Rapid crystallization of silicon films using Joule heating of metal films

50-nm thick amorphous silicon films formed on glass substrates were crystallized by rapid Joule heating induced by an electrical current flowing in 100-nm-thick Cr strips formed adjacently to 200-nm-thick SiO₂ intermediate layers. 3-μs-pulsed voltages were applied to the Cr strips. Melting of the Cr strips caused a high Joule heating intensity of about 1×10⁶ W/cm². Raman scattering measurements revealed complete crystallization of the silicon films at a Joule heating energy of 1.9 J/cm² via the SiO₂ intermediate layer. Transmission electron microscopy measurements confirmed a crystalline grain size of 50–100 nm. 1-μm-long crystalline grain growth was also observed just beneath the edge of the Cr strips. The electrical conductivity increased from 10^-5 S/cm to 0.3 S/cm for 7×10¹⁷-cm^-3-phosphorus-doped silicon films because of activation of the phosphorus atoms because of crystallization. The numerical analysis showed a density of localized defect states at the mid gap of 8.0×10¹⁷ cm^-3. Oxygen plasma treatment at 250 °C and 100 W for 5 min reduced the density of the defect states to 2.7×10¹⁷ cm^-3. Received: 3 April 2001 / Accepted: 9 April 2001 / Published online: 25 July 2001     

Micro-Raman and ion channeling study of crystal damage in Si induced by focused Co ion beam implantation

The lattice damage of silicon produced by ion implantation at extremely high current density of 0.8 A/cm² (2.5᎒¹⁸ cm^-2 s^-1) was investigated. In a focused ion beam system, implantation was carried out with 70 keV Co ions, fluences of 1.2᎒¹⁶ cm^-2 and 6.7᎒¹⁵ cm^-2 into Si (111) at room temperature and elevated temperatures between 355 °C and 400 °C. Radiation damage measurements were performed by Rutherford backscattering/channeling spectroscopy and micro-Raman analysis. The radiation damage was studied as a function of pixel dwell-time and implantation temperature. The critical temperature for amorphization increases with current density. Although the fluence of the focused ion implantation was constant, crystalline layers were obtained for short and amorphous layers for long pixel dwell-times. The critical dwell-time of crystalline/amorphous transition increases with implantation temperature. From the results a typical time for defect annealing of 10^-5 s at 400 °C and an activation energy of (2.5ǂ.6) eV were deduced.     

Electrical and optical properties of indium tin oxide thin films grown by pulsed laser deposition

Indium tin oxide (ITO) thin films (200-400 nm in thickness) have been grown by pulsed laser deposition (PLD) on glass substrates without a post-deposition anneal. The electrical and optical properties of these films have been investigated as a function of substrate temperature and oxygen partial pressure during deposition. Films were deposited at substrate temperatures ranging from room temperature to 300 °C in O₂ partial pressures ranging from 0.1 to 100 mTorr. For 300 nm thick ITO films grown at room temperature in oxygen pressure of 10 mTorr, the electrical conductivity was 2.6᎒^-3 Q^-1cm^-1 and the average optical transmittance was 83% in the visible range (400-700 nm). For 300 nm thick ITO films deposited at 300 °C in 10 mTorr of oxygen, the conductivity was 5.2᎒^-3 Q^-1cm^-1 and the average transmittance in the visible range was 87%. Atomic force microscopy (AFM) measurements showed that the RMS surface roughness for the ITO films grown at room temperature was ~7 Å, which is the lowest reported value for the ITO films grown by any film growth technique at room temperature.     

Dependence of functional properties on processing in sol-gel (Pb,La)TiO3 thin films

Pb_0.88La_0.08TiO₃ films were processed on Si-based substrates by a diol-based sol-gel route from solutions with variable content of PbO excess. Crystallisation was performed at heating rates of 10 °C min^-1 and higher than 500 °C min^-1 (rapid heating). The pyroelectric coefficient was measured after poling the samples by two methods: applying a sinusoidal wave and applying a train of square pulses, with the latter showing a higher poling efficiency. The piezoelectric d₃₃ coefficient was determined by double-beam interferometry. Strain vs. field measurements provided evidence of 90° domain orientation in these films. Those crystallised at 10 °C min^-1 showed the highest functional properties (%=1.7᎒^-2 7C cm^-2 K^-1 and d₃₃=57 pm V^-1). This is a consequence of the higher stability of the 90° domains oriented during poling, caused by the lower tensile stress arising during preparation. The voltage responsivity of these films also benefited from the lower permittivity arising from their higher porosity. These films are good candidates for applications in infrared detectors and microelectromechanical devices.     

Transparent conducting AZO and ITO films produced by pulsed laser ablation at 355 nm

Thin films of aluminium-doped zinc oxide (AZO) and indium tin oxide (ITO) were deposited on glass substrates by laser ablation in an oxygen environment. The electrical and optical properties of films grown at various oxygen pressures were compared. With no substrate heating, highly transparent and conducting films were obtained with oxygen pressures between 15 and 23 mTorr for both materials. We obtained a specific resistivity of 1.8᎒^-3 Q cm for AZO and 1.1᎒^-3 Q cm for ITO. By heating the substrate to 160 °C or 200 °C, the resistivity was further reduced to 1.1᎒^-3 Q cm for AZO and 3.9᎒^-4 Q cm for ITO. The average transmission of visible light (450-750 nm) was between 82% and 98% in most cases. The results suggest that AZO is a promising alternative to ITO.     

Electrical activation of phosphorus-donors introduced in 6H-SiC by hot-implantation

Phosphorus ion (P⁺) implantations into 6H-SiC at room temperature (RT), 800 °C, and 1200 °C with mean concentrations of 1᎒¹⁸-5᎒¹⁹ /cm³ were performed to investigate the effects of hot-implantation on the electrical activation of P atoms. Improvement of the electrical activation of P atoms due to hot-implantation is found to depend on their implantation concentration, which can be divided into three regions. In the implantation with P in a low-concentration region (for example, 1᎒¹⁸ /cm³), no significant difference in the carrier concentrations among the samples implanted at RT and elevated temperatures is observed after annealing above 񫰸 °C. In a medium-concentration region, the carrier concentration increases with implantation temperature. When P ions were implanted in a high-concentration region (for example, 5᎒¹⁹ /cm³), the hot-implanted samples exhibit higher carrier concentration as compared with RT-implanted samples. Regarding hot-implantation, the carrier concentration in 800 °C-implanted samples is higher than that in the 1200 °C-implanted samples. This results can be interpreted as a degree of damage introduced by each implantation.     

Deposition of NbC thin films by pulsed laser ablation

Niobium carbide thin films were prepared by pulsed laser ablation of a stoichiometric NbC target. XeCl (308 nm, 30 ns) and Nd:YAG (266 nm, 5 ns) lasers operating at a repetition rate of 10 Hz were used. Films were deposited on Si (100) substrates at room temperature either in vacuum or in an argon atmosphere (2᎒^-1 mbar). Different laser fluences (2, 4 and 6 J/cm²) and different numbers of pulses (1᎒⁴, 2᎒⁴ and 4᎒⁴) were tested. For the first time, NbC films were prepared through a clean procedure without the addition of a hydrocarbon atmosphere. The phase constitution of the films, unit cell size, mean crystallite dimensions and preferred orientation are determined as a function of deposition conditions by X-ray diffraction. Complementary morphological and structural analysis of the films were performed by scanning electron microscopy, atomic force microscopy and Rutherford backscattering spectroscopy.     

Damage buildup and removal in Ca-ion-implanted GaN

Ca has been considered as a promising shallow acceptor in GaN and was chosen as a dopant for ion implantation with energy of 180 keV at room temperature. The as-implanted GaN films were characterized by Rutherford backscattering channeling, Raman spectroscopy, high-resolution X-ray diffraction, and compared with an unimplanted film as well as implanted samples subsequently annealed at 1150 °C for 15 s. The quantitative dependence of the damage buildup and its removal on the implantation dose has been determined. Lattice expansion that depends on dose and substrate temperature has been found. An initial amorphous component arises at a dose of 8᎒¹⁴ cm^-2. Implantation with higher doses causes unrecoverable damage that deteriorates the electrical properties. The possibilities to realize effective p-type doping by ion implantation are discussed.     

Growth of oriented Pb(ZrxTi1-x)O3 thin films on glass substrates by pulsed laser deposition

Oriented crystalline Pb(Zr_xTi_1-x)O₃ (x=0.53) (PZT) thin films were deposited on metallized glass substrates by pulsed laser deposition (1060-nm wavelength Nd:YAG laser light, 10-ns pulse duration, 10-Hz repetition rate, 0.35-J/pulse and 25-J/cm² laser fluence), from a commercial target at substrate temperatures in the range 380-400 °C. Thin films of 1-3 7m were grown on Au(111)/ Pt/NiCr/glass substrates with a rate of about 1 Å/pulse on an area of 1 cm². The deposited PZT films with perovskite structure were oriented along the (111) direction, as was revealed from X-ray diffraction spectra. Fourier transform infrared spectroscopy (FTIR) was performed on different PZT films so that their vibrational modes could be determined. Piezoelectric d₃₃ coefficients up to 30 pC/N were obtained on as-deposited films. Ferroelectric hysteresis loops at 100 Hz revealed a remanent polarization of 20 7C/cm² and a coercive field of 100 kV/cm.     

A comparison of the electron component within laser-ablated titanium plumes formed by UV and visible lasers

A Langmuir probe was used as a diagnostic of the temporally evolving electron number densities within a low-temperature laser-ablated titanium plasma expanding in vacuum. Measurements were made following ablation by a KrF excimer laser (248 nm, F=30 ns) and a frequency-doubled Nd:YAG laser (532 nm, F=7.5 ns) for laser power densities between 85 MW cm^-2 and 1130 MW cm^-2 on target. Electron number density data were obtained from the saturation electron current region of the probe (I/V) characteristic. Peak electron number densities in the range 1.5᎒¹⁰ cm^-3 to 1.5᎒¹³ cm^-3 were measured, at a distance of 5 cm along the target normal, for the laser power range investigated. Above ablation threshold the temporally integrated electron flux increased linearly with incident power density for both ablation wavelengths. The ablation thresholds, in terms of peak power density within the laser spot on the target, were found to be 85ᆨ MW cm^-2 for KrF ablation and 300ᇆ MW cm^-2for 2P YAG ablation.     

Quantitative ferroelectric characterization of single submicron grains in Bi-layered perovskite thin films

The local polarization state and the electromechanical properties of ferroelectric thin films can be probed via the converse piezoelectric effect using scanning force microscopy (SFM) combined with a lock-in technique. This method, denominated as piezoresponse SFM, was used to characterize at the nanoscale level ferroelectric SrBi₂Ta₂O₉ and Bi₄Ti₃O₁₂ thin films, grown by pulsed laser deposition. Two types of samples were studied: polycrystalline films, with grains having random orientations, and epitaxial films, consisting of (100)_orth- or (110)_orth-oriented crystallites, 100 nm to 2 7m in lateral size, which are embedded into a (001)-oriented matrix. The ferroelectric domain structure was imaged and the piezoelectric response under different external conditions was locally measured for each type of sample. Different investigation procedures are described in order to study the ferroelectric properties via the electromechanical response. A distinct ferroelectric behavior was found for single grains of SrBi₂Ta₂O₉ as small as 200 nm in lateral size, as well as for 1.2 7m쏿 nm crystallites of Bi₄Ti₃O₁₂. By probing separately the crystallites and the matrix the investigations have demonstrated at the nanoscale level that SrBi₂Ta₂O₉ has no spontaneous polarization along its crystallographic c-axis, whereas Bi₄Ti₃O₁₂ exhibits a piezoelectric behavior along both the a- and c-directions. The electrostriction coefficients were estimated to be 3᎒^-2 m⁴/C² for polycrystalline SrBi₂Ta₂O₉ and 7.7᎒^-3 m⁴/C² for c-orientedBi₄Ti₃O₁₂. Quantitative measurements at the nanoscale level, within the experimental errors give the same values for remanent polarization and coercive field as macroscopic ferroelectric measurements performed on the same samples.     

Thin tantalum pentoxide films deposited by photo-induced chemical vapor deposition using an injection liquid source

We report the growth of thin tantalum pentoxide films on Si (100) by ultraviolet-assisted injection liquid source (UVILS) chemical vapor deposition (CVD) at low temperatures (200-350 °C). This new technique combines the intense radiation from an excimer lamp (5=222 nm) with a novel injection liquid source capable of delivering precisely controllable quantities of a liquid metalorganic precursor into the CVD chamber. The composition and optical properties of the oxides were determined using a variety of standard characterization methods. After optimization of the deposition parameters, the best layers were incorporated into simple MOS test structures to enable electrical characterization. Refractive index values of 2.09ǂ.07, fixed oxide charge content of <5᎒¹⁰ cm^-2, breakdown fields higher than 2 MV/cm and dielectric constant values of 18-24 were readily achievable in the as-deposited films. These properties compare favorably with those for layers prepared by conventional thermal-CVD at significantly higher temperatures of 500 °C.     

Positron lifetime spectroscopic studies of as-grown 6H-silicon carbide

Positron lifetime spectroscopy has been employed to study the as-grown n-type 1.2᎒¹⁸ cm^-3 N-doped and p-type 1.8᎒¹⁸ cm^-3 Al-doped 6H-silicon carbide in the temperature range 10 K-300 K. For the p-type material, a positron trapping site, which has a lifetime of 225ᆟ ps, was found and is attributed to positron annihilating from the V_SiV_C divacancy-related defect having a neutral charge. For the case of the n-type material, a positron trapping centre having a lifetime of 200Nj ps, attributed to a V_Si-related defect, and a shallow trap were observed. The shallow trap, having binding energy of l8 meV was attributed to Rydberg-like states resulting from positron binding with a negative ion.     

RBS study on Na-implanted polystyrene at various doses

A study on the composition of Na-implanted polystyrene has been made by Rutherford backscattering spectroscopy (RBS). Substrates used were polystyrene (PS) dishes. Na ion implantation was performed at an energy of 50 keV with does ranging from 5᎒¹⁵ to 1᎒¹⁷ ions/cm². RBS was carried out with 1.5-MeV He⁺-ion beams and a fluence of 60 7C. The depth distribution of Na atoms showed a Gaussian distribution for the low dose. The profile is in a good agreement with a theoretical distribution calculated by a TRIM code. At the intermediate dose, the Na depth profile changed to a trapezoidal distribution. At the high dose, Na enrichment was found at the surface. Oxygen incorporation into PS is also observed. Na distribution behaviors in PS surface layer were discussed as a link to the O distribution.     

Rapid joule heating of metal films used to crystallize silicon films

We analyzed the rapid heating properties of 50-nm-thick silicon films via 250-nm-thick SiO₂ intermediate layers by heat diffusion from joule heating induced by electrical current flow in chromium strips. Numerical heat-flow simulation resulted in that the silicon films were heated to the melting point by a joule-heating intensity above 1 MW/cm². A marked increase in electrical conductance associated with silicon melting was experimentally detected. Taper-shaped chromium strips detected the temperature gradient in the lateral direction caused by the spatial distribution of the joule-heating intensity. Crystallization occurred according to the temperature gradient. A 2–4-μm lateral crystalline grain growth was demonstrated for the silicon films. Received: 20 November 2001 / Accepted: 22 November 2001 / Published online: 20 March 2002     

Femtosecond-pulse laser ablation of dental hydroxyapatite and single-crystalline fluoroapatite

Laser microdrilling of healthy human enamel and dentine using 300 fs pulses at a wavelength of 615 nm and 3 Hz repetition rate leads to an enhanced structuring quality in comparison with nanosecond-laser results. Microcracking and damage to neighboring tissue can be reduced. Ablation threshold fluences for 100 laser pulses of 0.3 J cm^-2 (human dentine), 0.6 J cm^-2 (human enamel) and 0.8 J cm^-2 (single crystalline fluoroapatite) could be determined. Ablation depths per pulse below 1 7m were observed.     

Defect generation in polycrystalline Cu(In,Ga)Se2 by high-energy electron irradiation

We investigate the degradation of ZnO/CdS/ Cu(In,Ga)Se₂ heterojunction solar cells for space applications and the defect generation in polycrystalline Cu(In,Ga)Se₂ thin films by irradiation with 1-MeV electrons with fluences J_e up to J_e=5᎒¹⁸ cm^-2. Notable degradation of the solar cell performance starts at fluences of J_e=10¹⁷ cm^-2 where the open circuit voltage decreases by about 5% while short circuit current and fill factor remain essentially unaffected. Thus, Cu(In,Ga)Se₂ solar cells withstand electron fluences which are higher by one order of magnitude or more when compared to other technologies. A model describes the absolute open circuit voltage loss considering the increase of space charge recombination by electron irradiation-induced defects. Defect analysis by admittance spectroscopy shows that acceptor defects with an energy distance of approximately 300 meV from the valence band are generated at a rate %=0.017 (ǂ.01) cm^-1.     

Pulsed-laser deposition of Ta-doped PZT ferroelectric films for memory applications using conductive oxide La0.25Sr0.75CoO3 and SrRuO3 electrodes

New methods for fabricating highly 𘚡¢-oriented and complete 𘜏¢-textured Pb(Ta_0.05Zr_0.48Ti_0.47)O₃ (PTZT) films on Pt/TiO₂/SiO₂/Si(001) substrates by pulsed-laser deposition have been developed using conductive oxide La_0.25Sr_0.75CoO₃ and SrRuO₃ electrodes. The 𘚡¢-preferred orientated PTZT ferroelectric capacitor was not subjected to loss of its polarization after 1᎒¹⁰ switching cycles at an applied voltage of 5 V and a frequency of 1 MHz, and the 𘜏¢-textured PTZT film capacitor retains 94.7% of its polarization after 1.5᎒¹⁰ switching cycles at 5 V and 50 kHz. The PTZT capacitors using these conductive oxide electrodes have low leakage current dominated by Schottky field emission mechanism.     

Pulsed laser deposition of carbon nitride films by a sub-ps laser

CN_x (0.01-2 to 0.6 mbar the nitrogen content of the films increases monotonously, as determined by X-ray photoelectron spectroscopy. Raman spectroscopy reveals that the films consist predominantly of highly amorphous carbon.     

Vacuum versus gas environment for the synthesis of nanocomposite films by pulsed-laser deposition

Nanocomposite films formed by Cu nanocrystals (NCs) with sizes <10 nm embedded in an amorphous Al₂O₃ host have been grown by alternate pulsed-laser deposition both in vacuum and in a buffer gas (Ar) up to pressures of 0.1 Torr. The dimensions, dimension distributions, and shape of the NC produced in vacuum and in Ar up to pressures of 5᎒^-3 Torr follow a similar trend as a function of the Cu areal density. This allows us to conclude that the nucleation and growth of the NC are dominated by processes occurring at the substrate surface rather than in the gas phase. For Ar pressures ̓᎒^-2 Torr, the anisotropy of the NC is enhanced, the deposition rate decreases abruptly and a significant amount of the buffer gas is incorporated into the host, thus leading to the formation of a porous material.