Microwave-induced low-temperature crystallization of amorphous Si thin films

Microwave heating was utilized for low-temperature crystallization of amorphous Si (a-Si) films. Microwave heating lowered the annealing temperature and reduced the annealing time. By microwave heating the hydrogen in the amorphous films was diffused out long before the nucleation of polycrystalline Si (poly-Si). The combination of NiCl₂ coating on a-Si and microwave heating greatly reduced crystallization temperature. The combination of metal-induced crystallization and microwave-induced crystallization might be a useful technique to develop high-quality poly-Si films at low temperature.     

Thermal conductivity of nanoscale polycrystalline ZnO thin films

Thermal conductivities (TCs) of ZnO thin films of thickness 80-276 nm prepared by sol-gel method are measured by the transient thermoreflectance (TTR) system. The obtained TCs ranging from 1.4 to 6.5 W/m K decrease while the thickness decrease. The measured TCs are much smaller than those of bulk ZnO, which is about 100 W/m K. The possible reasons for the decrease are the grain boundary and defects. The latter is the dominating one from the analysis.     

Microstructure and roughness improvement of polycrystalline Bi thin films upon pulsed-laser melting

Bismuth films with different thicknesses have been grown by do sputtering on substrates held at room temperature. The films are always formed by columnar crystals with a grain size comparable to the film thickness which lead to surface roughness. It increases with the thickness of the films and has a strong influence on the film optical properties. The films have been irradiated with nanosecond laser pulses, and real-time reflectivity measurements during the irradiation were used to follow the changes in the film optical properties. It will be shown that pulsed-laser irradiation of films thinner than 100 nm improves substantially their surface roughness and their crystalline quality by increasing the grain size at least one order of magnitude.     

多晶Si0.9654Mn0.0346:B薄膜的磁性研究

利用磁控溅射和快速热处理的方法制备了Mn,B共掺的多晶硅薄膜(Si0.9654Mn0.0346:B).磁性和结构研究发现薄膜有两个铁磁相.低温铁磁相来源于杂相Mn4Si7,高温铁磁相(居里温度TC～250K)是由Mn原子掺杂进入Si晶格导致.晶化后的薄膜利用射频等离子体增强化学气相沉积系统(PECVD)进行短暂(4min)的氢化处理后发现,薄膜的微结构没有发生变化而饱和磁化强度却随着载流子浓度的增大而增大.样品的饱和磁化强度和载流子浓度密切相关为验证在硅基磁半导体中磁性是以空穴为媒介的这一理论提供了有力的证据.     

On the mechanism of electronic transport in polycrystalline CdO thin films

Cadmium Oxide (CdO) thin films (d = 0.16−0.62 μm) were deposited onto glass substrates by thermal evaporation under vacuum (quasi closed volume technique) of high purity (99.99%) CdO polycrystalline powders. The substrate temperature was 300 and 473 K, respectively. After a post-deposition heat treatment, the temperature dependence of the electrical conductivity becomes reversible. The electronic transport mechanism in studied samples is explained in terms of Seto’s model for polycrystalline semiconducting films. The values of optical bandgap have been determined from absorption spectra.     

General electrical transport properties of polycrystalline multi-layered metallic thin films

We have derived, following the recent theoretical calculation of the electrical conductivity of multi-layered metallic thin films, a general solution of the electrical conductivity for those films with grain structures, since those structures give important contributions to the electrical transport properties of polycrystalline thin film. The temperature coefficients of resistivity have also been obtained.     

Thermal modeling of laser-annealing-induced crystallization of amorphous NiTi thin films

Laser annealing of shape memory alloy thin films provides new opportunities in actuator design and fabrication for microelectromechanical systems applications. In this paper, we present a three-dimensional thermal model to simulate the crystallization process when a laser beam is swept across an amorphous NiTi thin film. Experimental crystallite nucleation and growth rates are included in the model to enable prediction of the size of the crystallized region as a function of laser annealing parameters. The model can also be used to study the crystallization of other material systems by means of laser annealing. PACS 42.62.-b; 81.20.-n; 81.30.Kf     

Specific heat of amorphous and polycrystalline lead-bismuth films

The specific heat of Pb₇₀Bi₃₀-films produced by quench condensation has been measured in the amorphous and the polycrystalline phase at temperatures between 0.5 K and 2 K. No evidence could be found for theT-proportional term which has been observed on many amorphous dielectrics.These results completely agree with the observations on amorphous Bi-films and confirm once more the assumption that the existence of covalent bonds in addition to the structural disorder is essential for the occurrence of a linear term in the temperature dependence of the lattice heat.     

Microstructural changes in amorphous Si/crystalline Al thin bilayer films upon annealing

Microstructural changes occurring in a sputter deposited Si (150 nm, amorphous)/Al (50 nm, crystalline); {111} fibre textured bilayer, upon annealing at 523 K for 60 min in a vacuum of 2.0×10^-4 Pa, were analyzed employing X-ray diffraction, Auger electron spectroscopy, scanning electron microscopy, atomic force microscopy and focused-ion beam imaging. After the annealing the Al and Si sublayers had largely exchanged their locations in the bilayer; i.e. the Si layer was adjacent to the substrate after annealing. Simultaneously, the amorphous Si layer had crystallized into an aggregate of {111} oriented nanocrystals, with a crystallite size of about 15 nm. The Al layer, now adjacent to the surface, had formed a uniformly net-shaped layer in association with an increase of the surface roughness. Upon this rearrangement, the already initially present Al {111} fibre texture had become stronger, the Al crystallites had grown laterally and the macrostress in the Al layer had relaxed. An extensive analysis of thermodynamic driving forces for the transformation indicated that the largest gain in energy upon transformation is due to the crystallization of the amorphous Si. The only identifiable driving force for the layer exchange appears to be the release of elastic energy upon the rearrangement of the Si and Al phases in the layer. PACS 61.43.D; 61.72.C; 62.40; 65.70; 68.55.J; 68.60.BThis revised version was published online in September 2004. Due to technical problems the PDF of the previous version was incomplete.     

Laser scribing of polycrystalline thin films

We have investigated the use of several different types of lasers for scribing of the polycrystalline materials used for thin-film solar cells: CdTe, CuInGaSe₂ (CIGS), ZnO, SnO₂, Mo, Al, and Au. The lasers included four different neodymium–yttrium–aluminum garnet (Nd:YAG) (both 1064 and 532 nm wavelengths), a Cu vapor (511/578 nm), an XeCl excimer (308 nm), and a KrF excimer (248 nm). Pulse durations ranged from 0.1 to 250 ns. We found that the fundamental and frequency-doubled wavelengths of the Nd:YAG systems work well for almost all of the above materials except for the transparent conductor ZnO. The diode-laser-pumped Nd:YAG was particularly convenient to use. For ZnO the uv wavelengths of the two excimer lasers produced good results. Pulse duration was found generally not to be critical except for the case of CIGS on Mo where longer pulse durations (≥250 ns) are advantageous. The frequently observed problem of ridge formation along the edges of scribe lines in the semiconductor films can be eliminated by control of intensity gradients at the film through adjustment of the focus conditions.     

Crystallization of thin polycrystalline PZT films on Si/SiO2/Pt substrates

This paper reports on a study of crystallization of thin lead zirconate-titanate films deposited on Si/SiO₂/Pt substrates by RF magnetron sputtering at a low temperature and annealed at 540–580°C. In this temperature interval, one observes successively two first-order phase transitions: the low-temperature pyrochlore phase—perovskite-I phase and perovskite-I phase-perovskite-II phase transitions, which are accompanied by film volume shrinkage. The phase transformations have been studied by atomic force microscopy, scanning electron microscopy, X-ray diffraction and visual (optical) observation of the growth of islands of a new phase. It has been found that the dielectric parameters undergo substantial changes upon the transition from phase I to phase II. The origin of the observed effects has been discussed.     

Thermal stability of thin amorphous Ta-Si-N films used in Au/GaN metallization

Ta-Si-N ternary barrier films were obtained by reactive rf magnetron sputtering of a Ta₅Si₃ target in an Ar-N₂ gas discharge. The films were tested as diffusion barriers between Au and GaN layers. The efficiency of these films as diffusion-suppressing barriers is determined by transmission electron microscopy, secondary-ion mass spectroscopy, and X-ray diffraction analysis. It is shown that the diffusion barrier with optimized properties (Ta₃₄Si₂₅N₄₁) in an Au/GaN metallization system can be used to advantage at temperatures above 800°C. A correlation between the composition, microstructure, resistivity, thermal stability, and diffusion-suppressing properties of the films is discussed.     

Carrier transport of doped nanocrystalline Si formed by annealing of amorphous Si films at various temperatures

Phosphorus- and boron-doped hydrogenated amorphous silicon thin films were prepared by the plasma-enhanced chemical vapor deposition method. As-deposited samples were thermally annealed at various temperatures to get nanocrystalline Si with sizes around 10 nm. X-ray photoelectron spectroscopy measurements demonstrated the presence of boron and phosphorus in the doped films. It is found that the nanocrystallization occurs at around 600 °C for the B-doped films, while it is around 700-800 °C for the P-doped samples. For the P-doped samples, the dark conductivity decreases at first and then increases with the annealing temperature. While for the B-doped samples, the dark conductivity monotonously increases with increasing annealing temperature. As a result, the carrier transport properties of both P- and B-doped nanocrystalline Si films are dominated by the gradual activation of dopants in the films. The conductivity reaches 22.4 and 193 S cm⁻¹ for P- and B-doped sample after 1000 °C annealing.     

Charge carrier transport and d.c. conductivity in thin polycrystalline p-terphenyl films2

The electrical conductivity and charge carrier mobility in thin polycrystalline p-terphenyl layers have been measured. The transport and conductivity were interpreted in terms of a hopping mechanism. The activation energies of mobility and conductivity were obtained, and the density of states in the vicinity of the Fermi level 10²⁰ cm^?3 eV^?1 was estimated. The height of the potential barrier around the impurity levels changed according to the Poole-Frenkel effect.     

Temperature and thickness dependence of low temperature transport in amorphous silicon thin films: A comparison to amorphous germanium

The temperature and thickness dependence of the low temperature electrical transport of amorphous silicon thin films measured in-situ in ultra-high vacuum are presented. As for a-Ge there is an extended range of $\text{ln ? ∝ T}{}^{\mathrm{<mtext>?1</mtext><mtext>4</mtext>}}$ for thick films with $\text{ln ? ∝ S}{}_2\text{T}{}^{\mathrm{<mtext>?1</mtext><mtext>3</mtext>}}$ for thin films with $\text{S}{}_2\text{∝ d}{}^{\mathrm{<mtext>?1</mtext><mtext>3</mtext>}}$ as expected from a variable range tunneling mechanism.     

Effects of photoexcitation on the current transport mechanism in amorphous indium selenide thin films

The effect of photoexcitation on the current transport mechanism in amorphous indium selenide thin films was studied by means of dark and illuminated conductivity measurements as a function of temperature. Analysis of the dark electrical conductivity in the temperature range 110–320 K reveals behaviour characteristic of carriers excited to the conduction band and thermally assisted variable-range hopping (VRH) at the Fermi level above 280 K and below 220 K, respectively. In the temperature range 220–280 K, a mixed conduction mechanism was observed. A conductivity activation energy of ～300 meV (above 280 K), a density of localised states (evaluated assuming a localisation length of 5 Å) of 1.08 × 10²¹ cm^?3 eV^?1, an average hopping distance of 20.03 Å (at 120 K) and an average hopping energy of 27.64 meV have been determined from the dark electrical measurements. When the sample was exposed to illumination at a specific excitation flux and energy, the values of the conductivity activation energy, the average hopping energy and the average hopping range were significantly decreased. On the other hand, the density of localised states near the Fermi level increased when the light flux was increased. Such behaviour was attributed to a reversible Fermi level shift on photoexcitation.     

Two routes to polycrystalline CoSi2 thin films by co-sputtering Co and Si

Two processes for the fabrication of polycrystalline CoSi₂ thin films based on the codeposition of Co and Si by sputtering were studied and compared. The first process involved “annealing after deposition”, where Co and Si are codeposited at ambient temperature and then crystallized by annealing. This process yielded randomly oriented plate-like CoSi₂ grains with a grain size that is governed by the nanostructure of the as-deposited film. Polycrystalline CoSi₂ thin films were obtained at a process temperature of 170 °C, which was much lower than the annealing temperature of 500 °C needed for Co/Si bilayers. The second process involved “heating during deposition”, where Co and Si are codeposited on heated substrates. This process yielded CoSi₂ grains with a columnar structure, and the grain size and degree of (1 1 1) orientation are temperature dependent. The sheet resistance of the resulting films was determined by the preparation temperature regardless of the deposition process used, i.e. “annealing after deposition” or “heating during deposition”. Temperatures of 500 °C and higher were needed to achieve CoSi₂ resistivity of 40 μΩ cm or lower for both processes.     

Phase size effect in thin Ge-Se polycrystalline films

The Raman spectra of thin (d = 60–170 nm) Ge-Se polycrystalline films obtained by vacuum thermal evaporation of Ge₁₀Se₉₀ glass are investigated in the spectral range 110–310 cm^?1. The coexistence of the glasslike and crystalline phases α-Se, β-Se, and β-GeSe₂ is established using the X-ray diffraction method. Analysis of diffraction patterns and the Raman spectra of polycrystalline samples of various thicknesses demonstrates a phase size effect in the transition of Se from the α-monoclinic to the β monoclinic modification (d ～ 120 nm). It is found that the crystalline phase of Se is of the nanodisperse type with an average grain size of ～30–50 nm. Crystallites of β-GeSe₂ have an average size of ～100–130 nm.