In the present paper the authors present new results on thin (μc-SiC:H films deposited at low temperatures by the Very High Frequency - Glow Discharge technique (VHF-GD) at 70 MHz. The individual effects of each of the deposition parameters (methane and diborane gas phase ratios, input power, deposition temperature and pressure) are investigated with respect to the structural, optical and electrical properties of the films; the goal being the growth of optimised, thin μc-SiC:H layers for use as highly conductive and high gap window layers in solar cells.

Microcrystalline β-SiC films were deposited on silicon substrates by electron cyclotron resonance chemical vapor deposition (ECR-CVD) at 500°C utilizing a SiH4-CH4-H2 gas mixture. The effects of two important parameters on film growth, SiH4/CH4 flow ratio and microwave (MW) power, were investigated using X-ray photoelectron spectroscopy (XPS) along with the Fourier transform infrared spectra (FTIR). Results showed that the optimum flow ratio is about 0.5. Under the optimum flow ratio, a large MW power is favorable for the growth of high quality films with an ideal film stoichiometry. Surface morphology inspected by the contact mode atomic force microscopy (AFM) reveals that high MW powers not only improve the film crystallinity but also increase its surface roughness as well.

Continuous diamond films have been grown on porous silicon by hot filament chemical vapor deposition. The demonstration of diamond growth on porous silicon seems to suggest that porous silicon can act as a buffer layer for diamond growth on Si substrates, and that the nanoscale structures of porous silicon play an important role in nucleation and growth of diamond.

Flame grown diamond films, depending on the growth conditions may present various amounts of diamond like carbon (DLC) besides the diamond phase. A correlation of the morphology with the secondary electron emission, cathodoluminescence, photoluminescence, EPR and Raman data is presented for samples grown using in different ratios of oxygen and acetylene.

Transparent and insulating thin films have been grown by the plasma decomposition of B2H6, NH3, and H2, at a substrate temperature of 250°C. From chemical composition, transmission electron microscopy, infrared absorption, and optical absorption measurements, the thin films are determined to be a mixed phase of crystalline cubic boron nitride and amorphous hydrogenated boron nitride. Also, the films have significantly more boron than nitrogen, a large concentration of hydrogen, a very large bandgap, strong infrared aborption due to both hexagonal boron nitride and boron icosahedra, and good adhesion to various substrates.

Having an indirect fundamental bandgap, unlike III-V or II-VI compound semiconductors, silicon has not played a role in optoelectronic applications such as injection lasers and light emitting diodes. In an attempt to introduce a sufficient quantum size effect, we present the experimental results on a new type of silicon based superlattices consisting of alternating layers of silicon and monolayers of adsorbed gases, Si/IAG multilayers (Si/Interface Adsorbed Gas), constructed by repeated interruptions of silicon deposition with adsorbed gases of oxygen and hydrogen. Fairly strong visible luminescence has been observed.

Light emitting Si nanostructures were fabricated by recrystallizing Si/SiNx superlattices grown by plasma enhanced chemical vapor deposition. After recrystallisation by a laser annealing or by rapid thermal annealing the Raman spectra show clearly a confinement effect. A substantial photoluminescence around 470 to 550 nm and at 620 nm is observed after a hydrogen passivation step. The photoluminescence at 620 nm is assigned to carrier recombination via efficient surface states, whereas the blue emission at 470 to 550 nm shows a behaviour expected for quantum confinement effects.

The constrained crystallization in a-Si:H/a-SiNx:H multilayer structures by Ar ion laser annealing treatment has been studied by high-resolution transmission electron microscopy (HRTEM) and Raman scattering. HRTEM photograph shows that the a-Si:H layers crystallize without disturbing the multilayer structures and that the interfaces after the crystallization are atomically smooth and uniform. The lattice image of the Si crystallites arrayed one by one can be seen clearly in Si layers and the average size is roughly equal to the thickness of Si layer. The thermodynamics of constrained crystallization within multilayer structures has been discussed.

Rough-surface polycrystalline silicon films have been used for fabrication of electrically erasable-programmable read-only-memories (EEPROM). Silicon-Rich Oxides (SRO), also known as semi-insulating polycrystalline silicon (SIPOS), have been recommended for use as electron injectors. The advantage of SRO as injectors is that both the bottom and top surfaces of the film can be used to obtain high field enhancement. An ultra-thin multi-layer structure of silicon and silicon dioxide has been fabricated by low pressure chemical vapor deposition (LPCVD). High resolution TEM shows alternating layers of 50 A thick SiO2 and polycrystalline Si (grain size ∼ 80 A) films were deposited and MOS capacitors using this multilayer dielectric were studied to understand their electrical characteristics. Both I-V and C-V measurements show that the Fowler-Nordheim tunneling current is proportional to the number of polycrystalline layers. The “turn-on” voltage of the tunneling current is determined by the thickness of first SiO2 layer, and the effective dielectric constant varies from 3.9 to 9.1, proportional to the number of poly-Si layers within the multi-layer structure (MLS). For a 350 Å stack (7 layers), the interface trap density, Dit, was 3×1010 traps/cm2, and the effective dielectric constant was roughly 9.

Silicon oxynitride films, deposited by chemical vapour deposition using a high He dilution are investigated with respect to their photoluminescence properties. At low temperatures the PL spectra, which show broad maxima around 2 eV, consist of two contributions with different decay times: a ns-fast and a ms-slow component, the slow one disappearing above 80 K. To account for these findings and for absorption measurements, a model is proposed to describe the structure of the samples consisting of inclusions of Si rich regions in an a-SiOxNy:H matrix with a common molecular aggregate as luminescence center. The different PL lifetimes supposedly result from different feeding mechanisms. Such a behaviour may be present in oxidized porous Si as well.

We performed an X-ray diffraction study of amorphous-tetrahedrally-coordinated carbon (a-tC) films prepared by pulsed laser deposition (PLD). The samples' properties were analyzed as a function of laser energy and thickness. For all thicknesses and laser energies, films were made up of clusters with a basic unit size of 7 -11 nm. Thicker films, as well as films prepared at higher laser densities exhibit larger clusters, in the tens of nanometers. The clusters are not readily observable by AFM, which may indicate the presence of a flat (graphitized) top film surface.

The structure and composition of tetrahedral-coordinated amorphous diamondlike carbon films (a-tC) grown by pulsed laser deposition (PLD) of graphite has been studied with atomic force microscopy (AFM). The nanometer-scale surface structure has been studied as a function of growth parameters (e.g., laser energy density and film thickness) using contact-mode and tapping-mode AFM. Although the surfaces were found to be generally smooth, they exhibited reproducible structural features on several size scales which correlate with the variation of laser energy and the effects of excited ion etching.

A systematic study was performed to fabricate poly-Si thin films on glass substrates. Amorphous tissues were efficiently removed by forming a textured structure with the aid of atomic hydrogen. According to the real-time observation by spectroscopic ellipsometry(SE), the grain growth was enhanced by permeation of atomic hydrogen into the sub-surface. Hall measurements were made over a rather wide temperature range: 100 K--350 K. A rather high Hall mobility of 20 cm2/Vs or more was obtained at room temperature due to the reduction of amorphous tissues remaining at grain boundaries.

We have investigated the structure and crystallinity of poly SiGe and Ge films in the early stage of their growth prepared at < 450°C by means of a new type of thermal CVD from GeF4 and Si2H6. Raman study and SEM observation of the films revealed that the nucleation of crystallites took place directly on the substrate, followed by the grain growth in a manner of island growth. Thus, the crystallinity of the films is well established even in the very early stage of the growth, probably < 10 nm in thickness, in contrast to the poly Si growth in the low-temperature CVD precesses.

A deposition process has been developed which allows the growth of large grain (20+ μm) polysilicon films on SiO2 substrates at a growth temperature of 650° C. A thin layer of liquid Si-metal solution is formed on the substrate surface as the growth medium. This layer is kept saturated by Si flux from a DC magnetron sputter gun. XRD analysis of the deposited films show a strong (111) preferred orientation, with increasing integrated peak intensities with increasing depositon temperature and solution layer thickness. Films deposited using an In-Si solution are p-type, with carrier concentrations in the mid 1016 cm−3 range. Conductivities of ∼.2 (Ω cm)−1 were measured, with activation energies for both carrier generation and conductivity of about 135meV. The hole mobility was found to be ∼ 30 cm2 V−1s−1. A wetting layer is used which may have a detrimental effect on the minority carrier lifetime.

We investigate the crystalline and electrical quality of thin layers epitaxially grown on polycrystalline substrates from metallic solution by the method of electron beam induced current, transmission electron microscopy and etching experiments. We observe a reduced recombination strength of dislocations and small angle grain boundaries, i.e. an improved electrical quality of the epitaxial layer compared to the substrate. The improved quality can be attributed (i) to an altered structure of grain boundaries and dislocations and (ii) to a reduced defect density in the epitaxial layer.

We succeeded, for the first time, in depositing a silicon film which features 1000Å-wide single-crystalline grains embedded in a matrix of amorphous tissue. The deposition was done by plasma-enhanced CVD from silane diluted with hydrogen at a considerably high temperature (550°C). 5pm-thick undoped amorphous silicon film was deposited on the above film and was crystallized by a solid phase crystallization method. The polycrystalline silicon film which was obtained has a columnar structure and shows an extremely high electron mobility of 808 cm2/Vs.

Based on a previously acquired physical understanding of the excimer-laser-induced crystallization process, we have developed a new crystallization technique that produces controlled microstructures and possesses a wide processing window. A patterned oxide capping layer was used as an antireflective coating to induce complete melting of an Si film under an SiO2 pattern, and partial melting of the Si film in the areas not under the capping layer—allowing controlled super lateral growth to proceed from the incompletely melted portion of the film to the completely melted portion. For the simple stripes used in this investigation, when the width of the completely molten region is less than a critical distance (above which nucleation of solids occurs in the middle of the completely melted regions), the resulting microstructure has large and elongated grains with one precisely located grain boundary running parallel to the stripe In the middle of the oxide capped region.

Arrangement of TFT devices on the resulting Grain boundary Location-Controlled (GLC) Si films with one (or zero) grain boundaries located perpendicular to the flow of electrons within the active channel portion of the TFT devices is illustrated. Such devices are expected to possess performance and uniformity characteristics that are superior to currently available poly-Si TFT devices.

Fast-pulse laser crystallization of amorphous silicon thin films on non-crystalline substrates provides a low-temperature process for generating polycrystalline silicon. This process can be augmented by including laser doping to reduce the number of process steps in the fabrication of thin-film polysilicon devices. We have studied the simultaneous laser crystallization and laser doping process, starting with amorphous silicon on fused silica substrates and using the gas immersion technique for the doping. n-type and p-type doping employed PF5 and BF3 gases, respectively. Films were characterized both structurally and electrically. The grain size increases with increasing laser energy density as the film becomes fully melted and reaches a peak value, similar to laser crystallization without doping. The dopant concentration increases with the number of laser shots and, with 100 shots, achieves a high dose with a low sheet resistance below 1000 ohms/square, appropriate for devices. The dopant profile extends to a depth comparable to the melt depth, beyond which it falls off to the background level. Therefore, the doping depth and concentration can be controlled with the laser parameters.

In this paper we present results concerning the influence of laser energy and shot density on the electrical resistance, X-ray diffraction pattern, and structure obtained by SEM, on recrystallized a-Si:H thin films produced by using a Nd-YAG laser, working in a wavelength of 532 nm. The base material (undoped and doped a-Si:H) was obtained by Plasma Enhanced Chemical Vapour Deposition (PECVD). The structure and electrical characteristics of the recrystallized thin films are dependent on the laser beam energy density, beam spot size and the number of shots applied to the base a-Si:H thin film used. Overall, the data show recrystallized material with grain sizes larger than lµm, where the electrical resistance of both, undoped and doped materials, can be varied up to 5 orders of magnitude, by the proper choice of the recrystallization conditions.