Laterally seeded epitaxy enhancement in zone melting recrystallisation by increase of silicon film thickness

Polycrystalline silicon films with various thickness on SiO/sub 2/ with seeding windows were recrystallised at high scan speeds using RF-induced graphite strip heating. It has been found that the laterally seeded epitaxial widths of defect-free silicon films on SiO/sub 2/ are 40 and 53 mu m for film thicknesses of 350 and 500 nm, respectively. For a 1100 nm-thick silicon film, the epitaxy width reaches 100 mu m. The scan direction of the strip heater was perpendicular to seeding windows in the experiments.<>     

Work function of boron-doped polycrystallineSixGe1-x films

The work function of p-type polycrystalline Si_xGe_1-x films deposited by LPCVD using SiH₄ and GeH₄ was determined by CV measurements on MOS structures. Boron was introduced in the Si_xGe_1-x films either exsitu by ion implantation or insitu by adding B₂H₆ in the reactants during film deposition. The work function of the Si_xGe_1-x films is found to decrease as the Ge content increases; it is 5.16 eV for Si, 4.76 eV for Si_0.49Ge_0.51, and 4.67 eV for Ge. The work function of the Si and Ge films coincides well with that of single crystalline Si and Ge, respectively. It is also found that a thin Si adhesion layer of about 3 nm (nominal thickness), deposited prior to the Si_xGe_1-x, has a negligible effect on the work function determination     

High-mobility poly-Si TFTs fabricated on flexible stainless-steelsubstrates

High mobility polycrystalline Si thin-film transistors (poly-Si TFTs) are firstly fabricated on flexible stainless-steel substrates 100 μm thick through low-temperature processes where both active Si and gate SiO₂ films are deposited by glow-discharge sputtering and the Si films are crystallized by KrF excimer laser irradiation. The gate SiO₂ films are sputter-deposited in oxygen atmosphere from the SiO₂ target. Resulting poly-Si TFTs show excellent characteristics of mobility of 106 cm²/V·s and drain current on-off ratio of as high as 1×10⁶. Thus, the poly-Si TFTs are very promising for realizing novel flat panel displays of lightweight and rugged LCDs and LEDs     

Epitaxial growth of β-SiC on Si by RTCVD with C3H8 and SiH4

The authors established that β-SiC thin films can be grown epitaxially on (100) Si substrates by rapid thermal chemical vapor deposition (RTCVD) employing carbonization with C₃H₈ , as well as post-carbonization growth using SiH₄ and C ₃H₈ in H₂. They determined the optimum carbonization conditions with respect to reaction temperature and ramp rate, gas flow rates, etc. A possible mechanism, based on nucleation density and Si surface diffusion, has been proposed for the effect of C ₃H₈ flow rate in film thickness, morphology, and void formation. Void-free SiC films have been grown on Si at high C₃H₈ flow rates. The authors determined the optimum conditions for subsequent SiC growth with respect to temperature and Si/C ratio in the gas phase. They established that the resulting SiC thin films are monocrystalline by X-ray and electron diffraction. The SiC-Si interface was investigated by cross-section transmission electron microscopy and found to be sharp and intimate where no voids are present     

Effects of subgrain boundaries on carrier transport in zone-melting-recrystallized Si films on SiO2-coated Si substrates

The transport properties of zone-melting-recrystallized Si films on SiO2-coated Si substrates have been studied by the fabrication and characterization of thin-film resistors and n-channel MOSFET's. Subgrain boundaries, which are the predominant crystal defects in the films, have a relatively low trapping state density (7-8 × 10¹¹cm^-2) and low resistance. N-channel MOSFET's fabricated in the films exhibit high surface electron mobilities (∼ 640 cm²/V-s) for electron transport either parallel or perpendicular to the subgrain boundaries.     

Growth of GaN on Si(1 l 1) by Inserting 5AI/AIN Buffer Layer

GaN films with and without a Al/AIN buffer layers are grown on Si(111) substrate via metalorganic chemical vapor deposition (MOCVD),respectively.The films are characterized by optical microscopy( OM),X-ray diffraction rocking curve (XRDRC),and Raman scattering(RS). OM shows that the GaN film inserting with 8Al/AlN buffer layers has less cracks than film without any δAl/AIN buffer layers.XRDRC demonstrates good quality of the GaN film with δAl/AIN buffer layers and Raman scattering analyses reveal that it is an effective way to overcome the difficulties of growing GaN on Si(111)sub. strate by inserting δAl/AIN buffer layers.     

Size dependence of hall mobility and dislocation density in Ge heteroepitaxial layers grown by MBE on a SiO2 patterned Si template

We have investigated the size dependent properties of the Hall mobility and etch pit dislocations (EPDs) in germanium (Ge) heteroepitaxial layers. Pure Ge thin films were grown by molecular beam epitaxy (MBE) using pattern guided growth at 650 °C and compared with homoepitaxially grown films. The results show enhanced Hall mobility and lower dislocation density as the pattern size decreases. The number of EPDs was decreased by one order of magnitude and the Hall mobility measured with different sizes of van der Pauw patterns was enhanced by two times as the pattern size was decreased from 200×200 μm² to 3×3 μm². Raman spectroscopy was also employed to characterize residual strain and crystalline quality of the epitaxial films with respect to the pattern size. We conclude that nano-scale pattern guided heteroepitaxial growth of Ge may be a plausible method for monolithic integration of Ge optoelectronic or electronic devices onto a Si substrate.     

核化密度对硅上生长异质外延金刚石膜的影响

本文利用扫描电子显微镜及Raman谱等研究了Si（100）上异质外延金刚石膜的生长．金刚石膜是由微波等离子体CVD法制备的。实验结果表明核化密度对Si（100）上异质外延金刚石膜生长有重要的影响．过低或过高的核化密度都不可能形成异质外延金刚石膜。     

(Si/Ge)n多层薄膜的设计制备及光吸收性能

采用射频磁控溅射技术,在石英玻璃衬底上沉积了具有不同层数和厚度的(Si/Ge)n多层薄膜。XRD、Raman光谱测试表明,溅射态薄膜为微晶结构,在溅射过程中层间扩散形成Si-Ge振动键,溅射时间和薄膜层数影响着薄膜层间的扩散和结晶率;FESEM结果表明,薄膜表面由颗粒团簇构成,层与层之间有明显界面。UV-vis光谱测试表明,(Si/Ge)n多层薄膜在可见光范围内具有较宽的吸收,增加薄膜层数可扩大太阳能光谱的响应范围,而增加Si单层膜厚度对光吸收范围的影响较小。     

CVD生长Si基Si1-x-yGexCy合金层应变的研究

用Raman谱和AES能谱分析了用RTP/VLP-CVD方法生长在Si衬底上的SiGeC合金外延薄膜的应变。结果表明:用RTP/VLP-CVD方法生长的SiGeC合金中掺入的C呈间隙原子或替位原子的形式分布,其中大部分为间隙原子,少量为替位C原子,但是替位C原子的存在有效地调节了SiGeC合金层的应变;另外由于采用乙烯做C源,生长温度较高也使SiGeC合金层的应变部分被弛豫。由于C的掺入,Si基上生长SiGeC合金的应变和相同Ge含量的SiGe合金相比较大大减小,临界厚度大大增加,有利于在Si衬底上生长出达到一定厚度的更高质量的族元素合金半导体材料。     

Sub-bandgap refractive indexes and optical properties of Si-doped β-Ga2O3 semiconductor thin films

In this article, we present a theoretical study on the sub-bandgap refractive indexes and optical properties of Si-doped β-Ga₂O₃ thin films based on newly developed models. The measured sub-bandgap refractive indexes of β-Ga₂O₃ thin film are explained well with the new model, leading to the determination of an explicit analytical dispersion of refractive indexes for photon energy below an effective optical bandgap energy of 4.952 eV for the β-Ga₂O₃ thin film. Then, the oscillatory structures in long wavelength regions in experimental transmission spectra of Si-doped β-Ga₂O₃ thin films with different Si doping concentrations are quantitively interpreted utilizing the determined sub-bandgap refractive index dispersion. Meanwhile, effective optical bandgap values of Si-doped β-Ga₂O₃ thin films are further determined and are found to decrease with increasing the Si doping concentration as expectedly. In addition, the sub-bandgap absorption coefficients of Si-doped β-Ga₂O₃ thin film are calculated under the frame of the Franz–Keldysh mechanism due to the electric field effect of ionized Si impurities. The theoretical absorption coefficients agree with the available experimental data. These key parameters obtained in the present study may enrich the present understanding of the sub-bandgap refractive indexes and optical properties of impurity-doped β-Ga₂O₃ thin films.     

High-quality polycrystalline Si TFTs fabricated on stainless-steelfoils by using sputtered Si films

We have developed a low-temperature fabrication process (⩽ 200°C for high-quality polycrystalline Si thin-film transistors (poly-Si TFTs) on flexible stainless-steel foils. The fabrication processes is realized through sputter deposition of thin films, including active-Si and gate-SiO₂ films, crystallization of Si films by KrF excimer laser irradiation, and inductively coupled plasma hydrogenation. High-quality n- and p-channel poly-Si TFTs are successfully fabricated without suffering from problems of substrate bending, film ablation, or cracking in films. The resulting n- and p-channel poly-Si TFTs showed mobilities of 106 and 122 cm²/V·s, respectively. This paper describes the deposition and properties of the sputtered Si films and the fabrication process and electrical characteristics of the poly-SiTFTs     

Border-Trap Characterization in High-κ Strained-Si MOSFETs

In this letter, we focus on the border-trap characterization of TaN/HfO₂/Si and TaN/HfO₂/strained-Si/Si_0.8Ge_0.2 n-channel MOSFET devices. The equivalent oxide thickness for the gate dielectrics is 2 nm. Drain-current hysteresis method is used to characterize the border traps, and it is found that border traps are higher in the case of high-kappa films on strained- Si/Si_0.8Ge_0.2 .These results are also verified by the 1/f-noise measurements. Possible reasons for the degraded interface quality of high-kappa films on strained-Si are also proposed.     

Magnetron sputtering synthesis of silicon–carbon films: structural and optical characterization

This study deals with the growth control and characterization of wide band gap silicon–carbon films obtained by reactive hydrogen plasma sputtering. The films were grown in a pure hydrogen plasma with different values of the carbon-to-silicon sputtered area ratio, r_C. During deposition, the substrate temperature was maintained at 730°C. Infrared absorption, Raman scattering and X-ray photoelectron spectroscopy, in addition to optical absorption, were used for the investigations. For C-poor samples (r_C≤30%), Si nanocrystals were formed, together with a small fraction of amorphous SiC. Further increase of sputtered carbon (r_C≥35%) led to a drastic change, resulting in SiC crystallization at the expense of Si and a near-stoichiometric composition of the layers (C/Si atomic ratio of 1.04). Excess carbon in the layers segregates in graphitic-like configuration, being likely located in the intergrain regions. The abrupt structural change observed for 30%≤r_C≤35% is accompanied by a consistent widening of the optical band gap. This is observed by a significant blue shift of the optical absorption towards the values reported for single crystal SiC. The energy gap at which optical absorption is 5×10⁴ cm⁻¹ shifts from 2.2–2.3 eV to about 4.1 eV. This structural change also correlates with a significant decrease of the refractive index.     

Thin films of CoSi2 on Si1−yCy substrate layers

The reaction of Co with epitaxial Si_1−yC_y(001) films is investigated with regard to dependence on annealing temperature and C concentration y. Resistance measurements and RBS analysis reveal a small increase in the disilicide formation temperature. The electrical properties are very similar for thin CoSi₂ films grown at 650°C on Si_0.999C_0.001 and on Si. Whereas the CoSi₂ is fully polycrystalline on Si(001), partially oriented CoSi₂ has been observed on C-containing substrate layers. An increase of the number of epitaxially grown CoSi₂ crystallites has been observed with increasing C concentration.     

A comparative study of the passivation films on AlGaAs/GaAsheterojunction diodes and bipolar transistors

A series of Si-based thin films, including amorphous Si, SiC, as well as the conventional SiO_x and SiN_x, was investigated in terms of the electrical characteristics of GaAs/Al_0.3Ga_0.7As heterostructure diodes and heterojunction bipolar transistors (HBTs). All the films were found effective in reducing the leakage current and long term degradation. Less size-dependence of the current gain was found for the HBTs passivated by amorphous Si and SiC. In addition, the devices passivated by amorphous Si and SiC films exhibited better performance during high power operation. This is attributed to the high thermal conductivity of these two materials     

First stages of silicidation in Ti/Si thin films

The structural evolution in fiber-textured Ti/Si thin films was investigated by in-situ X-ray diffraction in the temperature range preceding the formation of silicide compounds. Abnormal thermal behaviour of both 002 and 101 diffraction profiles was observed at 360 and 450 °C, which could be understood in terms of Si diffusion, first in Ti grain boundaries, then into the grains. By combining ex-situ strain studies with analysis of the Si local environment in the whole Ti silicide family from Ti₅Si₃ to TiSi₂, it was possible to determine the stress-free lattice parameters of annealed films. They are significantly higher than the bulk parameters, and indicate that nearly 4.5 at.% Si is present in the Ti grains.     

磁控溅射生长SiC薄膜的拉曼光谱研究

用射频磁控溅射法在Si(100)和玻璃衬底上制备出衬底温度分别为300,450,600℃的碳化硅薄膜,并对薄膜进行了拉曼光谱和原子力显微镜测试分析。结果表明,用溅射法在玻璃衬底上生长出微晶SiC(μc-SiC)薄膜和在Si(100)衬底上生长出立方碳化硅(β-SiC)薄膜。并且薄膜材料的结晶度随着衬底温度的升高而改善。     

Electrical and structural properties of pulse laser-annealed polycrystalline silicon films

Doped epitaxial films of Si on single-crystal high-resistivity Si substrates have been prepared using ion implantation and Q-switched ruby laser annealing of LPCVD polycrystalline Si layers. Films, doped with B or As in the range 10¹⁷to 5 × 10²⁰cm^-3were studied by the measurement of their resistivities, Hall mobilities, and doping density profiles. The good film quality achieved permitted the fabrication of p-channel MOS transistors which, through measurements of threshold voltage and transconductance, yielded additional data on the surface mobility and the integrity of the Si-SiO2interface. The electrical properties of the films compared favorably with those of similarly doped single-crystal material, and transmission electron microscopy was used to confirm the good structural quality of the epitaxial growth.     

High performance poly-crystalline silicon thin film transistorsfabricated using remote plasma chemical vapor deposition of SiO2

A remote plasma chemical vapor deposition (RPCVD) of SiO₂ was investigated for forming an interface of SiO₂/Si at a low temperature below 300°C. A good SiO₂/Si interface was formed on Si substrates through decomposition and reaction of SiH₄ gas with oxygen radical by confining plasma using mesh plates. The density of interface traps (D_it) was as low as 3.4×10¹⁰ cm^-2eV^-1. N- and p-channel Al-gate poly-Si TFTs were fabricated at 270°C with SiO₂ films as a gate oxide formed by RPCVD and laser crystallized poly-crystalline films formed by a pulsed XeCl excimer laser. They showed good characteristics of a low threshold voltage of 1.5 V (n-channel) and -1.5 V (p-channel), and a high carrier mobility of 400 cm²/Vs