We have investigated nucleation and growth mechanism of nanocrystalline silicon (nc-Si) based on the experimental observation of plan-view transmission electron microscopy. Nanocrystalline Si has been prepared by hydrogen radical annealing of hydrogenated amorphous silicon (a-Si:H) layer, which is deposited on hydrogen radical treated a-Si:H buffer layer. Nanocrystallization depends critically upon hydrogen radical annealing time and the thickness ofa-Si:H layer. Hydrogen radicals play important roles in both nucleation and growth processes in a different way. Growth of nc-Si can be explained by “hydrogen diffusion model”, in which hydrogen radicals diffusing through a-Si:H layer to interface cause nanocrystallization. Our results imply that nuclei for nc-Si are generated at the interface between a-Si:H and under layer when treated by hydrogen radicals.

The bonding of Si atoms in μc-Si:H thin films has been investigated using X-ray photoelectron spectroscopy (XPS) in conjunction with infra-red spectroscopy (IR), secondary ion mass spectroscopy (SIMS) and analytical electron microscopy (TEM/EDX/EELS) data. By using a-Si:H and single crystal silicon as reference samples, structural and hydrogen effects could be assessed, since both a-Si:H and μc-Si:H have a similar concentration of hydrogen based on the N15 hydrogen profiling data, but different structures. On the other hand, single crystal silicon and μc-Si:H both have a diamond cubic structure based on electron diffraction data, but single crystal silicon contains little or no hydrogen except adsorbed at the surface. Based on the XPS and IR data, charge transfer of the Si2p core level towards a deep lying level was observed in the μc-Si:H material. IR measurements snowed a large amount of hydrogen was located in the grain boundaries. The charge transfer is mainly due to a change in the hydrogen bonding configuration. A well bonded oxide is formed in the μc-Si:H material near the surface with an almost complete absence of the Si3+ intermediate oxide state. The presence of a large amount of hydrogen (25 at.%) even at a high volume fraction (70%) of μc-phase may limit the oxidation and promote better oxide formation. The variation of the quality of the oxide/μc interface could be a possible explanation for the different photoluminescence observed by various groups for porous μc-Si material.

Successive deuterium diffusion and effusion experiments are performed on undoped microcrystalline silicon obtained from thermally crystallized sputtered amorphous silicon thin films. The effect of prior incorporation of deuterium during the amorphous film growth on the crystallization mechanism and on the microcrystalline film quality is probed by the use of the post hydrogenation procedure. In connection with the deuterium solubility as provided by secondary ion mass spectroscopy (SIMS) profiling, the analysis of the effusion spectra suggests the existence of large cavities in the crystallized a-Si:D films, containing most probably molecular hydrogen. They are absent in the corresponding crystallized non-deuterated a-Si films. Other deuterium configurations seem to be present in both kinds of samples such as weakly bonded deuterium in small clusters and at grain boundaries.

The hydrogenated nano-crystalline silicon (nc-Si:H) films have been deposited with PECVD method.1–2 The micro-structure of these films has been studied by TEM and HREM. The PECVD nc-Si:H films show fiber texture structure which is exceptional compared with the nano-size materials made by the method of compressing granules method. The fractal dimention of this texture structure has been calculated with a Fourier filtered image. The relationshisps between conductivity and temperature and micro-structure has also been studied and the mechanism of electron conduction is discussed.

Films of μc-Si:H have been deposited in a conventional PECVD system in order to investigate their structural and morphological properties. They consist of a mixed phase of Si crystallites (50–200 Å), surrounded by grain boundaries, and amorphous regions. In this paper we report results obtained by different characterization techniques which have been used to deduce grain size, microcrystallinity fraction and composition of the crystalline, amoiphous and grain boundary. The amorphous matrix can be considered a covalent network where tetrahedrically coordinated carbon atoms, with 1 on 9 bonds terminated by hydrogen, exist. They form a distribution of large aromatic clusters containing a great number of aromatic rings such as to remarkably reduce the number of network terminators (hydrogen atoms).

The strongly exothermic reactions of H and Cu with internal surfaces in Si and Ge were examined in experiments employing ion implantation, ion-beam analysis, transmission electron microscopy, and infrared spectroscopy. The dissociation energy of the Si-H surface bond was determined to be 2.6±0.1 eV, so that the monohydride is more stable than molecular H2, whose dissociation energy per atom is 2.26 eV. Initial experiments indicate a dissociation energy for the Ge-H surface bond of =1.9 eV. Copper is bound to the Si surface with an energy of 2.2±0.2 eV relative to solid solution, as compared to a reported binding energy of 1.5 eV for Cu in the precipitated Cu3Si phase.

The crystalline phase fraction (Xc) of amorphous-crystalline mixed phase Si films prepared by thermal annealing of a-Si:H films and by plasma CVD and chemical annealing methods was investigated by the EXAFS method. The EXAFS spectra of these films were represented by linear-combination of a-Si:H and c-Si EXAFS spectra. The values of Xc were analyzed by least-square curve fitting. The crystallinity was also analyzed by a Raman scattering method measured from both sides of the films. Then, the Xc values analyzed by the Raman method were calibrated by the EXAFS analysis results.

Several samples of thin-film silicon grown on oxidized Si, both oxidized and unoxidized, have been examined using spectroscopie ellipsometry (SE) and constant angle reflection interference spectroscopy (CARIS). The SE data was fit to 5- or 6- layer models of the sample near-surface region, using the optical functions of thin-film silicon determined from a previous work. Reasonable fits were obtained from samples containing amorphous Si (a-Si) or large-grain poly-crystalline Si (p-Si), but fits to samples containing small-grain, undoped p-Si were poor unless a 8–15 nm surface roughness layer is included. Furthermore, the optical functions of p-Si:ud are not consistent from sample to sample. The optical functions determined from SE measurements were then used to interpret CARIS measurements, extracting the thicknesses of the films, which are then compared with the thicknesses obtained from SE.

We discuss the preparation and electrical properties of B-doped μc-Si:H thin films prepared by reactive magnetron sputtering in a hydrogen containing ambient. The B-concentration, and hence the dark conductivity, have been varied by controlling the rf power supplied to two sputtering targets, one, of undoped c-Si, and the other of B-doped c-Si. Films deposited from either target alone display dark conductivity activation energies of approximately 0.5 eV due to Fermi level pinning by native donorlike defects and B-doping for samples prepared from the undoped and B-doped targets, respectively. Films deposited by simultaneously sputtering undoped and B-doped targets display activation energies which first increase to approximately 0.7 eV and then decrease as the fraction of power supplied to the B-doped target is increased. For the combination of deposition parameters used, the cross over point between B-compensated, n-type films, and B-doped p-type films occurs for powers of 50 W supplied to the B-doped target and 100 W to the undoped target. B-compensated samples display trends in photoconductive properties essentially identical to results for μc-Si:H samples prepared by remote plasma CVD. However, IR studies indicate that the material shows significant post-deposition oxide formation. TEM studies confirm the existence of a low-density, porous network. Work is underway to optimize the structural aspects of this material.

Microcrystalline films of thicknesses ranging from 0.3 to 1.1 μm have been deposited on oxidized silicon wafers by PECVD in a 50KHz capacitive discharge reactor at 450°C. Two series of films have been elaborated over a wide range of boron concentrations at the same H2:SiH4 ratio of 9:1. Cross section TEM micrographs showed the films to consist of two sublayers of distinct crystalline nature, whose relative thickness depends on the preparation conditions. With a strongly <220> textured microcrystalline structure, the overlayer snowed a columnar morphology, while the amorphous underlayer reached thicknesses of 350nm. Two additional striking features were observed by TEM: - The grains took two symmetrical orientations relative to the preferential [220] growth axis;- The interface between the amorphous and crystalline regions had a sawtooth pattern with a period around 300nm. In contrast to these microstructural results, the B-profile as measured by SIMS was found to be fiat accross the whole thickness. These local measurements are compared to the results of grazing X ray diffraction and Raman measurements. We observe and discuss a discrepancy between the X ray coherence length and the dimensions of the columns as observed by TEM. While optimized conditions lead to a vanishing amorphous sublayer, the more original features described above are tentatively interpreted taking into account the high compressive strains in the layers deposited at low plasma frequencies.

Photoluminescence (PL) has been investigated in hydrogenated microcrystalline silicon (μc-Si:H) samples as a function of boron doping for films prepared by remote plasma enhanced chemical vapor deposition. When the dark conductivity a is below about 10-5 S/cm, the PL spectra exhibit a shape which is close to that of the so-called band tail PL in undoped hydrogenated amorphous silicon (a-Si:H) at 77 K. When a increases, the PL intensity decreases at 77 K. For samples with a on the order of 10-3 S/cm, the PL spectra show only a narrow, low energy PL band which peaks around 0.8–0.9 eV. In these samples, the PL at higher energy is essentially not observable. This trend is similar to that which occurs in doped a-Si:H. However, for higher doping levels (σ ∼ 1 S/cm) the PL in μc-Si:H, although very weak, exhibits a broad band which contains intensity at higher energies. The absorption spectra in these samples, as measured by photothermal deflection spectroscopy (PDS), show the same relationships with the corresponding PL spectra as do the PDS spectra in doped a-Si:H.

Phosphorus doped μc-Sl:H films have been prepared in a PECVD system from SiH4 + PH3 + H2 gaseous mixtures. The films are obtained as a result of the competition between two simultaneously occuring processes: a deposition one and an etching one due to the high concentration of hydrogen in the plasma. This competition process favours the growth of films with crystalline structure.

Highly conductive μc-Si:H layers, in the range of 20 ∼ 30 S.cm-1, were obtained for samples in the range of 70 to 85 nm thick. From Raman Dispersion Spectroscopy and X-Ray Diffraction measurements, evidences of the dominant role of the crystalline phase in the charge transport mechanisms are shown.

Through Infrared Spectroscopy measurements it was possible to obtain the concentration of the SiHn groups on the μc-Si:H n+ structure and to Infer their role on the electrical properties of the films.

We report the results of a study in which we combined growth experiments with measurements of the nc-structure and of electrical transport Samples were prepared by plasma enhanced-CVD using SiF4 and H2 gases. We also added PH3 and H2 as control parameters for structural change. The microscopic structure was directly observed by TEM. Electron transport in nc-Si was investigated by Hall effect measurements performed at temperatures from 100K to 400K. We produced samples in which the Hall mobility was applied from general transport mechanism of poly crystalline silicon. However, from TEM observation, we conclude that dominant factor on electrical transport strongly depends on the sample structure, and nanocrystalline-silicon structure is so varied as to make it difficult to determine the transport mechanism without the observation of the microscopic structure.

Electroluminescence at room temperature with a peak energy between 1.6 and 1.8 eV is observed in a-SiC:H p-i-n devices containing thin injection layers of high bandgap a-SiC:H. The temperature dependence of electroluminescence between 80 K and 320 K is much weaker than expected from the photoluminescence signal. No shift of the electroluminescence spectrum is observed up to voltages of 20 V applied across a 110 nm thick device. The results are compared to well-known features of electroluminescence in a-Si:H devices.

The silicon—hydrogen bonding configuration studies of hydrogenated silicon films that were fabricated by diluted—hydrogen and hydrogen—atom—treatment methods are presented. The diluted—hydrogen samples tend to show a very sharp line—shape in the NMR spectra as the H2/SiH4 dilution ratio is increased and/or temperature is elevated. The addition of atomic hydrogen treatment can produce the same NMR spectra at a temperature lower than 200°C. The Raman scattering spectra show that the μc—Si phase can be formed by the atomic hydrogen treatment. The infrared absorption spectra also indicate an increase of SiH2 bonding configuration and a hydrogen content reduction when atomic hydrogen treatment is employed. These results suggest that the degree of crystallinity of hydrogenated silicon films can be systematically adjusted.

Amorphous semiconductors play a major role in the field of electronic imaging. The function of an image sensor is to generate an electrical signal corresponding to the light distribution in the optical image. The photodiodes convert light into electrical signal. We investigated the linear image sensor driven by thin film transistor as an switching element, with each photodiode connected to the corresponding thin film transistor. The photo/dark conductivity of photodiode are compared in the case of amorphous silicon and microcrystalline. The influences in contact resistance between microcrystalline n+ layer and the source/drain metal electrode, electron mobility, threshold voltage, and on-off current ratio of thin film transistor with intrinsic microcrystalline silicon channel layer were also investigated.

A new concept of thin film growth/regrowth process design taking atomic motions into account using molecular dynamics is proposed. In the system, a modified many-body Tersoff-type interatomic potential for silicon has been adopted. The mathematical derivation of higher order derivatives was rigorously treated. Among many applications, the solid phase growth process was studied. It has been found from simulation studies that the solid phase growth of crystalline silicon proceeded along the [110] direction layer by layer. Furthermore, it has been obtained that all the atoms are activated in an extremely thin amorphous silicon film. Based on simulated results, an experiment using an extremely thin amorphous silicon film was carried out. It has been found that the perfect spherical silicon crystals with a uniform size and spacing can be grown from a thin amorphous silicon film.

Poly-silicon films are obtained at temperatures as low as 400 °C by the catalytic chemical vapor deposition (cat-CVD) method, in which deposition gases are decomposed by the catalytic or pyrolytic reactions with a heated catalyzer near substrates. It is found that there are roughly two modes of deposition conditions such as low gas pressure mode and high gas pressure mode for obtaining poly-silicon films, and also that the Hall mobility of the cat-CVD poly-silicon films of low gas pressure mode sometimes exceeds over 100 cm2/Vs.

Thin film transistors were fabricated using polycrystalline silicon (poly-Si) film which were directly deposited on Corning 7059 glass substrates by plasma chemical vapor deposition method at very low temperature of 450°C. No annealing procedure was carried out in the fabrication process. The dependences of the crystallinity and the electrical properties on the poly-Si film thickness were investigated for three kinds of films deposited under different conditions. These dependences on the film thickness were found to be strongly influenced by the deposition condition, especially the reaction gas pressure. By choosing optimum poly-Si deposition condition carefully, high performance TFTs have been fabricated by this novel method.

We studied the growth of polycrystalline silicon by using remote plasma chemical vapour deposition technique. The effects of RF power and the substrate temperature on the structural properties have been investigated. With increasing the RF power, the crystalline volume fraction and the grain size increase up to 100W, but decrease for the further increase in power level. We obtained the poly-Si with the crystalline volume fraction of about 74 at.% at the substrate temperature of 330°C.