Ellipsometric and Raman spectroscopic study of nanocrystalline silicon thin films prepared by a rf magnetron sputtering technique

Abstract

The structure of nanocrystalline silicon thin films (nc-Si:H) deposited by rf magnetron sputtering of a high-purity crystalline silicon target using argon (30%) and hydrogen (70%) gas mixture, under different pressures (P = 2, 3 and 4 Pa) and different substrate temperature (Ts = 100, 150 and 200 °C), has been studied with spectroscopic ellipsometry (SE; 1.5–5 eV) complemented with Raman spectroscopy measurements. The ellipsometry data were carefully analyzed using the Brüggeman effective medium approximation and the Tauc–Lorentz model. The results of this investigation clearly show that the samples deposited at 2 Pa present a completely amorphous structure whatever the substrate temperature, while those deposited at 3 and 4 Pa exhibit a nanocrystalline structure. These results suggest the existence of a threshold pressure around 3 Pa for which crystallization occurs. The samples are well crystallized with a crystalline volume fraction ranging from about 60 to 90%, and exhibit a mixture of small and large crystallite sizes. The deposition temperature has practically no effect on the size of the crystallites and on the average crystalline volume fractions. These results are in good agreement with the Raman spectroscopy data, and suggest the formation of Si crystallites in the gas phase. The analysis of the ellipsometric spectra also shows that the bulk layer is initiated from an amorphous interface (a-Si:H) present in the first steps of the growth, and is followed by a less crystallized subsurface layer.

Structural properties of intrinsic and doped nc‐Si:H films prepared by RFMS: Study as function of deposition time and substrate temperature

“…The real ( 1 ε ) and the imaginary ( 2 ε ) parts, of the pseudo-dielectric function of each layer are calculated by assuming a mixture of three constituents, such as some a-Si, nc-Si-fine grains and the void [18] and are adjusted to the experimental ones. After several attempts of adjustments, the best model that well fitted our experimental SE data consisted of four layers, in good agreement with the growth mechanism processes proposed for PECVD polymorphous silicon material [19] and used in RFMS nc-Si:H analysis [3]. This model consists in: (i) an interface layer, composed of amorphous Si and voids, (ii) a bulk layer more crystallized and formed by a mixture of Si crystallites, amorphous Si and the void, (iii) a subsurface layer with the same composition but less crystallized than the bulk, and (iv) a roughness surface layer with also the same composition for the thick samples.…”

“…nc-Si:H films doped with boron (p type) or phosphorus (n type) were prepared by radiofrequency magnetron sputtering (RFMS) technique in the same conditions of the plasma used for the intrinsic optimized films (total pressure P = 3 Pa, power RF = 200 W, partial pressures of gases 70 % H 2 and 30 % Argon) and leading to high crystalline fractions [2,3]. Two deposition times (3 minutes and 30 minutes) and two substrate temperatures (room temperature and 100 °C) were used.…”

Structural characterization of superlattice of microcrystalline silicon carbide layers for photovoltaic application

“…A shoulder around 4.2 eV indicates the presence of nc-Si in the layers for all these samples. 25,26 Fig. 4 shows the Raman spectra of the #lc-SiC:H1 and #lc-SiC:H2 samples in the range 360 cm À1 to 600 cm À1 .…”

Effects of hydrogen atmosphere on pulsed-DC sputtered nanocrystalline Si:H films

“…Nevertheless, there have been few articles addressing this issue so far [4][5][6][7][8][9][10]. We are thus investigating the control of crystallinity including both the crystalline volume fraction and crystallite size of nc-Si:H thin films prepared by an pulsed-DC magnetron sputtering method, which possesses such intrinsic advantages as higher plasma density/activity and deposition rate in comparison to its DC and RF counterparts respectively.…”