We have investigated properties of nanocrystalline hydrogenated cubic silicon carbide (nc-3C-SiC:H) and silicon carbide: germanium alloy (nc-SiC:Ge:H) films deposited by hot-wire chemical vapor deposition (HWCVD) at low temperatures of about 300°C. we found that the density of charged defects was strongly influenced by grain size of the films. In-situ doping into nc-3C-SiC:H films was also carried out. N-type nc-3C-SiC:H films were successfully deposited by using phosphine (PH3) and hexamethyldisilazane (HMDS) as dopants. We found that HMDS is an effective n-type dopant for low temperature deposition of nc-3C-SiC:H films by HWCVD. For the deposition of p-type nc-3C-SiC:H with trimethylaluminum (TMA), it was found that the substrate temperature of above 300°C is required to activate the acceptors. We added dimethylgermane (DMG) into mixture of MMS and H2 to prepare nc-SiC:Ge:H films. The nc-SiC:Ge:H films with Ge mole fraction of 1.9% were successfully deposited.

It has been widely observed that thin film transistors (TFTs) incorporating an hydrogenated amorphous silicon (a-Si:H) channel exhibit a progressive shift in their threshold voltage with time upon application of a gate bias. This is attributed to the creation of metastable defects in the a-Si:H which can be removed by annealing the device at elevated temperatures with no bias applied to the gate, causing the threshold voltage to return to its original value. In this work, the defect creation and removal process has been investigated using both fully hydrogenated and fully deuterated amorphous silicon (a-Si:D) TFTs. In both cases, material was deposited by rf plasma enhanced chemical vapour deposition over a range of gas pressures to cover the a-g transition. The variation in threshold voltage as a function of gate bias stressing time, and annealing time with no gate bias, was measured. Using the thermalisation energy concept, it has been possible to quantitatively determine the distribution of energies required for defect creation and removal as well as the associated attempt-to-escape frequencies. The defect creation and removal process in a-Si:H is then discussed in the light of these results.

Experimental data on the room temperature blue light emission from nanocrystalline silicon carbide (nc-SiC) films are presented. The silicon carbide films were deposited on silicon substrates with a plasma enhanced chemical vapor deposition (PECVD) reactor from methyltrichlorosilane at substrate temperature in the range of 200-350°C. The film deposited at 350°C is nanostructured and X-ray diffraction proves the presence of the 3C-SiC crystallites. Infrared absorption spectroscopy in the region of Si-C, C-H, C-O, Si-H and Si-O bonds show the corresponding absorption bands. X-ray photoelectron spectroscopy studies confirm this bond picture. Photoluminescence was measured at 77 and 300 K. The bright blue emission has a double-peak structure at 415 and 437 nm. To clarify the origin of such an emission, tight binding molecular dynamics (TB-MD) simulations of several SiC and Si nanoclusters were carried out. Based on the temperature dependence of the photoluminescence and on the simulation data, a possible model of radiative recombination in nc-SiC films was proposed. According to this model, the emission bands at 415 and 437 nm are assigned to band-to-band and band-to-tail recombination in the nanocrystallite core. The recombination at band tails of the interface and Si-C-O-H amorphous tissue gives rise to a shoulder around 470 nm.

Efficient thin-film polycrystalline-silicon (pc-Si) solar cells on foreign substrates could lower the price of photovoltaic electricity. Aluminum-induced crystallization (AIC) of amorphous silicon followed by epitaxial thickening at high temperatures seems a good way to obtain efficient pc-Si solar cells. Due to its transparency and low cost, glass is well suited as substrate for pc-Si cells. However, most glass substrates do not withstand temperatures around 1000°C that are needed for high-temperature epitaxial growth. In this paper we investigate the use of experimental transparent glass-ceramics with high strain-point temperatures as substrates for pc-Si solar cells. AIC seed layers made on these substrates showed in-plane grain sizes up to 16 μm. Columnar growth was observed on these seed layers during high-temperature epitaxy. First pc-Si solar cells made on glass-ceramic substrates in substrate configuration showed efficiencies up to 4.5%, fill factors up to 75% and open-circuit voltage (Voc) values up to 536 mV. This is the highest Voc reported for pc-Si solar cells on glass and the best cell efficiency reported for cells made by AIC on glass.

Poly-silicon thin films on glass and Kapton® substrates are fabricated using laser initiated metal induced crystallization method. Amorphous silicon films of 200 nm thickness were deposited on the two substrates. The films were capped with 200 nm aluminum films. The annealing laser was a cw Argon-ion laser system. Laser power densities ranging from 4 to 9 W/cm2 were used in the annealing process. The samples were irradiated for various periods of time. X-ray diffraction patterns from the initial results indicated the crystallization of the films. Scanning electron microscopy showed dendritic growth in the annealed samples. The composition analysis of the samples indicated aluminum-silicon alloy regions in the films.

In this work, we report on nucleation and growth of silicon thin films on glass substrate with “five-fold” symmetry and “six-fold” symmetry by ceramics hot wire chemical vapor deposition. We observed “confinement of heat and photon” is a powerful approach in developing silicon thin films with novel structure, i.e. quasicrystalline silicon thin films on glass substrate. We found unambiguously that photons emitted from the hot filament influence the nucleation of nanocrystal silicon that produces new type of silicon thin films with “five-fold” symmetry and “six-fold” symmetry.

There proved a possibility of applying the self-organization theory to the growth of noncrystalline thin-films and to the detection of ordering in their structure. Methods of analyzing the dynamics of complex systems are modified so as to investigate the structure of noncrystalline thin films. There offered new principles of the construction of material growth control systems.

The effect of capping layer on metal induced crystallization of amorphous silicon was studied. Three sets of samples were prepared in this study. All samples had the basic layer structure of amorphous silicon layer deposited on a glass substrate. This was followed by a thin aluminum layer deposition. The second and third sets, however, had a third layer of amorphous silicon with thicknesses of 20 and 50 nm, respectively. These layers were deposited on top of the aluminum. The samples were annealed at 400°C for 15, 30 and 45 minutes. The crystallization fraction in the resultant films was analyzed using X-Ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy, and atomic force microscopy. It was observed that the capping layer reduces nodule formation improving the smoothness of the crystallized polysilicon films.

A series of four a Si,Ge:H alloy samples with Ge fractions near 30 at.% were deposited by hot-wire CVD (HWCVD) using a Ta filament maintained at 1800oC. During film growth, the level of oxygen contamination was varied from less than 1019 cm−3 to roughly 5 × 1020 cm−3 using a controlled air-leak. The electronic properties of these films were then characterized using transient photocapacitance (TPC) and transient photocurrent (TPI) spectroscopy, as well as the drive-level capacitance profiling (DLCP) techniques. We observed an unexpected systematic improvement of the electronic properties of these HWCVD a Si,Ge:H with increasing oxygen impurity level, which was reflected by a decrease in the deduced Urbach energies. Comparing these with films co-deposited on stainless-steel versus p+ c-Si substrates, we found significantly better electronic properties in the latter case. Comparisons of the TPC and TPI spectra indicated a very high level of hole collection, consistent with these narrow bandtail distributions.

We report a study of dynamic cracking in a silicon single crystal in which the ReaxFF reactive force field is used for about 3,000 atoms near the crack tip while the other 100,000 atoms of the model system are described with a simple nonreactive force field. The ReaxFF is completely derived from quantum mechanical calculations of simple silicon systems without any empirical parameters. This model has been successfully used to study crack dynamics in silicon, capable of reproducing key experimental results such as orientation dependence of crack dynamics (Buehler et al., Phys. Rev. Lett., 2006). In this article, we focus on crack speeds as a function of loading and crack propagation mechanisms. We find that the steady state crack speed does not increase continuously with applied load, but instead jumps to a finite value immediately after the critical load, followed by a regime of slow increase. Our results quantitatively reproduce experimental observations of crack speeds during fracture in silicon along the (111) planes, confirming the existence of lattice trapping effects. We observe similar effects in the (110) crack direction.

Heat dissipation rate of the thin film is theoretically related to the thickness of the film. As the film grows on a substrate of constant temperature, the heat dissipation rate would be lower when the film becomes thicker. It is difficult to observe rate change during the film growth through experiment. With MD simulation, this rate can be "observed". A system including Platinum substrate at constant temperature 300K is setup. The constant temperature is obtained by Phantom method.

The average temperature of aluminum thin film is 600K. For various thickness of the film: 3.656nm, 5.302nm, and 7.567nm. The average temperature decays exponentially. Through the simple equation T=(T0-Ts)exp(-kt/d2PCp)+Ts, the dissipation rate should follow the parameter R=k/d2PCp and the parameter α=k/£Cp is the thermal diffusivity. It is observed that the thermal diffusivity increases with film thickness increases.

Fabrication of hot-wire chemical vapor deposition (HWCVD) of amorphous silicon (a-Si) thin film transistors (TFT) on thin polyamide sheets is reported. A single graphite filament at 1500 °C was used for HWCVD and device quality amorphous silicon films were deposited with no thermal damage to plastic substrate. Top-gate staggered thin film transistors (TFTs) were fabricated at 150°C using hot-wire deposited a-Si channel, Plasma enhanced chemical vapor deposition (PECVD) silicon nitride gate dielectric, and microcrystalline n+ drain/source contacts. Low leakage current of 5×10-13 A, high switching current ratio of 1.3×107, and small sub threshold swing of 0.3 V/dec was obtained for TFTs with aspect ratio of 1300μm/100μm. The field effect mobility was extracted to be 0.34 cm2/V.s.

Experimental results on thin films of the new material GexC1-x, deposited by a unique dual plasma hollow cathode sputtering technique are presented here. The (Ge, C) system is extremely promising since the addition of C to Ge has reduced the lattice dimensions enough to allow a lattice match to silicon, while increasing the bandgap close to that of c-Si. The sputtering is accomplished by igniting a dc plasma of the Ar and H2 gases which are fed through Ge and C nozzles, cylindrical tubes 30 mm in length with an 8 mm O.D. and a 3 mm I.D.

The basic material, optical, and structural properties were analyzed. Film characterization was performed using Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Auger electron spectroscopy. Additional measurements such as Tauc bandgap, conductivity as a function of temperature and light intensity, and film uniformity have been made. The film properties from a variety of deposition conditions are discussed. The measurements made indicate that the films can be grown so that the C enters the material at lattice sites. In addition, the GexC1-x films absorb photons much more efficiently than either c-Si or c-Ge.

Initial results on Al doped films are presented.

Growth of Si thin films via metal-induced crystallization (MIC) has been demonstrated by several research groups. This process lowers the crystallization temperature compared to standard solid phase crystallization (SPC). Ni is the metal that is most often adopted for this purpose. In this work, a 20-50nm Ni layer was deposited by DC magnetron sputtering onto a 500nm SiO2 layer grown on silicon wafers, followed by Si deposition at 500°C without breaking vacuum. X-ray diffraction (XRD) results and cross-sectional transmission electron microscopy (XTEM) confirmed the formation of poly-Si in a columnar structure with grain sizes in the 100-300nm range. XTEM and XPS show that nickel silicide was formed at the Si-Ni interface. We find that doping type and concentration do not have a significant impact on the grain structure. SIMS reveals no significant loss or redistribution in doping concentration during sputtering.

The effect of conventional process parameters on the deposition of μc-Si:H solar cells is reviewed. Then, an approach to solar cell optimization is presented in which hidden, internal parameters are adjusted rather than conventional, external process parameters. The investigation focuses on deposition at low H2 dilution ratio and low total gas flow. A hidden parameter is identified through time resolved optical emission spectroscopy on SiH emission: Transient depletion of the SiH4 source gas leads to uncontrolled deposition conditions during the first 90 s after plasma ignition. There hardly is any effect on plasma properties and deposited film properties for the remainder of deposition after the transient depletion phase. As demonstrator a 9.5 % efficient single junction μc-Si:H solar cell was deposited from a pure SiH4 flow. A reinterpretation of the role of H2 dilution is discussed.

Simulation and FTIR analysis of the UV treatment impact on bond strengths of PECVD deposited silicon nitride films

We have fabricated and studied an un-cooled micro-bolometer with thermo-sensing layer sandwiched between two electrodes. The micro-bolometer has “bridge” configuration to provide sufficient thermo isolation of the thermo-sensing layer and is made on the surface of silicon wafer by means of surface micro-machining technique. The support layer of SiN and thermo-sensing layer of a-Ge:H,F have been deposited by low frequency PE CVD. The active area of the thermo-sensing layer is Ab=70x66 μm2. Temperature dependence of conductivity σ(T), current-voltage characteristics I(U), spectral noise density and thermal response time have been measured to characterize operation and to determine main performance characteristics. Activation energy of the thermo-sensing layer was Ea=0.34 eV providing thermal coefficient of resistance α=0.043 K-1. Pixel resistance was in the range Rb=(1÷30)x105 Ohm. Current and voltage responsivities were in the range RI=0.3÷14 AW-1 and RU=(1÷2)x105 VW-1, respectively. The value of detectivity was in the range of D*=(1÷40)x108 cmHz1/2W-1 and response time was τ=100 μs. The characteristics obtained in this micro-bolometer with sandwiched thermo-sensing layer make it promising for further development.

This work reports, for the first time, on the possibility of realizing surface micromachined silicon germanium structures at 210°C, which have extremely low strain gradient (μm-1). This extremely low strain gradient is obtained by tuning the physical properties of Si1-xGex, locally, without affecting the underlying layers, by excimer laser annealing. Tuning the laser annealing condition to optimize the physical properties of PECVD Si1-xGex is challenging, especially for films deposited at low temperatures (~ 250°C or lower) due to the high hydrogen content and the poor adhesion of these films. Furthermore, optimizing some properties might be at the cost of others. To clarify this issue, it is interesting to note that reducing the electrical resistivity implies using high laser pulse fluence. This however will increase mean stress, strain gradient and surface roughness as will be shown in this work.

This paper studies the poly-Si crystallization mechanism under the high power (200 W) Nd:YAG solid state pulsed laser annealing system. It is found that the Gaussian-distributed laser beam profile successfully produce large super lateral growth process window. The devices in the SLG process window exhibit field-effect mobility around 250 cm2/V.s and the threshold voltage lower than 1 V. The influence of a-Si film thickness and the laser scan pitch on the process window is also carefully investigated.

In this work Spectroscopic Ellipsometry (SE) was used to study metal induced crystallization (MIC) on amorphous silicon films in order to analyze the influence of different annealing conditions on their structural properties. The variation of the metal thickness has shown to be determinant on the time needed to full crystallize silicon films. Films of 100 nm thickness crystallize after 2h at 500°C using 1 nm of Ni deposited on it. When reducing the average metal thickness down to 0.05 nm the same silicon film will need almost 10 hours to be totally crystallized. Using a new approach on the modelling procedure of the SE data we show to be possible to determine the Ni remaining inside the crystallized films. The method consists in using Ni as reference on the Bruggeman Effective Medium Approximation (BEMA) layer that will simulated the optical response of the crystallized silicon. Silicon samples and metal layers with different thicknesses were analyzed and this new method has shown to be sensible to changes on the initial metal/silicon ratio. The nickel distribution inside the silicon layers was independently measured by Rutherford Backscattering Spectroscopy (RBS) to check the data obtained from the proposed approach.