The role of the surface reaction is discussed in the formation process of µc-Si:H in comparison to that of a-Si:H. It is suggested that the responsible radicals for the formation of µc-Si:H are SiH3 as same in the case of a-Si:H depositions. On the top film-growing surface, a lot of H atoms reach the surface during the course of the μc-Si:H growth giving rise to the change in the surface condition, i. e. the loss probability of SiH3 radicals is increased. At the same time, a full H-coverage of the surface is expected which enhances the surface diffusion of SiH3 radicals, leading to the appearance of a gc nucleus. Moreover, it is speculated that the reaction in the growth zone is not necessary for the nucleation process in µc-Si:H.

Microcrystalline Si was grown from SiF4 and H2 by plasma-enhanced chemical vapor deposition. The films are almost completely crystalline with a crystallite size (determined from Raman spectra) of about 60 Å. The optical absorption and the electrical conductivity of these films were studied. With increasing hydrogen content in the films, the dark conductivity decreases strongly and the activation of the conductivity increases. We explain the conductivity qualitatively in terms of a grain boundary model.

We have deposited microcrystalline, gc-Si, silicon films by using RF reactive magnetron sputtering (RMS) at high substrate temperatures, Ts > 500°C, and at a relatively low partial pressure of hydrogen, PH = 0.40 mTorr, and at low Ts ∼200- 300°C, but with a higher PH > 2 mTorr. We have detected μc-crystallinity by Raman scattering and transmission electron microscopy. We discuss differences in the growth mechanisms for formation of μc-Si under these two deposition conditions.

We report on the preparation and characterization of phosphorus doped gc-Si:H films produced by the very high frequency glow discharge (VHF-GD) at a plasma excitation frequency of 70 MHz. We present a systematic study of the deposition parameters i.e. hydrogen dilution of silane, VHF power density, gas phase doping ratio and deposition temperature and their influences on the electrical and structural properties of the material. In contrast to 13.56 MHz GD the VHF plasma conditions favour microcrystalline formation at low power densities; the resulting conductivities are significantly higher than those obtained at 13.56 MHz.

HRTEM measurements of silicon rich oxides (SRO) show silicon microcrystals in an oxide matrix [1]. Simple, reliable characterization of this two phase material has been a problem. Ellipsometric measurement of the refractive index is a convenient method for characterizing SRO films. Film composition can be related to the refractive index by Bruggeman's effective medium approximation. In this paper we demonstrate correlation of film compositions obtained by this technique with those obtained by Auger electron spectroscopy (AES)and Rutherford back scattering (RBS). We further demonstrate regimes of LPCVD growth where simple correlation of film composition with [N2 0]/[SiH4] gas ratios is not reliable.

Various methods for the preparation of microcrystalline (nanocrystalline) silicon are summarized and compared with respect to the possibility of the control of the materials quality and scaling of the deposition process to large area applications. It is shown that the deposition of a pure microcrystalline material is achieved under conditions close to partial chemical equilibrium. The mechanism of the crystallization during the growth will be briefly discussed.

The second part of the paper deals with the physical properties of pure microcrystalline silicon which is free of any amorphous phase detectable by X-ray diffraction, i.e. less than about 1 vol%. Several aspects of electric conductivity, optical absorption and Raman scattering which have been frequently misinterpreted in the literature will be reviewed.

The near surface layer and the bulk of νc-Si:H prepared with hydrogen dilution are investigated by Raman, optical absorption, and total yield photoelectron spectroscopies. The results show that for low hydrogen dilution ratios, microcrystallites appear in the bulk while the growing surface layer remains amorphous, indicating that microcrystallite formation takes place primarily in the sub-surface layer. At high hydrogen dilution ratios, microcrystallites are detected at both the bulk and the near surface layer. The defect density and hydrogen bonding configurations at various hydrogen dilution levels are presented.

The structural and optoelectronic properties of a new plasma-enhanced chemically vapour deposited Si:O:H:F alloy are reported taking into account respectively the results from X-ray diffraction, Raman and infrared absorption spectroscopy analysis and from dark and photo conductivity and optical absorption measurements. Films produced with a F2/SiH4 gas ratio (r) lower or equal than 0.4 are amorphous semiconducting Si:O:H:F alloys, whereas films deposited with r≤0.5 exhibit a multiphase structure consisting of silicon clusters embedded in an amorphous insulating fluorine doped silicon oxide tissue. The formation of silicon clusters is the result of a segregation process of the fluorine and oxygen atoms in the amorphous Si:O:H:F matrix.

The novel technique for the preparation of crystalline Si thin films termed “Spontaneous Chemical Deposition” has been proposed, in which silane decomposes spontaneously by gas phase reactions with fluorine at reduced pressure. The technique provided us the crystalline films in a wide range of the preparation conditions by a choice of the external parameters for the reactions. The films exhibited unique characteristics in the chemical structure and the optical and electrical properties, different from the conventional uc-Si:H thin films by the silane plasma processes.

The technique have been successfully applied for the homoepitaxial growth of Si thin films.

Results on characterisation of undoped, μc-Si:H films prepared by rf magnetron sputtering technique are presented. Highly conducting films (10−3 Δ−cm−1) were obtained at fairly low rf power density (l.2W/cm2). Critical parameters for obtaining microcrystalline phase were identified. The effect of humid ambient on film properties was looked into.

Effects of thermal annealing on the properties of amorphous hydrogenated carbon films have been studied with spectroscopic ellipsometry, electrical conductivity, and infrared and Raman spectroscopy. The results show that not only the optical and electrical properties, but also the infrared and Raman spectra, change significantly after annealing above 400°C. We suggest that thermal annealing makes amorphous hydrogenated carbon films more graphite-like, and the observed changes in the microstructure cause the changes in the optical and electrical properties.

CdS and CdSe films electrodeposited from chalcogen-containing non-aqueous electrolytes are shown to possess a nanocrystalline structure and exhibit 3-D quantum size effects. A large variation in optical transmission spectra, due for the most part to this sizequantization, is shown. Photoelectrochemical activity of the as-deposited films is discussed in terms of their nano-structure. Extension of the crystallite size effects to a metalinsulator transition in MoO2 deposited from a similar electrolyte is mentioned.

The structural and electrical properties of thin films of undoped and indium-doped cadmium selenide deposited on glass substrates have been investigated. The as-deposited films were found to be microcrystalline with grain size less than 10 nm. Grain growth occurred upon annealing. Enhanced grain growth was observed in the indium doped films. Transmission electron microscopy of in-situ annealed films revealed the formation of large single crystal areas having cubic structure with <111> as the dominant orientation. The resistivity and the effective electron mobility of polycrystalline cadmium selenide films were investigated as function of annealing conditions and device channel length. Reduction of the electrical resistivity and increase of the electron mobility was observed in devices with channel lengths less than 25μm.

We have used Resonant Raman scattering induced by pressure tuning to study the phase transition and electronic states of bulk and 60±20 Å colloidal microcrystallite CdS. The experimental results show that bulk CdS undergoes a well-defined first order phase transition at 27 kbar and that the intensity of the Raman scattering increases sharply when the level of the intermediate state (bound exciton I2) is close to the photon energy. After the phase transition no Raman scattering and photoluminescence can be observed. However, the phase transition in the colloidal CdS is quite different from the bulk CdS and the complete phase transition occurs above 60 kbar. Both bulk and colloidal CdS reverse to the original wurtzite phase after releasing the pressure.

Time-resolved edge emission spectra of CdSe clusters were measured at 80K. Cluster size and excitation Intensity dependences of the decay behavior were discussed in terms of the quantum size effect for electronic states.

We review structural and optical properties of CdSxSe1−x semiconductor nanoparticles embedded in an insulating glass matrix. Vibrational Raman scattering and x-ray diffraction can be used to determine the composition of the crystallites for all X and sizes. Debye-Scherrer broadening of x-ray diffraction peaks from the crystallites yields an average grain size in the semiconductor crystallites of 60Å for the series studied here. Small angle x-ray scattering reveals that the average particle diameter is close to 120Å. Optical absorption, photoluminescence, and photomodulated absorption spectra are interpreted within a spherical quantum well model. Electron-phonon coupling and size distribution effects on the spectra are also discussed.

Porous Vycor glass has been impregnated with semiconductors by pressure forcing the nonwetting semiconductor melt into the interconnected pores. Dense semiconductor mesh-like microstructures with a characteristic size of 50 Å can be fabricated by this technique. Measurements are reported which show the composites are suitable for both optical and transport studies, particularly those addressing quantum confinement of carriers and unusual electrical transport phenomena in this new class of materials.

Solid-state chemistry has been used to control both the size and the interconnection distance of small II-VI semiconductor moeities incorporated in zeolitic hosts with the sodalite-type structure. Structural characterization was carried out using X-ray Rietveld powder methods, and optical properties of these materials were also measured. These novel materials show quantum superlattice effects as evidenced by blue shifts in their optical absorption spectra.

Indium arsenide colloids have been prepared by passing arsine through an aqueous solution of the metal nitrate. Similar experiments with gallium solutions produced an extremely fine precipitate which has been tentatively identified as amorphous gallium arsenide. Attempts to precipitate aluminium arsenide from aqueous solutions or mixed organic solvent systems were unsuccessful. The materials were characterised by transmission electron microscopy, X-ray powder diffraction and and optical absorption spectroscopy.

The absorption characteristics of commercial CdS-containing yellow glass which shows constant transmitted intensity over a range of incident CW laser intensity have been studied at room temperature. Although the thick specimen (t>0.6 mm) shows only a broad step-like feature near λ>460 nm, a thin (t-0.09 mm) specimen shows two absorption features which can be interpreted as the first two quantum-confined exciton absorption features corresponding to a crystallite size of -45 Å. The absorption spectrum of a sample (t∼O.6 mm) heated for 15 min. at 700°C shows two new absorption features at 450 nm and 380 nm, which correspond to a much smaller crystallite size of -25 Å. This reduction in size is not inconsistent with estimates made from a well-known model for crystallite growth. Some consequences of these changes in the absorption features on the optical nonlinearities of the glass will be discussed.