 1150°C, which resulted in the precipitation of Si NCs with an average size of 4.1 and 3.3 nm, respectively. From the pressure dependence of the Raman spectra we extract a phonon pressure coefficient of 8.5 ± 0.3 cm −1 /GPa in both samples, notably higher than that of bulk Si (5.1 cm −1 /GPa). This result is ascribed to a strong pressure amplification effect due to the larger compressibility of the SiO 2 matrix. In turn, the PL spectra exhibit two markedly different contributions: a higher-energy band that redshifts with pressure, and a lower-energy band which barely depends on pressure and which can be attributed to defect-related emission. The pressure coefficients of the higher-energy contribution are (−27 ± 6) and (−35 ± 8) meV/GPa for the Si NCs with a size of 4.1 and 3.3 nm, respectively. These values are sizably higher than those of bulk Si (−14 meV/GPa). When the pressure amplification effect observed by Raman scattering is incorporated into the analysis of the PL spectra, it can be concluded that the pressure behavior of the high-energy PL band is consistent with that of the indirect transition of Si and, therefore, with the quantum-confined model for the emission of the Si NCs.

Size‐Controlled Si Nanocrystals Fabricated by Electron Beam Evaporation

“…Considering the peak energy values and the intensity behavior reported in the literature for Si NCs with similar sizes, our observations suggest that the low‐energy contribution is directly related to Si NCs emission via radiative electron‐hole recombination, whereas the high energy contribution could be associated to highly localized defect levels at the Si‐SiO 2 interface, in good agreement with Ref. .…”

“…In addition, the deconvolved peak at lower energies displays an overall intensity which is almost independent on L SRO , in contrast to the intensity of the higher‐energy contribution (blue squares), exhibiting a pronounced intensity quenching at larger L SRO [see Figure (e)]. Considering the peak energy values and the intensity behavior reported in the literature for Si NCs with similar sizes, our observations suggest that the low‐energy contribution is directly related to Si NCs emission via radiative electron‐hole recombination, whereas the high energy contribution could be associated to highly localized defect levels at the Si‐SiO 2 interface, in good agreement with Ref. .…”

“…Considering that the PL lineshape from Si NCs is constituted by a combination of Gaussian contributions (see, e.g., Refs. ), our spectra could be deconvolved using only two Gaussian functions in the energy domain, one of them centered at higher energies (around 750 nm) and another centered at lower energies (around 900 nm). The deconvolution of the PL spectra for samples with L SRO = 3.5 nm and L SRO = 4.7 nm is displayed in Figure (c), exhibiting excellent accordance between the experimental spectra and the Gaussian fits.…”

Modulation of the electroluminescence emission from ZnO/Si NCs/p-Si light-emitting devices via pulsed excitation

“…A subsequent high-temperature annealing treatment was carried out at 1150 C for 1 h in N 2 ambient, to induce phase separation resulting in the excess Si precipitation and crystallization in the form of Si NCs, followed by H 2 defect passivation at 450 C for 1 h. The material properties of analogous Si NC/ SiO 2 MLs concerning NC size, crystalline quality and optical absorption and emission have been reported in the past. [18][19][20][21][22][23] Finally, a 200-nm-thick ZnO film was deposited by ALD at 200 C (Refs. 15 and 16) and patterned by conventional photolithography, followed by full-area Al metallization of the rear side.…”