Optical and electronic properties of Si nanoclusters synthesized in inverse micelles

Abstract

Highly crystalline, size-selected silicon (Si) nanocrystals in the size range 2-10 nm were grown in inverse micelles and their optical absorption and photoluminescence (PL) properties were studied. High resolution TEM and electron diffraction results show that these nanocrystals retain their cubic diamond stuctures down to sizes -4 nm in diameter, and optical absorption data suggest that this structure and bulk-like properties are retained down to the smallest sizes produced (-1.8 nm diameter containing about 150 Si atoms). High pressure liquid chromatography techniques with on-line optical and electrical diagnostics were developed to purify and separate the clusters into pure, monodisperse populations. The optical absorption revealed features associated with both the indirect and direct bandgap transitions, and these transitions exhibited different quantum confinement effects. The indirect bandgap shifts from 1.1 eV in the bulk to -2.1 eV for nanocrystals -2 nm in diameter and the direct transition at T(Tz -TIS) blue shifts by 0.4 eV from its 3.4 eV bulk value over the same size range.Tailorable, visible, room temperature PL in the range 700-350 nm (1.8 -3.5 eV) was observed from these nanocrystals. The most intense PL was in the violet region of the spectrum (-400 nm) and is attributed to direct electron-hole recombination. Other less intense PL peaks are attributed to surface state and to indirect bandgap recombination. The results are compared to earlier work on Si clusters grown by other techniques and to the predictions of various model calculations.Currently, the wide variations in the theoretical predictions of the various models along with considerable uncertainties in experimental size determination for clusters less than 3-4 nm, make it difficult to select among competing models.-1-

Some aspects of pulsed laser deposition of Si nanocrystalline films

“…Our optical absorption spectra (Figure 2a) are rather similar to that obtained by other researcher groups for nc-Si [4,12]. The film thickness, measured by AFM, was used to calculate optical absorption coefficient.…”

Optical Properties of Nanostructured Silicon

“…The other methods to produce porous silicon-related nanostructures include reactive sputtering [17], solgel techniques [18], SiO 2 implantation [19], selfassembly [20], growth in inverse micelles [21,22], laser ablation [23], thermal annealing [24][25][26], thermal vaporization [27,28], decomposition of silanes [29][30][31][32][33], solution synthesis [34][35][36], hybrid techniques [37], and plasma processing [38][39][40].…”

Size tunable visible and near-infrared photoluminescence from vertically etched silicon quantum dots

“…Instead, dot sizes were determined by comparing the peak emission energy with the band-gaps obtained by previous theoretical and experimental work. 8,14 It is also critical to note that these dots are embedded in an oxide matrix which has been found 13,14 to redshift the peak emission by almost 1 eV compared to bare quantum dots or those with a hydrogen terminated surface. Based on data presented in Refs.…”

“…Although careful effort was made to produce quantum dots with diameters that had as narrow a size distribution as possible, the peak emission wavelength is a strong function of dot size 8,13 and even a change in diameter of 0.25 nm ͑about one monolayer of Si͒ can shift the peak emission energy up to 100 meV ͑30 nm͒. 8 Several causes, including noncircular mask patterning, debris on the wafer, and local etch variation could have such an impact on the peak emission wavelength.…”